NEMA connector

Power plugs and receptacles used in North America and some other regions

NEMA connectors are power plugs and sockets used for AC mains electricity in North America and other countries that use the standards set by the US National Electrical Manufacturers Association. 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) and Japan (JIS C 8303). Other plug and receptacle types are for special purposes or for heavy duty applications. The dimensional standard for electrical connectors is ANSI/NEMA WD 6 and is available from the NEMA website. The Edison screw was very successful, and quickly became the first de facto standard for electric connection. In the early 1900s, table and floor lamps became more popular, and sockets were mounted on walls for secondary connections. One big disadvantage of screw connectors was that the cord inevitably got twisted after being connected to the receptacle.

In 1903, Harvey Hubbell filled the , for a lightbulb socket adaptor and plug, also a standalone receptacle. The adaptor was screwed into the lightbulb socket, leaving a flat face with two holes to conveniently attach the plug. The same patent had a second design, with a wall attachable receptacle, capable of receiving the same plug, thus being the first socket and plug design patented in the US. Later in 1904, he changed the design to flat blades (a design later incorporated in the NEMA 2 series), filled under the Both these patents were granted in
In 1910, Hubbel worked on improving his popular flat blade design, filled in 1912. The new design had parallel blades, a more compact design and was easier to manufacture. This design was improved once again in 1915, introducing a polarized plug under the The flat blade plug which in subsequent years evolved to become NEMA 1 15 was born.

It is worth noting that in addition to Hubbell's system, circulated a large variety of different plugs and receptacles, some of them compatible with Hubbell's, some not. In 1919, Hubbell unsuccessfully tried to prevent other manufacturers from making receptacles and plugs to the dimensions used by Hubbell. The report of the court proceedings includes a comprehensive review of the development of the art in the US prior to 1919, based on evidence presented to the Court. Separable plugs had been available for more than a decade prior to Hubbell's 1904 design.

In 1926, the National Electrical Manufacturers Association (NEMA) was founded by the merger of the Electric Power Club and the Associated Manufacturers of Electrical Supplies and represented manufacturing companies of the electrical segment in a national level. NEMA provided a forum between companies for reaching standardization, but it was not until the 1940s that NEMA started to publish standards on receptacles and plugs, much later than UK, France and Germany. Since NEMA was a forum between manufacturers and not an governmental body, any decision had to be thoroughly discussed and agreed upon by its members, which substantially slowed the standardization process.

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).

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.

This series of devices is specified for 600 volt, two wire, non grounding devices. Identically to the NEMA 3 series, this is "reserved for future configurations" and no designs for this series exist and no devices have been manufactured.

All NEMA 5 devices are three wire grounding devices (hot–neutral–ground) rated for 125 V maximum, with the 5 15, 5 20 and 5 30 being grounded versions of the 1 15, 1 20 and 1 30, respectively. The addition is a diameter round or U shaped ground pin, longer than the power blades (so the device is grounded before the power is connected) and located from them by edge to edge or center to center. Compared to the 5 15P plug, the 5 20P plug has the neutral blade rotated 90° and shifted so its inner edge is approximately from the hot blade. The 5 20R receptacle has a T shaped neutral hole, to accept both 5 15P and 5 20P plugs. An acceptable alternative version of the 5 20R receptacle has a rectangular slot that will only accept 5 20P plugs. The 5 30 and 5 50 are physically larger, with between power pins; 5 30 also has an L shaped neutral blade. These larger sizes are uncommon, as twist locking plugs are generally used for high current applications. The neutral blade on 5 15P plugs is not always wider than the line blade, since the ground pin enforces polarity. The Electrical Safety Foundation International has stated: "Never remove the ground pin (the third prong) to make a three prong plug fit a two prong outlet". In addition to the dangers of breaking a ground connection, removing the ground pin to make it fit a 1 15R receptacle or extension cord, may result in the live–neutral polarity being lost. The 5 15R and 5 20R are by far the most common electrical receptacle in North America in buildings built since the mid twentieth century. It is usually installed in a duplex configuration; two receptacles may share a common circuit or may each be wired separately, sometimes to a switch. In 46 of the 50 United States and all of Canada, tamper resistant receptacles are required in new residential construction These prevent contact by objects like keys or paper clips inserted into the socket. This is accomplished by an interlocking mechanism that requires hot and neutral blades inserted simultaneously to release the small doors blocking the slots. The grounding slot is not blocked by a door. In stage lighting for film and theater, this connector is sometimes informally known as PBG (Parallel Blade with Ground), U ground, Edison or Hubbell, the name of a common manufacturer. (The name "Hubbell" can be confusing as several different connectors share this name depending on the company, industry, and use.) In the motion picture and TV production industries, an extension cord that uses this type of connector (usually with 12 AWG or 10 AWG wire) is called a "stinger". Generally, lighting technicians use these extension cords to deliver power to lights rated at 2,000 watts or less. Internationally, the NEMA 5 15P plug and NEMA 5 15R receptacle are the basis for the International Electrotechnical Commission's IEC 60906 2 standard IEC system of plugs and sockets outlets for household and similar purposes Part 2: Plugs and socket outlets 15 A 125 V a. c. and 20 A 125 V a. c.

