NEMA connector
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NEMA connectors are connectors used for mains power in the USA and various other countries that have adopted their wiring practices. Some types are found in nearly all buildings in the United States. Many of these standards are identical to their counterparts in Canada, although there are some exceptions. NEMA wiring devices are made in current ratings from 15 to 60 amperes, and voltage ratings from 125V to 600V. NEMA stands for the National Electrical Manufacturers Association, which publishes numerous electrical standards. The standard for electrical connectors is ANSI/NEMA WD-6.[1]
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[edit] NEMA Nomenclature
There are two basic classifications of NEMA device: straight-blade and locking. The twist-locking type is preferred in many industrial environments, while the residential and commercial environment is home to straight-blade devices. (Of course, the straight-blade 5-15 and 5-20 are found nearly everywhere.) Numbers prefixed by L are curved-blade, twist-locking connectors, others are straight blade non-locking.
The numeral preceding the hyphen in NEMA nomenclature indicates the configuration type, i.e. number of poles, number of wires, voltage, and whether single- or three-phase. A grounding type of device will be described as two-pole, three-wire; or four-pole, five-wire; etc. A non-grounding device will be two-pole, two wire; or three-pole, three-wire; etc.
The numeral following the hyphen is the rating of the device in amperes. The number is followed by the letter R to indicate a receptacle or the letter P to indicate a plug.
As an example, the 5-15R is the common 125V two-pole, three-wire receptacle. The L5-15R, while sharing the same rating, is a locking design which is not physically compatible with the straight-blade 5-15 design. The 5-30 has the same two-pole, three-wire configuration and 125V rating, but is rated 30 amperes.
Although there are several non-grounding device types in the NEMA standards, only a few of them are in widespread use today. These are the two-pole 1-15, still in use in millions of buildings built before 1965, and the three-pole 10-30 and 10-50.
The hole, near end of the power (non-ground) conductors of NEMA plugs, is included in the design to aid in arc quenching when the plug is removed under power.[citation needed]
[edit] Non-locking connectors
NEMA non-locking connectors all use blades of various flat and folded shapes (except for the "U-ground" pins used on grounding connectors) and the plugs can be detached from the receptacles simply by pulling back on the plug body. The connector families have been carefully designed so that grounding connectors for 120V and 208/240V cannot be accidentally intermated.
note: all references to left and right in this section are looking at the socket face with the earth pin at the bottom (as is conventional north american installation practice).
[edit] NEMA 1
All NEMA 1 devices are two-wire non-grounding devices rated for 125V maximum. NEMA 1-15P are the two-prong plugs commonly found on household lamps and consumer electronics such as clocks and radios. 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; 1-20P and 1-30P mate with a corresponding NEMA 5 receptacle.
[edit] NEMA 2
All NEMA 2 devices are two-wire non-grounding devices rated for 250V maximum. Standards exist for 2-15, 2-20 and 2-30. There is no 2-15R receptacle; 2-15P mates with a corresponding NEMA 6 receptacle.
[edit] NEMA 5
All NEMA 5 devices are three-wire grounding devices rated for 125V maximum, with the 5-15, 5-20 and 5-30 being grounded versions of the 1-15, 1-20 and 1-30, respectively. The 20 A plug has the neutral (left) pin rotated 90 degrees, and the 5-20R receptacle may have a T-shaped neutral hole, to accept both 5-15P and 5-20P plugs. The 5-30 uses an L-shaped neutral, and both it and the 5-50 are over-sized, but these configurations are uncommon, as twist-locking plugs are generally used for high-current applications. The 5-15 is by far the most common electrical outlet in North America in buildings built since the mid-twentieth century.
NEMA 5-15 and 5-20 wall receptacles can be found installed in several orientations. Neither NEMA, U.S. National Electrical Code nor Canadian Electrical Code specify a preferred orientation, and different orientations may be found in the same building.
The standard 5-15 (and its two pin counterpart) is sometimes called an "Edison plug". This is particularly common in the film and theatre industry, where it distinquishes it from more specialized theatrical connectors. This is perhaps a reference to the Consolidated Edison Company of New York, which supplies power to most New York theatres.[citation needed]
[edit] NEMA 6
All NEMA 6 devices are three-wire grounding devices used for 208V and 240V circuits and rated for 250V maximum, with the 6-15, 6-20 and 6-30 being grounded versions of the 2-15, 2-20 and 2-30, respectively. The 20 A plug has the right pin rotated 90 degrees, and the 6-20R receptacle may have a T-shaped left hand hole, to accept both 6-15P and 6-20P plugs. The 30A plug and socket look similar to the 15A one but larger. The higher-current versions are rare, with twist-locking plugs and direct wiring being far more common; generally 6-series non-locking plugs are used for such appliances as large room air conditioners, commercial kitchen equipment, and the occasional home arc welder.
