A plug is an object located on one end of a power cord that connects an electrical device to a receptacle. Most household electrical receptacles have a 15-amp rating, but they connect to a 20-amp circuit. You can use a device that has a 15-amp plug with either a 15- or 20-amp receptacle. Standard 15-amp receptacles are suitable for typical household appliances, lamps and other accessories. A 20-amp receptacle is for heavy-duty appliances and power tools, such as air compressors. Residential garages occasionally have 20-amp receptacles to accommodate larger power tools. The term "amp" is short for "ampere."
15 Amp Circuits
Household receptacles are connected using 12-gauge wire. The wire has a rating that allows it to carry up to 20 amps. In most home installations, several 15-amp receptacles connect to a 20-amp circuit breaker. This allows multiple devices to connect to a single 20-amp circuit as long as the total circuit load does not exceed 20 amps. If the load exceeds 20 amps for a long duration, the circuit breaker will open the circuit. If that occurs, you should remove one of the devices and reset the circuit breaker.
20 Amp Receptacles
Receptacles with a 20-amp rating look like 15-amp receptacles except they have an additional slot that allows you to insert a 20-amp plug into the receptacle. Table saws and other large equipment often require a dedicated 20-amp circuit. A dedicated 20-amp circuit means that wires run from the circuit breaker directly to a 20-amp outlet.
Most 20-amp receptacles are duplex receptacles. You can use the receptacle with two 15-amp devices, two 20-amp devices or one 15-amp and one 20-amp device. If the 20-amp device requires 20 amps to operate, it would not be advisable to connect another device to the receptacle. In fact, it would be advisable to install a single 20-amp receptacle instead of the duplex receptacle.
Almost all household appliances, lamps and power tools have 15-amp plugs, and almost all household receptacles have a 15-amp rating. If you need to change a receptacle from one rated at 15 amps to 20 amps and you are not comfortable working with electricity, you should hire a licensed electrician. Electricity can be extremely dangerous. Do not take chances with your life.