In most household circuits, 120 volts of electricity flows through the wires. This is enough energy to power most appliances, but large appliances like ovens need more volts to run. For these, homes have circuits capable of conducting 220 or (more commonly) 240 volts.
Volts and Amperes
A volt is the force in an electrical current. The amount of electricity moving through a point in a circuit is the amperage.
The combination of volts and amps determines how powerful a circuit is; i.e., its wattage. Most household circuits can provide up to 1,800 watts before becoming overloaded.
Connecting to the Grid
By the time electricity reaches your home its voltage has been reduced to 120 volts. A pair of 120-volt lines go into your home and attach to the circuit breaker box, providing a total of 240 volts of electricity.
220 vs. 240 volts
Until the 1970s, homes were wired for 220 volts, but contemporary homes are wired for 240 volts. Although the numbers are different, there is no difference in meaning.
A typical home circuit is 120 volts and 15 or 20 amps. Each circuit connects to one of the 120-volt lines in the breaker box.
Large appliances use 240 volts and 30 to 60 amps. A 240-volt circuit connects to both 120-volt lines in the breaker box.