All NEMA 6 devices are three wire grounding devices (hot hot ground) used for 208 and 240 V circuits and rated for 250 V maximum, with the 6 15, 6 20 and 6 30 being grounding versions of the 2 15, 2 20 and 2 30, respectively. The 6 15 resembles the 5 15, but with collinear horizontal pins, spaced center to center. The 20 A plug has a blade rotated 90° (opposite blade from what would be the "line" blade on a 2 15 or 5 15 plug. This prevents accidental insertion of plugs into outlets that use different voltages), and the 6 20R receptacle has a T shaped hole to accept both 6 15P and 6 20P plugs (similar to the 5 20R receptacle accepting 5 15P and 5 20P plugs). The 50 A (and 5 50) receptacles look like bigger versions of the 5 15 A. 6 15R and 6 20R receptacles are usually manufactured on the same assembly line as "Industrial" or "Commercial" grade 5 15R and 5 20R receptacles, with all 4 receptacles sharing the same "triple wipe" T contacts behind the varying faceplates. The faceplate bonded onto the receptacle determines the final configuration of the receptacle. NEMA 6 devices, while specified as 250 V, may be used for either 208 or 240 V circuits, generally depending on whether the building has a three phase or split phase power supply, respectively. The NEMA 6 20R or 6 30R found in many hotel and motel rooms is typically supplied with either split phase or two phases of three phase 208 V.

The higher current receptacles are rare, with twist locking plugs such as L6 30 and direct wiring being more common. Generally, 6 series non locking plugs are used for such appliances as large room air conditioners and commercial kitchen equipment; the occasional home arc welder also uses 6 50. Single phase 6 50 is commonly used on farms for silo unloaders, and is used with a 6 gauge flexible power cord up to 200 feet (61 m) long. The 6 50 receptacle charges electric vehicles at the same 32 or 40 ampere maximum from charging stations, on a short cord, as the more versatile 14 50 with its fourth prong neutral not used currently for any electric vehicle charging purposes.

NEMA 7 devices are three wire/prong (hot neutral ground) connectors rated at 277 V. The 15 A 7 15 plug has the crowsfoot current carrying pins of the Type I plug, but with a U shaped earth pin. The 7 20 version has an enlarged line/hot pin. 7 30 is a larger diameter connector, with an L shaped neutral, while the 7 50 has an enlarged neutral pin, compared with the hot.

NEMA 8 devices are specified for three wire, two pole, grounding devices for 480 volts. According to NEMA, this is "reserved for future configurations", so no designs for this series exist and no devices have been manufactured.

NEMA 9 devices are specified for three wire, two pole, grounding devices for 600 volts. According to NEMA, this is "reserved for future configurations", so no designs for this series exist and no devices have been manufactured.

