{"id":31009,"date":"2026-09-15T08:32:39","date_gmt":"2026-09-15T00:32:39","guid":{"rendered":"https:\/\/www.cnspd.com\/?p=31009"},"modified":"2026-09-15T08:42:31","modified_gmt":"2026-09-15T00:42:31","slug":"automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers","status":"publish","type":"post","link":"https:\/\/www.cnspd.com\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/","title":{"rendered":"Guida alla scelta degli interruttori di trasferimento automatico per costruttori di quadri elettrici e acquirenti OEM"},"content":{"rendered":"\t\t<div data-elementor-type=\"wp-post\" data-elementor-id=\"31009\" class=\"elementor elementor-31009\" data-elementor-post-type=\"post\">\n\t\t\t\t<div class=\"elementor-element elementor-element-e04ce1b e-flex e-con-boxed e-con e-parent\" data-id=\"e04ce1b\" 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-4e109b6 elementor-widget elementor-widget-html\" data-id=\"4e109b6\" 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#ats-selection-guide{\r\n  --ats-blue:#004898;\r\n  --ats-blue-2:#0b5ca8;\r\n  --ats-soft:#f7fbff;\r\n  --ats-soft-2:#eef5ff;\r\n  --ats-text:#243447;\r\n  --ats-heading:#162b3d;\r\n  --ats-muted:#617184;\r\n  --ats-border:#d9e5ef;\r\n  --ats-warning:#9a5b00;\r\n  --ats-warning-bg:#fff8e8;\r\n  --ats-success:#12623b;\r\n  max-width:840px;\r\n  margin:0 auto;\r\n  color:var(--ats-text);\r\n  font-family:inherit;\r\n  font-size:17px;\r\n  line-height:1.72;\r\n  overflow-wrap:anywhere;\r\n}\r\n\r\n#ats-selection-guide *{box-sizing:border-box}\r\n\r\n#ats-selection-guide p{margin:0 0 1em}\r\n\r\n#ats-selection-guide strong{color:#173247}\r\n\r\n#ats-selection-guide a{\r\n  color:var(--ats-blue);\r\n  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font-size:14px;\r\n}\r\n\r\n#ats-selection-guide .ats-decision{\r\n  display:grid;\r\n  grid-template-columns:36px minmax(0,1fr) minmax(0,1.1fr);\r\n  gap:10px 14px;\r\n  align-items:start;\r\n  padding:13px 0;\r\n  border-bottom:1px solid #e8eef3;\r\n}\r\n\r\n#ats-selection-guide .ats-decision:last-child{\r\n  border-bottom:0;\r\n}\r\n\r\n#ats-selection-guide .ats-decision-num{\r\n  display:flex;\r\n  width:30px;\r\n  height:30px;\r\n  align-items:center;\r\n  justify-content:center;\r\n  border-radius:7px;\r\n  background:var(--ats-blue);\r\n  color:#fff;\r\n  font-size:14px;\r\n  font-weight:800;\r\n}\r\n\r\n#ats-selection-guide .ats-decision strong{\r\n  display:block;\r\n  margin-bottom:2px;\r\n}\r\n\r\n#ats-selection-guide .ats-decision span{\r\n  color:var(--ats-muted);\r\n  font-size:15px;\r\n}\r\n\r\n#ats-selection-guide .ats-evidence-label{\r\n  display:inline-block;\r\n  margin-bottom:7px;\r\n  color:var(--ats-blue);\r\n  font-size:13px;\r\n  font-weight:700;\r\n  letter-spacing:.04em;\r\n  text-transform:uppercase;\r\n}\r\n\r\n\/* Inquiry buttons *\/\r\n#ats-selection-guide .ats-cta-actions{\r\n  display:flex;\r\n  align-items:center;\r\n  flex-wrap:wrap;\r\n  gap:12px;\r\n  margin-top:16px;\r\n}\r\n\r\n#ats-selection-guide .leeyee-about-btn-light{\r\n  display:inline-flex;\r\n  align-items:center;\r\n  justify-content:center;\r\n  min-height:50px;\r\n  padding:13px 25px;\r\n  border:1.5px solid #004898;\r\n  border-radius:7px;\r\n  background:#004898;\r\n  color:#fff;\r\n  font-family:inherit;\r\n  font-size:16px;\r\n  font-weight:700;\r\n  line-height:1.25;\r\n  text-align:center;\r\n  text-decoration:none;\r\n  cursor:pointer;\r\n  appearance:none;\r\n  -webkit-appearance:none;\r\n  box-shadow:0 5px 14px rgba(0,72,152,.14);\r\n  transition:\r\n    background-color .2s ease,\r\n    border-color .2s ease,\r\n    color .2s ease,\r\n    transform .2s ease,\r\n    box-shadow .2s ease;\r\n}\r\n\r\n#ats-selection-guide .leeyee-about-btn-light:hover{\r\n  border-color:#0b5ca8;\r\n  background:#0b5ca8;\r\n  color:#fff;\r\n  transform:translateY(-1px);\r\n  box-shadow:0 7px 18px rgba(0,72,152,.20);\r\n}\r\n\r\n#ats-selection-guide .leeyee-about-btn-light:focus-visible{\r\n  outline:3px solid rgba(0,72,152,.22);\r\n  outline-offset:3px;\r\n}\r\n\r\n#ats-selection-guide .leeyee-about-btn-light:active{\r\n  transform:translateY(0);\r\n  box-shadow:0 3px 8px rgba(0,72,152,.14);\r\n}\r\n\r\n#ats-selection-guide .leeyee-about-btn-light .w-btn-label{\r\n  display:block;\r\n  color:inherit;\r\n  font:inherit;\r\n  line-height:inherit;\r\n  pointer-events:none;\r\n}\r\n\r\n@media(max-width:768px){\r\n  #ats-selection-guide{\r\n    font-size:16.5px;\r\n    line-height:1.68;\r\n  }\r\n\r\n  #ats-selection-guide h2{\r\n    font-size:28px;\r\n  }\r\n\r\n  #ats-selection-guide h3{\r\n    font-size:22px;\r\n  }\r\n\r\n  #ats-selection-guide .ats-grid{\r\n    grid-template-columns:1fr;\r\n  }\r\n\r\n  #ats-selection-guide .ats-quick,\r\n  #ats-selection-guide .ats-checklist,\r\n  #ats-selection-guide .ats-note,\r\n  #ats-selection-guide .ats-warning,\r\n  #ats-selection-guide .ats-cta,\r\n  #ats-selection-guide .ats-example{\r\n    padding:19px 18px;\r\n  }\r\n\r\n  #ats-selection-guide .ats-table{\r\n    min-width:650px;\r\n    font-size:14.5px;\r\n  }\r\n\r\n  #ats-selection-guide .ats-decision{\r\n    grid-template-columns:34px 1fr;\r\n  }\r\n\r\n  #ats-selection-guide .ats-decision>div:last-child{\r\n    grid-column:2;\r\n  }\r\n}\r\n\r\n@media(max-width:600px){\r\n  #ats-selection-guide h2{\r\n    margin-top:1.8em;\r\n    font-size:26px;\r\n  }\r\n\r\n  #ats-selection-guide h3{\r\n    font-size:21px;\r\n  }\r\n\r\n  #ats-selection-guide .ats-lead{\r\n    font-size:18px;\r\n  }\r\n\r\n  #ats-selection-guide .ats-checklist ul{\r\n    columns:1;\r\n  }\r\n}\r\n\r\n@media(max-width:480px){\r\n  #ats-selection-guide .leeyee-about-btn-light{\r\n    width:100%;\r\n    min-height:50px;\r\n    padding:13px 18px;\r\n  }\r\n\r\n  #ats-selection-guide .ats-cta-actions{\r\n    width:100%;\r\n  }\r\n}\r\n\r\n@media(max-width:430px){\r\n  #ats-selection-guide{\r\n    font-size:16px;\r\n  }\r\n\r\n  #ats-selection-guide h2{\r\n    font-size:24px;\r\n  }\r\n\r\n  #ats-selection-guide h3{\r\n    font-size:20px;\r\n  }\r\n\r\n  #ats-selection-guide .ats-quick,\r\n  #ats-selection-guide .ats-checklist,\r\n  #ats-selection-guide .ats-note,\r\n  #ats-selection-guide .ats-warning,\r\n  #ats-selection-guide .ats-cta,\r\n  #ats-selection-guide .ats-example{\r\n    padding:17px 15px;\r\n    border-radius:10px;\r\n  }\r\n\r\n  #ats-selection-guide .ats-table{\r\n    min-width:620px;\r\n    font-size:13.5px;\r\n  }\r\n}\r\n<\/style>\r\n\r\n<article id=\"ats-selection-guide\">\r\n\r\n  <p class=\"ats-intro\">This automatic transfer switch selection guide is written for panel builders, generator integrators, electrical contractors, distributors and OEM buyers who already understand the basic purpose of an ATS and now need to specify the correct device for a real project. The selection should start with the power architecture and transferred load, then move through current, voltage, poles, neutral arrangement, transition method, short-circuit coordination and controller functions. If you first need the basic operating principle, see <a href=\"https:\/\/www.cnspd.com\/what-is-an-automatic-transfer-switch-how-ats-works-how-to-choose\/\">What Is an Automatic Transfer Switch?<\/a><\/p>\r\n\r\n  <section class=\"ats-quick\" aria-labelledby=\"ats-quick-answer\">\r\n    <span class=\"ats-kicker\">Quick Answer<\/span>\r\n\r\n    <div id=\"ez-toc-container\" class=\"ez-toc-v2_0_87 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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#how-do-you-select-an-automatic-transfer-switch\" >How do you select an automatic transfer switch?