{"id":30181,"date":"2026-07-17T14:13:21","date_gmt":"2026-07-17T06:13:21","guid":{"rendered":"https:\/\/www.cnspd.com\/?p=30181"},"modified":"2026-07-17T16:42:35","modified_gmt":"2026-07-17T08:42:35","slug":"4-20ma-surge-protector-selection-guide-for-2-wire-4-wire-and-hart-loops","status":"publish","type":"post","link":"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/","title":{"rendered":"4-20mA Surge Protector Selection Guide for 2-Wire, 4-Wire and HART Loops"},"content":{"rendered":"\t\t<div data-elementor-type=\"wp-post\" data-elementor-id=\"30181\" class=\"elementor elementor-30181\" data-elementor-post-type=\"post\">\n\t\t\t\t<div class=\"elementor-element elementor-element-89e5113 e-flex e-con-boxed e-con e-parent\" data-id=\"89e5113\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-9f181d2 elementor-widget elementor-widget-html\" data-id=\"9f181d2\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"html.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<style>\r\n\/* =========================================================\r\n   LEEYEE 4-20mA Signal SPD Selection Guide\r\n   Scoped styles only\r\n   ========================================================= *\/\r\n\r\n.ly420-page {\r\n  --ly420-primary: #004898;\r\n  --ly420-primary-dark: #00366f;\r\n  --ly420-primary-soft: #e9f3fb;\r\n  --ly420-secondary: #0d6f8c;\r\n  --ly420-success: #177245;\r\n  --ly420-warning: #915900;\r\n  --ly420-danger: #a93226;\r\n  --ly420-text: #1d2935;\r\n  --ly420-heading: #152b3f;\r\n  --ly420-muted: #5b6977;\r\n  --ly420-border: #d6e0e8;\r\n  --ly420-bg-soft: #f5f8fa;\r\n  --ly420-bg-dark: #0d3456;\r\n  --ly420-radius: 14px;\r\n  --ly420-shadow: 0 12px 34px rgba(24, 52, 77, 0.09);\r\n\r\n  width: 100%;\r\n  color: var(--ly420-text);\r\n  background: #fff;\r\n  font-family: inherit;\r\n  font-size: 17px;\r\n  line-height: 1.72;\r\n}\r\n\r\n.ly420-page,\r\n.ly420-page *,\r\n.ly420-page *::before,\r\n.ly420-page *::after {\r\n  box-sizing: border-box;\r\n}\r\n\r\n.ly420-page img {\r\n  display: block;\r\n  width: 100%;\r\n  max-width: 100%;\r\n  height: auto;\r\n}\r\n\r\n.ly420-page a {\r\n  color: var(--ly420-primary);\r\n  text-decoration-thickness: 1px;\r\n  text-underline-offset: 3px;\r\n}\r\n\r\n.ly420-page a:hover {\r\n  color: var(--ly420-primary-dark);\r\n}\r\n\r\n.ly420-container {\r\n  width: min(100% - 40px, 1160px);\r\n  margin-inline: auto;\r\n}\r\n\r\n.ly420-intro {\r\n  padding: 28px 0 18px;\r\n}\r\n\r\n.ly420-eyebrow {\r\n  display: inline-flex;\r\n  align-items: center;\r\n  gap: 8px;\r\n  margin: 0 0 14px;\r\n  color: var(--ly420-primary);\r\n  font-size: 13px;\r\n  font-weight: 800;\r\n  line-height: 1.35;\r\n  letter-spacing: 0.08em;\r\n  text-transform: uppercase;\r\n}\r\n\r\n.ly420-eyebrow::before {\r\n  width: 30px;\r\n  height: 3px;\r\n  border-radius: 999px;\r\n  background: var(--ly420-primary);\r\n  content: \"\";\r\n}\r\n\r\n.ly420-lead {\r\n  max-width: 960px;\r\n  margin: 0;\r\n  color: #344557;\r\n  font-size: 21px;\r\n  line-height: 1.62;\r\n}\r\n\r\n.ly420-lead strong {\r\n  color: var(--ly420-primary-dark);\r\n}\r\n\r\n.ly420-page h2,\r\n.ly420-page h3,\r\n.ly420-page h4 {\r\n  color: var(--ly420-heading);\r\n  font-weight: 800;\r\n  line-height: 1.28;\r\n  overflow-wrap: normal;\r\n  word-break: normal;\r\n  hyphens: none;\r\n}\r\n\r\n.ly420-page h2 {\r\n  margin: 58px 0 19px;\r\n  font-size: 34px;\r\n  letter-spacing: -0.025em;\r\n}\r\n\r\n.ly420-page h3 {\r\n  margin: 34px 0 13px;\r\n  font-size: 24px;\r\n}\r\n\r\n.ly420-page h4 {\r\n  margin: 22px 0 10px;\r\n  font-size: 19px;\r\n}\r\n\r\n.ly420-page p {\r\n  margin: 0 0 18px;\r\n}\r\n\r\n.ly420-page ul,\r\n.ly420-page ol {\r\n  margin: 0 0 21px;\r\n  padding-left: 23px;\r\n}\r\n\r\n.ly420-page li {\r\n  margin-bottom: 8px;\r\n}\r\n\r\n.ly420-anchor {\r\n  scroll-margin-top: 100px;\r\n}\r\n\r\n\/* =========================================================\r\n   Quick answer\r\n   ========================================================= *\/\r\n\r\n.ly420-quick-answer {\r\n  position: relative;\r\n  overflow: hidden;\r\n  margin: 28px 0 25px;\r\n  padding: 30px 32px;\r\n  border: 1px solid #bdd5ea;\r\n  border-left: 6px solid var(--ly420-primary);\r\n  border-radius: var(--ly420-radius);\r\n  background:\r\n    linear-gradient(\r\n      135deg,\r\n      rgba(255, 255, 255, 0.98),\r\n      rgba(235, 245, 253, 0.96)\r\n    );\r\n  box-shadow: var(--ly420-shadow);\r\n}\r\n\r\n.ly420-quick-answer::after {\r\n  position: absolute;\r\n  top: -65px;\r\n  right: -65px;\r\n  width: 180px;\r\n  height: 180px;\r\n  border-radius: 50%;\r\n  background: rgba(0, 72, 152, 0.06);\r\n  content: \"\";\r\n}\r\n\r\n.ly420-quick-answer h2 {\r\n  position: relative;\r\n  z-index: 1;\r\n  margin: 0 0 13px;\r\n  font-size: 27px;\r\n}\r\n\r\n.ly420-quick-answer p {\r\n  position: relative;\r\n  z-index: 1;\r\n  max-width: 990px;\r\n  margin-bottom: 13px;\r\n}\r\n\r\n.ly420-quick-answer p:last-child {\r\n  margin-bottom: 0;\r\n}\r\n\r\n.ly420-answer-line {\r\n  color: #123550;\r\n  font-size: 18px;\r\n  font-weight: 750;\r\n}\r\n\r\n\/* =========================================================\r\n   Recommended configurations\r\n   ========================================================= *\/\r\n\r\n.ly420-config-box {\r\n  margin: 25px 0 30px;\r\n  padding: 29px;\r\n  border: 1px solid #bad0e1;\r\n  border-radius: var(--ly420-radius);\r\n  background: #f6f9fc;\r\n}\r\n\r\n.ly420-config-box > h2 {\r\n  margin: 0 0 10px;\r\n  font-size: 27px;\r\n}\r\n\r\n.ly420-config-box > p {\r\n  max-width: 930px;\r\n  color: var(--ly420-muted);\r\n}\r\n\r\n.ly420-config-grid {\r\n  display: grid;\r\n  grid-template-columns: repeat(6, minmax(0, 1fr));\r\n  gap: 15px;\r\n  margin-top: 23px;\r\n}\r\n\r\n.ly420-config-card {\r\n  grid-column: span 2;\r\n  min-width: 0;\r\n  padding: 23px 22px;\r\n  border: 1px solid var(--ly420-border);\r\n  border-radius: 12px;\r\n  background: #fff;\r\n  box-shadow: 0 4px 14px rgba(24, 52, 77, 0.035);\r\n}\r\n\r\n.ly420-config-card:nth-child(4) {\r\n  grid-column: 2 \/ span 2;\r\n}\r\n\r\n.ly420-config-card:nth-child(5) {\r\n  grid-column: 4 \/ span 2;\r\n}\r\n\r\n.ly420-config-tag {\r\n  display: inline-flex;\r\n  margin-bottom: 13px;\r\n  padding: 5px 9px;\r\n  border-radius: 999px;\r\n  background: var(--ly420-primary-soft);\r\n  color: var(--ly420-primary-dark);\r\n  font-size: 10px;\r\n  font-weight: 850;\r\n  line-height: 1.3;\r\n  letter-spacing: 0.05em;\r\n  text-transform: uppercase;\r\n}\r\n\r\n.ly420-config-card h3 {\r\n  margin: 0 0 11px;\r\n  font-size: 21px;\r\n  line-height: 1.28;\r\n}\r\n\r\n.ly420-config-card p {\r\n  margin: 0 0 10px;\r\n  color: var(--ly420-muted);\r\n  font-size: 14px;\r\n  line-height: 1.6;\r\n}\r\n\r\n.ly420-config-card p:last-child {\r\n  margin-bottom: 0;\r\n}\r\n\r\n.ly420-config-card strong {\r\n  color: #203c51;\r\n}\r\n\r\n\/* =========================================================\r\n   Trust note and key cards\r\n   ========================================================= *\/\r\n\r\n.ly420-trust-note {\r\n  display: grid;\r\n  grid-template-columns: 54px minmax(0, 1fr);\r\n  gap: 17px;\r\n  align-items: start;\r\n  margin: 25px 0 28px;\r\n  padding: 22px 24px;\r\n  border: 1px solid #e3c986;\r\n  border-radius: 12px;\r\n  background: #fff9ea;\r\n}\r\n\r\n.ly420-trust-icon {\r\n  display: grid;\r\n  width: 48px;\r\n  height: 48px;\r\n  place-items: center;\r\n  border-radius: 50%;\r\n  background: #f5e5b7;\r\n  color: #6f4c00;\r\n  font-size: 22px;\r\n  font-weight: 900;\r\n}\r\n\r\n.ly420-trust-note h3 {\r\n  margin: 0 0 6px;\r\n  font-size: 19px;\r\n}\r\n\r\n.ly420-trust-note p {\r\n  margin: 0;\r\n  color: #665d47;\r\n  font-size: 14px;\r\n}\r\n\r\n.ly420-key-grid {\r\n  display: grid;\r\n  grid-template-columns: repeat(4, minmax(0, 1fr));\r\n  gap: 14px;\r\n  margin: 24px 0 10px;\r\n}\r\n\r\n.ly420-key-card {\r\n  min-width: 0;\r\n  padding: 20px;\r\n  border: 1px solid var(--ly420-border);\r\n  border-radius: 12px;\r\n  background: #fff;\r\n}\r\n\r\n.ly420-key-card strong {\r\n  display: block;\r\n  margin-bottom: 7px;\r\n  color: var(--ly420-primary-dark);\r\n  font-size: 16px;\r\n  line-height: 1.35;\r\n}\r\n\r\n.ly420-key-card span {\r\n  display: block;\r\n  color: var(--ly420-muted);\r\n  font-size: 14px;\r\n  line-height: 1.55;\r\n}\r\n\r\n\/* =========================================================\r\n   Table of contents\r\n   ========================================================= *\/\r\n\r\n.ly420-toc {\r\n  margin: 28px 0 42px;\r\n  padding: 24px 26px;\r\n  border: 1px solid var(--ly420-border);\r\n  border-radius: var(--ly420-radius);\r\n  background: var(--ly420-bg-soft);\r\n}\r\n\r\n.ly420-toc-title {\r\n  margin: 0 0 15px;\r\n  color: #18334a;\r\n  font-size: 17px;\r\n  font-weight: 800;\r\n}\r\n\r\n.ly420-toc-grid {\r\n  display: grid;\r\n  grid-template-columns: repeat(3, minmax(0, 1fr));\r\n  gap: 9px 24px;\r\n}\r\n\r\n.ly420-toc a {\r\n  display: block;\r\n  padding: 5px 0;\r\n  color: #355064;\r\n  font-size: 14px;\r\n  font-weight: 650;\r\n  line-height: 1.45;\r\n  text-decoration: none;\r\n}\r\n\r\n.ly420-toc a:hover {\r\n  color: var(--ly420-primary);\r\n  text-decoration: underline;\r\n}\r\n\r\n\/* =========================================================\r\n   Figures\r\n   ========================================================= *\/\r\n\r\n.ly420-figure {\r\n  width: 100%;\r\n  margin: 28px 0 38px;\r\n  overflow: hidden;\r\n  border: 1px solid var(--ly420-border);\r\n  border-radius: var(--ly420-radius);\r\n  background: #fff;\r\n  box-shadow: 0 10px 28px rgba(24, 52, 77, 0.08);\r\n}\r\n\r\n.ly420-figure img {\r\n  width: 100%;\r\n  aspect-ratio: 16 \/ 9;\r\n  object-fit: cover;\r\n  background: #f4f7f9;\r\n}\r\n\r\n.ly420-figure figcaption {\r\n  margin: 0;\r\n  padding: 15px 19px;\r\n  border-top: 1px solid var(--ly420-border);\r\n  background: #f7fafc;\r\n  color: #576977;\r\n  font-size: 13px;\r\n  line-height: 1.6;\r\n}\r\n\r\n.ly420-figure figcaption strong {\r\n  color: #203c51;\r\n}\r\n\r\n\/* =========================================================\r\n   Answer strip, steps and comparisons\r\n   ========================================================= *\/\r\n\r\n.ly420-answer-strip {\r\n  display: grid;\r\n  grid-template-columns: 160px minmax(0, 1fr);\r\n  gap: 20px;\r\n  align-items: start;\r\n  margin: 23px 0;\r\n  padding: 22px 24px;\r\n  border-radius: 12px;\r\n  background: #eef5fa;\r\n}\r\n\r\n.ly420-answer-strip-label {\r\n  color: var(--ly420-primary-dark);\r\n  font-size: 14px;\r\n  font-weight: 850;\r\n  letter-spacing: 0.04em;\r\n  text-transform: uppercase;\r\n}\r\n\r\n.ly420-answer-strip p {\r\n  margin: 0;\r\n  color: #30485b;\r\n}\r\n\r\n.ly420-steps {\r\n  display: grid;\r\n  gap: 14px;\r\n  margin: 24px 0 32px;\r\n  counter-reset: ly420-step;\r\n}\r\n\r\n.ly420-step {\r\n  display: grid;\r\n  grid-template-columns: 54px minmax(0, 1fr);\r\n  gap: 18px;\r\n  align-items: start;\r\n  padding: 21px 23px;\r\n  border: 1px solid var(--ly420-border);\r\n  border-radius: 12px;\r\n  background: #fff;\r\n  counter-increment: ly420-step;\r\n}\r\n\r\n.ly420-step::before {\r\n  display: grid;\r\n  width: 48px;\r\n  height: 48px;\r\n  place-items: center;\r\n  border-radius: 50%;\r\n  background: var(--ly420-primary);\r\n  color: #fff;\r\n  content: counter(ly420-step);\r\n  font-size: 17px;\r\n  font-weight: 850;\r\n}\r\n\r\n.ly420-step h3 {\r\n  margin: 0 0 7px;\r\n  font-size: 20px;\r\n}\r\n\r\n.ly420-step p {\r\n  margin: 0;\r\n  color: var(--ly420-muted);\r\n  font-size: 15px;\r\n}\r\n\r\n.ly420-comparison {\r\n  display: grid;\r\n  grid-template-columns: repeat(3, minmax(0, 1fr));\r\n  gap: 18px;\r\n  margin: 24px 0 34px;\r\n}\r\n\r\n.ly420-comparison-card {\r\n  position: relative;\r\n  overflow: hidden;\r\n  min-width: 0;\r\n  padding: 24px;\r\n  border: 1px solid var(--ly420-border);\r\n  border-radius: var(--ly420-radius);\r\n  background: #fff;\r\n}\r\n\r\n.ly420-comparison-card::before {\r\n  position: absolute;\r\n  top: 0;\r\n  left: 0;\r\n  width: 100%;\r\n  height: 5px;\r\n  background: var(--ly420-primary);\r\n  content: \"\";\r\n}\r\n\r\n.ly420-comparison-card h3 {\r\n  margin: 4px 0 13px;\r\n  font-size: 21px;\r\n}\r\n\r\n.ly420-comparison-card p,\r\n.ly420-comparison-card li {\r\n  color: var(--ly420-muted);\r\n  font-size: 14px;\r\n}\r\n\r\n.ly420-comparison-card ul {\r\n  margin-bottom: 0;\r\n}\r\n\r\n\/* =========================================================\r\n   Tables\r\n   ========================================================= *\/\r\n\r\n.ly420-table-wrap {\r\n  width: 100%;\r\n  margin: 23px 0 32px;\r\n  overflow-x: auto;\r\n  border: 1px solid var(--ly420-border);\r\n  border-radius: 12px;\r\n  background: #fff;\r\n  -webkit-overflow-scrolling: touch;\r\n}\r\n\r\n.ly420-table {\r\n  width: 100%;\r\n  min-width: 760px;\r\n  border-collapse: collapse;\r\n}\r\n\r\n.ly420-table th,\r\n.ly420-table td {\r\n  padding: 15px 17px;\r\n  border-right: 1px solid #e1e8ed;\r\n  border-bottom: 1px solid #e1e8ed;\r\n  vertical-align: top;\r\n  text-align: left;\r\n}\r\n\r\n.ly420-table th:last-child,\r\n.ly420-table td:last-child {\r\n  border-right: 0;\r\n}\r\n\r\n.ly420-table tr:last-child td {\r\n  border-bottom: 0;\r\n}\r\n\r\n.ly420-table th {\r\n  position: sticky;\r\n  top: 0;\r\n  z-index: 2;\r\n  background: #eaf2f8;\r\n  color: #17364f;\r\n  font-size: 14px;\r\n  font-weight: 850;\r\n  line-height: 1.4;\r\n}\r\n\r\n.ly420-table td {\r\n  color: #3c4e5d;\r\n  font-size: 14px;\r\n  line-height: 1.55;\r\n}\r\n\r\n.ly420-table td strong {\r\n  color: #17364f;\r\n}\r\n\r\n.ly420-table tr:nth-child(even) td {\r\n  background: #fbfcfd;\r\n}\r\n\r\n.ly420-responsibility-table {\r\n  min-width: 0;\r\n  table-layout: fixed;\r\n}\r\n\r\n.ly420-responsibility-table th:nth-child(1),\r\n.ly420-responsibility-table td:nth-child(1) {\r\n  width: 21%;\r\n}\r\n\r\n.ly420-responsibility-table th:nth-child(2),\r\n.ly420-responsibility-table td:nth-child(2),\r\n.ly420-responsibility-table th:nth-child(3),\r\n.ly420-responsibility-table td:nth-child(3) {\r\n  width: 39.5%;\r\n}\r\n\r\n\/* =========================================================\r\n   Callouts and formulas\r\n   ========================================================= *\/\r\n\r\n.ly420-callout {\r\n  margin: 24px 0;\r\n  padding: 23px 25px;\r\n  border-radius: 12px;\r\n}\r\n\r\n.ly420-callout h3,\r\n.ly420-callout h4 {\r\n  margin-top: 0;\r\n}\r\n\r\n.ly420-callout p:last-child,\r\n.ly420-callout ul:last-child {\r\n  margin-bottom: 0;\r\n}\r\n\r\n.ly420-callout--info {\r\n  border: 1px solid #bad4e9;\r\n  background: #edf6fc;\r\n}\r\n\r\n.ly420-callout--warning {\r\n  border: 1px solid #e5c98a;\r\n  background: #fff8e8;\r\n}\r\n\r\n.ly420-callout--danger {\r\n  border: 1px solid #e5b4ae;\r\n  background: #fff2f0;\r\n}\r\n\r\n.ly420-callout--success {\r\n  border: 1px solid #acd5bf;\r\n  background: #eef9f3;\r\n}\r\n\r\n.ly420-mini-label {\r\n  display: inline-flex;\r\n  margin-bottom: 10px;\r\n  padding: 4px 9px;\r\n  border-radius: 999px;\r\n  background: var(--ly420-primary);\r\n  color: #fff;\r\n  font-size: 11px;\r\n  font-weight: 850;\r\n  letter-spacing: 0.06em;\r\n  text-transform: uppercase;\r\n}\r\n\r\n.ly420-formula {\r\n  margin: 24px 0;\r\n  padding: 24px;\r\n  border-radius: 12px;\r\n  background: var(--ly420-bg-dark);\r\n  color: #fff;\r\n  text-align: center;\r\n}\r\n\r\n.ly420-formula-label {\r\n  display: block;\r\n  margin-bottom: 9px;\r\n  color: #b9d9f2;\r\n  font-size: 13px;\r\n  font-weight: 750;\r\n  letter-spacing: 0.05em;\r\n  text-transform: uppercase;\r\n}\r\n\r\n.ly420-formula-code {\r\n  display: block;\r\n  overflow-wrap: anywhere;\r\n  color: #fff;\r\n  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;\r\n  font-size: 18px;\r\n  font-weight: 750;\r\n  line-height: 1.55;\r\n}\r\n\r\n\/* =========================================================\r\n   Calculator\r\n   ========================================================= *\/\r\n\r\n.ly420-calculator {\r\n  margin: 30px 0 38px;\r\n  overflow: hidden;\r\n  border: 1px solid #b8ccdc;\r\n  border-radius: 16px;\r\n  background: #fff;\r\n  box-shadow: var(--ly420-shadow);\r\n}\r\n\r\n.ly420-calculator-head {\r\n  padding: 25px 28px;\r\n  background:\r\n    linear-gradient(\r\n      135deg,\r\n      var(--ly420-primary-dark),\r\n      var(--ly420-primary)\r\n    );\r\n  color: #fff;\r\n}\r\n\r\n.ly420-calculator-head h3 {\r\n  margin: 0 0 7px;\r\n  color: #fff;\r\n  font-size: 24px;\r\n}\r\n\r\n.ly420-calculator-head p {\r\n  margin: 0;\r\n  color: #dcecf9;\r\n  font-size: 14px;\r\n}\r\n\r\n.ly420-calculator-body {\r\n  padding: 28px;\r\n}\r\n\r\n.ly420-calc-grid {\r\n  display: grid;\r\n  grid-template-columns: repeat(4, minmax(0, 1fr));\r\n  gap: 18px;\r\n}\r\n\r\n.ly420-field {\r\n  min-width: 0;\r\n}\r\n\r\n.ly420-field label {\r\n  display: block;\r\n  min-height: 40px;\r\n  margin-bottom: 8px;\r\n  color: #294356;\r\n  font-size: 13px;\r\n  font-weight: 800;\r\n  line-height: 1.35;\r\n}\r\n\r\n.ly420-field-unit {\r\n  position: relative;\r\n}\r\n\r\n.ly420-field input {\r\n  width: 100%;\r\n  min-height: 48px;\r\n  padding: 10px 48px 10px 13px;\r\n  border: 1px solid #bdcbd5;\r\n  border-radius: 8px;\r\n  background: #fff;\r\n  color: #1d2935;\r\n  font: inherit;\r\n  font-size: 15px;\r\n  line-height: 1.2;\r\n  box-shadow: 0 4px 9px rgba(24, 52, 77, 0.07);\r\n}\r\n\r\n.ly420-field input:focus {\r\n  border-color: var(--ly420-primary);\r\n  outline: 3px solid rgba(0, 72, 152, 0.12);\r\n}\r\n\r\n.ly420-field-unit span {\r\n  position: absolute;\r\n  top: 50%;\r\n  right: 13px;\r\n  color: #687886;\r\n  font-size: 12px;\r\n  font-weight: 800;\r\n  transform: translateY(-50%);\r\n  pointer-events: none;\r\n}\r\n\r\n.ly420-calc-result {\r\n  display: grid;\r\n  grid-template-columns: repeat(3, minmax(0, 1fr));\r\n  gap: 15px;\r\n  margin-top: 26px;\r\n  padding-top: 24px;\r\n  border-top: 1px solid var(--ly420-border);\r\n}\r\n\r\n.ly420-result-box {\r\n  padding: 19px;\r\n  border-radius: 11px;\r\n  background: #eef5fa;\r\n}\r\n\r\n.ly420-result-box span {\r\n  display: block;\r\n  margin-bottom: 5px;\r\n  color: #506575;\r\n  font-size: 12px;\r\n  font-weight: 800;\r\n  line-height: 1.4;\r\n  text-transform: uppercase;\r\n}\r\n\r\n.ly420-result-box strong {\r\n  display: block;\r\n  color: var(--ly420-primary-dark);\r\n  font-size: 24px;\r\n  line-height: 1.25;\r\n}\r\n\r\n.ly420-result-status {\r\n  grid-column: 1 \/ -1;\r\n  margin: 0;\r\n  padding: 14px 16px;\r\n  border-radius: 9px;\r\n  background: #eef9f3;\r\n  color: var(--ly420-success);\r\n  font-size: 14px;\r\n  font-weight: 750;\r\n}\r\n\r\n.ly420-result-status.is-warning {\r\n  background: #fff4e1;\r\n  color: var(--ly420-warning);\r\n}\r\n\r\n.ly420-result-status.is-danger {\r\n  background: #fff0ee;\r\n  color: var(--ly420-danger);\r\n}\r\n\r\n.ly420-calc-disclaimer {\r\n  margin: 17px 0 0;\r\n  color: #6a7986;\r\n  font-size: 12px;\r\n  line-height: 1.55;\r\n}\r\n\r\n\/* =========================================================\r\n   Check grids, applications and mistakes\r\n   ========================================================= *\/\r\n\r\n.ly420-check-grid {\r\n  display: grid;\r\n  grid-template-columns: repeat(2, minmax(0, 1fr));\r\n  gap: 14px;\r\n  margin: 22px 0 32px;\r\n}\r\n\r\n.ly420-check-item {\r\n  position: relative;\r\n  min-width: 0;\r\n  padding: 18px 18px 18px 49px;\r\n  border: 1px solid var(--ly420-border);\r\n  border-radius: 10px;\r\n  background: #fff;\r\n  color: #405361;\r\n  font-size: 14px;\r\n  line-height: 1.55;\r\n}\r\n\r\n.ly420-check-item::before {\r\n  position: absolute;\r\n  top: 18px;\r\n  left: 18px;\r\n  display: grid;\r\n  width: 22px;\r\n  height: 22px;\r\n  place-items: center;\r\n  border-radius: 50%;\r\n  background: var(--ly420-primary);\r\n  color: #fff;\r\n  content: \"\u2713\";\r\n  font-size: 12px;\r\n  font-weight: 900;\r\n}\r\n\r\n.ly420-check-item strong {\r\n  display: block;\r\n  margin-bottom: 3px;\r\n  color: #20394c;\r\n}\r\n\r\n.ly420-app-grid {\r\n  display: grid;\r\n  grid-template-columns: repeat(4, minmax(0, 1fr));\r\n  gap: 15px;\r\n  margin: 24px 0 34px;\r\n}\r\n\r\n.ly420-app-card {\r\n  min-width: 0;\r\n  padding: 21px;\r\n  border: 1px solid var(--ly420-border);\r\n  border-radius: 12px;\r\n  background: #fff;\r\n}\r\n\r\n.ly420-app-card strong {\r\n  display: block;\r\n  margin-bottom: 8px;\r\n  color: var(--ly420-primary-dark);\r\n  font-size: 16px;\r\n  line-height: 1.35;\r\n}\r\n\r\n.ly420-app-card p {\r\n  margin: 0;\r\n  color: var(--ly420-muted);\r\n  font-size: 13px;\r\n  line-height: 1.55;\r\n}\r\n\r\n.ly420-mistakes {\r\n  display: grid;\r\n  gap: 13px;\r\n  margin: 22px 0 34px;\r\n}\r\n\r\n.ly420-mistake {\r\n  display: grid;\r\n  grid-template-columns: 34px minmax(0, 1fr);\r\n  gap: 13px;\r\n  align-items: start;\r\n  padding: 18px 20px;\r\n  border: 1px solid #e5c8c4;\r\n  border-radius: 10px;\r\n  background: #fff7f6;\r\n}\r\n\r\n.ly420-mistake::before {\r\n  display: grid;\r\n  width: 28px;\r\n  height: 28px;\r\n  place-items: center;\r\n  border-radius: 50%;\r\n  background: var(--ly420-danger);\r\n  color: #fff;\r\n  content: \"\u00d7\";\r\n  font-weight: 900;\r\n}\r\n\r\n.ly420-mistake strong {\r\n  color: #6f2821;\r\n}\r\n\r\n.ly420-mistake p {\r\n  margin: 4px 0 0;\r\n  color: #665451;\r\n  font-size: 14px;\r\n}\r\n\r\n\/* =========================================================\r\n   Model approval process\r\n   ========================================================= *\/\r\n\r\n.ly420-approval {\r\n  margin: 27px 0 39px;\r\n  padding: 29px;\r\n  border: 1px solid #b7d0e4;\r\n  border-radius: var(--ly420-radius);\r\n  background: #f5faff;\r\n}\r\n\r\n.ly420-approval h3 {\r\n  margin: 0 0 9px;\r\n}\r\n\r\n.ly420-approval > p {\r\n  color: var(--ly420-muted);\r\n}\r\n\r\n.ly420-approval-grid {\r\n  display: grid;\r\n  grid-template-columns: repeat(4, minmax(0, 1fr));\r\n  gap: 13px;\r\n  margin-top: 21px;\r\n}\r\n\r\n.ly420-approval-step {\r\n  min-width: 0;\r\n  padding: 19px;\r\n  border: 1px solid #c9dceb;\r\n  border-radius: 10px;\r\n  background: #fff;\r\n}\r\n\r\n.ly420-approval-step span {\r\n  display: grid;\r\n  width: 30px;\r\n  height: 30px;\r\n  margin-bottom: 10px;\r\n  place-items: center;\r\n  border-radius: 50%;\r\n  background: var(--ly420-primary);\r\n  color: #fff;\r\n  font-size: 13px;\r\n  font-weight: 900;\r\n}\r\n\r\n.ly420-approval-step strong {\r\n  display: block;\r\n  margin-bottom: 6px;\r\n  color: #17364f;\r\n  font-size: 15px;\r\n}\r\n\r\n.ly420-approval-step p {\r\n  margin: 0;\r\n  color: var(--ly420-muted);\r\n  font-size: 13px;\r\n  line-height: 1.55;\r\n}\r\n\r\n\/* =========================================================\r\n   Simple enquiry checklist\r\n   ========================================================= *\/\r\n\r\n.ly420-order-box {\r\n  margin: 28px 0 40px;\r\n  padding: 30px;\r\n  border: 1px solid #b7d0e4;\r\n  border-radius: 16px;\r\n  background: #f5faff;\r\n}\r\n\r\n.ly420-order-head {\r\n  display: grid;\r\n  grid-template-columns: minmax(0, 1fr) minmax(280px, 0.7fr);\r\n  gap: 32px;\r\n  align-items: end;\r\n  margin-bottom: 24px;\r\n}\r\n\r\n.ly420-order-label {\r\n  display: inline-block;\r\n  margin-bottom: 8px;\r\n  color: var(--ly420-primary);\r\n  font-size: 12px;\r\n  font-weight: 800;\r\n  letter-spacing: 0.07em;\r\n  text-transform: uppercase;\r\n}\r\n\r\n.ly420-order-head h3 {\r\n  margin: 0;\r\n  font-size: 26px;\r\n}\r\n\r\n.ly420-order-head > p {\r\n  margin: 0;\r\n  color: var(--ly420-muted);\r\n  font-size: 14px;\r\n  line-height: 1.6;\r\n}\r\n\r\n.ly420-simple-order-grid {\r\n  display: grid;\r\n  grid-template-columns: repeat(3, minmax(0, 1fr));\r\n  gap: 14px;\r\n}\r\n\r\n.ly420-simple-order-item {\r\n  display: grid;\r\n  grid-template-columns: 38px minmax(0, 1fr);\r\n  gap: 13px;\r\n  align-items: start;\r\n  min-width: 0;\r\n  padding: 18px;\r\n  border: 1px solid #d4e0e9;\r\n  border-radius: 11px;\r\n  background: #fff;\r\n}\r\n\r\n.ly420-simple-order-item > span {\r\n  display: grid;\r\n  width: 34px;\r\n  height: 34px;\r\n  place-items: center;\r\n  border-radius: 50%;\r\n  background: #e7f1fa;\r\n  color: var(--ly420-primary);\r\n  font-size: 12px;\r\n  font-weight: 850;\r\n}\r\n\r\n.ly420-simple-order-item strong {\r\n  display: block;\r\n  margin-bottom: 4px;\r\n  color: #17364f;\r\n  font-size: 15px;\r\n}\r\n\r\n.ly420-simple-order-item p {\r\n  margin: 0;\r\n  color: #607180;\r\n  font-size: 13px;\r\n  line-height: 1.5;\r\n}\r\n\r\n.ly420-order-easy-note {\r\n  display: flex;\r\n  gap: 8px 12px;\r\n  align-items: baseline;\r\n  margin-top: 18px;\r\n  padding: 15px 17px;\r\n  border-radius: 9px;\r\n  background: #e7f2fb;\r\n  color: #385369;\r\n  font-size: 14px;\r\n  line-height: 1.55;\r\n}\r\n\r\n.ly420-order-easy-note strong {\r\n  flex: 0 0 auto;\r\n  color: #00417f;\r\n}\r\n\r\n\/* =========================================================\r\n   Related guides\r\n   ========================================================= *\/\r\n\r\n.ly420-related {\r\n  margin: 43px 0;\r\n}\r\n\r\n.ly420-related h2 {\r\n  margin-bottom: 15px;\r\n}\r\n\r\n.ly420-related-grid {\r\n  display: grid;\r\n  grid-template-columns: repeat(3, minmax(0, 1fr));\r\n  gap: 15px;\r\n}\r\n\r\n.ly420-related-card {\r\n  display: block;\r\n  min-width: 0;\r\n  padding: 21px;\r\n  border: 1px solid var(--ly420-border);\r\n  border-radius: 12px;\r\n  background: #fff;\r\n  color: inherit !important;\r\n  text-decoration: none !important;\r\n  transition:\r\n    transform 0.2s ease,\r\n    box-shadow 0.2s ease,\r\n    border-color 0.2s ease;\r\n}\r\n\r\n.ly420-related-card:hover {\r\n  border-color: #a6c8e2;\r\n  transform: translateY(-2px);\r\n  box-shadow: 0 9px 25px rgba(24, 52, 77, 0.09);\r\n}\r\n\r\n.ly420-related-card strong {\r\n  display: block;\r\n  margin-bottom: 7px;\r\n  color: var(--ly420-primary-dark);\r\n  font-size: 16px;\r\n}\r\n\r\n.ly420-related-card span {\r\n  display: block;\r\n  color: var(--ly420-muted);\r\n  font-size: 13px;\r\n  line-height: 1.55;\r\n}\r\n\r\n\/* =========================================================\r\n   Lightweight article CTA\r\n   ========================================================= *\/\r\n\r\n.ly420-cta {\r\n  display: grid;\r\n  grid-template-columns: minmax(0, 1fr) 280px;\r\n  gap: 42px;\r\n  align-items: center;\r\n  margin: 52px 0;\r\n  padding: 40px;\r\n  border-radius: 17px;\r\n  background:\r\n    radial-gradient(\r\n      circle at top right,\r\n      rgba(255, 255, 255, 0.12),\r\n      transparent 38%\r\n    ),\r\n    linear-gradient(\r\n      135deg,\r\n      #0c3151 0%,\r\n      #004898 100%\r\n    );\r\n  color: #fff;\r\n}\r\n\r\n.ly420-cta-copy {\r\n  min-width: 0;\r\n}\r\n\r\n.ly420-cta h2 {\r\n  max-width: 680px;\r\n  margin: 0 0 12px;\r\n  color: #fff;\r\n  font-size: 30px;\r\n  line-height: 1.25;\r\n  letter-spacing: -0.02em;\r\n}\r\n\r\n.ly420-cta p {\r\n  max-width: 720px;\r\n  margin: 0;\r\n  color: #dceaf5;\r\n  font-size: 15px;\r\n  line-height: 1.7;\r\n}\r\n\r\n.ly420-cta-actions {\r\n  display: flex;\r\n  min-width: 0;\r\n  justify-content: flex-end;\r\n}\r\n\r\n.ly420-btn {\r\n  display: inline-flex;\r\n  width: 100%;\r\n  min-height: 52px;\r\n  align-items: center;\r\n  justify-content: center;\r\n  padding: 13px 20px;\r\n  border: 1px solid #fff;\r\n  border-radius: 8px;\r\n  background: #fff;\r\n  color: #00417f !important;\r\n  font-size: 14px;\r\n  font-weight: 850;\r\n  line-height: 1.3;\r\n  text-align: center;\r\n  text-decoration: none !important;\r\n  cursor: pointer;\r\n  transition:\r\n    transform 0.2s ease,\r\n    box-shadow 0.2s ease,\r\n    background 0.2s ease;\r\n}\r\n\r\n.ly420-btn span {\r\n  display: inline-block;\r\n  color: #00417f !important;\r\n}\r\n\r\n.ly420-btn:hover {\r\n  background: #eef6fc;\r\n  color: #00366f !important;\r\n  transform: translateY(-1px);\r\n  box-shadow: 0 9px 22px rgba(0, 0, 0, 0.18);\r\n}\r\n\r\n.ly420-btn:hover span {\r\n  color: #00366f !important;\r\n}\r\n\r\n\/* =========================================================\r\n   FAQ and sources\r\n   ========================================================= *\/\r\n\r\n.ly420-faq {\r\n  margin: 25px 0 42px;\r\n  border-top: 1px solid var(--ly420-border);\r\n}\r\n\r\n.ly420-faq details {\r\n  border-bottom: 1px solid var(--ly420-border);\r\n}\r\n\r\n.ly420-faq summary {\r\n  position: relative;\r\n  padding: 19px 44px 19px 2px;\r\n  color: #213c50;\r\n  font-size: 17px;\r\n  font-weight: 800;\r\n  line-height: 1.45;\r\n  cursor: pointer;\r\n  list-style: none;\r\n}\r\n\r\n.ly420-faq summary::-webkit-details-marker {\r\n  display: none;\r\n}\r\n\r\n.ly420-faq summary::after {\r\n  position: absolute;\r\n  top: 18px;\r\n  right: 5px;\r\n  display: grid;\r\n  width: 26px;\r\n  height: 26px;\r\n  place-items: center;\r\n  border-radius: 50%;\r\n  background: #eaf2f8;\r\n  color: var(--ly420-primary);\r\n  content: \"+\";\r\n  font-size: 18px;\r\n  font-weight: 800;\r\n}\r\n\r\n.ly420-faq details[open] summary::after {\r\n  content: \"\u2212\";\r\n}\r\n\r\n.ly420-faq-answer {\r\n  padding: 0 42px 18px 2px;\r\n  color: var(--ly420-muted);\r\n  font-size: 15px;\r\n}\r\n\r\n.ly420-faq-answer p:last-child {\r\n  margin-bottom: 0;\r\n}\r\n\r\n.ly420-sources {\r\n  margin: 50px 0 20px;\r\n  padding-top: 28px;\r\n  border-top: 1px solid var(--ly420-border);\r\n}\r\n\r\n.ly420-sources h2 {\r\n  margin-top: 0;\r\n  font-size: 25px;\r\n}\r\n\r\n.ly420-sources