The electric circuits in a standard house electrical wiring system in the United States is generally comprised of 120-volts or 240-volts. It is governed by the National Electrical Code (NEC), which is published by the National Fire Protection Association (NFPA 70). As an example, the current code dictates that three-pronged, polarized receptacles are to be used in all new home construction, in addition to, outlining the use of ground fault interrupters (GFI) in locations where an electrical appliance may be subjected to moisture, you mostly recognize these in kitchens and bathrooms.
The standard household electrical outlet consists of two three-pronged, polarized receptacles. Each receptacle has a 120-volt ‘hot’ wire, a neutral wire and a grounding wire. For higher power applications like clothes dryers, electric ranges and air conditioners, a single receptacle is used where two of the prongs are a hot wire and the third a neutral, which can be used to produce a 240-volt circuit.