NEMA 10 connectors are a now deprecated type that had formerly been popular in the United States for use with high power electric clothes dryers, kitchen ranges, and other high power equipment. NEMA 14 30R and 50R connectors have generally replaced NEMA 10 equipment for these applications. NEMA 10s are classified as 125/250 V non grounding (hot hot neutral), and were designed to be used in a manner that indirectly grounds the appliance frame to the neutral, which was common before the requirement of a separate safety ground was incorporated in the National Electrical Code. As commonly used, 10 30 and 10 50 plugs required the frame of the appliance to be indirectly grounded via a strap connecting to the neutral blade. Safe operation relied on the neutral conductor in turn being connected to system ground at the circuit breaker or fuse box. If the neutral conductor were to break, disconnect, or develop high resistance, the appliance frame could become energized to dangerous voltages. Modern practice is to require a separate safety grounding conductor whose only purpose is to divert unsafe voltages, and which does not carry significant current during normal operation. Relying on the neutral conductor was a legal grounding method for electric ranges and clothes dryers, under the National Electrical Code from the 1947 to the 1993 editions (banned in 1996 edition). Since North American dryers and ranges have certain components (timers, lights, fans, etc.) that run on 120 V, this means that the neutral wire indirectly used for grounding would also carry current, even under non fault conditions. Although this is contrary to modern grounding practice, such "grandfathered" installations remain common in older homes in the United States.

NEMA 11 series devices are three wire, three pole, non grounding devices for 3 phase 250 volt designs and equipment parts are specified by NEMA for 20 ampere (11 20), 30 ampere (11 30), and 50 ampere (11 50) devices.

NEMA 12 series devices are three wire, three pole, non grounding devices for 3 phase, 480 volt equipment. According to NEMA, this is "reserved for future configurations", so no designs for this series exist and no devices have been manufactured.

NEMA 13 series devices are three wire, three pole, non grounding devices for 3 phase, 600 volt equipment. According to NEMA, this is "reserved for future configurations", so no designs for this series exist and no devices have been manufactured.

These sockets and plugs are four prong (see receptacle chart above) grounding devices (hot hot neutral ground) available in ratings from 15 to 60 A. The voltage rating is 250 V. Of the straight blade NEMA 14 devices, only 14 50 and 14 30 are in common use and either may be used for home charging of electric vehicles. The 14 30 is limited to 30 amperes (24 amperes continuous) and used mainly for some electric clothes dryers and some electric cooking stoves. The NEMA 14 connectors are essentially the replacements for the older NEMA 10 connectors described above, but with the addition of a dedicated grounding connection. All NEMA 14 devices offer two hots, a neutral, and a ground, allowing for both 120 and 240 V when supplied by split phase power, or 120 and 208 V if the supply is three phase. The 14 30 has a rating of 30 A, and an L shaped neutral blade. The 14 50 has a rating of 50 A, and a straight neutral blade sized so that it does not mate with 14 30 connectors. NEMA 14 50 devices are frequently found in RV parks, since they are used for "shore power" connections of larger recreational vehicles. Also, it was formerly common to connect mobile homes to utility power via a 14 50 device. Newer applications include Tesla's Mobile Connector for vehicle charging, which formally recommended the installation of a 14 50 receptacle for home use. The 6 50 is a smaller size receptacle that charges at the same 32 or 40 ampere maximum from electric vehicle charging stations as this more versatile 14 50 with its fourth prong neutral not used currently for any electric vehicle charging purposes.

NEMA 15 are three pole and ground connectors (phase A, phase B, phase C, ground) rated for 208 V. Intended for delta three phase circuits with ground and no neutral. The straight blades all carry one of the three phases.

NEMA 20 series devices are specified for 347/600Y three pole, four 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 21 series devices are specified for three pole plus neutral, five wire grounding devices for 3 phase 120/208Y supplies. According to NEMA, NEMA 21 straight blade devices are "reserved for future configurations", so no designs for this series exist and no devices have been manufactured. There are however NEMA L21 series locking devices for 20 and 30 ampere devices specified and available for these applications.

NEMA 22 series devices are specified for three pole plus neutral, five wire grounding devices for 3 phase 277/480Y supplies. According to NEMA, NEMA 22 straight blade devices are "reserved for future configurations", so no designs for this series exist and no devices have been manufactured. There are however NEMA L22 series locking devices for 20 and 30 ampere devices specified and available for these applications.

