What is an AC Power Plug?

Dale Marshall

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.

A socket that can accept an AC power plug.
A socket that can accept an AC power plug.

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.

A 220 volt AC power plug.
A 220 volt AC power plug.

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.

230 volt grounded British plug.
230 volt grounded British plug.

Electrical outlets for larger loads, typically 220 – 240 volts, have a different number and alignment of slots, and the AC power plugs for those devices, such as electric dryers and stoves, have larger and heavier prongs shaped and oriented to fit the outlets. Overall in the United States, there are eight different types of AC power plugs

One of the main drawbacks of the American plug-and-outlet system is that the design makes it possible for the prongs to become energized — carry current — before the plug is completely inserted into the outlet and the face of the grip comes in contact with the outlet's faceplate. It's possible, then, for a person to touch the metal prongs of a plug while they're conducting electricity, and getting a shock in the process. It's also possible for a partially-inserted plug to be energized, with the exposed prongs carrying current, posing a significant fire hazard.

Electrical outlets in North America and some parts of South America will accommodate the standard US AC power plugs, called the Type A and Type B plugs. Type A is a two-blade plug, polarized or unpolarized, and type B is a three-prong plug. Some Type B plugs are made for a 20-amp circuit, and have an angled neutral blade.

Worldwide, a dozen different types of plugs are used with corresponding electrical outlets. In each of them, the AC power plug contains the male components of the electrical connection, which are inserted into the female components of the electrical outlet. In many cases, safety elements are incorporated into the design; for example, many outlets are recessed so that the the grip of the plug fits into the recess before the prongs make contact with the power source and are energized, eliminating any possibility of coming in contact with any part of the plug's prongs while they're conducting current.

Due to the multiplicity of AC power plug designs worldwide, and the fact that an AC power plug will fit only those outlets specifically designed for it, travelers must always find out about the outlets wherever they're traveling to and acquire adapters for those devices, such as computers and shavers, they'll be bringing with them.

An grounded American AC power plug.
An grounded American AC power plug.

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Discussion Comments


I'm glad this article mentioned shock and fire hazards associated with American AC power plugs. I have always dreaded the idea of plugging up an unfamiliar appliance into a standard electrical outlet. I got badly shocked when I was a child, and I've been afraid of electricity ever since. I wish there was a way I could turn off the power to the outlet first, and then plug the appliance fully into the socket before restoring it. I'm always concerned about sparks triggering a fire.


When we moved into our first rental home, I discovered that all of the electrical outlets weren't designed for polarized or grounded power plugs. My landlord said he didn't have the money to hire an electrician, so he gave me a dozen or so AC power plug adapters with non-polarized prongs instead. I had to put them on every electrical device we had, until I decided it was better to get some grounded power strips and plug just about everything in them.

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