QO Circuit Breakers provide the high level of protection you expect from Square D. When it comes to electrical protection, fast response is critical and QO circuit breakers can trip faster than the blink of an eye. Trip reaction within 1/60th of a second. The exclusive QO Visi-Trip instantly identifies a tripped circuit breaker with a red indicator window. The Visi-Trip reduces the number of call backs, as well as the chance that other circuits will be turned off accidentally. This breaker will work only in Square D branded residential panels. Typical application for a double pole 40 Amp breaker include overload and short circuit protection for electric ranges.