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Ungrounded (left) and grounded (right) power plugs Common North American 125-volt receptacles. All accept a 1-15P plug; the two on the left also accept grounded 5-15P plugs; the second from the left also accepts 5-20P plugs. The NEMA 5-15R device on the far left is most common; the two rightmost designs are typically seen in older buildings.
English: A selection of NEMA receptacles, showing ground, neutral, and hot/line pins. Earth/ground is dark green, neutral is white, and hot/line is black. Typical modern North American uses for common receptacles are shown in purple. Sadly, this is not an exhaustive list.
Terminals for the neutral (grounded) conductor in general, and for receptacles, plugs, and connectors specifically, are required to be substantially white in color [NEC 200.9, NEC 200.10 (B)], and if the terminal itself is not visible, the hole leading to it must be marked with the word "white" or the letter "W".
The National Electrical Manufacturers Association (NEMA) [5] is the largest trade association of electrical equipment manufacturers in the United States. [6] Founded in 1926, it advocates for the industry and publishes standards for electrical products. Notably, the form of US household electrical outlets and plugs is specified by NEMA.
Grounded vs ungrounded NEMA plugs. The NEMA 5-15 plug has two flat parallel blades like NEMA 1-15, and a ground (earth) pin. [49] It is rated 15 A at 125 volts. The ground pin is longer than the line and neutral blades, such that an inserted plug connects to ground before power.
Three-prong plugs do not fit into the older, two-prong receptacles. [7] When used as intended, the ground pin of the 3-wire receptacle is to be connected to a grounded cover screw, or to an external ground. In 1969, Underwriters Laboratories mandated three-prong plugs on major appliances for safety. [7]
NEMA connectors implement these requirements. The NEC also permits grounding-type receptacles in non-grounded wiring protected by a GFCI; this only applies when old non-grounded receptacles are replaced with grounded receptacles, and the new receptacles must be marked with 'No equipment ground' and 'GFCI Protected' .
The term plug is in general and technical use in all forms of English, common alternatives being power plug, [1] electric plug, [2] and (in the UK) plug top. [3] The normal technical term (in both British and International English) for an AC power socket is socket-outlet, [4] but in non-technical common use a number of other terms are used.