Function

ABB SMCB operate according to a voltage-independent principle.

They do not require an auxiliary source, neither for making /

breaking contact nor for the protective function. For overload

tripping, a thermostatic bimetal is used. As usual for circuit-

breakers, it is necessary to separate the main contacts in a time

less than 1ms by using a short-circuit “hammer trip” solenoid to

ensure effective short-circuit limitation. When the downstream

protection device has tripped because of a short-circuit, the

contact tips reclose automatically through a simple spring-type

system without requiring auxiliary energy.

If a short-circuit occurs between the S 750 (DR) and the

downstream circuit-breaker, another bimetal release enables

short-time delayed tripping. Both the selective release and the

overload release trip the mechanism and ensure that the contact

tips remain in the open position enabling isolating. The current

is limited and the arc is quenched as in the case of standard

circuit-breakers by means of quick contact opening by a “ham

mer trip” solenoid and quick build-up of the arc voltage in the

quenching chamber.