120 and 240 Volt Receptacles

Learn about receptacles. Find tips and information on varieties of receptacles such as grounded 15-amp, 120 volt, 20-amp, GFCI receptacles, undergrounded receptacles, and more. From DIY Advice.
Understanding Receptacles

The 120-volt duplex receptacle (a receptacle with two outlets) is the workhorse of any residential electrical system. Because household wiring has remained standardized almost from the time it was introduced, you can plug even the oldest tools and appliances into a modern duplex receptacle.

Receptacles are easy to replace, so install new ones if your old receptacles are damaged, paint-encrusted, or simply ugly. However, do not replace an older, ungrounded receptacle with a three-hole receptacle unless you can be sure it is grounded.

If the wires connecting to a receptacle are 12-gauge or thicker and the circuit is protected by a 20-amp breaker or fuse, you can safely install a 20-amp receptacle. Otherwise install a standard 15-amp receptacle. Amp ratings are printed or stamped on the side of the receptacle. Some people prefer to mount the receptacle in the box with the ground hole on top; others prefer it on the bottom. Safety is not affected by the choice. For appearance, be consistent.

Standard receptacles are fine for most purposes. But if a receptacle is to receive a lot of use or is in a high-traffic area -- a busy hallway, for example -- purchase a spec-rated or commercial receptacle, which is stronger.

Grounded 15-Amp, 120-Volt Receptacle

The most common electrical device in your home is probably a grounded 15-amp, 120-volt receptacle. It supplies adequate power for all but the most power-hungry appliances and tools.


A GFCI (ground fault circuit interrupter) receptacle provides extra protection against shocks and is required by code in damp areas.

20-Amp Receptacle

If a receptacle's neutral slot (the longer one) has a horizontal leg, it is rated at 20 amps. Codes often call for 20-amp receptacles in kitchens or workshops, where power use is heavy.

Ungrounded Receptacle

An ungrounded receptacle has two slots and no grounding hole. If one slot is longer than the other, the outlet is polarized.

240-Volt Receptacles

Appliances that use 240 volts are all rated for certain levels of amperage and have plugs configured to fit only one type of receptacle. Here are the common types:

A dryer receptacle supplies the heating element with 240 volts and the timer and buzzer with 120 volts. The receptacle shown requires four wires; older models use only three wires.

An electric range receptacle provides 240 volts for the heating elements and 120 volts for the clock, timer, and light.

This single-outlet air-conditioner receptacle provides 240 volts only. Check your air-conditioner to make sure its amperage and plug configuration match the receptacle.


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