<\/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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#1-use-this-ats-selection-sequence-before-comparing-models\" >1. Use this ATS selection sequence before comparing models<\/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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#2-what-size-automatic-transfer-switch-do-you-need\" >2. What size automatic transfer switch do you need?<\/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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#3-utility-generator-utility-utility-or-generator-generator\" >3. Utility-generator, utility-utility or generator-generator?<\/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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#4-how-do-you-choose-2p-3p-or-4p-ats\" >4. How do you choose 2P, 3P or 4P ATS?<\/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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#5-open-transition-vs-delayed-transition-vs-closed-transition\" >5. Open transition vs delayed transition vs closed transition<\/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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#6-pc-class-vs-cb-class-ats-decide-who-clears-a-short-circuit\" >6. PC class vs CB class ATS: decide who clears a short circuit<\/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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#7-short-circuit-capability-the-ats-current-rating-is-not-enough\" >7. Short-circuit capability: the ATS current rating is not enough<\/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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#8-integrated-controller-or-separate-ats-controller\" >8. Integrated controller or separate ATS controller?<\/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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#9-generator-start-signals-dry-contacts-and-remote-monitoring\" >9. Generator start signals, dry contacts and remote monitoring<\/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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#10-match-the-ats-to-the-load-type-and-utilisation-category\" >10. Match the ATS to the load type and utilisation category<\/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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#11-where-does-leeyee-ats-63-fit\" >11. Where does LEEYEE ATS-63 fit?<\/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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#12-common-ats-selection-mistakes-that-cause-panel-rework\" >12. Common ATS selection mistakes that cause panel rework<\/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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#13-before-ordering-ats-rfq-checklist-for-panel-builders-and-oem-buyers\" >13. Before ordering: ATS RFQ checklist for panel builders and OEM buyers<\/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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#need-the-ats-configuration-checked-before-panel-approval\" >Need the ATS configuration checked before panel approval?<\/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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#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-17\" href=\"#\" data-href=\"https:\/\/www.cnspd.com\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#related-reading\" >Related reading<\/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\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/#references\" >References<\/a><\/li><\/ul><\/nav><\/div>\n<h2 id=\"ats-quick-answer\"><span class=\"ez-toc-section\" id=\"how-do-you-select-an-automatic-transfer-switch\"><\/span>How do you select an automatic transfer switch?<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n    <p class=\"ats-lead\">Start with the electrical system, not with the ampere number on the front of the ATS.<\/p>\r\n\r\n    <p>Confirm the two power sources and the load that will actually pass through the transfer point. Then calculate the preliminary design current, confirm system voltage and phase, decide whether the neutral must be switched, choose the required transition method, define the short-circuit protection architecture, and specify generator control, dry contacts or communications where required.<\/p>\r\n\r\n    <p>For IEC projects, transfer switching equipment is covered by IEC 60947-6-1. The current edition is IEC 60947-6-1:2026, published on 2 April 2026. It covers transfer switching equipment within its stated voltage scope and includes dedicated requirements for closed-transition ATSE and stand-alone ATS controllers. [1]\r\n\r\n    <div class=\"ats-table-wrap\">\r\n      <table class=\"ats-table\">\r\n        <thead>\r\n          <tr>\r\n            <th>Selection Question<\/th>\r\n            <th>What to Confirm<\/th>\r\n            <th>Common Wrong Shortcut<\/th>\r\n          <\/tr>\r\n        <\/thead>\r\n        <tbody>\r\n          <tr>\r\n            <td>What will the ATS carry?<\/td>\r\n            <td>Full service, essential-load feeder, generator output or dedicated equipment<\/td>\r\n            <td>\u201cMatch the generator kW\u201d<\/td>\r\n          <\/tr>\r\n          <tr>\r\n            <td>What current is required?<\/td>\r\n            <td>Actual transferred-load design current and switching duty<\/td>\r\n            <td>\u201cUse the main breaker number automatically\u201d<\/td>\r\n          <\/tr>\r\n          <tr>\r\n            <td>2P, 3P or 4P?<\/td>\r\n            <td>Phase conductors plus neutral and grounding strategy<\/td>\r\n            <td>\u201cThree phase always means 4P\u201d<\/td>\r\n          <\/tr>\r\n          <tr>\r\n            <td>Open or closed transition?<\/td>\r\n            <td>Load interruption tolerance and source relationship<\/td>\r\n            <td>\u201cClosed transition means zero outage in every event\u201d<\/td>\r\n          <\/tr>\r\n          <tr>\r\n            <td>PC or CB class?<\/td>\r\n            <td>Who provides short-circuit interruption and protection<\/td>\r\n            <td>\u201cCB class is always better\u201d<\/td>\r\n          <\/tr>\r\n          <tr>\r\n            <td>Need generator or BMS control?<\/td>\r\n            <td>Start\/stop, delays, dry contacts, alarms and communication<\/td>\r\n            <td>\u201cAutomatic means every control function is included\u201d<\/td>\r\n          <\/tr>\r\n        <\/tbody>\r\n      <\/table>\r\n    <\/div>\r\n\r\n    <p class=\"ats-caption\"><strong>Buyer meaning:<\/strong> the most useful input is a one-line diagram. If that is unavailable, send both source details, load current and type, phase, neutral\/grounding arrangement, required transition method, upstream protection and controller I\/O requirements.<\/p>\r\n\r\n    <div class=\"ats-cta-actions\">\r\n      <button type=\"button\" class=\"leeyee-about-btn-light leeyee-site-popup-btn\" aria-label=\"Send Your ATS Requirement\">\r\n        <span class=\"w-btn-label\">Send Your ATS Requirement<\/span>\r\n      <\/button>\r\n    <\/div>\r\n  <\/section>\r\n\r\n  <figure class=\"ats-core-figure\">\r\n    <img fetchpriority=\"high\" src=\"https:\/\/www.cnspd.com\/wp-content\/uploads\/2026\/09\/automatic-transfer-switch-selection-flow-chart.webp\" alt=\"Automatic transfer switch selection flow for panel builders and OEM buyers\" width=\"1448\" height=\"1086\" loading=\"eager\" decoding=\"async\">\r\n    <figcaption>ATS selection should follow the system decision path: sources, transferred load, electrical parameters, pole and neutral arrangement, transition method, protection, control functions and final model verification.