SHORT TIME RATING OF CIRCUIT BREAKER

Circuit breaker is required to perform the following three duties:

1. It must be capable of opening the faulty circuit and breaking the fault current.

2. It must be capable of being closed on to a fault.

3.  Must be capable of carrying fault current for a short time while another breaker is clearing the fault. 

Depending on the above duties circuit breaker has three ratings breaking capacity, making capacity and short time capacity.

SHORT TIME RATING

It is the period for which the circuit breaker is able to carry fault current while remaining closed. The fault on the system of very temporary nature persist for 1 or 2 sec after which the fault will be cleared, so the breaker should not be tripped in such situations. This means the circuit breakers should be able to carry high current safely for some specified period while remaining closed. i.e they should have short time rating. It depends on its ability to withstand electromagnetic force effects and temperature rise.