ol {\r\n  padding-left: 21px;\r\n}\r\n\r\n.ly420-sources li {\r\n  margin-bottom: 11px;\r\n  color: #657582;\r\n  font-size: 13px;\r\n  line-height: 1.6;\r\n}\r\n\r\n.ly420-sources a {\r\n  overflow-wrap: anywhere;\r\n}\r\n\r\n\/* =========================================================\r\n   Responsive: 1440\r\n   ========================================================= *\/\r\n\r\n@media (max-width: 1440px) {\r\n  .ly420-container {\r\n    width: min(100% - 44px, 1120px);\r\n  }\r\n\r\n  .ly420-page h2 {\r\n    font-size: 33px;\r\n  }\r\n}\r\n\r\n\/* =========================================================\r\n   Responsive: 1366\r\n   ========================================================= *\/\r\n\r\n@media (max-width: 1366px) {\r\n  .ly420-container {\r\n    width: min(100% - 42px, 1080px);\r\n  }\r\n\r\n  .ly420-lead {\r\n    font-size: 20px;\r\n  }\r\n\r\n  .ly420-page h2 {\r\n    font-size: 32px;\r\n  }\r\n}\r\n\r\n\/* =========================================================\r\n   Responsive: 1280\r\n   ========================================================= *\/\r\n\r\n@media (max-width: 1280px) {\r\n  .ly420-container {\r\n    width: min(100% - 40px, 1030px);\r\n  }\r\n\r\n  .ly420-key-grid,\r\n  .ly420-app-grid {\r\n    grid-template-columns: repeat(2, minmax(0, 1fr));\r\n  }\r\n\r\n  .ly420-toc-grid {\r\n    grid-template-columns: repeat(2, minmax(0, 1fr));\r\n  }\r\n\r\n  .ly420-calc-grid {\r\n    grid-template-columns: repeat(4, minmax(0, 1fr));\r\n  }\r\n\r\n  .ly420-field label {\r\n    min-height: 46px;\r\n  }\r\n}\r\n\r\n\/* =========================================================\r\n   Responsive: 1024\r\n   ========================================================= *\/\r\n\r\n@media (max-width: 1024px) {\r\n  .ly420-container {\r\n    width: min(100% - 36px, 930px);\r\n  }\r\n\r\n  .ly420-page {\r\n    font-size: 16px;\r\n  }\r\n\r\n  .ly420-page h2 {\r\n    margin-top: 50px;\r\n    font-size: 30px;\r\n  }\r\n\r\n  .ly420-page h3 {\r\n    font-size: 22px;\r\n  }\r\n\r\n  .ly420-comparison {\r\n    grid-template-columns: 1fr;\r\n  }\r\n\r\n  .ly420-config-grid {\r\n    grid-template-columns: repeat(2, minmax(0, 1fr));\r\n  }\r\n\r\n  .ly420-config-card,\r\n  .ly420-config-card:nth-child(4),\r\n  .ly420-config-card:nth-child(5) {\r\n    grid-column: auto;\r\n  }\r\n\r\n  .ly420-config-card:last-child {\r\n    grid-column: 1 \/ -1;\r\n  }\r\n\r\n  .ly420-calc-grid {\r\n    grid-template-columns: repeat(2, minmax(0, 1fr));\r\n  }\r\n\r\n  .ly420-field label {\r\n    min-height: 0;\r\n  }\r\n\r\n  .ly420-approval-grid {\r\n    grid-template-columns: repeat(2, minmax(0, 1fr));\r\n  }\r\n\r\n  .ly420-cta {\r\n    grid-template-columns: minmax(0, 1fr) 260px;\r\n    gap: 30px;\r\n    padding: 34px;\r\n  }\r\n}\r\n\r\n\/* =========================================================\r\n   Responsive: 912\r\n   ========================================================= *\/\r\n\r\n@media (max-width: 912px) {\r\n  .ly420-container {\r\n    width: min(100% - 34px, 840px);\r\n  }\r\n\r\n  .ly420-quick-answer {\r\n    padding: 27px;\r\n  }\r\n\r\n  .ly420-answer-strip {\r\n    grid-template-columns: 130px minmax(0, 1fr);\r\n  }\r\n\r\n  .ly420-order-head {\r\n    grid-template-columns: 1fr;\r\n    gap: 10px;\r\n    align-items: start;\r\n  }\r\n\r\n  .ly420-simple-order-grid {\r\n    grid-template-columns: repeat(2, minmax(0, 1fr));\r\n  }\r\n}\r\n\r\n\/* =========================================================\r\n   Responsive: 820\r\n   ========================================================= *\/\r\n\r\n@media (max-width: 820px) {\r\n  .ly420-container {\r\n    width: min(100% - 32px, 760px);\r\n  }\r\n\r\n  .ly420-lead {\r\n    font-size: 19px;\r\n  }\r\n\r\n  .ly420-page h2 {\r\n    font-size: 28px;\r\n  }\r\n\r\n  .ly420-toc-grid,\r\n  .ly420-check-grid {\r\n    grid-template-columns: 1fr;\r\n  }\r\n\r\n  .ly420-related-grid {\r\n    grid-template-columns: 1fr;\r\n  }\r\n\r\n  .ly420-calc-result {\r\n    grid-template-columns: 1fr 1fr;\r\n  }\r\n\r\n  .ly420-result-box:last-of-type {\r\n    grid-column: 1 \/ -1;\r\n  }\r\n\r\n  .ly420-cta {\r\n    grid-template-columns: 1fr;\r\n    gap: 24px;\r\n  }\r\n\r\n  .ly420-cta-actions {\r\n    width: 100%;\r\n    max-width: 340px;\r\n    justify-content: flex-start;\r\n  }\r\n}\r\n\r\n\/* =========================================================\r\n   Responsive: 768\r\n   ========================================================= *\/\r\n\r\n@media (max-width: 768px) {\r\n  .ly420-container {\r\n    width: min(100% - 30px, 710px);\r\n  }\r\n\r\n  .ly420-intro {\r\n    padding-top: 20px;\r\n  }\r\n\r\n  .ly420-page h2 {\r\n    margin-top: 45px;\r\n    font-size: 27px;\r\n  }\r\n\r\n  .ly420-quick-answer h2,\r\n  .ly420-config-box > h2 {\r\n    font-size: 24px;\r\n  }\r\n\r\n  .ly420-key-grid,\r\n  .ly420-app-grid {\r\n    grid-template-columns: 1fr 1fr;\r\n  }\r\n\r\n  .ly420-step {\r\n    grid-template-columns: 46px minmax(0, 1fr);\r\n    gap: 14px;\r\n    padding: 19px;\r\n  }\r\n\r\n  .ly420-step::before {\r\n    width: 42px;\r\n    height: 42px;\r\n  }\r\n\r\n  .ly420-responsibility-wrap {\r\n    overflow: visible;\r\n    border: 0;\r\n    background: transparent;\r\n  }\r\n\r\n  .ly420-responsibility-table,\r\n  .ly420-responsibility-table tbody,\r\n  .ly420-responsibility-table tr,\r\n  .ly420-responsibility-table td {\r\n    display: block;\r\n    width: 100%;\r\n  }\r\n\r\n  .ly420-responsibility-table {\r\n    min-width: 0;\r\n  }\r\n\r\n  .ly420-responsibility-table thead {\r\n    position: absolute;\r\n    width: 1px;\r\n    height: 1px;\r\n    overflow: hidden;\r\n    clip: rect(0 0 0 0);\r\n  }\r\n\r\n  .ly420-responsibility-table tr {\r\n    margin-bottom: 15px;\r\n    overflow: hidden;\r\n    border: 1px solid var(--ly420-border);\r\n    border-radius: 11px;\r\n    background: #fff;\r\n  }\r\n\r\n  .ly420-responsibility-table td,\r\n  .ly420-responsibility-table td:nth-child(1),\r\n  .ly420-responsibility-table td:nth-child(2),\r\n  .ly420-responsibility-table td:nth-child(3) {\r\n    width: 100%;\r\n    padding: 14px 16px;\r\n    border-right: 0;\r\n    border-bottom: 1px solid #e1e8ed;\r\n    background: #fff !important;\r\n  }\r\n\r\n  .ly420-responsibility-table td:last-child {\r\n    border-bottom: 0;\r\n  }\r\n\r\n  .ly420-responsibility-table td::before {\r\n    display: block;\r\n    margin-bottom: 5px;\r\n    color: var(--ly420-primary-dark);\r\n    content: attr(data-label);\r\n    font-size: 11px;\r\n    font-weight: 850;\r\n    letter-spacing: 0.05em;\r\n    text-transform: uppercase;\r\n  }\r\n\r\n  .ly420-responsibility-table td:first-child {\r\n    background: #eaf2f8 !important;\r\n  }\r\n\r\n  .ly420-responsibility-table td:first-child::before {\r\n    display: none;\r\n  }\r\n}\r\n\r\n\/* =========================================================\r\n   Responsive: 600\r\n   ========================================================= *\/\r\n\r\n@media (max-width: 600px) {\r\n  .ly420-container {\r\n    width: min(100% - 26px, 560px);\r\n  }\r\n\r\n  .ly420-page {\r\n    font-size: 15.5px;\r\n    line-height: 1.68;\r\n  }\r\n\r\n  .ly420-lead {\r\n    font-size: 18px;\r\n    line-height: 1.58;\r\n  }\r\n\r\n  .ly420-page h2 {\r\n    margin-top: 41px;\r\n    font-size: 25px;\r\n  }\r\n\r\n  .ly420-page h3 {\r\n    font-size: 20px;\r\n  }\r\n\r\n  .ly420-quick-answer {\r\n    padding: 23px 21px;\r\n    border-left-width: 5px;\r\n  }\r\n\r\n  .ly420-config-box {\r\n    padding: 22px 20px;\r\n  }\r\n\r\n  .ly420-config-grid,\r\n  .ly420-key-grid,\r\n  .ly420-app-grid,\r\n  .ly420-calc-grid,\r\n  .ly420-simple-order-grid,\r\n  .ly420-approval-grid {\r\n    grid-template-columns: 1fr;\r\n  }\r\n\r\n  .ly420-config-card:last-child {\r\n    grid-column: auto;\r\n  }\r\n\r\n  .ly420-trust-note,\r\n  .ly420-answer-strip {\r\n    grid-template-columns: 1fr;\r\n    gap: 9px;\r\n  }\r\n\r\n  .ly420-figure {\r\n    margin: 23px 0 31px;\r\n  }\r\n\r\n  .ly420-figure figcaption {\r\n    padding: 13px 15px;\r\n    font-size: 12.5px;\r\n  }\r\n\r\n  .ly420-calculator-head,\r\n  .ly420-calculator-body {\r\n    padding: 22px 20px;\r\n  }\r\n\r\n  .ly420-calc-result {\r\n    grid-template-columns: 1fr;\r\n  }\r\n\r\n  .ly420-result-box:last-of-type {\r\n    grid-column: auto;\r\n  }\r\n\r\n  .ly420-order-box,\r\n  .ly420-approval {\r\n    padding: 22px 19px;\r\n  }\r\n\r\n  .ly420-order-head h3 {\r\n    font-size: 22px;\r\n  }\r\n\r\n  .ly420-order-easy-note {\r\n    display: block;\r\n  }\r\n\r\n  .ly420-order-easy-note strong {\r\n    display: block;\r\n    margin-bottom: 4px;\r\n  }\r\n\r\n  .ly420-cta {\r\n    margin: 43px 0;\r\n    padding: 27px 22px;\r\n  }\r\n\r\n  .ly420-cta h2 {\r\n    font-size: 25px;\r\n  }\r\n\r\n  .ly420-cta-actions {\r\n    max-width: none;\r\n  }\r\n\r\n  .ly420-btn {\r\n    width: 100%;\r\n  }\r\n}\r\n\r\n\/* =========================================================\r\n   Responsive: 540\r\n   ========================================================= *\/\r\n\r\n@media (max-width: 540px) {\r\n  .ly420-container {\r\n    width: min(100% - 24px, 510px);\r\n  }\r\n\r\n  .ly420-toc {\r\n    padding: 21px 19px;\r\n  }\r\n\r\n  .ly420-table {\r\n    min-width: 690px;\r\n  }\r\n\r\n  .ly420-responsibility-table {\r\n    min-width: 0;\r\n  }\r\n\r\n  .ly420-formula {\r\n    padding: 20px 16px;\r\n  }\r\n\r\n  .ly420-formula-code {\r\n    font-size: 15px;\r\n  }\r\n\r\n  .ly420-mistake {\r\n    padding: 16px;\r\n  }\r\n}\r\n\r\n\/* =========================================================\r\n   Responsive: 480\r\n   ========================================================= *\/\r\n\r\n@media (max-width: 480px) {\r\n  .ly420-container {\r\n    width: calc(100% - 22px);\r\n  }\r\n\r\n  .ly420-eyebrow {\r\n    font-size: 11px;\r\n  }\r\n\r\n  .ly420-page h2 {\r\n    font-size: 23px;\r\n  }\r\n\r\n  .ly420-quick-answer h2,\r\n  .ly420-config-box > h2 {\r\n    font-size: 22px;\r\n  }\r\n\r\n  .ly420-answer-line {\r\n    font-size: 16px;\r\n  }\r\n\r\n  .ly420-step {\r\n    grid-template-columns: 39px minmax(0, 1fr);\r\n    padding: 17px;\r\n  }\r\n\r\n  .ly420-step::before {\r\n    width: 36px;\r\n    height: 36px;\r\n    font-size: 14px;\r\n  }\r\n\r\n  .ly420-calculator-head h3 {\r\n    font-size: 21px;\r\n  }\r\n\r\n  .ly420-result-box strong {\r\n    font-size: 22px;\r\n  }\r\n\r\n  .ly420-faq summary {\r\n    font-size: 16px;\r\n  }\r\n}\r\n\r\n\/* =========================================================\r\n   Responsive: 430\r\n   ========================================================= *\/\r\n\r\n@media (max-width: 430px) {\r\n  .ly420-container {\r\n    width: calc(100% - 20px);\r\n  }\r\n\r\n  .ly420-page {\r\n    font-size: 15px;\r\n  }\r\n\r\n  .ly420-lead {\r\n    font-size: 17px;\r\n  }\r\n\r\n  .ly420-quick-answer,\r\n  .ly420-config-box,\r\n  .ly420-toc,\r\n  .ly420-figure {\r\n    border-radius: 11px;\r\n  }\r\n\r\n  .ly420-table th,\r\n  .ly420-table td {\r\n    padding: 13px 14px;\r\n  }\r\n\r\n  .ly420-callout {\r\n    padding: 20px 18px;\r\n  }\r\n\r\n  .ly420-cta {\r\n    padding: 24px 19px;\r\n  }\r\n\r\n  .ly420-cta h2 {\r\n    font-size: 23px;\r\n  }\r\n}\r\n\r\n\/* =========================================================\r\n   Responsive: 414\r\n   ========================================================= *\/\r\n\r\n@media (max-width: 414px) {\r\n  .ly420-page h2 {\r\n    font-size: 22px;\r\n  }\r\n\r\n  .ly420-page h3 {\r\n    font-size: 19px;\r\n  }\r\n\r\n  .ly420-quick-answer {\r\n    padding: 21px 18px;\r\n  }\r\n\r\n  .ly420-config-box,\r\n  .ly420-calculator-head,\r\n  .ly420-calculator-body,\r\n  .ly420-order-box,\r\n  .ly420-approval {\r\n    padding-inline: 18px;\r\n  }\r\n}\r\n\r\n\/* =========================================================\r\n   Responsive: 390\r\n   ========================================================= *\/\r\n\r\n@media (max-width: 390px) {\r\n  .ly420-container {\r\n    width: calc(100% - 18px);\r\n  }\r\n\r\n  .ly420-page h2 {\r\n    font-size: 21.5px;\r\n  }\r\n\r\n  .ly420-toc a,\r\n  .ly420-check-item {\r\n    font-size: 13.5px;\r\n  }\r\n\r\n  .ly420-step h3 {\r\n    font-size: 18px;\r\n  }\r\n\r\n  .ly420-formula-code {\r\n    font-size: 14px;\r\n  }\r\n}\r\n\r\n\/* =========================================================\r\n   Responsive: 375\r\n   ========================================================= *\/\r\n\r\n@media (max-width: 375px) {\r\n  .ly420-lead {\r\n    font-size: 16.5px;\r\n  }\r\n\r\n  .ly420-quick-answer h2,\r\n  .ly420-config-box > h2 {\r\n    font-size: 20px;\r\n  }\r\n\r\n  .ly420-cta h2 {\r\n    font-size: 23px;\r\n  }\r\n}\r\n\r\n\/* =========================================================\r\n   Responsive: 360\r\n   ========================================================= *\/\r\n\r\n@media (max-width: 360px) {\r\n  .ly420-container {\r\n    width: calc(100% - 16px);\r\n  }\r\n\r\n  .ly420-page {\r\n    font-size: 14.5px;\r\n  }\r\n\r\n  .ly420-page h2 {\r\n    font-size: 21px;\r\n  }\r\n\r\n  .ly420-step {\r\n    grid-template-columns: 35px minmax(0, 1fr);\r\n    gap: 10px;\r\n    padding: 15px;\r\n  }\r\n\r\n  .ly420-step::before {\r\n    width: 33px;\r\n    height: 33px;\r\n  }\r\n\r\n  .ly420-calculator-head,\r\n  .ly420-calculator-body,\r\n  .ly420-cta {\r\n    padding-inline: 16px;\r\n  }\r\n}\r\n\r\n\/* =========================================================\r\n   Responsive: 320\r\n   ========================================================= *\/\r\n\r\n@media (max-width: 320px) {\r\n  .ly420-container {\r\n    width: calc(100% - 14px);\r\n  }\r\n\r\n  .ly420-page {\r\n    font-size: 14px;\r\n  }\r\n\r\n  .ly420-page h2 {\r\n    font-size: 20px;\r\n  }\r\n\r\n  .ly420-lead {\r\n    font-size: 16px;\r\n  }\r\n\r\n  .ly420-quick-answer,\r\n  .ly420-config-box,\r\n  .ly420-toc,\r\n  .ly420-calculator-body,\r\n  .ly420-order-box,\r\n  .ly420-approval {\r\n    padding-inline: 14px;\r\n  }\r\n\r\n  .ly420-step {\r\n    grid-template-columns: 1fr;\r\n  }\r\n\r\n  .ly420-step::before {\r\n    margin-bottom: 2px;\r\n  }\r\n\r\n  .ly420-faq summary {\r\n    padding-right: 35px;\r\n    font-size: 15px;\r\n  }\r\n}\r\n<\/style>\r\n\r\n<article\r\n  class=\"ly420-page\"\r\n  id=\"4-20ma-signal-spd-guide\"\r\n  lang=\"en\"\r\n>\r\n  <div class=\"ly420-container\">\r\n\r\n    <header class=\"ly420-intro\">\r\n      <p class=\"ly420-eyebrow\">\r\n        Industrial Instrumentation Selection Guide\r\n      <\/p>\r\n\r\n      <p class=\"ly420-lead\">\r\n        Selecting a <strong>4-20mA surge protector<\/strong> is not only a\r\n        question of surge current. The signal SPD must match the loop voltage,\r\n        two-wire or four-wire circuit, transmitter power arrangement, PLC or\r\n        DCS input, HART communication and the voltage available across the\r\n        complete current loop.