<\/figcaption>\r\n  <\/figure>\r\n\r\n  <figure class=\"ats-product-img\">\r\n    <span class=\"ats-evidence-label\">Product Evidence<\/span>\r\n    <img src=\"https:\/\/www.cnspd.com\/wp-content\/uploads\/2026\/06\/2.png\" alt=\"LEEYEE ATS-63 2P and 4P automatic transfer switches for compact backup power panels\" loading=\"lazy\" decoding=\"async\">\r\n    <figcaption>LEEYEE ATS-63 is available in 2P and 4P versions. Pole count, current rating and physical similarity alone are not enough to approve an ATS for a project.<\/figcaption>\r\n  <\/figure>\r\n\r\n  <h2><span class=\"ez-toc-section\" id=\"1-use-this-ats-selection-sequence-before-comparing-models\"><\/span>1. Use this ATS selection sequence before comparing models<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n  <p>The fastest way to avoid a wrong ATS purchase is to keep the engineering decisions in the correct order. Rated current matters, but it is only one part of the selection.<\/p>\r\n\r\n  <div class=\"ats-note\">\r\n\r\n    <div class=\"ats-decision\">\r\n      <div class=\"ats-decision-num\">1<\/div>\r\n      <div>\r\n        <strong>Define the two sources<\/strong>\r\n        <span>Utility, generator, second utility, inverter or another approved source.<\/span>\r\n      <\/div>\r\n      <div>State which source is preferred and whether both sources can be available at the same time.<\/div>\r\n    <\/div>\r\n\r\n    <div class=\"ats-decision\">\r\n      <div class=\"ats-decision-num\">2<\/div>\r\n      <div>\r\n        <strong>Define the transferred load<\/strong>\r\n        <span>Full service, essential-load board, process, machine or selected circuits.<\/span>\r\n      <\/div>\r\n      <div>The ATS must be selected for the current and switching duty that actually pass through the transfer point.<\/div>\r\n    <\/div>\r\n\r\n    <div class=\"ats-decision\">\r\n      <div class=\"ats-decision-num\">3<\/div>\r\n      <div>\r\n        <strong>Confirm voltage, phase and frequency<\/strong>\r\n        <span>Check Source A, Source B and the load.<\/span>\r\n      <\/div>\r\n      <div>Both sources must be suitable for the load and for the selected ATS operating range.<\/div>\r\n    <\/div>\r\n\r\n    <div class=\"ats-decision\">\r\n      <div class=\"ats-decision-num\">4<\/div>\r\n      <div>\r\n        <strong>Resolve neutral and pole count<\/strong>\r\n        <span>2P, 3P or 4P follows the conductor and grounding design.<\/span>\r\n      <\/div>\r\n      <div>Do not decide pole count before deciding whether the neutral must remain solid or be transferred.<\/div>\r\n    <\/div>\r\n\r\n    <div class=\"ats-decision\">\r\n      <div class=\"ats-decision-num\">5<\/div>\r\n      <div>\r\n        <strong>Choose the transition method<\/strong>\r\n        <span>Open, delayed or closed transition.<\/span>\r\n      <\/div>\r\n      <div>Base the choice on load interruption tolerance, residual voltage and whether temporary source paralleling is permitted.<\/div>\r\n    <\/div>\r\n\r\n    <div class=\"ats-decision\">\r\n      <div class=\"ats-decision-num\">6<\/div>\r\n      <div>\r\n        <strong>Coordinate ATS class and protection<\/strong>\r\n        <span>PC or CB architecture plus the required protective devices.<\/span>\r\n      <\/div>\r\n      <div>Verify the prospective fault current and the exact ATS manufacturer's short-circuit data.<\/div>\r\n    <\/div>\r\n\r\n    <div class=\"ats-decision\">\r\n      <div class=\"ats-decision-num\">7<\/div>\r\n      <div>\r\n        <strong>Specify control functions<\/strong>\r\n        <span>Generator start, timing, status, alarms, remote I\/O and communications.<\/span>\r\n      <\/div>\r\n      <div>List required functions explicitly instead of assuming they are included with every automatic transfer switch.<\/div>\r\n    <\/div>\r\n\r\n    <div class=\"ats-decision\">\r\n      <div class=\"ats-decision-num\">8<\/div>\r\n      <div>\r\n        <strong>Approve the exact model<\/strong>\r\n        <span>Ratings, wiring, terminals, dimensions, documents and OEM details.<\/span>\r\n      <\/div>\r\n      <div>Keep the approved model code tied to the project drawing and purchase order.<\/div>\r\n    <\/div>\r\n\r\n  <\/div>\r\n\r\n  <p class=\"ats-buyer-meaning\"><strong>Buyer meaning:<\/strong> two transfer switches marked \u201c63 A, 4P\u201d can still differ in utilisation category, short-circuit capability, transition method, control functions, terminal capacity and certification scope.<\/p>\r\n\r\n  <h2><span class=\"ez-toc-section\" id=\"2-what-size-automatic-transfer-switch-do-you-need\"><\/span>2. What size automatic transfer switch do you need?<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n  <p>The current rating should be selected from the <strong>actual transferred-load design current and duty<\/strong>. Generator power is useful source information, but generator kW or kVA alone does not define the correct ATS rating.<\/p>\r\n\r\n  <p class=\"ats-table-note\">The most important step is identifying where the ATS sits in the one-line diagram before calculating its current.<\/p>\r\n\r\n  <div class=\"ats-table-wrap\">\r\n    <table class=\"ats-table\">\r\n      <thead>\r\n        <tr>\r\n          <th>ATS Location<\/th>\r\n          <th>Main Sizing Basis<\/th>\r\n          <th>Secondary Check<\/th>\r\n        <\/tr>\r\n      <\/thead>\r\n      <tbody>\r\n        <tr>\r\n          <td>Full-service transfer<\/td>\r\n          <td>Maximum design current through the transferred service path<\/td>\r\n          <td>Generator capacity, load management, protection and fault current<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>Essential-load board<\/td>\r\n          <td>Calculated current of the transferred essential loads<\/td>\r\n          <td>Feeder protection and load-shedding strategy<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>Dedicated equipment<\/td>\r\n          <td>Equipment design current and switching duty<\/td>\r\n          <td>Starting current and acceptable interruption<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>Utility-to-utility transfer<\/td>\r\n          <td>Load current that either source must supply<\/td>\r\n          <td>Neutral design, source relationship and transition requirement<\/td>\r\n        <\/tr>\r\n      <\/tbody>\r\n    <\/table>\r\n  <\/div>\r\n\r\n  <p class=\"ats-buyer-meaning\"><strong>Procurement conclusion:<\/strong> establish the transferred current path before selecting an ATS frame size.<\/p>\r\n\r\n  <h3>Preliminary ATS current calculations<\/h3>\r\n\r\n  <p>If project data is supplied in apparent power, the following equations can estimate current during early selection. For three-phase calculations, use line-to-line voltage and assume a balanced load. These calculations are preliminary; final ATS approval still requires the actual load characteristics, utilisation category, installation conditions and manufacturer data.<\/p>\r\n\r\n  <div class=\"ats-formula\">Single-phase: I (A) \u2248 S (kVA) \u00d7 1000 \u00f7 V<\/div>\r\n\r\n  <div class=\"ats-formula\">Three-phase: I (A) \u2248 S (kVA) \u00d7 1000 \u00f7 (\u221a3 \u00d7 V<sub>LL<\/sub>)<\/div>\r\n\r\n  <div class=\"ats-example\">\r\n    <span class=\"ats-kicker\">Example<\/span>\r\n    <h3>30 kVA, 400 V three-phase distribution load<\/h3>\r\n    <div class=\"ats-formula\">30 \u00d7 1000 \u00f7 (1.732 \u00d7 400) \u2248 43.3 A<\/div>\r\n    <p>The calculated current is approximately <span class=\"ats-result\">43.3 A<\/span>. A 50 A current option may therefore be a starting point from current alone. The next checks are neutral switching, utilisation category, installation conditions and short-circuit coordination.