ABB STOTZ selective main circuit breakers operate voltage-independent

Function

STOTZ selective main circuit breakers operate voltage-independent. They do not require

auxiliary energy for switching the device on or off or for their protection functionality.

A straight forward design ensures the reliable protection function. The functional elements

consist of proven electromechanical components specifically designed for these requirements.

For overload tripping, a thermostatic bimetal is used, as in the case of a standard circuit

breaker. And also as for circuit-breakers, it is necessary to separate main contacts quickly

by using a short-circuit “hammer trip” solenoid to ensure effective short-circuit limitation.

When the downstream protective device has tripped because of a short circuit, the contact

tips reclose again. This occurs without auxiliary voltage through a simple spring-type system.

If a short circuit occurs between the S 750 and the downstream mcb, another bimetal release

enables the short-time delay tripping. Both the selective release and the overload release

trip the mechanism and ensure that contact tips remain in the open position to comply with

isolation requirements.

The current is limited and the arc is quenched as in the case of circuit-breakers.

The underlying switching principle makes a special selectivity behaviour possible: current

limiting selectivity. When a short circuit occurs, the S 750 supports the downstream mcb

and also limits the energy that has an impact on the installation and – subsequently – on the

network of the supplier. The selectivity behaviour of the S 750 offers major advantages over

fuse-based technologies.