\r\n      <\/p>\r\n    <\/header>\r\n\r\n    <section\r\n      class=\"ly420-quick-answer ly420-anchor\"\r\n      id=\"quick-answer\"\r\n    >\r\n      <div id=\"ez-toc-container\" class=\"ez-toc-v2_0_85 counter-hierarchy ez-toc-counter ez-toc-custom ez-toc-container-direction\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><\/span><\/div>\n<nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#quick-answer-what-spd-should-be-used-for-a-4-20ma-loop\" >Quick answer: what SPD should be used for a 4-20mA loop?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#recommended-protection-configurations\" >Recommended protection configurations<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#how-to-select-a-4-20ma-signal-spd\" >How to select a 4-20mA signal SPD<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#two-wire-three-wire-and-four-wire-4-20ma-loops\" >Two-wire, three-wire and four-wire 4-20mA loops<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#active-and-passive-4-20ma-loops\" >Active and passive 4-20mA loops<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#what-voltage-rating-should-the-4-20ma-spd-have\" >What voltage rating should the 4-20mA SPD have?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#will-an-spd-cause-voltage-drop-in-a-4-20ma-loop\" >Will an SPD cause voltage drop in a 4-20mA loop?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#can-a-signal-spd-affect-4-20ma-measurement-accuracy\" >Can a signal SPD affect 4-20mA measurement accuracy?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#how-to-select-a-hart-compatible-surge-protector\" >How to select a HART-compatible surge protector<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-10\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#should-the-spd-be-installed-at-the-field-instrument-or-control-cabinet\" >Should the SPD be installed at the field instrument or control cabinet?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-11\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#shielding-din-rail-grounding-and-equipotential-bonding\" >Shielding, DIN-rail grounding and equipotential bonding<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-12\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#4-20ma-spd-selection-for-hazardous-areas-and-ex-i-loops\" >4-20mA SPD selection for hazardous areas and Ex i loops<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-13\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#what-the-buyer-provides-and-what-the-spd-supplier-confirms\" >What the buyer provides and what the SPD supplier confirms<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-14\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#model-confirmation-before-a-project-or-oem-order\" >Model confirmation before a project or OEM order<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-15\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#typical-industrial-applications\" >Typical industrial applications<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-16\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#common-4-20ma-spd-selection-mistakes\" >Common 4-20mA SPD selection mistakes<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-17\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#what-to-send-for-a-4-20ma-spd-recommendation\" >What to send for a 4-20mA SPD recommendation<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-18\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#related-leeyee-technical-guides\" >Related LEEYEE technical guides<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-19\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#need-help-selecting-a-4-20ma-signal-spd\" >Need help selecting a 4-20mA signal SPD?<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-20\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#frequently-asked-questions\" >Frequently asked questions<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-2'><a class=\"ez-toc-link ez-toc-heading-21\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/pt\/4-20ma-signal-spd\/#technical-references\" >Technical references<\/a><\/li><\/ul><\/nav><\/div>\n<h2><span class=\"ez-toc-section\" id=\"quick-answer-what-spd-should-be-used-for-a-4-20ma-loop\"><\/span>\r\n        Quick answer: what SPD should be used for a 4-20mA loop?\r\n      <span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <p class=\"ly420-answer-line\">\r\n        For a typical 24V two-wire, loop-powered transmitter, use a signal SPD\r\n        designed for one floating two-conductor current loop.\r\n      <\/p>\r\n\r\n      <p>\r\n        Confirm that the SPD maximum continuous operating voltage is above the\r\n        highest normal loop voltage. Then check the series resistance or\r\n        voltage drop at maximum loop current, leakage current, protection\r\n        level, grounding method and HART compatibility.\r\n      <\/p>\r\n\r\n      <p>\r\n        A four-wire transmitter normally has a separate power input and\r\n        4-20mA output. Its power conductors and signal conductors must be\r\n        evaluated as different circuits. One two-wire signal SPD may not\r\n        protect the complete instrument.\r\n      <\/p>\r\n    <\/section>\r\n\r\n    <section\r\n      class=\"ly420-config-box\"\r\n      id=\"common-configurations\"\r\n    >\r\n      <h2><span class=\"ez-toc-section\" id=\"recommended-protection-configurations\"><\/span>Recommended protection configurations<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <p>\r\n        Use this matrix for initial planning. Final model confirmation still\r\n        requires basic loop and equipment information.\r\n      <\/p>\r\n\r\n      <div class=\"ly420-config-grid\">\r\n        <article class=\"ly420-config-card\">\r\n          <span class=\"ly420-config-tag\">Common loop<\/span>\r\n          <h3>2-wire, 24V transmitter<\/h3>\r\n\r\n          <p>\r\n            Use one matched signal SPD for the floating current-loop pair.\r\n          <\/p>\r\n\r\n          <p>\r\n            <strong>Confirm:<\/strong> UC, series resistance, leakage current\r\n            and line-to-line\/earth protection.\r\n          <\/p>\r\n        <\/article>\r\n\r\n        <article class=\"ly420-config-card\">\r\n          <span class=\"ly420-config-tag\">Smart instrument<\/span>\r\n          <h3>2-wire HART loop<\/h3>\r\n\r\n          <p>\r\n            Use a 4-20mA signal SPD with explicit HART compatibility.\r\n          <\/p>\r\n\r\n          <p>\r\n            <strong>Confirm:<\/strong> capacitance, frequency response, loop\r\n            impedance and voltage drop.\r\n          <\/p>\r\n        <\/article>\r\n\r\n        <article class=\"ly420-config-card\">\r\n          <span class=\"ly420-config-tag\">Separate circuits<\/span>\r\n          <h3>4-wire transmitter<\/h3>\r\n\r\n          <p>\r\n            Evaluate the instrument power input and 4-20mA output separately.\r\n          <\/p>\r\n\r\n          <p>\r\n            <strong>Confirm:<\/strong> power voltage, output type, isolation and\r\n            signal reference.\r\n          <\/p>\r\n        <\/article>\r\n\r\n        <article class=\"ly420-config-card\">\r\n          <span class=\"ly420-config-tag\">High exposure<\/span>\r\n          <h3>Outdoor or long cable<\/h3>\r\n\r\n          <p>\r\n            Evaluate field-side and cabinet-entry protection for both ends.\r\n          <\/p>\r\n\r\n          <p>\r\n            <strong>Confirm:<\/strong> cable route, LPZ boundary, enclosure,\r\n            shield and bonding.\r\n          <\/p>\r\n        <\/article>\r\n\r\n        <article class=\"ly420-config-card\">\r\n          <span class=\"ly420-config-tag\">Hazardous area<\/span>\r\n          <h3>Ex i instrument loop<\/h3>\r\n\r\n          <p>\r\n            Use only an SPD approved and coordinated for the intrinsically\r\n            safe circuit.\r\n          <\/p>\r\n\r\n          <p>\r\n            <strong>Confirm:<\/strong> Ex approval, entity parameters, barrier,\r\n            earthing and installation zone.\r\n          <\/p>\r\n        <\/article>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <div class=\"ly420-trust-note\">\r\n      <div class=\"ly420-trust-icon\" aria-hidden=\"true\">!<\/div>\r\n\r\n      <div>\r\n        <h3>Why there is no universal \u201c24V 4-20mA\u201d model<\/h3>\r\n\r\n        <p>\r\n          Two loops with the same nominal voltage may have different power\r\n          sources, input burdens, grounding references, HART requirements and\r\n          hazardous-area conditions. A final model should not be selected from\r\n          \u201c24V, 4-20mA\u201d alone.\r\n        <\/p>\r\n      <\/div>\r\n    <\/div>\r\n\r\n    <div\r\n      class=\"ly420-key-grid\"\r\n      aria-label=\"Key 4-20mA SPD selection points\"\r\n    >\r\n      <div class=\"ly420-key-card\">\r\n        <strong>Match the circuit<\/strong>\r\n        <span>\r\n          Two-wire floating, common-reference, three-wire or four-wire.\r\n        <\/span>\r\n      <\/div>\r\n\r\n      <div class=\"ly420-key-card\">\r\n        <strong>Protect the voltage margin<\/strong>\r\n        <span>\r\n          Calculate SPD and cable voltage drop at maximum loop current.\r\n        <\/span>\r\n      <\/div>\r\n\r\n      <div class=\"ly420-key-card\">\r\n        <strong>Confirm HART<\/strong>\r\n        <span>\r\n          A 4-20mA rating alone does not prove HART transparency.\r\n        <\/span>\r\n      <\/div>\r\n\r\n      <div class=\"ly420-key-card\">\r\n        <strong>Plan both ends<\/strong>\r\n        <span>\r\n          Outdoor and interbuilding loops may need field and cabinet SPDs.\r\n        <\/span>\r\n      <\/div>\r\n    <\/div>\r\n\r\n    <nav class=\"ly420-toc\" aria-label=\"Article contents\">\r\n      <p class=\"ly420-toc-title\">In this guide<\/p>\r\n\r\n      <div class=\"ly420-toc-grid\">\r\n        <a href=\"#selection-process\">Selection process<\/a>\r\n        <a href=\"#loop-types\">2-wire vs 4-wire<\/a>\r\n        <a href=\"#active-passive\">Active and passive loops<\/a>\r\n        <a href=\"#voltage-rating\">SPD voltage rating<\/a>\r\n        <a href=\"#voltage-budget\">Loop voltage budget<\/a>\r\n        <a href=\"#accuracy\">Accuracy and leakage<\/a>\r\n        <a href=\"#hart\">HART compatibility<\/a>\r\n        <a href=\"#installation-position\">Installation position<\/a>\r\n        <a href=\"#shield-grounding\">Shield and grounding<\/a>\r\n        <a href=\"#hazardous-area\">Hazardous areas<\/a>\r\n        <a href=\"#buyer-supplier-table\">Buyer and supplier data<\/a>\r\n        <a href=\"#ordering-checklist\">Simple enquiry checklist<\/a>\r\n      <\/div>\r\n    <\/nav>\r\n\r\n    <section class=\"ly420-anchor\" id=\"selection-process\">\r\n      <h2><span class=\"ez-toc-section\" id=\"how-to-select-a-4-20ma-signal-spd\"><\/span>How to select a 4-20mA signal SPD<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <p>\r\n        Start with the loop drawing rather than the SPD catalogue. Two systems\r\n        described as \u201c24V 4-20mA\u201d may use different power sources, grounding\r\n        references and conductor arrangements.\r\n      <\/p>\r\n\r\n      <div class=\"ly420-steps\">\r\n        <div class=\"ly420-step\">\r\n          <div>\r\n            <h3>Identify the complete circuit<\/h3>\r\n\r\n            <p>\r\n              Confirm whether the instrument is two-wire loop-powered,\r\n              three-wire or four-wire self-powered.\r\n            <\/p>\r\n          <\/div>\r\n        <\/div>\r\n\r\n        <div class=\"ly420-step\">\r\n          <div>\r\n            <h3>Find the source of loop power<\/h3>\r\n\r\n            <p>\r\n              Determine whether the PLC\/DCS input, an external supply or the\r\n              field instrument provides loop power.\r\n            <\/p>\r\n          <\/div>\r\n        <\/div>\r\n\r\n        <div class=\"ly420-step\">\r\n          <div>\r\n            <h3>Determine the highest normal voltage<\/h3>\r\n\r\n            <p>\r\n              Include supply tolerance and the maximum voltage that can remain\r\n              continuously on the protected conductors.\r\n            <\/p>\r\n          <\/div>\r\n        <\/div>\r\n\r\n        <div class=\"ly420-step\">\r\n          <div>\r\n            <h3>Match the SPD circuit topology<\/h3>\r\n\r\n            <p>\r\n              Choose protection for a floating pair, common-reference circuit,\r\n              or separate signal and power circuits.\r\n            <\/p>\r\n          <\/div>\r\n        <\/div>\r\n\r\n        <div class=\"ly420-step\">\r\n          <div>\r\n            <h3>Check signal transparency<\/h3>\r\n\r\n            <p>\r\n              Review series resistance, voltage drop, leakage current,\r\n              capacitance and HART compatibility.\r\n            <\/p>\r\n          <\/div>\r\n        <\/div>\r\n\r\n        <div class=\"ly420-step\">\r\n          <div>\r\n            <h3>Confirm installation conditions<\/h3>\r\n\r\n            <p>\r\n              Specify field or cabinet mounting, grounding, terminal size,\r\n              hazardous-area approval and environmental requirements.\r\n            <\/p>\r\n          <\/div>\r\n        <\/div>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section class=\"ly420-anchor\" id=\"loop-types\">\r\n      <h2><span class=\"ez-toc-section\" id=\"two-wire-three-wire-and-four-wire-4-20ma-loops\"><\/span>Two-wire, three-wire and four-wire 4-20mA loops<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <p>\r\n        The number of conductors changes how power, signal and surge\r\n        protection are arranged. A two-wire loop normally uses the same pair\r\n        for power and measurement. A four-wire transmitter normally separates\r\n        its power input from its analog output.\r\n      <\/p>\r\n\r\n      <figure class=\"ly420-figure\">\r\n        <img loading=\"lazy\"\r\n          src=\"https:\/\/www.cnspd.com\/wp-content\/uploads\/2026\/07\/4-20ma-two-wire-loop-surge-protection-architecture.webp\"\r\n          alt=\"Two-wire 4-20mA current loop surge protection architecture with field-side and control-cabinet SPDs\"\r\n          loading=\"lazy\"\r\n          decoding=\"async\"\r\n          width=\"1600\"\r\n          height=\"900\"\r\n        >\r\n\r\n        <figcaption>\r\n          <strong>Typical two-wire 4-20mA protection architecture:<\/strong>\r\n          the same pair supplies the field transmitter and returns the\r\n          measured current to the PLC or DCS. Long outdoor or interbuilding\r\n          loops may require coordinated protection at both ends.