220-Volt Appliances

• Dryers are examples of appliances that run on 220-volt power, as opposed to smaller ones, like a television or blender, that require only 110 volts. Electricity comes into the electric panel in the form of 2 hot wires at a voltage of 110 volts and a neutral one. Most of the outlets in a typical house supply 110-volt power and use only one of these hot wires, but outlets that supply 220-volt power, such as those for dryers, use both of them. 220-volt plugs and outlets thus have two prongs that connect to hot terminals and one that connects to neutral.
  
  

Grounding Requirements

• The National Electric Code has required 110-volt circuits to have a separate wire for grounding since the 1960s, but did not extend this requirement to 220-volt circuits until the 1990s. Prior to the change, grounding in 220-volt circuits was accomplished by the neutral wire, which is connected to ground at the electric panel. Article 250.140 of the 2005 Code permits the owner of a new dryer with a 4-prong plug to retrofit it with a 3-prong plug, or pigtail, to connect it to a 3-wire circuit. It is also permissible to connect a 3-prong dryer to a 4-wire circuit.
  
  

The Importance of Grounding

• When everything is working as it should, the hot wires supply electrical energy and the neutral wire returns it back to the source in an unbroken loop. In the event of a loose connection or insulation failure, however, any metal part of an appliance or plug in contact with an energized wire itself becomes energized, and anyone touching it gives the electricity a path to earth and gets a shock. A ground wire provides an alternate path to earth so that when an accidental break occurs, the surge trips the breaker and shuts off the power.
  
  

Retrofitting Dryer Plugs

• If your dryer has a 3-prong plug and your house has 4-wire circuitry, or vice-versa, you can retrofit the plug with a replacement, called a pigtail. To replace a 3-prong plug with one that has 4 prongs, connect the extra wire in the 4-prong pigtail, which is usually green, to the metal casing of the dryer by means of a grounding screw. The dryer may already have one or you can install it yourself. To replace a 4-prong plug with a 3-prong pigtail, connect the ground terminal inside the dryer to the neutral terminal with a piece of copper metal or wire.