AC power cords are distinguished by plug type.
AC power cords use alternating electric current that periodically experiences reversal of direction. AC cords follow strict specifications in manufacturing, regulating wire size and shape and ensuring current and voltage ratings are balanced. Cords have both male and female ends; the female attaches directly to electrical appliances and the male connects to an electrical power socket. Cords themselves are designed similarly to all others, with the plug end indicating the different type and safety features incorporated.
Polarized
Polarized electrical cords are designed to include a special plug shape that ensures the electricity flows along the proper wires for safety. The plug end is designed to only enter a socket one way to guarantee the electrical poles are oriented correctly. One plug prong is slightly larger than the other to facilitate this. Certain appliances like toasters and blenders don't have internal safety switches, so the polarized cords are important in their use.
Non-Polarized
Non-polarized cords don't have different-sized prongs to their plug ends and are designed to plug into sockets either way. This makes it so that the neutral and live wires are connected randomly. These cords, without pre-designed safety requirements, rely on the device to which the cord is attached to have shutoff and polarity shifting features. These cords often have heavier insulation around the wires than polarized cords.
Grounded
Grounded cords may have plug ends of polarized or non-polarized varieties. These include a third prong or grounding rod to divert any stray voltage into the ground and away from users and the connected equipment. These cords are the highest-rated for safety and are seen on all equipment that draws large amounts of electricity to operate or has sensitive electronic circuitry requiring greater safety.
History
The first power cords were hardwired directly to Edison lamp holders and used for both lighting and household or industrial equipment. The common two-prong electrical cord and plug was invented by Harvey Hubbell in 1904. His design was quickly adopted into widespread use. Three-prong grounded cords and polarized cords were developed to incorporate greater safety into electric devices.
Composition and Uses
AC cords are primarily made of thin copper wire surrounded by insulating plastic and rubber, with the prong contacts made of either steel or brass and plated with zinc, nickel or tin. Cords are used for commercial, retail, electronic, residential and industrial applications. They are commonly attached to computers, lighting, household appliances and power tools.
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