\r\n        <\/figcaption>\r\n      <\/figure>\r\n\r\n      <div class=\"ly420-comparison\">\r\n        <article class=\"ly420-comparison-card\">\r\n          <h3>Two-wire loop-powered<\/h3>\r\n\r\n          <p>\r\n            Power and signal use the same conductor pair.\r\n          <\/p>\r\n\r\n          <ul>\r\n            <li>Usually requires one protected floating pair.<\/li>\r\n            <li>SPD voltage drop forms part of the voltage budget.<\/li>\r\n            <li>Confirm active or passive AI arrangement.<\/li>\r\n            <li>Check HART when a smart transmitter is used.<\/li>\r\n          <\/ul>\r\n        <\/article>\r\n\r\n        <article class=\"ly420-comparison-card\">\r\n          <h3>Three-wire transmitter<\/h3>\r\n\r\n          <p>\r\n            The instrument normally has supply positive, supply common and a\r\n            separate output conductor.\r\n          <\/p>\r\n\r\n          <ul>\r\n            <li>The signal may share the supply reference.<\/li>\r\n            <li>A floating-pair SPD may not match the circuit.<\/li>\r\n            <li>Confirm which conductors carry normal current.<\/li>\r\n            <li>Provide a wiring diagram before final selection.<\/li>\r\n          <\/ul>\r\n        <\/article>\r\n\r\n        <article class=\"ly420-comparison-card\">\r\n          <h3>Four-wire self-powered<\/h3>\r\n\r\n          <p>\r\n            The instrument has a separate power input and an independent\r\n            4-20mA output.\r\n          <\/p>\r\n\r\n          <ul>\r\n            <li>Evaluate power and signal as separate surge paths.<\/li>\r\n            <li>The signal output may be active or isolated.<\/li>\r\n            <li>Power voltage may differ from signal voltage.<\/li>\r\n            <li>One signal SPD may not protect all conductors.<\/li>\r\n          <\/ul>\r\n        <\/article>\r\n      <\/div>\r\n\r\n      <figure class=\"ly420-figure\">\r\n        <img loading=\"lazy\"\r\n          src=\"https:\/\/www.cnspd.com\/wp-content\/uploads\/2026\/07\/4-20ma-two-wire-vs-four-wire-spd-selection.webp\"\r\n          alt=\"Comparison of surge protection selection for two-wire and four-wire 4-20mA instrumentation loops\"\r\n          loading=\"lazy\"\r\n          decoding=\"async\"\r\n          width=\"1600\"\r\n          height=\"900\"\r\n        >\r\n\r\n        <figcaption>\r\n          <strong>Two-wire versus four-wire selection:<\/strong>\r\n          a two-wire loop combines power and signal on one pair. A four-wire\r\n          transmitter normally has separate power and signal paths that\r\n          require separate evaluation.\r\n        <\/figcaption>\r\n      <\/figure>\r\n\r\n      <div class=\"ly420-callout ly420-callout--warning\">\r\n        <h3>Do not select the SPD only from terminal count<\/h3>\r\n\r\n        <p>\r\n          A four-wire transmitter does not automatically require one\r\n          four-channel signal SPD. Confirm the power input, analog output,\r\n          internal isolation and grounding reference first.\r\n        <\/p>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section class=\"ly420-anchor\" id=\"active-passive\">\r\n      <h2><span class=\"ez-toc-section\" id=\"active-and-passive-4-20ma-loops\"><\/span>Active and passive 4-20mA loops<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <p>\r\n        \u201cActive\u201d and \u201cpassive\u201d describe which device supplies loop power. This\r\n        changes the normal voltage and reference present on the conductors.\r\n      <\/p>\r\n\r\n      <div class=\"ly420-table-wrap\">\r\n        <table class=\"ly420-table\">\r\n          <thead>\r\n            <tr>\r\n              <th>Arrangement<\/th>\r\n              <th>Who supplies loop power?<\/th>\r\n              <th>Typical connection<\/th>\r\n              <th>What must be confirmed?<\/th>\r\n            <\/tr>\r\n          <\/thead>\r\n\r\n          <tbody>\r\n            <tr>\r\n              <td><strong>Active AI<\/strong><\/td>\r\n              <td>PLC or DCS analog input<\/td>\r\n              <td>AI card powers a passive two-wire transmitter.<\/td>\r\n              <td>AI supply voltage and circuit reference.<\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td><strong>Passive AI<\/strong><\/td>\r\n              <td>External loop power supply<\/td>\r\n              <td>Supply, transmitter and passive AI are connected in series.<\/td>\r\n              <td>Supply tolerance, AI burden and grounding reference.<\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td><strong>Active transmitter output<\/strong><\/td>\r\n              <td>The field instrument<\/td>\r\n              <td>A self-powered instrument drives a passive AI.<\/td>\r\n              <td>Output voltage, common-mode limits and isolation.<\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td><strong>Analog output loop<\/strong><\/td>\r\n              <td>PLC\/DCS AO card or external supply<\/td>\r\n              <td>AO controls a valve positioner or actuator.<\/td>\r\n              <td>Whether the AO is sourcing or sinking.<\/td>\r\n            <\/tr>\r\n          <\/tbody>\r\n        <\/table>\r\n      <\/div>\r\n\r\n      <div class=\"ly420-callout ly420-callout--warning\">\r\n        <span class=\"ly420-mini-label\">Procurement warning<\/span>\r\n\r\n        <p>\r\n          A request that only says \u201c24V, 4-20mA SPD\u201d may not be enough for a\r\n          final model. A basic wiring diagram, terminal photo or equipment\r\n          model can usually resolve the missing information.\r\n        <\/p>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section class=\"ly420-anchor\" id=\"voltage-rating\">\r\n      <h2><span class=\"ez-toc-section\" id=\"what-voltage-rating-should-the-4-20ma-spd-have\"><\/span>What voltage rating should the 4-20mA SPD have?<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <p>\r\n        Select the signal SPD from the highest voltage that can remain\r\n        continuously on the protected conductors\u2014not from the 4mA or 20mA\r\n        signal values.\r\n      <\/p>\r\n\r\n      <div class=\"ly420-answer-strip\">\r\n        <div class=\"ly420-answer-strip-label\">Selection rule<\/div>\r\n\r\n        <p>\r\n          The SPD maximum continuous operating voltage must be above the\r\n          highest normal circuit voltage, including supply tolerance, while\r\n          remaining low enough to provide a useful protection level.\r\n        <\/p>\r\n      <\/div>\r\n\r\n      <div class=\"ly420-check-grid\">\r\n        <div class=\"ly420-check-item\">\r\n          <strong>Nominal voltage<\/strong>\r\n          The normal system voltage for which the SPD is designed.\r\n        <\/div>\r\n\r\n        <div class=\"ly420-check-item\">\r\n          <strong>Maximum continuous operating voltage<\/strong>\r\n          The highest voltage that may remain applied without normal\r\n          conduction.\r\n        <\/div>\r\n\r\n        <div class=\"ly420-check-item\">\r\n          <strong>Protection level<\/strong>\r\n          Check line-to-line and line-to-earth values when separately listed.\r\n        <\/div>\r\n\r\n        <div class=\"ly420-check-item\">\r\n          <strong>Equipment withstand level<\/strong>\r\n          Residual voltage must remain compatible with the protected interface.\r\n        <\/div>\r\n      <\/div>\r\n\r\n      <div class=\"ly420-callout ly420-callout--danger\">\r\n        <h3>Lower UC is not automatically better<\/h3>\r\n\r\n        <p>\r\n          If the SPD continuous working voltage is below the actual loop\r\n          voltage, it may conduct during normal operation, increase leakage or\r\n          fail prematurely.\r\n        <\/p>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section class=\"ly420-anchor\" id=\"voltage-budget\">\r\n      <h2><span class=\"ez-toc-section\" id=\"will-an-spd-cause-voltage-drop-in-a-4-20ma-loop\"><\/span>Will an SPD cause voltage drop in a 4-20mA loop?<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <p>\r\n        Yes. A series-connected signal SPD normally introduces resistance or\r\n        another series impedance. At 20mA, that impedance creates a voltage\r\n        drop.\r\n      <\/p>\r\n\r\n      <p>\r\n        A small voltage loss does not normally create a proportional current\r\n        measurement error. The transmitter regulates the requested current\r\n        while sufficient voltage remains across its terminals.\r\n      <\/p>\r\n\r\n      <div class=\"ly420-formula\">\r\n        <span class=\"ly420-formula-label\">\r\n          Remaining loop voltage\r\n        <\/span>\r\n\r\n        <span class=\"ly420-formula-code\">\r\n          Vremaining = Vsupply(min) \u2212 Vtransmitter(min) \u2212 VAI \u2212 Vbarrier \u2212\r\n          VSPD \u2212 Vsafety\r\n        <\/span>\r\n      <\/div>\r\n\r\n      <div class=\"ly420-formula\">\r\n        <span class=\"ly420-formula-label\">\r\n          Maximum remaining series resistance\r\n        <\/span>\r\n\r\n        <span class=\"ly420-formula-code\">\r\n          Ravailable = Vremaining \u00f7 Iloop(max)\r\n        <\/span>\r\n      <\/div>\r\n\r\n      <p>Include the following series loads:<\/p>\r\n\r\n      <ul>\r\n        <li>PLC or DCS analog-input burden;<\/li>\r\n        <li>cable loop resistance;<\/li>\r\n        <li>cabinet-side and field-side SPDs;<\/li>\r\n        <li>intrinsic-safety barriers or isolators;<\/li>\r\n        <li>loop-powered displays or test terminals;<\/li>\r\n        <li>engineering safety margin.<\/li>\r\n      <\/ul>\r\n\r\n      <figure class=\"ly420-figure\">\r\n        <img loading=\"lazy\"\r\n          src=\"https:\/\/www.cnspd.com\/wp-content\/uploads\/2026\/07\/4-20ma-loop-voltage-budget-and-spd-voltage-drop.webp\"\r\n          alt=\"4-20mA loop voltage budget showing transmitter, PLC input, cable, barrier and SPD voltage drops\"\r\n          loading=\"lazy\"\r\n          decoding=\"async\"\r\n          width=\"1600\"\r\n          height=\"900\"\r\n        >\r\n\r\n        <figcaption>\r\n          <strong>4-20mA loop voltage budget:<\/strong>\r\n          the supply must cover the transmitter minimum voltage, PLC\/DCS input\r\n          burden, cable resistance, barriers, SPD voltage drops and a safety\r\n          margin.\r\n        <\/figcaption>\r\n      <\/figure>\r\n\r\n      <div\r\n        class=\"ly420-calculator\"\r\n        id=\"ly420-loop-calculator\"\r\n      >\r\n        <div class=\"ly420-calculator-head\">\r\n          <h3>4-20mA loop voltage budget calculator<\/h3>\r\n\r\n          <p>\r\n            Use the minimum supply voltage and maximum expected loop current\r\n            for a conservative preliminary check.\r\n          <\/p>\r\n        <\/div>\r\n\r\n        <div class=\"ly420-calculator-body\">\r\n          <div class=\"ly420-calc-grid\">\r\n            <div class=\"ly420-field\">\r\n              <label for=\"ly420-supply\">\r\n                Minimum loop supply voltage\r\n              <\/label>\r\n\r\n              <div class=\"ly420-field-unit\">\r\n                <input\r\n                  id=\"ly420-supply\"\r\n                  type=\"number\"\r\n                  value=\"21.6\"\r\n                  min=\"0\"\r\n                  step=\"0.1\"\r\n                >\r\n                <span>V<\/span>\r\n              <\/div>\r\n            <\/div>\r\n\r\n            <div class=\"ly420-field\">\r\n              <label for=\"ly420-transmitter\">\r\n                Transmitter minimum voltage\r\n              <\/label>\r\n\r\n              <div class=\"ly420-field-unit\">\r\n                <input\r\n                  id=\"ly420-transmitter\"\r\n                  type=\"number\"\r\n                  value=\"10.5\"\r\n                  min=\"0\"\r\n                  step=\"0.1\"\r\n                >\r\n                <span>V<\/span>\r\n              <\/div>\r\n            <\/div>\r\n\r\n            <div class=\"ly420-field\">\r\n              <label for=\"ly420-burden\">\r\n                AI burden resistance\r\n              <\/label>\r\n\r\n              <div class=\"ly420-field-unit\">\r\n                <input\r\n                  id=\"ly420-burden\"\r\n                  type=\"number\"\r\n                  value=\"250\"\r\n                  min=\"0\"\r\n                  step=\"1\"\r\n                >\r\n                <span>\u03a9<\/span>\r\n              <\/div>\r\n            <\/div>\r\n\r\n            <div class=\"ly420-field\">\r\n              <label for=\"ly420-current\">\r\n                Maximum loop current\r\n              <\/label>\r\n\r\n              <div class=\"ly420-field-unit\">\r\n                <input\r\n                  id=\"ly420-current\"\r\n                  type=\"number\"\r\n                  value=\"20\"\r\n                  min=\"0.1\"\r\n                  step=\"0.1\"\r\n                >\r\n                <span>mA<\/span>\r\n              <\/div>\r\n            <\/div>\r\n\r\n            <div class=\"ly420-field\">\r\n              <label for=\"ly420-other-drop\">\r\n                Barrier and fixed voltage drop\r\n              <\/label>\r\n\r\n              <div class=\"ly420-field-unit\">\r\n                <input\r\n                  id=\"ly420-other-drop\"\r\n                  type=\"number\"\r\n                  value=\"1.5\"\r\n                  min=\"0\"\r\n                  step=\"0.1\"\r\n                >\r\n                <span>V<\/span>\r\n              <\/div>\r\n            <\/div>\r\n\r\n            <div class=\"ly420-field\">\r\n              <label for=\"ly420-spd-count\">\r\n                Number of SPD locations\r\n              <\/label>\r\n\r\n              <div class=\"ly420-field-unit\">\r\n                <input\r\n                  id=\"ly420-spd-count\"\r\n                  type=\"number\"\r\n                  value=\"2\"\r\n                  min=\"0\"\r\n                  step=\"1\"\r\n                >\r\n                <span>pcs<\/span>\r\n              <\/div>\r\n            <\/div>\r\n\r\n            <div class=\"ly420-field\">\r\n              <label for=\"ly420-spd-drop\">\r\n                Voltage drop per SPD\r\n              <\/label>\r\n\r\n              <div class=\"ly420-field-unit\">\r\n                <input\r\n                  id=\"ly420-spd-drop\"\r\n                  type=\"number\"\r\n                  value=\"0.3\"\r\n                  min=\"0\"\r\n                  step=\"0.01\"\r\n                >\r\n                <span>V<\/span>\r\n              <\/div>\r\n            <\/div>\r\n\r\n            <div class=\"ly420-field\">\r\n              <label for=\"ly420-margin\">\r\n                Design safety margin\r\n              <\/label>\r\n\r\n              <div class=\"ly420-field-unit\">\r\n                <input\r\n                  id=\"ly420-margin\"\r\n                  type=\"number\"\r\n                  value=\"1\"\r\n                  min=\"0\"\r\n                  step=\"0.1\"\r\n                >\r\n                <span>V<\/span>\r\n              <\/div>\r\n            <\/div>\r\n          <\/div>\r\n\r\n          <div class=\"ly420-calc-result\" aria-live=\"polite\">\r\n            <div class=\"ly420-result-box\">\r\n              <span>AI voltage drop<\/span>\r\n              <strong id=\"ly420-result-ai\">5.00 V<\/strong>\r\n            <\/div>\r\n\r\n            <div class=\"ly420-result-box\">\r\n              <span>Total SPD voltage drop<\/span>\r\n              <strong id=\"ly420-result-spd\">0.60 V<\/strong>\r\n            <\/div>\r\n\r\n            <div class=\"ly420-result-box\">\r\n              <span>Series resistance allowance<\/span>\r\n              <strong id=\"ly420-result-resistance\">150 \u03a9<\/strong>\r\n            <\/div>\r\n\r\n            <p\r\n              class=\"ly420-result-status\"\r\n              id=\"ly420-result-status\"\r\n            >\r\n              The example retains positive voltage margin. Confirm the actual\r\n              equipment data before final selection.