Circuit breakers are the electrical devices that are installed in your service panel that look like toggle switches. They attach to the hot bus bars in the service panel and the hot wires in your branch circuits. They protect branch circuits from overloads when too many electrical devices are drawing too much power and also short circuits. When installing a circuit breaker, make sure you have the right type of breaker that fits in your service panel (or circuit breaker box). Also, make sure you match the right type of Romex wiring with the right circuit breaker. 15 Amp circuit breakers use 14 gauge wires and 20 amp circuit breakers use 12 gauge wires.