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 (-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) numeralsnumerals (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.

+ NEMA receptacle chart (non-twist lock) V NEMA 15 A (12) 20 A (16) 30 A (24) [8 AWG] 50 A (40) [8/6 AWG] 60 A (48) [6 AWG] 70 A (56) [6/4 AWG] 90 A (72) [4 AWG] Receptacle Plug Receptacle Plug Receptacle Plug Receptacle Plug Receptacle Plug Receptacle Plug Receptacle Plug 125 V 1 1-15R 1-15P 5-20R 1-20P 5-30R 1-30P - - - - 250 V 2 6-15R 2-15P 2-20R 2-20P 2-30R 2-30P - - - - 150 V 3 144-2-12S 144-2-12P 144-2-16S 144-2-16P - - - - - 125 V 5 5-15R 5-15P 5-20R 5-20P 5-30R 5-30P 5-50R 5-50P - - - 250 V 6 6-15R 6-15P 6-20R 6-20P 6-30R 6-30P 6-50R 6-50P - - - 277 V 7 7-15R 7-15P 7-20R 7-20P 7-30R 7-30P 7-50R 7-50P - - - 150 V 8 - - 144-3-24S 144-3-24P 144-3-40S 144-3-40P - - - 125 / 250 V 10 - 10-20R 10-20P 10-30R 10-30P 10-50R 10-50P - - - 3Φ250 V 11 11-15R 11-15P 11-20R 11-20P 11-30R 11-30P 11-50R 11-50P - - - 150 / 300 V 12 - - - - - 288-4-56S 288-4-56P 288-4-72S 288-4-72P 125 / 250 V 14 14-15R 14-15P 14-20R 14-20P 14-30R 14-30P 14-50R 14-50P 14-60R 14-60P - - 3Φ250 V 15 15-15R 15-15P 15-20R 15-20P 15-30R 15-30P 15-50R 15-50P 15-60R 15-60P - - 3ΦY120 / 208 V 18 18-15R 18-15P 18-20R 18-20P 18-30R 18-30P 18-50R 18-50P 18-60R 18-60P - -

+ NEMA classes Pole configuration 120/208/240 V service 277/480 V service 347/600 V service 240/415 V service Voltage Grounded Voltage Grounded Voltage Grounded Voltage Grounded no yes no yes no yes no yes hot–neutral 120 V 1; ML1 5; TTSS1; ML2 277 V 3 7 347 V - 24 240 V - 25 hot–hot 240 V (split-phase)208 V (wye) 2 6 480 V - 8 600 V 4 9 415 V - - hot–hot–neutral 120/240 V (split-phase)120/208 V (wye) 10; ML3 14; SS2 277/480 V - - 347/600 V - - 240/415 V - - hot–hot–hot 240 V (delta)208 V (wye) 11 15 480 V 12 16 600 V 13 17 415 V - - hot–hot–hot–neutral 120/208 V 18 21 277/480 V 19 22 347/600 V 20 23 240/415 V - 26

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).

NEMA 1 This two-prong design, with two flat parallel non-coplanar blades and slots, is used in most of North America and on the east coast of South America on lamps; consumer electronics such as clocks, radios, and battery chargers; and other double-insulated small appliances that do not require grounding (earthing).

All NEMA 1 devices are two-wire non-grounding devices (hot-neutral) rated for 125 V maximum. 1-15P plugs have two parallel flat blades, wide, thick, long, and spaced apart.

1-15R receptacles have been prohibited in new construction in the United States and Canada since 1962, but remain in many older buildings, and this obsolete design is still available for repair use only. Since January 1, 1974, all new power outlets are required to have a ground connection, using grounded receptacles (typically 5-15R or 5-20R) that accept both grounded and non-grounded plugs. Replacement of obsolete NEMA 1 receptacles requires either rewiring with an additional ground conductor for a NEMA5 receptacle, or a NEMA5 receptacle complete with a ground fault circuit interrupter for two-wire non-grounded configurations (when a ground conductor is not available).

Ungrounded NEMA 1 plugs are still popularly used by manufacturers of small appliances and electronic devices because of the design's low cost and compact size, and they are upward compatible with modern grounded NEMA5 receptacles. Standards permit ungrounded plugs where the appliance does not require grounding due to low risk of leakage current, such as on double-insulated devices.

In older plug designs both blades were the same width, so the plug could be inserted into the receptacle either way around. Many plugs manufactured since 1948 are polarized; the neutral blade is wide, wider than the line blade, so the plug can be inserted only one way. Polarized 1-15P plugs will not fit into unpolarized receptacles, which have only narrow slots. Polarized 1-15P plugs will fit 5-15R grounded receptacles, which have the same wider slot for the neutral blade. Some devices that do not distinguish between neutral and line, such as internally isolated AC adapters, are still produced with unpolarized narrow blades. Cheater plug adapters allow a three-prong grounded 5-15P plug to be mated to a non-grounded 1-15R receptacle. The adapters include a spade lug to allow connecting to ground, often via the cover screw used to attach the outlet faceplate. These adapters are illegal in some jurisdictions, in particular throughout Canada.

There are some obsolete 1-15R or 1-20R (120V, 15 or 20A) receptacles which are mechanically able to accept 1-15P (120V), 1-20P (120V), 2-15P (240V), or 2-20P (240V) plugs. These receptacles are typically found in older residential buildings and are not allowed to be installed under current NEC codes. In addition to the lack of grounding, these obsolete receptacles could allow a connected device to overheat and create a fire hazard if a device designed for the wrong voltage is connected. These problematic outlets are easily identifiable due to their lack of ground, along with both openings on the receptacle face being a sideways T-shaped opening that appear to be mirrored on the vertical center line of the face. Due to the potential danger of a voltage mismatch, whenever possible these receptacles should be replaced. Depending on local code, replacement with a "repair" approved non-grounded receptacle may be sufficient.

The Japanese plug and socket with narrow insulating faces appear and work physically identical to NEMA 1-15, and such non-grounded receptacles are still common in Japan (though grounded 5-15R and 5-20R receptacles are slowly becoming more common). The Japanese system incorporates stricter dimensional requirements for the plug housing, different marking requirements, and mandatory testing and approval by METI or JIS.

NEMA standards exist for 1-15P, 1-20P and 1-30P plugs, and the 1-15R receptacle. There are no 1-20R and 1-30R receptacles, because 1-20P and 1-30P can mate with a corresponding NEMA 5 receptacle.

NEMA 2 All NEMA 2 devices are two-wire non-grounding devices (hot-hot) rated for 250 V maximum. Although standards exist for 2-15, 2-20 and 2-30, this series is obsolete, and only Hubbell still manufactures 2-20 devices (for repair purposes).

NEMA 3 This series of devices is specified for 277-volt, two-wire, non-grounding devices. According to NEMA, this is "reserved for future configurations", so no designs for this series exist and no devices have been manufactured.

NEMA 4