\r\n            <\/p>\r\n          <\/div>\r\n\r\n          <p class=\"ly420-calc-disclaimer\">\r\n            This calculator is a preliminary engineering aid and does not\r\n            replace the actual loop drawing or equipment datasheets.\r\n          <\/p>\r\n        <\/div>\r\n      <\/div>\r\n\r\n      <div class=\"ly420-callout ly420-callout--info\">\r\n        <h3>Example interpretation<\/h3>\r\n\r\n        <p>\r\n          If two SPDs each drop 0.3V at 20mA, they consume 0.6V together. This\r\n          may be acceptable in a simple loop but important in a long circuit\r\n          that also contains a 250\u03a9 input and a safety barrier.\r\n        <\/p>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section class=\"ly420-anchor\" id=\"accuracy\">\r\n      <h2><span class=\"ez-toc-section\" id=\"can-a-signal-spd-affect-4-20ma-measurement-accuracy\"><\/span>Can a signal SPD affect 4-20mA measurement accuracy?<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <p>\r\n        A properly selected SPD should remain electrically transparent during\r\n        normal operation.\r\n      <\/p>\r\n\r\n      <div class=\"ly420-table-wrap\">\r\n        <table class=\"ly420-table\">\r\n          <thead>\r\n            <tr>\r\n              <th>Characteristic<\/th>\r\n              <th>Possible effect<\/th>\r\n              <th>Supplier data to check<\/th>\r\n            <\/tr>\r\n          <\/thead>\r\n\r\n          <tbody>\r\n            <tr>\r\n              <td><strong>Series resistance<\/strong><\/td>\r\n              <td>Consumes loop voltage at high current.<\/td>\r\n              <td>Resistance per conductor and voltage drop at 20mA.<\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td><strong>Leakage current<\/strong><\/td>\r\n              <td>May add offset in high-accuracy circuits.<\/td>\r\n              <td>Maximum leakage at UC and operating temperature.<\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td><strong>Conductor imbalance<\/strong><\/td>\r\n              <td>May reduce common-mode noise rejection.<\/td>\r\n              <td>Matched protection paths for the signal pair.<\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td><strong>Capacitance and bandwidth<\/strong><\/td>\r\n              <td>May affect HART communication.<\/td>\r\n              <td>HART compatibility and frequency response.<\/td>\r\n            <\/tr>\r\n          <\/tbody>\r\n        <\/table>\r\n      <\/div>\r\n\r\n      <div class=\"ly420-callout ly420-callout--success\">\r\n        <h3>Important distinction<\/h3>\r\n\r\n        <p>\r\n          A small SPD voltage drop does not normally create a proportional\r\n          scaling error. It reduces the voltage available to the transmitter.\r\n          If the margin becomes insufficient, the loop may fail to reach the\r\n          expected high-end current.\r\n        <\/p>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section class=\"ly420-anchor\" id=\"hart\">\r\n      <h2><span class=\"ez-toc-section\" id=\"how-to-select-a-hart-compatible-surge-protector\"><\/span>How to select a HART-compatible surge protector<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <p>\r\n        HART superimposes a digital communication signal on the conventional\r\n        4-20mA loop. An SPD may pass DC current but still attenuate HART\r\n        communication.\r\n      <\/p>\r\n\r\n      <div class=\"ly420-check-grid\">\r\n        <div class=\"ly420-check-item\">\r\n          <strong>HART compatibility<\/strong>\r\n          Do not infer compatibility from a general 4-20mA description.\r\n        <\/div>\r\n\r\n        <div class=\"ly420-check-item\">\r\n          <strong>Frequency response<\/strong>\r\n          The SPD must pass the communication signal without excessive loss.\r\n        <\/div>\r\n\r\n        <div class=\"ly420-check-item\">\r\n          <strong>Series impedance<\/strong>\r\n          Include the SPD in the complete HART loop calculation.\r\n        <\/div>\r\n\r\n        <div class=\"ly420-check-item\">\r\n          <strong>Capacitance<\/strong>\r\n          Excessive capacitance may load the communication signal.\r\n        <\/div>\r\n\r\n        <div class=\"ly420-check-item\">\r\n          <strong>Network arrangement<\/strong>\r\n          Confirm point-to-point or multidrop operation.\r\n        <\/div>\r\n\r\n        <div class=\"ly420-check-item\">\r\n          <strong>Barrier compatibility<\/strong>\r\n          The isolator or Ex i barrier must also support HART.\r\n        <\/div>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section\r\n      class=\"ly420-anchor\"\r\n      id=\"installation-position\"\r\n    >\r\n      <h2><span class=\"ez-toc-section\" id=\"should-the-spd-be-installed-at-the-field-instrument-or-control-cabinet\"><\/span>\r\n        Should the SPD be installed at the field instrument or control cabinet?\r\n      <span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <p>\r\n        The correct position depends on cable exposure, lightning protection\r\n        zones, building entry points and the equipment requiring protection.\r\n      <\/p>\r\n\r\n      <div class=\"ly420-table-wrap\">\r\n        <table class=\"ly420-table\">\r\n          <thead>\r\n            <tr>\r\n              <th>Installation condition<\/th>\r\n              <th>Recommended consideration<\/th>\r\n              <th>Reason<\/th>\r\n            <\/tr>\r\n          <\/thead>\r\n\r\n          <tbody>\r\n            <tr>\r\n              <td><strong>Outdoor transmitter with long cable<\/strong><\/td>\r\n              <td>Evaluate field-side and cabinet-entry protection.<\/td>\r\n              <td>Both ends contain sensitive electronics.<\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td><strong>Cable between buildings<\/strong><\/td>\r\n              <td>Protect at each building entry and coordinate bonding.<\/td>\r\n              <td>The cable crosses different equipotential zones.<\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td><strong>Tank, mast or pump station<\/strong><\/td>\r\n              <td>Use a field-compatible SPD near the instrument.<\/td>\r\n              <td>Remote outdoor locations face higher exposure.<\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td><strong>Short wiring inside one cabinet<\/strong><\/td>\r\n              <td>Two SPDs are not automatically required.<\/td>\r\n              <td>The complete circuit may remain in one protected zone.<\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td><strong>Field junction box<\/strong><\/td>\r\n              <td>Choose the cable entry or equipment boundary.<\/td>\r\n              <td>The SPD should be close to the protection-zone boundary.<\/td>\r\n            <\/tr>\r\n          <\/tbody>\r\n        <\/table>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section class=\"ly420-anchor\" id=\"shield-grounding\">\r\n      <h2><span class=\"ez-toc-section\" id=\"shielding-din-rail-grounding-and-equipotential-bonding\"><\/span>Shielding, DIN-rail grounding and equipotential bonding<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <p>\r\n        A signal SPD requires a low-impedance discharge path. The PE terminal,\r\n        grounding foot or bonded DIN rail must connect to the local\r\n        equipotential bonding system with the shortest practical route.\r\n      <\/p>\r\n\r\n      <div class=\"ly420-check-grid\">\r\n        <div class=\"ly420-check-item\">\r\n          <strong>DIN-rail contact<\/strong>\r\n          Confirm whether the SPD grounds through the rail or a separate PE.\r\n        <\/div>\r\n\r\n        <div class=\"ly420-check-item\">\r\n          <strong>Bonded rail<\/strong>\r\n          A metal rail is not automatically an effective protective earth.\r\n        <\/div>\r\n\r\n        <div class=\"ly420-check-item\">\r\n          <strong>Short discharge path<\/strong>\r\n          Avoid long, coiled or unnecessarily routed grounding conductors.\r\n        <\/div>\r\n\r\n        <div class=\"ly420-check-item\">\r\n          <strong>Shield arrangement<\/strong>\r\n          Follow the project EMC and bonding concept.\r\n        <\/div>\r\n\r\n        <div class=\"ly420-check-item\">\r\n          <strong>Direct or indirect shield earthing<\/strong>\r\n          Some applications require special shield bonding arrangements.\r\n        <\/div>\r\n\r\n        <div class=\"ly420-check-item\">\r\n          <strong>Separate functions<\/strong>\r\n          The cable shield does not automatically replace the SPD PE path.\r\n        <\/div>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section class=\"ly420-anchor\" id=\"hazardous-area\">\r\n      <h2><span class=\"ez-toc-section\" id=\"4-20ma-spd-selection-for-hazardous-areas-and-ex-i-loops\"><\/span>4-20mA SPD selection for hazardous areas and Ex i loops<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <p>\r\n        A standard industrial signal SPD should not be placed in an\r\n        intrinsically safe loop without verification.\r\n      <\/p>\r\n\r\n      <ul>\r\n        <li>Confirm ATEX, IECEx or locally required approval;<\/li>\r\n        <li>confirm the installation zone and protection concept;<\/li>\r\n        <li>check maximum voltage and current parameters;<\/li>\r\n        <li>check SPD capacitance and inductance;<\/li>\r\n        <li>coordinate the SPD with the barrier or isolator;<\/li>\r\n        <li>confirm the permitted earthing method;<\/li>\r\n        <li>check HART or SIL requirements where applicable.<\/li>\r\n      <\/ul>\r\n\r\n      <div class=\"ly420-callout ly420-callout--danger\">\r\n        <h3>Approval of the SPD alone is not enough<\/h3>\r\n\r\n        <p>\r\n          The transmitter, cable, SPD, barrier and installation arrangement\r\n          must be evaluated as one intrinsically safe circuit.\r\n        <\/p>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section\r\n      class=\"ly420-anchor\"\r\n      id=\"buyer-supplier-table\"\r\n    >\r\n      <h2><span class=\"ez-toc-section\" id=\"what-the-buyer-provides-and-what-the-spd-supplier-confirms\"><\/span>What the buyer provides and what the SPD supplier confirms<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <p>\r\n        The buyer only needs to provide information already available. The SPD\r\n        supplier should use it to confirm the detailed product parameters.\r\n      <\/p>\r\n\r\n      <div class=\"ly420-table-wrap ly420-responsibility-wrap\">\r\n        <table class=\"ly420-table ly420-responsibility-table\">\r\n          <thead>\r\n            <tr>\r\n              <th>Selection item<\/th>\r\n              <th>Buyer or engineer provides<\/th>\r\n              <th>SPD supplier confirms<\/th>\r\n            <\/tr>\r\n          <\/thead>\r\n\r\n          <tbody>\r\n            <tr>\r\n              <td data-label=\"Selection item\">\r\n                <strong>Loop topology<\/strong>\r\n              <\/td>\r\n\r\n              <td data-label=\"Buyer or engineer provides\">\r\n                Two-wire, three-wire or four-wire information, drawing or\r\n                terminal photo.\r\n              <\/td>\r\n\r\n              <td data-label=\"SPD supplier confirms\">\r\n                Matching protection modes, terminal arrangement and circuit\r\n                reference.\r\n              <\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td data-label=\"Selection item\">\r\n                <strong>Power arrangement<\/strong>\r\n              <\/td>\r\n\r\n              <td data-label=\"Buyer or engineer provides\">\r\n                PLC\/DCS card, transmitter or power-supply model where\r\n                available.\r\n              <\/td>\r\n\r\n              <td data-label=\"SPD supplier confirms\">\r\n                Suitability for the normal circuit voltage and current path.\r\n              <\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td data-label=\"Selection item\">\r\n                <strong>Working voltage<\/strong>\r\n              <\/td>\r\n\r\n              <td data-label=\"Buyer or engineer provides\">\r\n                Nominal loop voltage, for example 24V DC.\r\n              <\/td>\r\n\r\n              <td data-label=\"SPD supplier confirms\">\r\n                Nominal voltage and maximum continuous operating voltage.\r\n              <\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td data-label=\"Selection item\">\r\n                <strong>Voltage margin<\/strong>\r\n              <\/td>\r\n\r\n              <td data-label=\"Buyer or engineer provides\">\r\n                Equipment models or available loop data.\r\n              <\/td>\r\n\r\n              <td data-label=\"SPD supplier confirms\">\r\n                Series resistance and voltage drop at maximum current.\r\n              <\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td data-label=\"Selection item\">\r\n                <strong>Measurement accuracy<\/strong>\r\n              <\/td>\r\n\r\n              <td data-label=\"Buyer or engineer provides\">\r\n                Special accuracy requirement, when applicable.\r\n              <\/td>\r\n\r\n              <td data-label=\"SPD supplier confirms\">\r\n                Leakage current at UC and over the operating temperature range.\r\n              <\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td data-label=\"Selection item\">\r\n                <strong>Protection performance<\/strong>\r\n              <\/td>\r\n\r\n              <td data-label=\"Buyer or engineer provides\">\r\n                Indoor, outdoor, interbuilding or other exposure information.