As the scope of safety relays in factories becomes more and more extensive, some people still do not know how to connect safety relays correctly and in a standardized manner. This has led to certain economic losses and casualties. For example, a sawing machine in a company alarmed at night, and it was found that the light of the safety relay module was not on. After investigation, it was found that the front fuse was burned. After replacing the fuse, the relay still did not work, and the smell of burnt hair could be smelled. Later, it was found that the wiring of the safety relay was wrong. The INK terminal was not connected to 24V as required. The original relay reset used internal power supply, and the external power supply was not connected after replacement, etc., which caused the relay to be damaged. For this reason, the following safety relay wiring specifications are sorted out
I. Core principles
Independent isolation: The safety circuit (emergency stop/safety door) is completely separated from the non-safety circuit (control/signal), and there is no common line or terminal.
Dual redundancy: The input must have dual contacts and dual wires, and different terminals are connected; the wires are of the same material (copper) and the same cross-section (≥0.5mm²).
II. Input circuit
Use normally closed contacts (normal on, fault off), and disable normally open (anti-adhesion).
Double conductors are routed in separate slots, and the emergency stop button is mechanically forced to disconnect.
Wire gauge: fixed ≥0.5mm², movable ≥0.75mm², insulation ≥500V; stripping 1~2mm, cold pressing terminal.
III. Output circuit
Safety load (contactor/driver) requires dual output contact series control, and 5A fuse in series.
Equipped with normally closed feedback contact connected to special terminal, independent monitoring of load status.
IV. Power supply and grounding
Independent power supply (AC220V/DC24V), not shared with PLC, etc.; 1A fuse/MCB in series at the input end.
PE terminal is connected to safety ground alone, not in series; wire ≥1.5mm², grounding resistance ≤4Ω.
V. Terminals and wiring
Use anti-loosening terminal, M3 torque 0.8~1.2N・m, M4 1.5~2.5N・m.
The wire runs along the groove, with a bend diameter ≥6 times the wire diameter; anti-vibration straps are used at vibration locations, the wire tube has a temperature resistance of ≥80℃, and the safety circuit is recommended to be orange.
VI. Test Verification
Function: Emergency stop is normally on, output is off; single-circuit fault action, dual-circuit fault cannot be reset.
Insulation ≥10MΩ (500V meter), grounding continuity ≤0.1Ω (milliohm meter).
VII. Taboos and Basis
It is forbidden to connect non-safety loads to safety outputs and use non-certified intermediate relays; apply anti-loosening glue to terminals at vibration locations, and add dust covers after wiring.
Basis: EN ISO 13849-1, IEC 61508, GB 50254 and brand manual.
