If all the breakers in your house added up to 765 amps how big of a generator would you need to buy?

Answer 1

You would size the generator to match the main breaker size rather than on the sum of all the breakers. The main breaker size depends on the specific model of the circuit breaker panel - 100 Amps is typical for a house. The main breaker protects the circuit panel's bus bars from overheating, and the bus bar size is what limits the maximum power through the panel. Power = Volts x Amps, so a 100 Amp panel at 240 Volts could be operated by a 24,000 Watt (24 kW) generator. That's a pretty big generator in household terms, so often only a subset of the circuits would be allocated to the generator. Or, you just be careful not to turn everything on when using the generator. The actual Watts used depends on what's turned on, not the generator size or total capacity of all the circuit breakers. If you turn on too much stuff with an undersized generator, the generator's overload protection will trip and cut it off. Or if you load all the circuit breakers to capacity the main breaker will trip. In addition to these basic considerations there are a considerable amount of electrical codes governing connecting a generator to your house. The major one is to have a switch that prevents connecting your generator to the utility input, which precludes you from inadvertently energizing the utility lines.