\r\n              <\/td>\r\n\r\n              <td data-label=\"SPD supplier confirms\">\r\n                Protection levels, test waveform and surge-current values.\r\n              <\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td data-label=\"Selection item\">\r\n                <strong>HART communication<\/strong>\r\n              <\/td>\r\n\r\n              <td data-label=\"Buyer or engineer provides\">\r\n                HART required or not required.\r\n              <\/td>\r\n\r\n              <td data-label=\"SPD supplier confirms\">\r\n                HART compatibility, capacitance and frequency response.\r\n              <\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td data-label=\"Selection item\">\r\n                <strong>Hazardous area<\/strong>\r\n              <\/td>\r\n\r\n              <td data-label=\"Buyer or engineer provides\">\r\n                Hazardous-area requirement and barrier model where available.\r\n              <\/td>\r\n\r\n              <td data-label=\"SPD supplier confirms\">\r\n                Approval scope, entity parameters and permitted earthing.\r\n              <\/td>\r\n            <\/tr>\r\n\r\n            <tr>\r\n              <td data-label=\"Selection item\">\r\n                <strong>Installation<\/strong>\r\n              <\/td>\r\n\r\n              <td data-label=\"Buyer or engineer provides\">\r\n                Field, cabinet or both-end installation.\r\n              <\/td>\r\n\r\n              <td data-label=\"SPD supplier confirms\">\r\n                Mounting, terminal, temperature and grounding arrangement.\r\n              <\/td>\r\n            <\/tr>\r\n          <\/tbody>\r\n        <\/table>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section>\r\n      <h2><span class=\"ez-toc-section\" id=\"model-confirmation-before-a-project-or-oem-order\"><\/span>Model confirmation before a project or OEM order<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <p>\r\n        LEEYEE can start from basic information and request additional data\r\n        only when it is necessary for final model confirmation.\r\n      <\/p>\r\n\r\n      <div class=\"ly420-approval\">\r\n        <h3>Four-step confirmation process<\/h3>\r\n\r\n        <div class=\"ly420-approval-grid\">\r\n          <div class=\"ly420-approval-step\">\r\n            <span>1<\/span>\r\n            <strong>Review available information<\/strong>\r\n\r\n            <p>\r\n              Check the loop type, voltage and connected equipment.\r\n            <\/p>\r\n          <\/div>\r\n\r\n          <div class=\"ly420-approval-step\">\r\n            <span>2<\/span>\r\n            <strong>Match electrical limits<\/strong>\r\n\r\n            <p>\r\n              Confirm UC, load current, protection level and voltage drop.\r\n            <\/p>\r\n          <\/div>\r\n\r\n          <div class=\"ly420-approval-step\">\r\n            <span>3<\/span>\r\n            <strong>Verify special requirements<\/strong>\r\n\r\n            <p>\r\n              Check HART, Ex i, mounting, terminals and environment.\r\n            <\/p>\r\n          <\/div>\r\n\r\n          <div class=\"ly420-approval-step\">\r\n            <span>4<\/span>\r\n            <strong>Confirm the order<\/strong>\r\n\r\n            <p>\r\n              Approve the datasheet, label, packaging and quantity.\r\n            <\/p>\r\n          <\/div>\r\n        <\/div>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section>\r\n      <h2><span class=\"ez-toc-section\" id=\"typical-industrial-applications\"><\/span>Typical industrial applications<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <div class=\"ly420-app-grid\">\r\n        <article class=\"ly420-app-card\">\r\n          <strong>Water and wastewater<\/strong>\r\n\r\n          <p>\r\n            Level, pressure, flow, pH and conductivity transmitters connected\r\n            to remote PLC or SCADA panels.\r\n          <\/p>\r\n        <\/article>\r\n\r\n        <article class=\"ly420-app-card\">\r\n          <strong>Pump stations<\/strong>\r\n\r\n          <p>\r\n            Outdoor pressure and level instruments with long signal cables.\r\n          <\/p>\r\n        <\/article>\r\n\r\n        <article class=\"ly420-app-card\">\r\n          <strong>Process plants<\/strong>\r\n\r\n          <p>\r\n            DCS instrument loops in chemical, food, oil, gas and manufacturing\r\n            facilities.\r\n          <\/p>\r\n        <\/article>\r\n\r\n        <article class=\"ly420-app-card\">\r\n          <strong>Tank farms<\/strong>\r\n\r\n          <p>\r\n            Remote level and temperature transmitters in exposed locations.\r\n          <\/p>\r\n        <\/article>\r\n\r\n        <article class=\"ly420-app-card\">\r\n          <strong>Factory automation<\/strong>\r\n\r\n          <p>\r\n            Analog sensors outside the main control cabinet or near large\r\n            machinery.\r\n          <\/p>\r\n        <\/article>\r\n\r\n        <article class=\"ly420-app-card\">\r\n          <strong>Building management<\/strong>\r\n\r\n          <p>\r\n            Long analog loops between plant rooms and monitoring panels.\r\n          <\/p>\r\n        <\/article>\r\n\r\n        <article class=\"ly420-app-card\">\r\n          <strong>Renewable-energy sites<\/strong>\r\n\r\n          <p>\r\n            Meteorological and auxiliary process instruments on exposed cable\r\n            routes.\r\n          <\/p>\r\n        <\/article>\r\n\r\n        <article class=\"ly420-app-card\">\r\n          <strong>OEM control panels<\/strong>\r\n\r\n          <p>\r\n            Repeatable analog-input protection for standardized cabinet\r\n            projects.\r\n          <\/p>\r\n        <\/article>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section>\r\n      <h2><span class=\"ez-toc-section\" id=\"common-4-20ma-spd-selection-mistakes\"><\/span>Common 4-20mA SPD selection mistakes<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <div class=\"ly420-mistakes\">\r\n        <div class=\"ly420-mistake\">\r\n          <div>\r\n            <strong>Selecting only by the \u201c24V\u201d label<\/strong>\r\n\r\n            <p>\r\n              Products with the same label may have different UC, leakage,\r\n              resistance and protection levels.\r\n            <\/p>\r\n          <\/div>\r\n        <\/div>\r\n\r\n        <div class=\"ly420-mistake\">\r\n          <div>\r\n            <strong>Ignoring two-wire and four-wire differences<\/strong>\r\n\r\n            <p>\r\n              A four-wire transmitter may have separate power and signal surge\r\n              paths.\r\n            <\/p>\r\n          <\/div>\r\n        <\/div>\r\n\r\n        <div class=\"ly420-mistake\">\r\n          <div>\r\n            <strong>Checking surge current but not voltage drop<\/strong>\r\n\r\n            <p>\r\n              A high surge rating does not prove suitability for a loop with\r\n              limited voltage margin.\r\n            <\/p>\r\n          <\/div>\r\n        <\/div>\r\n\r\n        <div class=\"ly420-mistake\">\r\n          <div>\r\n            <strong>Assuming every 4-20mA SPD supports HART<\/strong>\r\n\r\n            <p>\r\n              HART also depends on frequency response, capacitance and series\r\n              impedance.\r\n            <\/p>\r\n          <\/div>\r\n        <\/div>\r\n\r\n        <div class=\"ly420-mistake\">\r\n          <div>\r\n            <strong>Protecting only the PLC end<\/strong>\r\n\r\n            <p>\r\n              A remote field instrument can also be damaged by induced surge\r\n              energy.\r\n            <\/p>\r\n          <\/div>\r\n        <\/div>\r\n\r\n        <div class=\"ly420-mistake\">\r\n          <div>\r\n            <strong>Using a poor grounding path<\/strong>\r\n\r\n            <p>\r\n              Good laboratory parameters cannot compensate for a long or\r\n              unbonded discharge path.\r\n            <\/p>\r\n          <\/div>\r\n        <\/div>\r\n\r\n        <div class=\"ly420-mistake\">\r\n          <div>\r\n            <strong>Applying a normal SPD to an Ex i loop<\/strong>\r\n\r\n            <p>\r\n              Approval and entity parameters must be verified for the complete\r\n              circuit.\r\n            <\/p>\r\n          <\/div>\r\n        <\/div>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section\r\n      class=\"ly420-anchor\"\r\n      id=\"ordering-checklist\"\r\n    >\r\n      <h2><span class=\"ez-toc-section\" id=\"what-to-send-for-a-4-20ma-spd-recommendation\"><\/span>What to send for a 4-20mA SPD recommendation<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <p>\r\n        Send any information you already have. You do not need to prepare\r\n        every item before contacting us.\r\n      <\/p>\r\n\r\n      <div class=\"ly420-order-box\">\r\n        <div class=\"ly420-order-head\">\r\n          <div>\r\n            <span class=\"ly420-order-label\">\r\n              Simple enquiry checklist\r\n            <\/span>\r\n\r\n            <h3>Six details are usually enough to start<\/h3>\r\n          <\/div>\r\n\r\n          <p>\r\n            No loop drawing? Send an equipment datasheet, terminal photo or\r\n            existing SPD model. We will help identify the circuit.\r\n          <\/p>\r\n        <\/div>\r\n\r\n        <div class=\"ly420-simple-order-grid\">\r\n          <div class=\"ly420-simple-order-item\">\r\n            <span>01<\/span>\r\n\r\n            <div>\r\n              <strong>Loop type<\/strong>\r\n              <p>2-wire, 3-wire or 4-wire<\/p>\r\n            <\/div>\r\n          <\/div>\r\n\r\n          <div class=\"ly420-simple-order-item\">\r\n            <span>02<\/span>\r\n\r\n            <div>\r\n              <strong>Loop voltage<\/strong>\r\n              <p>For example: 24V DC<\/p>\r\n            <\/div>\r\n          <\/div>\r\n\r\n          <div class=\"ly420-simple-order-item\">\r\n            <span>03<\/span>\r\n\r\n            <div>\r\n              <strong>HART requirement<\/strong>\r\n              <p>Required or not required<\/p>\r\n            <\/div>\r\n          <\/div>\r\n\r\n          <div class=\"ly420-simple-order-item\">\r\n            <span>04<\/span>\r\n\r\n            <div>\r\n              <strong>Connected equipment<\/strong>\r\n              <p>Transmitter or PLC\/DCS card model<\/p>\r\n            <\/div>\r\n          <\/div>\r\n\r\n          <div class=\"ly420-simple-order-item\">\r\n            <span>05<\/span>\r\n\r\n            <div>\r\n              <strong>Installation position<\/strong>\r\n              <p>Field, cabinet or both ends<\/p>\r\n            <\/div>\r\n          <\/div>\r\n\r\n          <div class=\"ly420-simple-order-item\">\r\n            <span>06<\/span>\r\n\r\n            <div>\r\n              <strong>Order requirement<\/strong>\r\n              <p>Quantity, logo and packaging needs<\/p>\r\n            <\/div>\r\n          <\/div>\r\n        <\/div>\r\n\r\n        <div class=\"ly420-order-easy-note\">\r\n          <strong>Not sure about the loop type?<\/strong>\r\n\r\n          <span>\r\n            Send a wiring diagram, equipment photo, terminal photo or existing\r\n            product model. LEEYEE will review it before recommending an SPD.\r\n          <\/span>\r\n        <\/div>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section class=\"ly420-related\">\r\n      <h2><span class=\"ez-toc-section\" id=\"related-leeyee-technical-guides\"><\/span>Related LEEYEE technical guides<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <div class=\"ly420-related-grid\">\r\n        <a\r\n          class=\"ly420-related-card\"\r\n          href=\"https:\/\/www.cnspd.com\/plc-surge-protection\/\"\r\n          target=\"_blank\"\r\n          rel=\"noopener noreferrer\"\r\n        >\r\n          <strong>PLC Surge Protection Guide<\/strong>\r\n\r\n          <span>\r\n            Protect PLC power, analog I\/O, digital I\/O and communication lines.\r\n          <\/span>\r\n        <\/a>\r\n\r\n        <a\r\n          class=\"ly420-related-card\"\r\n          href=\"https:\/\/www.cnspd.com\/surge-protection-for-industrial-control-panels\/\"\r\n          target=\"_blank\"\r\n          rel=\"noopener noreferrer\"\r\n        >\r\n          <strong>Industrial Control Panel Surge Protection<\/strong>\r\n\r\n          <span>\r\n            Plan coordinated protection for power, control voltage and field\r\n            instruments.\r\n          <\/span>\r\n        <\/a>\r\n\r\n        <a\r\n          class=\"ly420-related-card\"\r\n          href=\"https:\/\/www.cnspd.com\/shop\/surge-protective-device\/\"\r\n          target=\"_blank\"\r\n          rel=\"noopener noreferrer\"\r\n        >\r\n          <strong>Surge Protective Device Collections<\/strong>\r\n\r\n          <span>\r\n            Browse AC, DC and signal SPD categories.\r\n          <\/span>\r\n        <\/a>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section class=\"ly420-cta\">\r\n      <div class=\"ly420-cta-copy\">\r\n        <h2><span class=\"ez-toc-section\" id=\"need-help-selecting-a-4-20ma-signal-spd\"><\/span>Need help selecting a 4-20mA signal SPD?<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n        <p>\r\n          Send a wiring diagram, terminal photo, transmitter model or existing\r\n          SPD model. LEEYEE will help identify the loop and confirm the\r\n          suitable protection configuration.\r\n        <\/p>\r\n      <\/div>\r\n\r\n      <div class=\"ly420-cta-actions\">\r\n        <a\r\n          href=\"javascript:void(0);\"\r\n          class=\"ly420-btn leeyee-site-popup-btn\"\r\n          aria-label=\"Request a 4-20mA signal SPD recommendation\"\r\n        >\r\n          <span>Request SPD Recommendation<\/span>\r\n        <\/a>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section>\r\n      <h2><span class=\"ez-toc-section\" id=\"frequently-asked-questions\"><\/span>Frequently asked questions<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <div class=\"ly420-faq\">\r\n        <details>\r\n          <summary>\r\n            Can the same SPD be used for all 4-20mA loops?\r\n          <\/summary>\r\n\r\n          <div class=\"ly420-faq-answer\">\r\n            <p>\r\n              No. Two-wire, three-wire and four-wire circuits may use different\r\n              power sources, conductor arrangements and grounding references.\r\n            <\/p>\r\n          <\/div>\r\n        <\/details>\r\n\r\n        <details>\r\n          <summary>\r\n            Is a 24V signal SPD always correct for a 24V loop?