<\/p>\r\n  <\/div>\r\n\r\n  <div class=\"ats-warning\">\r\n    <strong>Do not turn a preliminary current calculation into a final ATS approval.<\/strong> Oversizing the ampere rating cannot correct a wrong neutral arrangement, unsuitable utilisation category, insufficient short-circuit capability or missing control functions.\r\n  <\/div>\r\n\r\n  <h2><span class=\"ez-toc-section\" id=\"3-utility-generator-utility-utility-or-generator-generator\"><\/span>3. Utility-generator, utility-utility or generator-generator?<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n  <p>The source arrangement changes the operating sequence. A technically useful ATS enquiry should therefore identify both sources instead of saying only \u201cdual power\u201d.<\/p>\r\n\r\n  <div class=\"ats-grid\">\r\n\r\n    <div class=\"ats-card\">\r\n      <h3>Utility \u2192 Generator<\/h3>\r\n      <p>Confirm source-failure sensing, generator start command, generator source acceptance, transfer delay, retransfer delay and generator stop sequence. Cummins documents these as separate stages in a typical automatic utility-generator transfer sequence. [5]\r\n    <\/div>\r\n\r\n    <div class=\"ats-card\">\r\n      <h3>Utility \u2192 Utility<\/h3>\r\n      <p>An engine-start sequence is normally unnecessary. Define preferred source, source acceptance conditions, transfer\/retransfer delays and the permitted transition method.<\/p>\r\n    <\/div>\r\n\r\n    <div class=\"ats-card\">\r\n      <h3>Generator \u2192 Generator<\/h3>\r\n      <p>Confirm how each generator is started and stopped, which source has priority, whether alternation is required and how the system responds if a source fails to become acceptable.<\/p>\r\n    <\/div>\r\n\r\n    <div class=\"ats-card\">\r\n      <h3>Utility \u2192 Inverter \/ ESS<\/h3>\r\n      <p>Confirm inverter output voltage and frequency, neutral bonding, source behaviour and the inverter manufacturer's transfer requirements before fixing the ATS configuration.<\/p>\r\n    <\/div>\r\n\r\n  <\/div>\r\n\r\n  <figure class=\"ats-core-figure\">\r\n    <img loading=\"lazy\" src=\"https:\/\/www.cnspd.com\/wp-content\/uploads\/2026\/09\/utility-generator-ats-operating-sequence.webp\" alt=\"Utility generator automatic transfer switch operating sequence from mains failure to generator cooldown\" width=\"1448\" height=\"1086\" loading=\"lazy\" decoding=\"async\">\r\n    <figcaption>Typical open-transition utility-generator sequence: detect unacceptable utility power, start the generator, confirm the alternate source, transfer the load, verify utility restoration, retransfer and then complete the generator stop sequence. Actual timers and acceptance limits are controller- and project-specific. [5]<\/figcaption>\r\n  <\/figure>\r\n\r\n  <div class=\"ats-warning\">\r\n    <strong>ATS switching time is not the same as total backup restoration time.<\/strong> In a generator application, the outage can also include source-failure detection, generator starting, voltage\/frequency stabilization and programmed transfer delay. [5]\r\n  <\/div>\r\n\r\n  <h2><span class=\"ez-toc-section\" id=\"4-how-do-you-choose-2p-3p-or-4p-ats\"><\/span>4. How do you choose 2P, 3P or 4P ATS?<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n  <p>Choose the pole configuration from the conductors that must be transferred and from the system neutral\/grounding design. Phase count by itself is not enough.<\/p>\r\n\r\n  <p class=\"ats-table-note\">Focus on what happens to the neutral conductor. That decision usually explains the difference between 3P and 4P transfer arrangements.<\/p>\r\n\r\n  <div class=\"ats-table-wrap\">\r\n    <table class=\"ats-table\">\r\n      <thead>\r\n        <tr>\r\n          <th>Configuration<\/th>\r\n          <th>Common Direction<\/th>\r\n          <th>Project Check<\/th>\r\n        <\/tr>\r\n      <\/thead>\r\n      <tbody>\r\n        <tr>\r\n          <td><strong>2P<\/strong><\/td>\r\n          <td>Common in single-phase arrangements where two conductors are transferred<\/td>\r\n          <td>Confirm which conductor is neutral, bonding and local requirements<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td><strong>3P<\/strong><\/td>\r\n          <td>Three phase conductors switched while neutral remains solid, or a three-wire system<\/td>\r\n          <td>Confirm that a continuous neutral is correct for the grounding design<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td><strong>4P<\/strong><\/td>\r\n          <td>L1, L2, L3 and neutral are transferred<\/td>\r\n          <td>Confirm that switched-neutral operation is required by the source and grounding arrangement<\/td>\r\n        <\/tr>\r\n      <\/tbody>\r\n    <\/table>\r\n  <\/div>\r\n\r\n  <p>Schneider Electric's ASCO guidance distinguishes transfer switches with solid and switched neutrals. It states that selecting a solid or switched neutral depends on the electrical distribution system and the grounding relationship of the alternate source, including separately derived source arrangements. [4]\r\n\r\n  <figure class=\"ats-core-figure\">\r\n    <img loading=\"lazy\" src=\"https:\/\/www.cnspd.com\/wp-content\/uploads\/2026\/09\/2p-3p-4p-ats-neutral-selection-diagram.webp\" alt=\"Comparison of 2P 3P and 4P automatic transfer switch neutral arrangements\" width=\"1448\" height=\"1086\" loading=\"lazy\" decoding=\"async\">\r\n    <figcaption>2P, 3P and 4P selection should follow the conductor and neutral strategy. A three-phase system does not automatically require a switched neutral, and a 4P ATS is not universally better than a 3P arrangement. Final selection must match the project's grounding design and applicable rules. [4]<\/figcaption>\r\n  <\/figure>\r\n\r\n  <div class=\"ats-note\">\r\n    <strong>LEEYEE ATS-63 product boundary:<\/strong> the current ATS-63 product page lists <span class=\"ats-pill\">2P<\/span><span class=\"ats-pill\">4P<\/span> versions. It does not list a 3P version. If a project specifically requires three-pole transfer with a solid neutral, do not assume the 4P version is an automatic substitute. Confirm the one-line diagram and required neutral treatment first. [6]\r\n  <\/div>\r\n\r\n  <figure>\r\n    <span class=\"ats-evidence-label\">Wiring Evidence<\/span>\r\n    <img src=\"https:\/\/www.cnspd.com\/wp-content\/uploads\/2026\/06\/Wiring-instructions-guide-for-ATS.png\" alt=\"LEEYEE ATS-63 wiring guide showing normal source backup source and load connections\" loading=\"lazy\" decoding=\"async\">\r\n    <figcaption>Model-specific wiring information is part of selection approval. Verify terminal identification, conductor arrangement and the exact model wiring diagram before panel assembly or energization.<\/figcaption>\r\n  <\/figure>\r\n\r\n  <h2><span class=\"ez-toc-section\" id=\"5-open-transition-vs-delayed-transition-vs-closed-transition\"><\/span>5. Open transition vs delayed transition vs closed transition<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n  <p><strong>Open transition<\/strong> is a break-before-make transfer. The connected source is disconnected before the alternate source is connected, so a short interruption occurs.<\/p>\r\n\r\n  <p><strong>Delayed transition<\/strong> is an open transition with an intentional OFF interval. This can be useful when residual voltage, motors, transformers or process behaviour require a pause before the alternate source is connected.