An AC power plug is a portable electrical connector which consists at the minimum of two metal contact prongs designed to make contact with matching points connected to a power supply, usually contained in a protected electrical outlet. Except for the actual metal contacts, an AC power plug is protected by an insulated grip that’s designed for ease of insertion into, or extraction from, a power outlet. Power is transmitted from the plug to the device by means of an insulated cable.
AC power plugs, and the outlets they plug into, conform to the electrical codes of the nation they’re located in, which vary greatly from one nation to another, and considerable debate exists as to the efficacy of each. They all have at least two prongs — one, called “live” or “hot,” and a second prong, usually called “neutral” or “cold.” Many have a third prong, which conducts current only in the case of insulation failure in the device. These prongs fit into the slots on the electrical outlet and make contact with metal elements inside the outlet that are wired into corresponding components of the electrical system.
Even within a country, AC electrical plugs differ based on the size of the load they’re designed to transmit. The “standard” AC power plug in the United States is designed for household current, which is up to 15 amps at 125 volts. It consists of two parallel metal blades, each 0.625 inches (1.6 cm) long and 0.25 inches (6.35 mm) wide, and may include a third prong: a rigid cylindrical metal pin the same length as the blades, which fits into a matching hole in the electrical outlet. Since the 1950s, many AC power outlets have been manufactured with polarized slots, with the neutral slot being wider than the hot slot. This configuration ensures that a polarized AC power plug, with a wider neutral blade, can only be inserted in the outlet the proper way, ensuring the proper flow of electricity inside the device.