\r\n          <\/summary>\r\n\r\n          <div class=\"ly420-faq-answer\">\r\n            <p>\r\n              Not automatically. Compare the SPD maximum continuous operating\r\n              voltage with the highest normal loop voltage and supply\r\n              tolerance.\r\n            <\/p>\r\n          <\/div>\r\n        <\/details>\r\n\r\n        <details>\r\n          <summary>\r\n            Does SPD resistance change the 4-20mA reading?\r\n          <\/summary>\r\n\r\n          <div class=\"ly420-faq-answer\">\r\n            <p>\r\n              Normally, SPD resistance consumes loop voltage rather than\r\n              creating a proportional scaling error. If the voltage margin\r\n              becomes insufficient, the loop may fail to reach full-scale\r\n              current.\r\n            <\/p>\r\n          <\/div>\r\n        <\/details>\r\n\r\n        <details>\r\n          <summary>\r\n            Should a 4-20mA loop be protected at both ends?\r\n          <\/summary>\r\n\r\n          <div class=\"ly420-faq-answer\">\r\n            <p>\r\n              Both-end protection is often useful for outdoor, long-distance\r\n              or interbuilding circuits. It is not mandatory for every short\r\n              internal connection.\r\n            <\/p>\r\n          <\/div>\r\n        <\/details>\r\n\r\n        <details>\r\n          <summary>\r\n            Can a standard 4-20mA SPD pass HART communication?\r\n          <\/summary>\r\n\r\n          <div class=\"ly420-faq-answer\">\r\n            <p>\r\n              Only when its capacitance, frequency response and series\r\n              impedance are suitable. Explicit HART compatibility should be\r\n              confirmed.\r\n            <\/p>\r\n          <\/div>\r\n        <\/details>\r\n\r\n        <details>\r\n          <summary>\r\n            Does a four-wire transmitter need two SPDs?\r\n          <\/summary>\r\n\r\n          <div class=\"ly420-faq-answer\">\r\n            <p>\r\n              It may require separate protection for its power input and signal\r\n              output. The final arrangement depends on the wiring and internal\r\n              isolation.\r\n            <\/p>\r\n          <\/div>\r\n        <\/details>\r\n\r\n        <details>\r\n          <summary>\r\n            Can the cable shield replace the SPD earth connection?\r\n          <\/summary>\r\n\r\n          <div class=\"ly420-faq-answer\">\r\n            <p>\r\n              No. Shield termination and SPD protective earthing perform\r\n              related but different functions.\r\n            <\/p>\r\n          <\/div>\r\n        <\/details>\r\n\r\n        <details>\r\n          <summary>\r\n            Which standard applies to 4-20mA signal SPDs?\r\n          <\/summary>\r\n\r\n          <div class=\"ly420-faq-answer\">\r\n            <p>\r\n              IEC 61643-21 covers requirements and tests for\r\n              signalling-network SPDs. IEC 61643-22 provides selection and\r\n              application principles.\r\n            <\/p>\r\n          <\/div>\r\n        <\/details>\r\n      <\/div>\r\n    <\/section>\r\n\r\n    <section class=\"ly420-sources\">\r\n      <h2><span class=\"ez-toc-section\" id=\"technical-references\"><\/span>Technical references<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n      <ol>\r\n        <li>\r\n          IEC,\r\n          <a\r\n            href=\"https:\/\/webstore.iec.ch\/en\/publication\/69085\"\r\n            target=\"_blank\"\r\n            rel=\"noopener noreferrer\"\r\n          >\r\n            IEC 61643-21:2025 \u2014 Requirements and test methods for SPDs\r\n            connected to telecommunications and signalling networks\r\n          <\/a>.\r\n        <\/li>\r\n\r\n        <li>\r\n          IEC,\r\n          <a\r\n            href=\"https:\/\/webstore.iec.ch\/en\/publication\/22772\"\r\n            target=\"_blank\"\r\n            rel=\"noopener noreferrer\"\r\n          >\r\n            IEC 61643-22:2015 \u2014 Selection and application principles\r\n          <\/a>.\r\n        <\/li>\r\n\r\n        <li>\r\n          FieldComm Group,\r\n          <a\r\n            href=\"https:\/\/www.fieldcommgroup.org\/sites\/default\/files\/imce_files\/technology\/documents\/HART_ApplicationGuide_r7.1.pdf\"\r\n            target=\"_blank\"\r\n            rel=\"noopener noreferrer\"\r\n          >\r\n            HART Application Guide\r\n          <\/a>.\r\n        <\/li>\r\n\r\n        <li>\r\n          Texas Instruments,\r\n          <a\r\n            href=\"https:\/\/www.ti.com\/lit\/ug\/tidu299\/tidu299.pdf\"\r\n            target=\"_blank\"\r\n            rel=\"noopener noreferrer\"\r\n          >\r\n            Low-Cost Loop-Powered 4-20mA Transmitter Reference Design\r\n          <\/a>.\r\n        <\/li>\r\n\r\n        <li>\r\n          LEEYEE,\r\n          <a\r\n            href=\"https:\/\/www.cnspd.com\/plc-surge-protection\/\"\r\n            target=\"_blank\"\r\n            rel=\"noopener noreferrer\"\r\n          >\r\n            PLC Surge Protection Guide\r\n          <\/a>.\r\n        <\/li>\r\n      <\/ol>\r\n    <\/section>\r\n\r\n  <\/div>\r\n<\/article>\r\n\r\n<script>\r\ndocument.addEventListener('DOMContentLoaded', function () {\r\n  'use strict';\r\n\r\n  \/* =======================================================\r\n     4-20mA loop voltage budget calculator\r\n     ======================================================= *\/\r\n\r\n  var calculator = document.getElementById(\r\n    'ly420-loop-calculator'\r\n  );\r\n\r\n  if (calculator) {\r\n    var inputs = calculator.querySelectorAll(\r\n      'input[type=\"number\"]'\r\n    );\r\n\r\n    var supplyInput = document.getElementById(\r\n      'ly420-supply'\r\n    );\r\n\r\n    var transmitterInput = document.getElementById(\r\n      'ly420-transmitter'\r\n    );\r\n\r\n    var burdenInput = document.getElementById(\r\n      'ly420-burden'\r\n    );\r\n\r\n    var currentInput = document.getElementById(\r\n      'ly420-current'\r\n    );\r\n\r\n    var otherDropInput = document.getElementById(\r\n      'ly420-other-drop'\r\n    );\r\n\r\n    var spdCountInput = document.getElementById(\r\n      'ly420-spd-count'\r\n    );\r\n\r\n    var spdDropInput = document.getElementById(\r\n      'ly420-spd-drop'\r\n    );\r\n\r\n    var marginInput = document.getElementById(\r\n      'ly420-margin'\r\n    );\r\n\r\n    var aiResult = document.getElementById(\r\n      'ly420-result-ai'\r\n    );\r\n\r\n    var spdResult = document.getElementById(\r\n      'ly420-result-spd'\r\n    );\r\n\r\n    var resistanceResult = document.getElementById(\r\n      'ly420-result-resistance'\r\n    );\r\n\r\n    var statusResult = document.getElementById(\r\n      'ly420-result-status'\r\n    );\r\n\r\n    function safeNumber(input, fallback) {\r\n      var value = parseFloat(input.value);\r\n\r\n      return Number.isFinite(value)\r\n        ? value\r\n        : fallback;\r\n    }\r\n\r\n    function calculateLoopBudget() {\r\n      var supply = Math.max(\r\n        0,\r\n        safeNumber(supplyInput, 0)\r\n      );\r\n\r\n      var transmitter = Math.max(\r\n        0,\r\n        safeNumber(transmitterInput, 0)\r\n      );\r\n\r\n      var burden = Math.max(\r\n        0,\r\n        safeNumber(burdenInput, 0)\r\n      );\r\n\r\n      var currentMilliamp = Math.max(\r\n        0.1,\r\n        safeNumber(currentInput, 20)\r\n      );\r\n\r\n      var currentAmp = currentMilliamp \/ 1000;\r\n\r\n      var otherDrop = Math.max(\r\n        0,\r\n        safeNumber(otherDropInput, 0)\r\n      );\r\n\r\n      var spdCount = Math.max(\r\n        0,\r\n        safeNumber(spdCountInput, 0)\r\n      );\r\n\r\n      var spdDropEach = Math.max(\r\n        0,\r\n        safeNumber(spdDropInput, 0)\r\n      );\r\n\r\n      var safetyMargin = Math.max(\r\n        0,\r\n        safeNumber(marginInput, 0)\r\n      );\r\n\r\n      var aiDrop = burden * currentAmp;\r\n      var totalSpdDrop = spdCount * spdDropEach;\r\n\r\n      var remainingVoltage =\r\n        supply -\r\n        transmitter -\r\n        aiDrop -\r\n        otherDrop -\r\n        totalSpdDrop -\r\n        safetyMargin;\r\n\r\n      var availableResistance =\r\n        remainingVoltage > 0\r\n          ? remainingVoltage \/ currentAmp\r\n          : 0;\r\n\r\n      aiResult.textContent =\r\n        aiDrop.toFixed(2) + ' V';\r\n\r\n      spdResult.textContent =\r\n        totalSpdDrop.toFixed(2) + ' V';\r\n\r\n      resistanceResult.textContent =\r\n        Math.max(\r\n          0,\r\n          Math.round(availableResistance)\r\n        ) + ' \u03a9';\r\n\r\n      statusResult.classList.remove(\r\n        'is-warning',\r\n        'is-danger'\r\n      );\r\n\r\n      if (remainingVoltage <= 0) {\r\n        statusResult.classList.add('is-danger');\r\n\r\n        statusResult.textContent =\r\n          'No positive voltage remains for additional series resistance. Review the supply, transmitter, input burden, barrier and SPD voltage drop.';\r\n      } else if (remainingVoltage < 1.5) {\r\n        statusResult.classList.add('is-warning');\r\n\r\n        statusResult.textContent =\r\n          'The remaining voltage margin is small. Check cable resistance, supply tolerance and transmitter compliance voltage.';\r\n      } else {\r\n        statusResult.textContent =\r\n          'The preliminary calculation retains positive voltage margin. Confirm the actual equipment data before final selection.';\r\n      }\r\n    }\r\n\r\n    inputs.forEach(function (input) {\r\n      input.addEventListener(\r\n        'input',\r\n        calculateLoopBudget\r\n      );\r\n\r\n      input.addEventListener(\r\n        'change',\r\n        calculateLoopBudget\r\n      );\r\n    });\r\n\r\n    calculateLoopBudget();\r\n  }\r\n\r\n  \/* =======================================================\r\n     LEEYEE quote popup\r\n     ======================================================= *\/\r\n\r\n  var quoteButtons = document.querySelectorAll(\r\n    '.leeyee-site-popup-btn'\r\n  );\r\n\r\n  quoteButtons.forEach(function (button) {\r\n    button.addEventListener('click', function (event) {\r\n      event.preventDefault();\r\n\r\n      var realPopupTrigger = document.querySelector(\r\n        '.w-popup.ush_popup_1 .w-popup-trigger'\r\n      );\r\n\r\n      if (realPopupTrigger) {\r\n        realPopupTrigger.click();\r\n      } else {\r\n        window.open(\r\n          'https:\/\/www.cnspd.com\/contact\/',\r\n          '_blank',\r\n          'noopener,noreferrer'\r\n        );\r\n      }\r\n    });\r\n  });\r\n});\r\n<\/script>\r\n\r\n<script type=\"application\/ld+json\">\r\n{\r\n  \"@context\": \"https:\/\/schema.org\",\r\n  \"@type\": \"FAQPage\",\r\n  \"mainEntity\": [\r\n    {\r\n      \"@type\": \"Question\",\r\n      \"name\": \"Can the same SPD be used for all 4-20mA loops?\",\r\n      \"acceptedAnswer\": {\r\n        \"@type\": \"Answer\",\r\n        \"text\": \"No. Two-wire, three-wire and four-wire circuits may use different power sources, conductor arrangements and grounding references.\"\r\n      }\r\n    },\r\n    {\r\n      \"@type\": \"Question\",\r\n      \"name\": \"Is a 24V signal SPD always correct for a 24V loop?\",\r\n      \"acceptedAnswer\": {\r\n        \"@type\": \"Answer\",\r\n        \"text\": \"Not automatically. Compare the SPD maximum continuous operating voltage with the highest normal loop voltage and supply tolerance.\"\r\n      }\r\n    },\r\n    {\r\n      \"@type\": \"Question\",\r\n      \"name\": \"Does SPD resistance change the 4-20mA reading?\",\r\n      \"acceptedAnswer\": {\r\n        \"@type\": \"Answer\",\r\n        \"text\": \"Normally, SPD resistance consumes loop voltage rather than creating a proportional scaling error. If the voltage margin becomes insufficient, the loop may fail to reach full-scale current.\"\r\n      }\r\n    },\r\n    {\r\n      \"@type\": \"Question\",\r\n      \"name\": \"Should a 4-20mA loop be protected at both ends?\",\r\n      \"acceptedAnswer\": {\r\n        \"@type\": \"Answer\",\r\n        \"text\": \"Both-end protection is often useful for outdoor, long-distance or interbuilding circuits. It is not mandatory for every short internal connection.\"\r\n      }\r\n    },\r\n    {\r\n      \"@type\": \"Question\",\r\n      \"name\": \"Can a standard 4-20mA SPD pass HART communication?\",\r\n      \"acceptedAnswer\": {\r\n        \"@type\": \"Answer\",\r\n        \"text\": \"Only when its capacitance, frequency response and series impedance are suitable. Explicit HART compatibility should be confirmed.\"\r\n      }\r\n    },\r\n    {\r\n      \"@type\": \"Question\",\r\n      \"name\": \"Does a four-wire transmitter need two SPDs?\",\r\n      \"acceptedAnswer\": {\r\n        \"@type\": \"Answer\",\r\n        \"text\": \"It may require separate protection for its power input and signal output. The final arrangement depends on the wiring and internal isolation.\"\r\n      }\r\n    },\r\n    {\r\n      \"@type\": \"Question\",\r\n      \"name\": \"Can the cable shield replace the SPD earth connection?\",\r\n      \"acceptedAnswer\": {\r\n        \"@type\": \"Answer\",\r\n        \"text\": \"No. Shield termination and SPD protective earthing perform related but different functions.\"\r\n      }\r\n    },\r\n    {\r\n      \"@type\": \"Question\",\r\n      \"name\": \"Which standard applies to 4-20mA signal SPDs?\",\r\n      \"acceptedAnswer\": {\r\n        \"@type\": \"Answer\",\r\n        \"text\": \"IEC 61643-21 covers requirements and tests for signalling-network SPDs. IEC 61643-22 provides selection and application principles.\"\r\n      }\r\n    }\r\n  ]\r\n}\r\n<\/script>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"<p>Industrial Instrumentation Selection Guide Selecting a 4-20mA surge protector is not only a question of surge current. The signal SPD must match the loop voltage, two-wire or four-wire circuit, transmitter power arrangement, PLC or DCS input, HART communication and the voltage available across the complete current loop. Quick answer: what SPD should be used for&#8230;<\/p>","protected":false},"author":18,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1,488,422],"tags":[],"class_list":["post-30181","post","type-post","status-publish","format-standard","hentry","category-news","category-surge-protection","category-industry-news"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.9 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>4-20mA Surge Protector Guide: 2-Wire, 4-Wire &amp; HART | LEEYEE<\/title>\n<meta name=\"description\" content=\"Select the right 4-20mA surge protector for 2-wire, 4-wire and HART loops. 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