Overload and maximum interrupting capacities are specified for each series, defined as the maximum current levels that can be switched safely for a minimum of 40 operations, and a minimum of 3 operations respectively. For thermal circuit breakers back-up protection is advised if higher currents are possible. Please contact us for further advice on specific applications.
IEC 60934/EN 60934 defines interrupting capacity as the rated conditional short circuit current performance. According to category PC1, this is the value of rated conditional short circuit current (interrupting capacity) for which the prescribed conditions do not include fitness of the CBE for its further use. PC2 is defined as the value of rated conditional short circuit current for which the prescribed conditions do include fitness of the CBE for its further use.
The switching sequence for short circuit tests is normally abbreviated as follows, according to relevant international CBE standards.
O Break operation (open)
The circuit breaker in the closed position is caused to open through a short circuit current applied by means of a separate switch. Referenced as co (closed open) in earlier specifications.
CO Make operation with subsequent break operation (close open)
The circuit breaker in the open condition is closed onto a sustained short circuit and must immediately re-open. This operating mode requires the circuit breaker to be fail-safe as the actuator cannot be released as quickly as the circuit breaker mechanism will open. Referenced as oco (open close open) in earlier specifications.
t Time period between switching operations
Normally 3 minutes, or the period required before the circuit breaker can be re-set.
Common switching sequences are: O-t-CO or O-t-CO-t-CO.