The circuit breaker trips.

Si può dire che il breaker è un interruttore, che è pilotato dal "trip unit".

TripUnits.html : For a circuit breaker to be effective, it needs to have some intelligence to enable it to perform automatically or respond to a command. Without this capability, a circuit breaker would just be a fancy switch. A trip unit is the circuit breaker's intelligence.

Oppure...
Thermal trip current breaker

The thermal trip element circuit breaker, like a delay fuse, will protect
a circuit against a small overload that continues for a long time. ( http://www.tpub.com/neets/book3/8j.htm )