A device which looks like a switch and is usually located inside the electrical breaker panel or circuit breaker box. It is designed to (1) shut of the power to portions or all of the house and (2) to limit the amount of power flowing through a circuit (measured in amperes). 110 volt household circuits require a fuse or circuit breaker with a rating of 15 or a maximum of 20 amps. 220 volt circuits may be designed for higher amperage loads e.g. a hot water heater may be designed for a 30 amp load and would therefore need a 30 amp fuse or breaker.