All household circuit breakers are either single-pole or double-pole. Generally speaking, 15-amp and 20-amp breakers are single-pole; 30-amp, 40-amp, 50-amp and higher-amperage breakers are double-pole and typically are twice as wide as single-pole breakers.
"Pole" refers to how the breaker connects to the service panel. In the back of the panel, there are two metal plates, called bus bars. Each bus bar provides 120 volts of electricity. When a single-pole breaker is snapped into the panel, it makes an electrical connection with one of the bus bars to supply 120 volts for its circuit. A double-pole breaker connects to both of the bus bars to supply 240 volts.
Single-pole breakers supply all of the standard circuits in the house, including those for lighting, outlets, ceiling and vent fans, and small appliances. Each double-pole breaker usually supplies power to a single large appliance, such as a clothes dryer, range, air conditioner, or electric hot water heater.
