How to Identify All the Sockets in My Wall

Measure the width of the outlet. Generally, the width of standard 15-amp, 125-volt outlets' faces are 1 1/4 inches wide while 30- and 50-amp, 250-volt outlets for large appliances are 2 1/8 inches wide.

Determine the size and pattern of the holes in the receptacle. For example, note if the slots for the plug are two equally sized, parallel, vertical slots or if one slot is longer than the other. In both cases, the outlet is an ungrounded, 125-volt outlet. However, modern appliances such as lamps, coffee pots, crockpots and TV plugs have one larger prong and will not fit into the old-style, single-size slots.

Look for a third hole in the outlet, with a rounded end that is centered on the parallel slots. The third hole is for the grounding prong. Washers, refrigerators, gas dryers and stoves, electric drills and computers all use 15-amp, 125-volt, three-prong grounded plugs.

Check for small buttons labeled "Test" and "Reset" between the two receptacles. These are ground-fault circuit interrupter-protected 15-amp, 125-volt outlets. They are used in bathrooms, kitchens, laundry rooms and other areas of the home where you are exposed to water. If you drop a hair dryer into a wet sink, the GFCI outlet automatically cuts the power to the outlet, preventing electrocution.

Look for unusual configurations of slots. For example, the two slots might be horizontal rather than vertical and centered on the ground. This is a 15-amp, 250-volt, three-prong grounded outlet used for some window air conditioners or in offices for copiers and other electronic devices.

Compare the angle and location of the slots on other unusually configured outlets. The outlet might have two vertical slots, with one shaped like a sideways T. It is a 20-amp, 125-volt outlet used for older model air conditioners, large electric heaters and in commercial offices. On the other hand, if the outlet has one horizontal and one vertical slot that looks like a sideways T, centered on a ground, it is a 20-amp, 250-volt outlet used for large air conditioners, shop equipment such as air compressors and in commercial offices.

Note the receptacle pattern on 2 1/8 inch outlets. The larger outlets are either 30- or 50-amp, 250-volt outlets. Generally, only two such outlets are in a home: one behind an electric stove and the other behind the clothes dryer. Other specialized 250-volt outlets for kilns, electric welders or recreational vehicle hook-ups are sometimes found in the garage.