ABB SMCB operate according to a voltage-independent principle

Purpose

– Ensure power supply capability over a large temperature range

– Protect wires and cables in case of operational overload or short-circuit

– Additional limitation of let-through current and let-through

energy in case of short-circuit tripping in final circuit

– Disconnection and isolation of the system, also by ordinary people

– Special selectivity with respect to downstream circuit

breakers and upstream fuses

– Ensure a high availability of the electrical power supply

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.

This operating principle achieves a particularly high selective behaviour

– the current-limiting selectivity.

In case of short-circuit in final circuits, the S 750 (DR) supports the downstream

circuit breaker and limits the energy and thus minimizes the im

pact on the whole installation and the feeding supply network.

This selective behaviour of the S 750 (DR) offers major advanta

ges compared to fuse-based technologies.