NEMA connectors are power plugs and sockets used for AC mains electricity in North America, Central America, Japan, Taiwan and other countries that use the standards set by the US National Electrical Manufacturers Association. They are defined by the IEC as the Type A and Type B plugs. NEMA wiring devices are made in current ratings from 15 to 60 amperes (A), with voltage ratings from 125 to 600 volts (V). Different combinations of contact blade widths, shapes, orientations, and dimensions create non-interchangeable connectors that are unique for each combination of voltage, electric current carrying capacity, and grounding system. NEMA 1-15P (two-pole, no ground) and NEMA 5-15P (two-pole with ground pin) plugs are used on common domestic electrical equipment, and NEMA 5-15R is the standard 15-ampere electric receptacle (outlet) found in the United States, and under relevant national standards, in Canada (CSA C22.2 No. 42), Mexico (NMX-J-163-ANCE), Japan (JIS C 8303), and Taiwan. The dimensional standard for electrical connectors is ANSI/NEMA WD-6 and is available from the NEMA website. Other plug and receptacle types are for special purposes or for heavy-duty applications.
Nomenclature
NEMA connectors are named following an alphanumeric code consisting of: (optional L for locking) numerals – numerals (suffix R for receptacle or P for plug).There are two basic classifications of NEMA connectors: straight-blade and locking. The metal conductive blades are often informally called prongs (as in 3-prong plug). Numbers prefixed by 'L' are curved-blade, twist-locking connectors. Twist-locking types are used for heavy industrial and commercial equipment, where increased protection against accidental disconnection is required. The numerals preceding the hyphen encode the number of poles (current-carrying terminals) and wires connected to it, the voltage, and single- or three-phase power. A connector with ground terminal has more wires than poles: two-pole, three-wire; or four-pole, five-wire; etc. A non-grounded device may be two-pole, two-wire; three-pole, three-wire; etc. The numerals following the hyphen is the current rating of the device in amperes. This number is followed by the letter 'R' to indicate a receptacle (socket) or 'P' to indicate a plug (prongs). As an example, the 5-15R is the common 125 V two-pole, three-wire receptacle rated for 15 A. The L5-15R, while sharing the same electrical rating, is a locking design that is not physically compatible with the straight-blade 5-15 design. The 5-30R has the same two-pole, three-wire configuration and 125 V rating, but is rated for 30 A. Although there are several non-grounding device types in the NEMA standards, only three of them are in widespread use today. These are the two-pole 1-15, still in use in millions of buildings built before the 1960s, and the three-pole 10-30 and 10-50. Other types of NEMA connectors that do not follow this nomenclature include: the ML series (so-called "Midget Locking" connectors named for their diminutive size), TT (for connecting travel trailers and other recreational vehicles to external power sources), SS series ("ship-to-shore" connectors for connecting boats to shore power) and the FSL series (used in military and aircraft applications). The small hole near the end of the power (non-ground) blades of some NEMA plugs is used for convenience in manufacturing; if present, it must be of specified diameter and position. Small specialized padlocks are available to fit these holes, allowing "lockout" of hazardous equipment, by physically preventing insertion of locked plugs into a power receptacle. Since at least 1949, numerous receptacle devices have also been invented to use these holes to hold the prongs inside the receptacle slots, using a corresponding latch or locking mechanism. The blades of a NEMA connector are identified within the dimensional standard as follows: 'G' identifies the grounding conductor, 'W' identifies the (grounded) neutral conductor, and 'X', 'Y', and 'Z' are the "hot" line conductors. Single-phase connectors have only a single terminal identified as 'X' or two terminals, 'X' and 'Y'. Three-phase connectors will use 'X', 'Y' and 'Z'. Criticism has been aimed at the design leaving a gap with exposed prongs. This safety flaw has been exploited by a January 2020 Internet phenomenon known as the Penny Outlet Challenge, where conductive materials, usually coins or paper clips were dropped into the gap, causing electric sparks, which once led to a building evacuation in Westford Academy.
Non-locking connectors NEMA non-locking connectors all use blades of various flat and folded shapes (except for the round pins used on grounding connectors). The plugs can be detached from the receptacles by pulling back on the plug body. These connector families have been designed so that connectors of differing types cannot be accidentally intermated. NEMA wall receptacles can be found installed in any orientation. None of the relevant standards and codes—NEMA, the US National Electrical Code, the Canadian Electrical Code, and the National Electrical Contractors Association's installation standard (NEIS 130-2016)—specifies a preferred orientation. The latter only requires a consistent orientation for sockets installed together or nearby. In practice, most receptacles have their ground blade on the bottom; in this case, the neutral blade is on the upper left and the hot blade is on the upper right. All descriptions below assume this orientation (i.e., clockwise order is ground, neutral, hot for 120 V receptacle versions; and counter-clockwise for plug versions).
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