<\/p>\r\n\r\n  <p><strong>Closed transition<\/strong> allows a brief overlap between two acceptable and synchronized sources during an eligible transfer. IEC 60947-6-1:2026 includes specific requirements for ATSE with closed-transition capability in Annex D. [1]\r\n\r\n  <div class=\"ats-table-wrap\">\r\n    <table class=\"ats-table\">\r\n      <thead>\r\n        <tr>\r\n          <th>Transition<\/th>\r\n          <th>Source Sequence<\/th>\r\n          <th>Selection Trigger<\/th>\r\n        <\/tr>\r\n      <\/thead>\r\n      <tbody>\r\n        <tr>\r\n          <td>Open<\/td>\r\n          <td>Source 1 opens \u2192 Source 2 closes<\/td>\r\n          <td>A brief interruption is acceptable<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>Delayed<\/td>\r\n          <td>Source 1 opens \u2192 OFF delay \u2192 Source 2 closes<\/td>\r\n          <td>The load or residual voltage requires a deliberate pause<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>Closed<\/td>\r\n          <td>Synchronized sources overlap briefly<\/td>\r\n          <td>Planned transfer should minimize interruption and temporary paralleling is permitted<\/td>\r\n        <\/tr>\r\n      <\/tbody>\r\n    <\/table>\r\n  <\/div>\r\n\r\n  <div class=\"ats-warning\">\r\n    <strong>Closed transition does not guarantee zero interruption during every failure.<\/strong> Schneider Electric notes that when the normal source has already failed, transfer to the emergency source must occur without the failed source being available for synchronized overlap. Closed-transition operation is relevant when both sources are live, acceptable and synchronized. [3]\r\n  <\/div>\r\n\r\n  <p class=\"ats-buyer-meaning\"><strong>Engineering meaning:<\/strong> a critical no-break load may still require a UPS or another continuity architecture. Do not specify closed transition merely because a project uses the phrase \u201cno downtime\u201d.<\/p>\r\n\r\n  <h2><span class=\"ez-toc-section\" id=\"6-pc-class-vs-cb-class-ats-decide-who-clears-a-short-circuit\"><\/span>6. PC class vs CB class ATS: decide who clears a short circuit<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n  <p>IEC 60947-6-1 classifies transfer switching equipment according to short-circuit capability. ABB summarizes the practical distinction between Class PC and Class CB as follows. [2]\r\n\r\n  <div class=\"ats-table-wrap\">\r\n    <table class=\"ats-table\">\r\n      <thead>\r\n        <tr>\r\n          <th>Class<\/th>\r\n          <th>Short-Circuit Role<\/th>\r\n          <th>Panel Design Meaning<\/th>\r\n        <\/tr>\r\n      <\/thead>\r\n      <tbody>\r\n        <tr>\r\n          <td><strong>Class PC<\/strong><\/td>\r\n          <td>Capable of making and withstanding short-circuit currents but not intended to break them<\/td>\r\n          <td>Short-circuit interruption must be provided by appropriately coordinated protective devices<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td><strong>Class CB<\/strong><\/td>\r\n          <td>Capable of making, withstanding and intended to break short-circuit currents, with overcurrent releases<\/td>\r\n          <td>Breaker-based transfer architecture; system protection and selectivity still require engineering review<\/td>\r\n        <\/tr>\r\n      <\/tbody>\r\n    <\/table>\r\n  <\/div>\r\n\r\n  <p class=\"ats-buyer-meaning\"><strong>Buyer meaning:<\/strong> Class PC is not an inferior version of Class CB. They are different transfer and protection architectures. Select the architecture required by the project rather than treating the class name as a quality grade.<\/p>\r\n\r\n  <h2><span class=\"ez-toc-section\" id=\"7-short-circuit-capability-the-ats-current-rating-is-not-enough\"><\/span>7. Short-circuit capability: the ATS current rating is not enough<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n  <p>A normal-current rating such as 63 A tells the buyer about the ATS operating-current range under stated conditions. It does not by itself prove that the transfer equipment is suitable for the prospective fault current at the installation point.<\/p>\r\n\r\n  <p>For IEC projects, verify the exact transfer switch short-circuit data and the manufacturer-specified protective-device conditions. Depending on the ATS design, relevant parameters can include withstand capability, making capability or a conditional short-circuit rating. The required check must use the exact model documentation rather than a generic ATS value. [1][2]\r\n\r\n  <p>For North American projects, UL Solutions identifies UL 1008 as the applicable transfer-switch standard within its certification scope. The product marking and tested conditions must be checked for the exact device and application. [7]\r\n\r\n  <div class=\"ats-warning\">\r\n    <strong>Do not copy the upstream breaker's interrupting rating into the ATS specification.<\/strong> The breaker or fuse and the ATS perform different functions during a fault. Verify the approved combination and available fault current before releasing the panel design.\r\n  <\/div>\r\n\r\n  <h2><span class=\"ez-toc-section\" id=\"8-integrated-controller-or-separate-ats-controller\"><\/span>8. Integrated controller or separate ATS controller?<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n  <p>Some automatic transfer switches combine the switching mechanism and controller in one device. Other systems use separate switching devices with a stand-alone ATS controller. IEC 60947-6-1:2026 explicitly includes stand-alone ATS controllers in Annex E. [1]\r\n\r\n  <div class=\"ats-grid\">\r\n\r\n    <div class=\"ats-card\">\r\n      <h3>Integrated ATS Controller<\/h3>\r\n      <ul>\r\n        <li>Compact panel architecture<\/li>\r\n        <li>Less external control wiring<\/li>\r\n        <li>Useful when the built-in sequence matches the project<\/li>\r\n      <\/ul>\r\n    <\/div>\r\n\r\n    <div class=\"ats-card\">\r\n      <h3>Separate ATS Controller<\/h3>\r\n      <ul>\r\n        <li>More flexible sensing and timing options<\/li>\r\n        <li>Potentially more I\/O and communication functions<\/li>\r\n        <li>Useful for larger or more complex transfer assemblies<\/li>\r\n      <\/ul>\r\n    <\/div>\r\n\r\n  <\/div>\r\n\r\n  <p>For OEM panel design, ask which sensing, timing, I\/O and communication functions are required. A display screen alone does not define the controller capability.<\/p>\r\n\r\n  <h2><span class=\"ez-toc-section\" id=\"9-generator-start-signals-dry-contacts-and-remote-monitoring\"><\/span>9. Generator start signals, dry contacts and remote monitoring<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n  <p>Automatic transfer operation does not mean that every ATS includes the same external control interfaces. Generator control, dry contacts and communications should therefore be specified individually.<\/p>\r\n\r\n  <h3>Generator start and stop sequence<\/h3>\r\n\r\n  <p>In a typical utility-generator arrangement, the ATS control monitors the normal source. When the source remains unacceptable for the programmed delay, it signals the generator to start. The controller then waits for the generator source to reach acceptable conditions before transferring the load. When normal power returns and remains acceptable, the controller can begin the retransfer sequence and subsequently initiate the generator stop sequence. [5]\r\n\r\n  <h3>Dry contacts<\/h3>\r\n\r\n  <p>A dry contact is a voltage-free relay contact used to exchange a status or command signal with another controller. Project requirements may include source availability, transfer position, alarm, remote test, inhibit or generator start. The exact NO\/NC logic and contact rating must be confirmed from the selected controller documentation.