NEMA 23 series devices are specified for three pole plus neutral, five wire grounding devices for 3 phase 347/600Y supplies. According to NEMA, NEMA 23 straight blade devices are "reserved for future configurations", so no designs for this series exist and no devices have been manufactured. There are however NEMA L23 series locking devices for 20 and 30 ampere devices specified and available for these applications.

NEMA 24 Series devices are specified for two pole, three wire grounding devices for 347V A/C power.

The NEMA TT 30 (TT stands for Travel Trailer) connector is a 120 V 30 A recreational vehicle standard (hot neutral ground), also known as RV 30. The TT 30R receptacle is commonly available in nearly all RV parks in the United States and Canada, and all but the largest RVs manufactured since the 1970s use this plug to connect to power feeds. The appearance of this plug is sometimes confused with a NEMA 10 connector, rated for 240 V, but the NEMA TT 30 is a 120 V device. The hot and neutral blades are angled at 45° from vertical and 90° to each other, unlike NEMA 10 devices (where the angles are 30° and 60° respectively), also the plug is slightly smaller than a NEMA 10 and larger than ordinary 5 15P plugs. The ground pin is round, like those on straight blade NEMA grounding devices. Referring to the picture, the orientation is the same as the NEMA 5 plug and receptacle, with the neutral blade on the lower right. Adapters are available with the TT 30P plug on one side and a 5 15R or 5 20R receptacle on the other side. When a power feed cord is detachable from an RV, an L5 30P is usually used on the RV end of the cord.

Twist locking connectors were first invented by Harvey Hubbell III in 1938 and "Twist Lock" remains a registered trademark of Hubbell Incorporated, although the term is used generically to refer to NEMA locking connectors manufactured by any company. Locking connectors use curved blades. Once pushed into the receptacle, the plug is twisted and its now rotated blades latch into the receptacle. To unlatch the plug, the rotation is reversed. The locking coupling makes for a more reliable connection in commercial and industrial settings, where vibration or incidental impact could disconnect a non locking connector. Locking connectors come in a variety of standardized configurations that follow the same general naming scheme except that the designations include an "L" for "locking". Locking connectors are designed so that different voltages and current ratings can not be accidentally intermated. Many specific types exist; only a few are listed below. Other types include special purpose connectors for boats, 400 Hz circuits such as used for aircraft, and direct current applications. One apparent disadvantage of twist lock connectors is that in the event that the cable is accidentally pulled too hard, rather than the plug falling out of the receptacle, exposed conductors may come out of the plug, causing dangerous shorts or shock hazards if the circuit is live. This is resolved in most cases by the connector having a robust integral strain relief.

ML series "Midget Locking" connectors are for 15 A applications where a larger locking connector would not fit. ML 1 connectors are two pole, no ground, rated for 125 V.
ML 2 connectors are two pole with ground, rated for 125 V.
ML 3 connectors are for three pole no ground (hot neutral hot) rated for 125/250 V.

SS series "Ship to shore" connectors are for 50 A marine shore power applications. SS1 50 connectors are two pole with ground, rated for 125 V.
SS2 50 connectors are three pole with ground (hot neutral hot) rated for 125/250 V.

NEMA L1 series devices are single pole plus neutral, two wire, non grounding devices for 125 volts single phase. Designs and devices for 15 ampere devices (L1 15) exist.

NEMA L2 series devices are two pole, two wire, non grounding devices for 250 volts single phase. Designs and devices for 20 ampere devices (L2 20) exist.

These devices would have been for 277 and 600 volt two pole, two wire non grounding devices similar to the straight blade NEMA 3 and 4 families, but were never specified by NEMA.

NEMA L5 connectors are a series of two pole and ground locking connectors rated for 125 V. L5 30R receptacles are common at marinas that provide power to docked boats. They are also found on some RVs for connecting to shore power. RVs in the US are equipped for 120 V 30 A or 240 V 50 A service, and use a cord to connect to a receptacle at the campsite, usually on a power pedestal with one or more receptacles providing 120 V 30 A (TT30R), 240 V 50 A (14 50R), or 120 V 15/20 A (5 20R) service. Locking receptacles appropriate for the voltage and current are used on the RV end of the cord, along with non locking plugs on the end connecting to the pedestal.

