Índice
Does a sensor line need surge protection?
A sensor line needs a surge-risk check when it runs outdoors, between buildings or over a long distance.
These cable routes can carry induced surge voltage into a PLC, RTU or control cabinet. This can happen even when the main power supply already has an SPD. [1][2][3]
LEEYEE option for RS485 and industrial data lines
The LY10 is the currently published LEEYEE option for RS485 and industrial data or control signal applications.
LY10 DIN-rail data signal surge protector
It is intended for RS485, telemetry, PLC communication, remote control and related industrial data lines. [4]
Confirm the voltage version, conductor assignment, data rate and grounding method before ordering.
A 24V line, 4–20mA loop and RS485 line need different checks
Voltage is only the first parameter. The SPD must also allow the normal signal to pass without causing an error.
| Signal | Uso típico | Confirm first | Principal risco | Next action |
|---|---|---|---|---|
| 24V DC sensor power | Power supply for proximity sensors, transmitters or remote instruments | Uc / MCOV Atual Polarity | The SPD may create too much voltage drop or may not carry the required current. | Confirm whether the cable carries power only or combines power and signal conductors. [1][5] |
| 4–20mA or HART | Pressure, flow, level and process transmitters | Loop voltage Resistance HART | Extra resistance can use part of the voltage needed by the transmitter. | Send the loop supply, transmitter datasheet and analog-input data. [5][6] |
| 0–10V AI or AO | Analog sensors, actuators and PLC analog I/O | Leakage Capacitance Referência | Leakage or electrical loading can shift the measured value. | Provide the signal range, source impedance and acceptable measurement error. [5][6] |
| RS485 or Modbus | PLC networks, BMS, telemetry and remote I/O | Baud rate Capacitance Wire count | Too much capacitance can distort the data signal and cause communication errors. | Use the RS485 guide for detailed A/B wiring, shield and termination checks. [1][4][6] |
| DI or DO | Proximity switches, dry contacts, alarms and transistor outputs | PNP / NPN Load current Common wire | The wrong circuit may connect shared references or overload the protector. | Confirm the input/output type, voltage, current and shared common conductor. [5] |
Install the SPD where the exposed cable enters the protected zone
Protect the cabinet end first. Add field-side protection when the remote device or cable route is also exposed. [2][3][7]
Cabinet-entry protection
Install the SPD near the cable-entry or marshalling area. Do not carry a long unprotected field cable beside the PLC. [2][7]
Field-side protection
Add protection near an outdoor transmitter, mast, tank, pump or remote junction box when the field device is exposed. [2][3]
Protection at both ends
Evaluate both ends when the cable crosses buildings, outdoor areas, lightning protection zones or separate bonding zones. [2][3][7]
Keep the SPD bonding connection short. A long conductor adds inductive voltage during a surge. This can increase the voltage seen by the protected equipment. [6][7]
Four SPD parameters that can affect normal operation
These parameters explain why a protector cannot be selected by voltage alone.
1. Series resistance
This is the extra resistance added by the SPD to the circuit.
2. Leakage current
This is a small current that may flow through the SPD during normal operation.
3. Capacitance and bandwidth
These parameters show how easily a changing data signal can pass through the protector.
4. Grounding and shield arrangement
The SPD needs a short discharge path to the local equipotential system.
Information required before model, sample or quotation confirmation
A request that says only “24V signal SPD” is not enough for reliable selection.
24V, 4–20mA, HART, 0–10V, RS485, DI, DO or another signal.
Nominal voltage and the highest continuous voltage.
Two-, three- or four-wire circuit and conductor assignment.
Loop, sensor-supply or digital-output load current.
Baud rate, HART, resistance, leakage or capacitance limits.
Length, route, outdoor exposure and inter-building sections.
Cabinet entry, field device, junction box or both ends.
Local bonding point, shield termination and reference method.
Temperature, IP rating, outdoor and hazardous-area needs.
Logo, label, terminal marks, quantity, packaging and documents.
Who normally specifies or purchases sensor-line SPDs?
Control-cabinet manufacturers
For PLC, RTU, analog I/O, remote I/O and field-cable entry protection.
Industrial system integrators
For water treatment, factory automation, BMS, telemetry and process-control projects.
OEM and private-label buyers
For model matching, terminal marking, branded labels, packaging and bulk supply.
Water and pump projects
For outdoor level, pressure, flow, float-switch and remote-station signals.
Factory maintenance teams
For repeated sensor failures, unstable PLC channels and exposed instrument lines.
Industrial distributors
For stocked signal-SPD ranges that must cover clearly defined voltages and signal types.
Send the loop diagram—not only “24V signal SPD”
LEEYEE can review the signal type, voltage, wire count, current, cable route, mounting method and OEM requirements before model confirmation.
Sensor line surge protection questions
Does every outdoor sensor need a surge protector?
Not automatically. Check the cable length, outdoor exposure, lightning protection zones, equipment value and existing protection. Outdoor exposure is a strong reason to perform a surge-risk assessment. [2][3]
Should sensor-line SPDs be installed at both ends?
Evaluate both ends when the cable crosses buildings, outdoor areas or separate local bonding zones. A short internal cable inside one well-bonded structure may not need the same arrangement. [2][3][7]
Can one SPD protect both 24V power and a 4–20mA signal?
Only when it is designed for that exact combined circuit. A power pair and an analog signal pair may have different current, resistance, leakage and protection-mode requirements. [5][6]
Can a signal SPD affect measurement or communication?
Yes, if it is selected incorrectly. Series resistance can affect a current loop. Leakage can affect an analog voltage. Excessive capacitance can affect a data signal. [5][6]
What information is required for model confirmation?
Provide the signal type, voltage, wire count, current, data rate or HART requirement, cable route, installation position, grounding arrangement and environment. [1][2]
Authoritative sources used in this guide
- [1] IEC 61643-21:2025 — Low-voltage surge protective devices connected to telecommunications and signalling networks: performance requirements and testing methods.
- [2] IEC 61643-22:2015 — Selection, operation, location and coordination principles for telecommunications and signalling network SPDs.
- [3] IEC 62305-4:2024 — Protection of electrical and electronic systems within structures against lightning electromagnetic effects.
- [4] LEEYEE LY10 Data Signal Surge Protective Device — Published voltage, current, transmission-rate, insertion-loss and DIN-rail installation data.
- [5] Phoenix Contact — Fundamentals for Surge Protection — Instrumentation and control circuits, floating 4–20mA loops, binary signals and resistance measurements.
- [6] Eaton MTL — Lightning and Surge Protection: Basic Principles — Signal-SPD operation, series impedance, leakage, capacitance and effects on normal signal circuits.
- [7] Eaton MTL — Earthing Guide for Surge Protection — Equipotential bonding, cable screens, local earth connections and field-to-control-room installations.
Final selection must be checked against the sensor, transmitter, PLC or controller datasheet, the project lightning-risk assessment and the selected SPD technical data.