<\/p>\r\n\r\n  <h3>Remote monitoring<\/h3>\r\n\r\n  <p>For BMS, PLC, telecom or unmanned installations, replace the vague requirement \u201cremote monitoring\u201d with a defined I\/O or protocol list. Typical project questions include:<\/p>\r\n\r\n  <ul>\r\n    <li>Is Source A available?<\/li>\r\n    <li>Is Source B available?<\/li>\r\n    <li>Which source is connected to the load?<\/li>\r\n    <li>Is there a common alarm output?<\/li>\r\n    <li>Is remote test, transfer or inhibit required?<\/li>\r\n    <li>Is a generator start\/stop output required?<\/li>\r\n    <li>Is RS485, Modbus, Ethernet or another protocol required?<\/li>\r\n  <\/ul>\r\n\r\n  <div class=\"ats-note\">\r\n    <strong>Do not assume these functions are standard on LEEYEE ATS-63.<\/strong> The current ATS-63 product page publishes its main electrical ratings and control-voltage information, but it does not publish a general Modbus or BMS communication feature set. Projects requiring these functions should be confirmed before quotation or moved to a different ATS\/controller architecture. [6]\r\n  <\/div>\r\n\r\n  <h2><span class=\"ez-toc-section\" id=\"10-match-the-ats-to-the-load-type-and-utilisation-category\"><\/span>10. Match the ATS to the load type and utilisation category<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n  <p>The same current number can represent different switching duties. General distribution loads, motors, transformers, UPS inputs and mixed loads can impose different starting, inrush and transfer requirements.<\/p>\r\n\r\n  <p class=\"ats-table-note\">Do not stop at the running current. For motor- or transformer-heavy panels, load duty becomes a major selection factor.<\/p>\r\n\r\n  <div class=\"ats-table-wrap\">\r\n    <table class=\"ats-table\">\r\n      <thead>\r\n        <tr>\r\n          <th>Load Type<\/th>\r\n          <th>What Changes the Selection<\/th>\r\n          <th>What to Send the Supplier<\/th>\r\n        <\/tr>\r\n      <\/thead>\r\n      <tbody>\r\n        <tr>\r\n          <td>General distribution \/ resistive<\/td>\r\n          <td>Design current, voltage and required utilisation category<\/td>\r\n          <td>Load schedule or feeder design current<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>Motors \/ pumps \/ compressors<\/td>\r\n          <td>Starting current, switching duty, residual voltage and restart sequence<\/td>\r\n          <td>Motor kW, starting method and operating duty<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>Transformers<\/td>\r\n          <td>Magnetizing inrush and transfer timing<\/td>\r\n          <td>Transformer kVA and available inrush information<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>UPS \/ VFD \/ sensitive electronics<\/td>\r\n          <td>Ride-through capability, source quality and interruption tolerance<\/td>\r\n          <td>Equipment input specification and acceptable transfer break<\/td>\r\n        <\/tr>\r\n      <\/tbody>\r\n    <\/table>\r\n  <\/div>\r\n\r\n  <p class=\"ats-buyer-meaning\"><strong>Engineering meaning:<\/strong> if the project is motor-heavy, do not assume that a compact AC-31B ATS is suitable simply because its ampere rating exceeds the motor running current.<\/p>\r\n\r\n  <h2><span class=\"ez-toc-section\" id=\"11-where-does-leeyee-ats-63-fit\"><\/span>11. Where does LEEYEE ATS-63 fit?<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n  <p>LEEYEE ATS-63 is a compact DIN-rail automatic transfer switch for smaller AC backup systems. The current LEEYEE product page lists 6 A, 10 A, 16 A, 20 A, 25 A, 32 A, 40 A, 50 A and 63 A ratings; 2P and 4P configurations; AC110 V, AC220 V and AC400 V versions; 50\/60 Hz; Class PC; AC-31B utilisation category; transfer switching time below 50 ms; and rated short-circuit current Iq of 5 kA. [6]\r\n\r\n  <figure class=\"ats-spec-img\">\r\n    <span class=\"ats-evidence-label\">Model Evidence<\/span>\r\n    <img src=\"https:\/\/www.cnspd.com\/wp-content\/uploads\/2026\/06\/4.png\" alt=\"LEEYEE ATS-2P63 side label showing model-specific automatic transfer switch electrical data\" loading=\"lazy\" decoding=\"async\">\r\n    <figcaption>The exact ATS label, current product data and wiring documentation should be checked during project approval. Do not generalize one ATS-63 model's data to another transfer-switch family.<\/figcaption>\r\n  <\/figure>\r\n\r\n  <div class=\"ats-table-wrap\">\r\n    <table class=\"ats-table\">\r\n      <thead>\r\n        <tr>\r\n          <th>ATS-63 Can Be a Starting Point When\u2026<\/th>\r\n          <th>Use Another ATS Architecture When\u2026<\/th>\r\n        <\/tr>\r\n      <\/thead>\r\n      <tbody>\r\n        <tr>\r\n          <td>The required operating current is within the listed 6\u201363 A range and the exact model rating matches.<\/td>\r\n          <td>The transferred load exceeds 63 A.<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>2P or 4P matches the approved conductor and neutral arrangement.<\/td>\r\n          <td>The project specifically requires a 3P or another transfer configuration.<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>The load duty is compatible with the listed AC-31B utilisation category.<\/td>\r\n          <td>The load requires another utilisation category or model-specific switching performance.<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>The project can accept the transfer behaviour of the selected ATS-63 model.<\/td>\r\n          <td>Closed transition, bypass\/isolation or source synchronization is required.<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>The project short-circuit conditions and protection match the documented device limits.<\/td>\r\n          <td>The available fault current or required coordination is outside the documented application.<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>Basic compact two-source automatic transfer is required.<\/td>\r\n          <td>Advanced communication, event logging or complex generator sequencing is mandatory.<\/td>\r\n        <\/tr>\r\n      <\/tbody>\r\n    <\/table>\r\n  <\/div>\r\n\r\n  <p>For the current model parameters, installation limits, dimensions and wiring information, use the <a href=\"https:\/\/www.cnspd.com\/products\/leeyee-automatic-transfer-switch-solar-backup\/\">LEEYEE ATS-63 product page<\/a>. A selection guide should direct a buyer to the correct architecture; it should not force every project into one compact ATS model.