Number of short-circuit tripping operations by circuit breakers according to IEC and UL
How often is a circuit breaker required to be able to trip in accordance with IEC or UL 489 in the event of a short circuit? Is the continued use of a circuit breaker permitted following a short circuit tripping operation?
Statements regarding the continued use of circuit breakers following short circuit tripping operations in the IEC and UL markets can be found below
The following applies for the IEC market:
The corresponding circuit breaker standard, IEC 60947-2, states the following in Sections 8.3.4 and 8.3.5:
The testing sequence for the rated service short-circuit breaking capacity Icu is O – t - CO, i.e. the circuit breaker must interrupt a short circuit, remain disconnected for an interval of 3 minutes before being switched back to the short circuit to interrupt it again. Permanent changes to the overload characteristic are permitted and the circuit breaker must no longer posses the full current carrying capacity.
The rated service short-circuit breaking capacity Ics has the following testing sequence: O - t CO - t - CO, i.e. short-circuit tripping operation, interval of 3 minutes, switching back to the existing short circuit and tripping it again, another interval of 3 minutes, switching back to the short circuit a further time and tripping it again. The circuit breaker must be able to carry the full current at all times and the overload characteristic may not permanently change.
The following applies for the UL market:
Similar to the P1 (Icu) testing sequence given in IEC 60947-2, according to UL489, a circuit breaker must be able to interrupt a short circuit twice (O - t - CO).
This is described in UL489 section "7.1.11 High Available Fault Current Test Sequence".
Replacement of the affected circuit breaker is at the discretion of the user (depending on the state of the breaker) or depends on the short-circuit breaking capacity value (Icu, Ics) that was used to select the circuit breaker.