NEMA L6 connectors are rated for a maximum of 250 volts. They are intended for two pole, three wire, line line earth (or hot hot ground) circuits with a nominal supply voltage of 208 or 240 volts, depending on phase configuration. The L6 connector does not provide a neutral connection. L6 20 connectors provide a maximum of 20 amperes and are commonly found in power distribution units (PDUs) used in the information technology sector. Most often, these connectors can be found in server rooms and data centers where the connectors are used to power equipment such as servers, backup systems and UPS units. L6 30 connectors provide a maximum of 30 amperes and tend to be used in heavy industry sectors. For example, welders and other manufacturing machinery where industrial equipment or large power tools are commonplace.

NEMA L7 are two pole and ground connectors rated for 277 V. Typically, these connectors are found in commercial or industrial lighting circuits, especially where metal halide lamps are common.

NEMA L8 are two pole and ground connectors rated for 480 V. Intended for three wire hot hot ground circuits.

NEMA L9 are two pole and ground connectors rated for 600 V. Intended for three wire hot hot ground circuits.

NEMA L10 series devices are two pole plus neutral, three wire, non grounding devices for 125/250 volts single phase. These are deprecated due to the lack of grounding but L10 20 and L10 30 devices are specified by NEMA and are commercially available.

NEMA L11 series devices are three pole, three wire, non grounding devices for three phase 250 volt devices. Designs exist for 15 ampere (L11 15), 20 ampere (L11 20), and 30 ampere (L11 30) devices, and L11 20 and L11 30 devices were commercially available from at least one manufacturer (Bryant Electric).

NEMA L12 series devices are three pole, three wire, non grounding devices for three phase 480 volt devices. Designs exist for 20 ampere (L12 20), and 30 ampere (L12 30) devices, and L12 20 and L12 30 devices were commercially available from at least one manufacturer (Bryant Electric).

NEMA L13 series devices are three pole, three wire, non grounding devices for three phase 600 volt devices. Designs exist for 30 ampere (L13 30) devices and L13 30 devices were commercially available from at least one manufacturer (Bryant Electric).

NEMA L14 are three pole and ground connectors rated for 125/250 V. Intended for three pole, four wire hot hot neutral ground circuits with a nominal supply voltages of 240 or 208 V hot to hot and 120 V hot to neutral. These connectors are common on household backup generators, and on racks of power amplifiers in large audio systems.

NEMA L15 are three pole and ground connectors rated for 250 V. Intended for three phase circuits.

NEMA L16 are three pole and ground connectors rated for 480 V. Intended for three phase circuits.

NEMA L17 are three pole and ground connectors rated for 600 V. Intended for three phase circuits.

NEMA L18 are four pole no ground connectors rated for 120/208 V. Intended for wye three phase circuits.

NEMA L19 series devices are three pole, four wire, non grounding devices for three phase 277/480 volt devices. Designs exist for 20 ampere (L19 20), and 30 ampere (L19 30) devices, and L19 20 and L19 30 devices were commercially available from at least one manufacturer (Bryant Electric).

NEMA L20 series devices are three pole, four wire, non grounding devices for three phase 347/600 volt devices. Designs exist for 20 ampere (L12 20), and 30 ampere (L20 30) devices, and L20 20 and L20 30 devices were commercially available from at least one manufacturer (Bryant Electric).

NEMA L21 are four pole and ground connectors rated for 120/208 V. Intended for wye three phase circuits with both neutral and ground. The pin in the middle is ground, and the blade with a right angle on the tab is neutral. These connectors are common in live event power distribution. Many event production companies use power distributors with camlock connectors for feeder cable, and 12 or more L21 30 connectors which can each be broken out to three individual 120 V circuits via the use of a stringer box.

NEMA L22 are four pole and ground connectors rated for 277/480 V. Intended for wye three phase circuits with both neutral and ground. The pin in the middle is ground, and the blade with a right angle on the tab is neutral.

