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Types of 220 Outlets
Most US homes are wired with 110-volt breakers and power outlets (which actually range from 110 to 125 volts), but some larger appliances use higher voltage and may need 220 outlets. There are two main types of 220 outlets, and they require extra precautions and special equipment for wiring. Wiring 220 outlets can be particularly dangerous, so hire a professional, unless you are very experienced with electrical work. If you do it yourself, always turn off power to the circuit before beginning.
Three- and Four-Prong Outlets
Dryers, ranges, refrigerators and other large appliances require 220 outlets. The power requirements are clearly marked on the appliances, which also have one of two unusual types of plug.
The traditional configuration for 220 outlets has three large rectangular holes arranged in a triangular pattern. Two slots are for black and red circuit wires. The third slot is for a neutral wire, which should be connected to a neutral bar in the electric panel.
Most new dryers and other appliances have four-hole plugs, as required by the latest electric codes. In this type of installation, the ground and neutral wires are connected separately, requiring a special type of electric cable. The 220 outlets also must be connected to a special type of double breaker. It can be connected to a pair of 110-volt breakers, but a fault might only trip one breaker if the both breakers are not stuck together.
Designated 220 outlets are necessary for dryers and other large home appliances. However, if you have a foreign computer or other device, you should not rewire your home and add 220 outlets. Instead, use either a basic step-up voltage transformer for small electronics (but not hair dryers), or a heavy-duty transformer for larger loads. They convert 220-volt devices to safely run on 120 voltage, and typically have European- or Asian-style plugs. Do not try to use adapter plugs in 110 outlets to directly plug in devices designed for 220 outlets. You can damage components and create a fire hazard.
To hook up a dryer, fridge, range or other large appliance, you may need to install either three- or four-prong 220 outlets. Both take special equipment and probably some professional help.
Author Steve Graham is an expert on green building who writes for several home improvement publications. He's full of great, practical home improvement answers, and incidentally, he's pretty funny-so send him a message.