How to Identify Electrical Outlets

Before you start any home project that involves working with American electrical outlets, having the skill to identify exactly what it is you will be working with is important.

How to Identify Electrical Outlets

Usually it isn't necessary to open the outlet itself for identification, much less to ascertain the grounding, voltage and amperage either, typically you can just observe the number of and direction of the slots, as well as any additional holes or buttons, and refer to that to identify the outlet.

Look at the outlet. Use a flashlight to illuminate dark outlets. Count how many slots and holes it has available for a plug. Determine whether these slots are vertical, horizontal, or both.

Note whether there are any holes beneath or beside the slots. Traditionally, these "holes" will appear to be half-rounded with a flat bottom. These "half-round" holes are used for the third or ground wire on appliance plugs.

Determine whether the outlet is a grounded or ungrounded. Common in older homes, an ungrounded outlet usually has only two vertical slots of the same size. A grounded outlet will have two vertical slots and a half-rounded hole. The two slots may be the same size or of varying lengths. If they are of varying lengths, it indicates that it is what is called a "polarized" outlet.

Determine if the outlet is a ground-fault circuit interruption (GFCI) outlet. Usually found in kitchens and bathrooms (or other moist locations), a GFCI outlet will usually have two slots and a half hole in addition to a reset and/or test button. A GFCI outlet is designed to automatically cut off the power in case of an electrical short.

Ascertain the voltage for the outlet. Most common 110 volt household outlets (whether ungrounded, grounded, or GFCI) are either white, beige, or cream in color and have two to three holes that are used by the plug. Most 220 volt outlets have a combination of three to four slots and/or holes and may, on occasion, be black in color.

Determine the amperage of the outlet. Most grounded household outlets are 15 amp however if there is a sideways "T-shaped" slot, this usually indicates a 20 amp circuit. For older homes, the cover plate may need to be removed using a screwdriver in order to verify amperage on the label or imprinted coding. For larger outlets, a 20-amp 220 volt receptacles usually has one straight slot, a "T-shaped" slot, and a half-rounded hole. Whereas a 30 amp 220 volt receptacle has a four-pronged outlet with two slots, an "L-shaped" slot, and a half-rounded hole.

Determine if the outlet is "tamper-resistant" or not. Tamper resistant outlets have small springs that close off the slots of an outlet with "shutters" to prevent children from being injured by playing with them. These types of receptacles have only been recently added to the requirements for the National Electrical Code (NEC) for use in new and updated homes.

Things You Will Need

  • Flashlight
  • Screwdriver


  • Always confirm amperage and voltage with a tester.
  • Always replace an outlet with one appropriate for the circuit and wiring.


  • Always make sure the power is off when working with outlets.
  • Never wire a three prong outlet to a two-wire circuit.
  • Consult a licensed electrician if you have any further concerns.

About the Author

Mychal Deehn is a freelance writer based in the Carolinas. Her background includes experience in the areas of web and graphic design, residential construction, home maintenance and improvement, animal care and training, general accounting, art, and homeschooling.