ECN Forum Forums General Topics of the Trade General Discussion Area Breaker: 250V or 125V?

I purchased a refurbished battery backup that uses 125V/30A single phase power from a L5-30R receptacle. The on-board breaker is replaceable on the rear and is listed at 250V/30A. The reported trip amperage is 37.5A. Will this breaker throw at 4687W (125V) or not until 9375W (250V)?

The breaker doesn't care about the load watts. In its themal mode (overload) it only cares about the watts caused by the current flowing through its thermal element. These watts are based on the impedance of the thermal element and the current (amps).
Don