NEMA L23 are four pole and ground connectors rated for 347/600 V. Intended for wye three phase circuits with both neutral and ground. The pin in the middle is ground, and the blade with a right angle on the tab is neutral.

Over time, electrical codes in the US and Canada began to require additional safety features in the basic NEMA 5 15R and 5 20R configurations to address specific electric shock hazard concerns. The safety features listed below are not mutually exclusive; for example, tamper resistant GFCI receptacles are available.

These versions of the 5 15R or 5 20R receptacle are residual current devices, and have "Test" and "Reset" buttons (and sometimes an indicator light which may be normally on or normally off per the vendor's design). In the US and Canada, GFCI protection is required for receptacles in many potentially wet locations, including outside outlets, bathrooms, and some places in kitchens, basements, and crawl spaces. This is an expedient way to provide that protection at the receptacle itself. These safety devices work by comparing the currents flowing in the live and neutral conductors, and disconnect the circuit if their difference exceeds 4 to 6 milliamperes. Installing a single receptacle is often cheaper or more convenient than providing this GFCI protection at the circuit breaker. In addition, a tripped GFCI receptacle may be more easily noticed and reset, as compared to a tripped GFCI located in a remote circuit breaker panel far from the point of usage. Like most current interrupting devices, a GFCI receptacle can optionally be wired to feed additional "downstream" outlets; correctly installing one GFCI receptacle in a circuit can protect all the plugs, lights, switches, and wiring which receive power from it. This allows for cost effective retrofits on older installations where branch circuits were often daisy chained between wet and dry locations. A GFCI receptacle may be installed indoors where it is sheltered from dampness and corrosion, while still protecting an outdoors receptacle wired downstream. GFCIs are also recommended for power tool outlets and any locations where children might insert conductive objects into the receptacles. and the 2009 Canadian Electrical Code, listed tamper resistant receptacles that address electric shock hazards to children must now be installed in almost all areas of new or renovated dwellings. According to statistics cited by the NFPA, the code change adds only $40 to the cost of building an average, 75 receptacle home in the US. This safety measure reduces shock hazards to a child that attempts to insert a single conductive object into the receptacle. Inserting a normal, two blade electrical plug applies simultaneous pressure on both sides of the receptacle to open an internal, spring loaded shutter, but a foreign object fails to do so and therefore cannot make contact with the live electrical contacts. However, the device can still be defeated by inserting two objects simultaneously. Despite its weaknesses, the tamper resistant receptacle is superior to protective plastic outlet caps which must be individually installed on each receptacle (and are a choking hazard when removed), and to sliding covers that children easily learn to defeat. requires each portable air conditioner sold in the United States to have either a leakage current detector interrupter (LCDI) or a ground fault circuit interrupter (GFCI) protective device built into its power cord. The device can be integral with the power plug, or a separate module within 12 inches of the plug. The protection device is equipped with "Test" and "Reset" buttons on the housing. An LCDI cord has a fine wire mesh around the conductors, and circuitry to detect current leaking from the conductors to the mesh, which would happen if the cord were damaged or frayed. The plugs are normal NEMA 5 15, 5 20, 6 15, 6 20, or 6 30 plugs, depending on the air conditioner design, and are typically molded on designs.

Most duplex receptacles have metal tabs connecting the top and bottom receptacles. These tabs can be broken off to allow the top and bottom receptacles to be wired onto separate circuits. This may allow for one switched receptacle for a lamp, or for two separate supply circuits when heavy loads are anticipated. Two branch circuits may optionally share a common neutral wire terminating on duplex receptacles, a condition sometimes referred to as "split wiring", "split receptacle", or "half split".

The dimensions and configurations for NEMA connectors are given in ANSI/NEMA standard WD 6. which specifies construction performance (e. g. durability, electrical safety, and fire resistance) for NEMA connectors. These additional requirements allow connectors to be manufactured to be compliant with the National Electrical Code. The Defense Logistics Agency and General Services Administration maintain Federal Specification W C 596 and its associated specification sheets. This specification references WD 6 and UL 498, and provides additional durability and electrical safety performance criteria for connectors intended for military use.