<\/p>\r\n\r\n  <h2><span class=\"ez-toc-section\" id=\"12-common-ats-selection-mistakes-that-cause-panel-rework\"><\/span>12. Common ATS selection mistakes that cause panel rework<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n  <div class=\"ats-table-wrap\">\r\n    <table class=\"ats-table\">\r\n      <thead>\r\n        <tr>\r\n          <th>Mistake<\/th>\r\n          <th>Why It Creates Risk<\/th>\r\n          <th>Better Check<\/th>\r\n        <\/tr>\r\n      <\/thead>\r\n      <tbody>\r\n        <tr>\r\n          <td>Choosing by generator kW only<\/td>\r\n          <td>Generator power does not directly define the transferred-load current or ATS duty<\/td>\r\n          <td>Calculate the current at the actual transfer point<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>Choosing 4P only because the system is three-phase<\/td>\r\n          <td>Neutral switching depends on the grounding and source arrangement<\/td>\r\n          <td>Confirm the neutral strategy first<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>Ignoring utilisation category<\/td>\r\n          <td>Motor and transformer switching duties can differ from general distribution duty<\/td>\r\n          <td>Match the load and required utilisation category<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>Ignoring available fault current<\/td>\r\n          <td>An ATS can carry normal current but still be unsuitable for the project fault condition<\/td>\r\n          <td>Verify short-circuit data and protective-device coordination<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>Assuming \u201cautomatic\u201d includes every generator or BMS function<\/td>\r\n          <td>Controller I\/O and communication vary by model<\/td>\r\n          <td>Provide a defined sequence and I\/O list<\/td>\r\n        <\/tr>\r\n        <tr>\r\n          <td>Approving from a product photo and ampere label<\/td>\r\n          <td>Wiring, terminals, dimensions, controller logic and documents can differ<\/td>\r\n          <td>Approve the exact item code and technical documentation<\/td>\r\n        <\/tr>\r\n      <\/tbody>\r\n    <\/table>\r\n  <\/div>\r\n\r\n  <h2><span class=\"ez-toc-section\" id=\"13-before-ordering-ats-rfq-checklist-for-panel-builders-and-oem-buyers\"><\/span>13. Before ordering: ATS RFQ checklist for panel builders and OEM buyers<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n  <section class=\"ats-checklist\">\r\n    <span class=\"ats-kicker\">RFQ \/ OEM Checklist<\/span>\r\n\r\n    <h3>Send these parameters before requesting a model recommendation<\/h3>\r\n\r\n    <ul>\r\n      <li>Normal source type<\/li>\r\n      <li>Alternate source type<\/li>\r\n      <li>Preferred source<\/li>\r\n      <li>Source A voltage<\/li>\r\n      <li>Source B voltage<\/li>\r\n      <li>System frequency<\/li>\r\n      <li>Single-phase or three-phase<\/li>\r\n      <li>Transferred-load design current<\/li>\r\n      <li>Load type and inrush information<\/li>\r\n      <li>2P \/ 3P \/ 4P requirement<\/li>\r\n      <li>Neutral and grounding arrangement<\/li>\r\n      <li>Open \/ delayed \/ closed transition<\/li>\r\n      <li>PC or CB requirement if specified<\/li>\r\n      <li>Prospective fault current<\/li>\r\n      <li>Upstream breaker or fuse<\/li>\r\n      <li>Generator start\/stop requirement<\/li>\r\n      <li>Transfer and retransfer delays<\/li>\r\n      <li>Required dry-contact I\/O<\/li>\r\n      <li>Required communication protocol<\/li>\r\n      <li>Manual\/test\/bypass requirement<\/li>\r\n      <li>Panel mounting space<\/li>\r\n      <li>Ambient temperature and altitude<\/li>\r\n      <li>Target market and standard<\/li>\r\n      <li>Required certificates or documents<\/li>\r\n      <li>Quantity<\/li>\r\n      <li>OEM label or packaging requirement<\/li>\r\n    <\/ul>\r\n\r\n    <div class=\"ats-copy\">\r\n      <strong>Copyable ATS enquiry format:<\/strong><br>\r\n      \u201cNeed ATS for [utility-generator \/ utility-utility \/ generator-generator \/ other]. Source A: [V \/ Hz \/ phase]. Source B: [V \/ Hz \/ phase]. Transferred load: [A + load type]. Pole requirement: [2P \/ 3P \/ 4P]. Neutral: [solid \/ switched \/ unknown]. Transition: [open \/ delayed \/ closed]. Upstream protection: [device and rating]. Available fault current: [kA if known]. Generator start: [yes \/ no]. Dry contacts: [list]. Communication: [protocol]. Quantity: [ ]. Destination: [ ]. Required standard\/documents: [ ].\u201d\r\n    <\/div>\r\n  <\/section>\r\n\r\n  <section class=\"ats-cta\">\r\n    <span class=\"ats-kicker\">Technical Confirmation<\/span>\r\n\r\n    <h2><span class=\"ez-toc-section\" id=\"need-the-ats-configuration-checked-before-panel-approval\"><\/span>Need the ATS configuration checked before panel approval?<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n    <p>Send the one-line diagram or the checklist above. LEEYEE can review whether the requested current, voltage, pole arrangement and ATS-63 operating range match the stated project conditions before quotation or sample approval.<\/p>\r\n\r\n    <p>If the project falls outside the documented ATS-63 range, the transfer architecture should be reconsidered rather than forcing the compact model into the design.<\/p>\r\n\r\n    <div class=\"ats-cta-actions\">\r\n      <button type=\"button\" class=\"leeyee-about-btn-light leeyee-site-popup-btn\" aria-label=\"Request ATS Selection Review\">\r\n        <span class=\"w-btn-label\">Request ATS Selection Review<\/span>\r\n      <\/button>\r\n    <\/div>\r\n  <\/section>\r\n\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  <h3>What size automatic transfer switch do I need?<\/h3>\r\n  <p>Start with the design current that will actually pass through the transfer point. Then select an available ATS rating that can carry that duty and verify voltage, phase, utilisation category, neutral arrangement, transition method, installation conditions and short-circuit coordination.<\/p>\r\n\r\n  <h3>Should the ATS match the generator rating or the main breaker?<\/h3>\r\n  <p>Neither rule is universally correct. A full-service ATS may need to carry the normal service path even where the generator is smaller and load management is used. An essential-load ATS can instead be selected around the transferred essential-load feeder. The one-line diagram determines which current path matters.<\/p>\r\n\r\n  <h3>Do I need a 3P or 4P ATS for a three-phase system?<\/h3>\r\n  <p>Use a three-pole arrangement when the three phase conductors are transferred and a solid neutral is correct for the system. Use a four-pole arrangement when the neutral also needs to be transferred. The final decision depends on the grounding and source arrangement and applicable project requirements. [4]\r\n\r\n  <h3>Is a 4P ATS always safer than a 3P ATS?<\/h3>\r\n  <p>No. More poles do not automatically mean a safer design. Switching the neutral must be intentional and compatible with the system grounding arrangement.<\/p>\r\n\r\n  <h3>What is the difference between Class PC and Class CB ATS?<\/h3>\r\n  <p>Class PC transfer equipment can make and withstand short-circuit current but is not intended to interrupt it. Class CB equipment is capable of making, withstanding and interrupting short-circuit current and includes overcurrent releases. [2]\r\n\r\n  <h3>Does an automatic transfer switch provide overload or short-circuit protection?<\/h3>\r\n  <p>Do not assume that it does. A Class PC ATS depends on appropriately coordinated protective devices for short-circuit interruption. A Class CB architecture includes overcurrent releases, but the complete system still requires protection and selectivity review. [2]\r\n\r\n  <h3>Does an ATS need a generator start contact?<\/h3>\r\n  <p>A utility-generator system normally requires a defined interface to start the generator unless another controller performs that function. The contact type, logic, timing and generator-controller compatibility must be confirmed for the actual system. [5]\r\n\r\n  <h3>Does every ATS have dry contacts or Modbus?<\/h3>\r\n  <p>No. Status contacts, remote commands and communications are controller-specific features. Put the required I\/O and protocol into the project specification or RFQ.<\/p>\r\n\r\n  <h3>Can closed transition eliminate every power interruption?<\/h3>\r\n  <p>No. Closed transition can minimize interruption during an eligible transfer between two live, synchronized sources. If the normal source has already failed, it is not available for overlap with the alternate source. [3]\r\n\r\n  <h3>What standard applies to ATS in IEC projects?