Voltage Requirements

• The utility company serves most homes with single-phase electric current at about 110 to 125 volts. Utilities supply this voltage on each of two hot wires that enter your home along with a third wire, termed "neutral." Most outlets in the home are served by one or the other of the hot wires, because most power uses require only 110 volts. For appliances and some shop tools that require 220 volts, outlets are connected to both hot wires.
  
  

110-volt Wiring

• The house's main service panel accepts the two incoming hot wires and routes their power via two copper bus bars -- one for each hot wire -- to branch circuits throughout the house. Circuit breakers for 110-volt branch circuits connect to the copper bus bars. Each 110-volt branch circuit has a hot wire and a grounded conductor, informally but incorrectly called a "neutral" wire. Grounded conductors on two-wire systems normally carry current. Current is carried to the fixture or receptacle by the hot wire, back to the service panel by the grounded conductor, and to earth by the earth ground. The grounded conductor is different from a ground wire, which is used to connect an electrical device directly to a grounding electrode. A ground wire carries no current under normal circumstances.
  
  

110/220-Volt Appliances

• Appliances such as electric ranges and clothes dryers contain components that use both 220 volts and 110 volts. The heating elements require 220 volts. The electronics and timers and the dryer's drum require 110 volts. Only one hot wire serves the 110-volt portion of the appliance, and the neutral carries any imbalance back to the service panel.
  
  

Earth Ground

• The National Electrical Code has stringent requirements for a home's grounding system. Without a ground, a person could receive a dangerous shock if the hot wire were to contact the metal cover of the appliance. The properly installed earth ground instead carries the stray current to ground. Earth ground connects to copper water pipes where they enter the home or to two copper ground rods driven into the earth outside the home.