This circuit breaker was slightly different in size from my circuit breakers in my 53 year old panel. and there, so it's installed using the old switch as a guide. It seems to work. I bought it to add an oscillator input to my panel. A double pole latching switch was required to avoid mains power supply. Works fine with my lock. Since Zinsco has been out of business for many years this was the only alternative to a used jackhammer.