Although the trip coil of a low voltage circuit breaker does not 'generate' surges itself, if a surge (overvoltage) enters the trip coil, it can cause malfunction (abnormal trip), internal insulation damage, or mechanical failure.

Trip coil and surge effects

If a surge voltage is directly applied to the trip coil, the internal drive elements (such as SCRs) may malfunction, causing the circuit breaker to trip even when a momentary surge, rather than a normal current leak or accident, occurs. This can lead to unnecessary, repeated tripping, even when no actual fault is present. High-energy surges can cause coil insulation breakdown, fire, and shortened lifespan. In other words, the trip coil can be sensitive to surge-induced events.

Actual causes of surge inflow

• Sudden overvoltage and surges caused by external lightning, switching, and turning on/off large loads can be applied to the trip coil through the distribution line.

• MOV (surge protection device) built into circuit breakers also exists to respond to surges, but has limitations.

Prevention and Countermeasures

• By installing surge absorbers such as trip coils, surge protectors (SPDs), and MOVs in parallel at the circuit input terminal, you can block and absorb sudden surge voltages.

• When selecting a protection element, the operating characteristics are carefully adjusted so that they do not affect the normal operation of the trip coil.

• When designing wiring, grounding and protective devices should be added around the circuit breaker and trip coil to minimize the surge path into the internal circuit.

• The trip coil drive circuit and control input require the application of fault detection and malfunction prevention devices such as explosion-proof, insulated, double shielded, and impedance monitoring.

summation

Although the trip coil does not directly generate a surge, unnecessary tripping and damage may occur when a surge is applied to the trip coil, so protective measures such as an SPD (surge protective device) are required.