Electricity comes into a house through two legs, each 110 volts. (Together, 220 volts).

There are two types of breakers; a two-pole breaker for 220 volts, and a single pole for 110 volts. On the handle of each breaker is a number that indicates the amperage rating.

Power travels through electrical wires from the panel to the outlet. The standard outlet in most houses is a 20 amp duplex. This kind of outlet would be used for a residential size air compressor. The faceplate of each outlet is particular to the voltage amperage and phasing of the outlet.

The outlet next to the air compressor outlet is a 220 volt, 30 amp outlet (used for clothes dryers and some shop equipment). It has a neutral and ground configuration.

There are also twist-lock outlets and straight blade outlets. With twist lock outlets, turn them after inserting the plug to keep the plug from coming out of the wall. Some outlets may have a red ring around them. That is a three-phase outlet. These are not found in residential homes, but may be found in a shop outside the home.

Each outlet has a National Electrical Manufacturers Association number. The first two digits indicate the type of faceplate; the last two indicate the amperage for which the outlet is rated.