Application issues[ edit ] Designs of plugs and sockets have gradually developed to reduce the risk of electric shock and fire.
This should protect users from electric shock. Sockets may also appear on portable equipment, such as portable generatorextension cords or power stripsbut are still generally the outlet slots of the connection that provides the electricity.
This is commonly called simply earth, or in US English, ground. The appliance need only to be tested to the power inlet. However, CE marking is sometimes fraudulently used on universal sockets.
Clockwise from top left: Also shown right is the rating on the C13 connector at the other end of the 10 A V appliance cord. Polarization[ edit ] Where the building wiring system defines a "neutral" conductor that is close to earth potential, it is an advantage for appliance designers to preserve that distinction. Some plugs have built-in fuses for safety.
To avoid this, users must know the voltage requirements of their appliances, as well as the local voltage of the socket they are using. Wiring systems where both circuit conductors have a significant potential with respect to earth do not benefit from polarized plugs. Lamps with screw bases connect the shell of the lamp socket to the neutral conductor.
A so-called 'universal socket', which meets no standard texas holdem in asia but is intended to accept a outlet slots of different plug types.
Adapters and converters[ edit ] Plugs and sockets are usually designed as a system to meet standards for safety and reliability.
They can allow plugging of V equipment into V mains, potentially resulting in equipment damage. Plugs and power cords have a rated voltage V and rated current A assigned to them by the manufacturer, and these values are required by IEC which might not be legally binding in a given country to be marked on the plug.
Special purpose plugs and sockets[ edit ] Special purpose sockets may be found in residential, industrial, commercial or institutional buildings.
If the failed insulation is of low enough resistance, this will also cause fuses or circuit breakers to open, isolating the faulty appliance from the electric supply. Different types of plug are used for different IEC appliance classes.
Examples of systems using special purpose sockets include: History of AC power plugs and sockets When electricity was first introduced in houses, in the s, it was used primarily for lighting. According to British author John Mellanby,  the first shuttered socket was introduced by British manufacturer Crompton, in Chinese dual socket accepting both unearthed 2-pin upper and earthed 3-pin lower plugs.
One common approach for other appliances such as vacuum cleaners, electric fans, smoothing irons, and curling-tong heaters was to connect them to light-bulb sockets using lampholder plugs.
Class Ifor example, refers to earthed equipment that requires a third contact in the plug and socket, while Class II refers to unearthed equipment protected by double insulation. They are sometimes used in China  and other Asian countries, such as India,  Indonesia,  Japan,  Singapore,  Taiwan,  and the Philippines.
Mains-powered appliances that have exposed conductive parts are required by most regulations and standards to use a three-wire mains cord and plug. A wall socket or outlet also known outlet slots a power point in the UK,  receptacle in the US,  general purpose outlet or GPO in Australia and New Zealand,  and less commonly plug socket  or wall plug  built into the wall of a building, connected to energized electrical wires.
The earth pin in the plug is connected to the appliance chassis.
Because it has holes it is known as a female connector. Similarly, the single-pole switch of the appliance is connected in series with the energized wire. Some types can also include fuses and switches. Voltage rating of plugs and power cords[ edit ] NEMA type B plugs with current and voltage ratings shown left on label 7 A V and centre on engagement face 10 A V.
The earliest standard on a national scale for plug and wall socket forms was set in An earthed Thai socket that appears to comply with figure 4 of TIS Some types of socket have male pins and the matching plugs have female contacts, but for safety reasons these are only used for earthing grounding in US English.
A plug also known as plug top in the UK  generally has matching pins also known blades or prongs in the US, especially if flat so it is known as a male connector, and it is connected by a mains cable power cord or physically built into a piece of electrical equipment that consumes electricity.
In some cases, users are not protected from contact with live electrical leads in exposed sockets or half-inserted plugs. The latter feature prevents foreign objects from contacting live parts of the socket. Electrical insulation of the pin shanks was added to some designs, to reduce live contact exposure when a plug was partly inserted in a socket; Mellanby shows such a plug from British manufacturer Diamond H, dated Earthing grounding [ edit ] A third contact for a connection to earth is intended to protect against insulation failure of the connected device.
The assigned class depends on whether the device is earthed and the degree of insulation it incorporates.
AC power plugs and sockets - Wikipedia