A fault behind a CB (downstream) is a fault that may occur between a circuit breaker already open and a CT, which is fed from the remote end.

Fault behind CB protection recognizes such faults through the current criterion, if the circuit breaker does not provide a signal from its auxiliary contacts that it is closed after the time delay set at CBF_1: Delay/fault beh. CB has elapsed.

When such a fault behind CB is recognized the signal CBF_1: Fault behind CB is issued. In such a case the far end circuit breaker may be triggered by an InterMiCOM teleprotection interface. This may also prevent an unwanted triggering of the circuit breaker failure function.