Electrical Supply

• Electric utilities provide single-phase 240-volt electric current to most homes over three wires. Two "hot" wires each carry 120 volts and the third wire is a neutral wire. The voltage between either "hot" wire and the neutral is 120 volts and between both "hot" wires is 240 volts.
  
  

Distribution

• Distribution of the electrical supply takes place at the main service panel, sometimes called a breaker box or fuse box. The supply lines connect directly to the main circuit breaker which supplies power to two separate panel bus bars, one for each "hot" supply line. Each bus provides 120 volts to branch circuit breakers. Double breakers control 240 volts, while single breakers control 120 volts.
  
  

Circuit Breakers

• Circuit breakers prevent wires from carrying too much current. A wire carrying too much current will overheat and could possibly cause a fire. Circuit breaker size is based on the current-carrying capacity of the wires that connect to it.
  
  

Wiring

• The house wiring connects circuit breakers, ground and neutral bus bars in the service panel to outlets, switches and appliances. Outlets may be either light fixtures or receptacles and may be controlled by switches. Some appliances connect directly to the wiring, others connect to a receptacle using a plug on a cord.