A circuit breaker is an overload switch that prevents the current in a particular electric circuit from exceeding the capacity of a line. Fuses perform the same function in older systems. If too many appliances are plugged into a circuit, calling for more power than the capacity of the circuit, the breaker reacts by switching off (tripping) the circuit. This prevents damage to the wiring, fires, or in the case of a defective appliance, further damage to the appliance.
The maximum current of each breaker or fuse is rated in amperes. Typically a kitchen range requires a breaker of 40 to 50 amperes; a water heater, one of 30 to 40 amperes. These circuits are 240-volt lines controlled by double breakers. The remaining breakers on the power distribution panel are for 15 or 20 amperes, controlling 120-volt general-purpose circuits for lights and small appliances. The large breaker marked Main turns off all power in the house.
Most modern breakers have three positions: On, when power is flowing in the circuit; Off, to shut off power from the line; and tripped, a midway position showing that the circuit has been overloaded and is off. A few breakers have only on and off positions. Sometimes a red flag shows in a tripped breaker.
To restore power to a tripped circuit, remove the overload by unplugging or switching off extra appliances, then move the breaker handle to Off and then firmly to On.
If a major appliance trips the line repeatedly and you sure the circuit is not overloaded, call a service person.