<\/h3>\r\n  <p>IEC 60947-6-1 is the core international standard for transfer switching equipment within its scope. The current fourth edition, IEC 60947-6-1:2026, applies to transfer switching equipment up to 1,000 V AC or 1,500 V DC and includes dedicated annexes for closed-transition ATSE and stand-alone ATS controllers. [1]\r\n\r\n  <h3>Is LEEYEE ATS-63 suitable for motor loads?<\/h3>\r\n  <p>The current ATS-63 product data lists utilisation category AC-31B. Do not automatically specify it for a motor-heavy application that requires another utilisation category. Provide the motor and switching-duty information for project confirmation or select equipment with the required duty rating. [6]\r\n\r\n  <div class=\"ats-related\">\r\n    <h2><span class=\"ez-toc-section\" id=\"related-reading\"><\/span>Related reading<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n    <p>For the operating principle and basic terminology, read <a href=\"https:\/\/www.cnspd.com\/what-is-an-automatic-transfer-switch-how-ats-works-how-to-choose\/\">What Is an Automatic Transfer Switch?<\/a>. For the current compact ATS model parameters, dimensions and wiring data, see the <a href=\"https:\/\/www.cnspd.com\/products\/leeyee-automatic-transfer-switch-solar-backup\/\">LEEYEE ATS-63 product page<\/a>.<\/p>\r\n  <\/div>\r\n\r\n  <h2><span class=\"ez-toc-section\" id=\"references\"><\/span>References<span class=\"ez-toc-section-end\"><\/span><\/h2>\r\n\r\n  <ol class=\"ats-ref\">\r\n\r\n    <li>[1] IEC. <em>IEC 60947-6-1:2026 \u2014 Low-voltage switchgear and controlgear \u2014 Part 6-1: Multiple function equipment \u2014 Transfer switching equipment.<\/em> Fourth edition, published 2 April 2026. <a href=\"https:\/\/webstore.iec.ch\/en\/publication\/90494\" target=\"_blank\" rel=\"noopener\">IEC official publication page<\/a>.<\/li>\r\n\r\n    <li>[2] ABB. <em>How to Select an Automatic Transfer Switch Class.<\/em> Technical white paper explaining IEC Class PC, Class CB and Class CC transfer switching equipment and their short-circuit functions. <a href=\"https:\/\/library.e.abb.com\/public\/a0a6a4a06b204e7bbf5988e6d35ee364\/ATS%20white%20paper_1SCC303022C0201_20-09.pdf\" target=\"_blank\" rel=\"noopener\">ABB technical white paper<\/a>.<\/li>\r\n\r\n    <li>[3] Schneider Electric. <em>What Is a Transfer Switch?<\/em> Technical explanation of ATS operation and closed-transition behaviour during transfer and retransfer. <a href=\"https:\/\/www.se.com\/us\/en\/work\/featured-articles\/what-is-a-transfer-switch\/\" target=\"_blank\" rel=\"noopener\">Schneider Electric technical article<\/a>.<\/li>\r\n\r\n    <li>[4] Schneider Electric \/ ASCO. <em>Neutral Configurations in Transfer Switches.<\/em> Data bulletin covering solid-neutral and switched-neutral configurations and their relationship to alternate-source grounding. <a href=\"https:\/\/www.se.com\/us\/en\/download\/document\/ASC-DB-NCTS\/\" target=\"_blank\" rel=\"noopener\">Schneider Electric \/ ASCO data bulletin<\/a>.<\/li>\r\n\r\n    <li>[5] Cummins. <em>Application Manual \u2014 Transfer Switches.<\/em> Technical application guidance describing normal-source monitoring, generator start, transfer delay, retransfer and generator stop sequence. <a href=\"https:\/\/incal.cummins.com\/www\/literature\/applicationmanuals\/t-011_p38-48.pdf\" target=\"_blank\" rel=\"noopener\">Cummins transfer-switch application manual<\/a>.<\/li>\r\n\r\n    <li>[6] LEEYEE. <em>ATS-63 Automatic Transfer Switch for Solar &amp; Home Backup.<\/em> Current product data for rated current, 2P\/4P configurations, voltage, frequency, Class PC, AC-31B, Iq, transfer time, environmental limits, dimensions and wiring information. <a href=\"https:\/\/www.cnspd.com\/products\/leeyee-automatic-transfer-switch-solar-backup\/\" target=\"_blank\" rel=\"noopener\">LEEYEE ATS-63 product page<\/a>.<\/li>\r\n\r\n    <li>[7] UL Solutions. <em>Switch Certification and Evaluation Services.<\/em> Transfer-switch certification and evaluation information, including UL 1008. <a href=\"https:\/\/www.ul.com\/services\/switch-certification-and-evaluation-services\" target=\"_blank\" rel=\"noopener\">UL Solutions<\/a>.<\/li>\r\n\r\n  <\/ol>\r\n\r\n  <p class=\"ats-small\">Engineering note: final ATS selection must follow the project one-line diagram, applicable local electrical requirements, the exact transfer-switch and controller documentation, and the approved short-circuit\/protection coordination. Where a source, neutral, load-duty, fault-current or controller requirement is unknown, treat it as an open project-confirmation item rather than assuming a value.<\/p>\r\n\r\n<\/article>\r\n\r\n<script>\r\n(function () {\r\n  function initLeeyeeAtsPopupButtons() {\r\n    var article = document.getElementById('ats-selection-guide');\r\n\r\n    if (!article) {\r\n      return;\r\n    }\r\n\r\n    var aboutPopupButtons = article.querySelectorAll('.leeyee-site-popup-btn');\r\n\r\n    aboutPopupButtons.forEach(function (button) {\r\n      if (button.getAttribute('data-leeyee-popup-bound') === '1') {\r\n        return;\r\n      }\r\n\r\n      button.setAttribute('data-leeyee-popup-bound', '1');\r\n\r\n      button.addEventListener('click', function () {\r\n        var realPopupTrigger = document.querySelector('.w-popup.ush_popup_1 .w-popup-trigger');\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'\r\n          );\r\n        }\r\n      });\r\n    });\r\n  }\r\n\r\n  if (document.readyState === 'loading') {\r\n    document.addEventListener('DOMContentLoaded', initLeeyeeAtsPopupButtons);\r\n  } else {\r\n    initLeeyeeAtsPopupButtons();\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>This automatic transfer switch selection guide is written for panel builders, generator integrators, electrical contractors, distributors and OEM buyers who already understand the basic purpose of an ATS and now need to specify the correct device for a real project. The selection should start with the power architecture and transferred load, then move through current,&#8230;<\/p>","protected":false},"author":18,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[490,1,422],"tags":[],"class_list":["post-31009","post","type-post","status-publish","format-standard","hentry","category-isolator-switching","category-news","category-industry-news"],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.3 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Automatic Transfer Switch Selection Guide | ATS Selection for OEM Panels<\/title>\n<meta name=\"description\" content=\"Select an automatic transfer switch by current, 2P\/3P\/4P, neutral, source type, open or closed transition, PC vs CB class, fault current and generator control.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.cnspd.com\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/\" \/>\n<meta property=\"og:locale\" content=\"it_IT\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Automatic Transfer Switch Selection Guide | ATS Selection for OEM Panels\" \/>\n<meta property=\"og:description\" content=\"Select an automatic transfer switch by current, 2P\/3P\/4P, neutral, source type, open or closed transition, PC vs CB class, fault current and generator control.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.cnspd.com\/it\/automatic-transfer-switch-selection-guide-for-panel-builders-and-oem-buyers\/\" \/>\n<meta property=\"og:site_name\" content=\"Surge Protector, Surge Arrestor, Isolating Switch - 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