Operating characteristics described in our catalog (if there is no "Note" particularly) mean operating time when it starts to carry current from the condition that current does not load to NFB (cooled with room temperature). This is called as Cold start operating characteristic. On the other hand, Hot start operating characteristic is operating time when it starts to carry specified overload current from the condition certain current loads to circuit breaker. The operating time is shorter than that of Cold start. Since overload is generally considered at initial current, considering Cold start characteristic is sufficient. However, in the case of resistance welding machine and intermittent operation, considering Hot start characteristic is needed since overload occurs from the condition that circuit breaker is not enough to be cooled.