NEMA 6 devices while specified as 240V may be used for either 208V or 240V circuits.
[edit] NEMA 10
NEMA 10 devices are a curious throwback to an earlier time. They are classified as 125/250V non-grounding, yet they are usually used in a manner that effectively grounds the appliance, albeit not in a manner consistent with most modern practice.
As commonly used, 10-30 and 10-50 plugs have the frame of the appliance grounded through the neutral pin. This was a legal grounding method under the National Electrical Code for electric ranges and electric clothes dryers from the 1947 to the 1996 edition. Since North American dryers and ranges have certain parts (timers, lights, fans, etc.) that run on 120V, this means that the wire used for grounding is also carrying current. Although this is contrary to modern grounding practice, such installations remain extremely common in the United States and are relatively safe, because the larger conductors used are less likely to be broken than the smaller conductors used in ordinary appliance cords.
Persons moving their older appliances to newer NEMA 14-equipped buildings (or vice-versa) should have the cords replaced by a qualified electrician.
NEMA 10-20 devices are very rare nowadays. There is also a similar obsolete design, lacking a NEMA configuration number, rated 125V 15A/ 250V 10A which is nearly identical to the AS/NZS 3112 standard used in Australia/New Zealand. These are also extremely rare.
[edit] NEMA 14
The NEMA 14 devices are 4-wire grounding devices available in ratings from 15A to 60A. Of the straight-blade NEMA 14 devices, only the 14-30 and 14-50 are common. The 14-30 is used for electric clothes dryers and the 14-50 for electric cooking ranges. The voltage rating is a design maximum of 125/250V. They are essentially the replacements for the connectors above with the addition of a separate grounding connection.
All NEMA 14 devices offer two hots, a neutral and a ground, allowing for both 120V and 240V (or 120V and 208V if the supply system is three phase wye rather than split phase or three phase center tapped delta) appliances. They differ in rating and shape of the neutral pin. The 14-30 has a rating of 30A and an L-shaped neutral pin. The 14-50 has a rating of 50 A and a straight neutral pin sized so that it will not fit in the slot of a 14-30.
NEMA 14-30 devices are most commonly found serving electrically heated clothes dryers, while 14-50 devices most commonly serve kitchen ranges. In the United States, these are generally found in buildings constructed after the 1996 National Electrical Code, although they are also found in considerably earlier mobile homes. In Canada, the use of NEMA 10 devices was discontinued much earlier (if it was ever permitted at all), so NEMA 14 devices are more common there.
[edit] Twist-locking connectors
  L21-30 Plug and receptacle |
Twist-locking connectors were first invented by Harvey Hubbell III in 1938 and "Twist-Lock" remains a registered trademark of Hubbell Incorporated to this day,[2] although the term tends to be used generically to refer to NEMA twist-locking connectors manufactured by any company. Unlike non-locking connectors, twist-locking connectors all use curved blades that have shapes that conform to portions of the circumference of a circle. Once pushed into the receptacle, the plug is twisted and its now-rotated prongs latch into the receptacle. To unlatch the plug, the rotation is reversed. The locking coupling makes for a very reliable connection in commercial and industrial settings.
Like non-locking connectors, these come in a variety of standardized configurations and follow the same general naming scheme except that they all begin with an "L" for "locking". Once again, the connector families are designed so that 120V connectors , 208/240V connectors, and various other, higher-voltage connectors can not be accidentally intermated. Many specific types exist; only a few are listed below.
[edit] NEMA L5
NEMA L5 connectors are a series of twist-locking connectors used for 120V, single-pole circuits. The L5-30 is a very popular configuration even on circuits of less than 30 amps owing to its very rugged construction.
[edit] NEMA L6
NEMA L6 connectors are a similar series of twist-locking connectors used for 208/240V circuits.
[edit] NEMA L7
NEMA L7 connectors are used for 277V circuits (typically, commercial or industrial lighting circuits).
[edit] NEMA L21
The type L21-30-P and L21-20-P are 30A and 20A plugs for 208Y/120V three phase connections. These plugs connect to type L21-30-R and type L21-20-R receptacles, respectively. The middle prong is ground, and the prong with a right angle on the tab (nearest the "L2130P" indicated on the plug pictured) is neutral.
[edit] Ground fault circuit interrupter (GFCI) sockets
These versions of the 5-15 socket are residual-current devices and have Test and Reset buttons (and sometimes an indicator light). In the U.S. and Canada they are required in many potentially wet locations, including outside outlets, bathrooms, some places in kitchens, basements and crawl spaces. They work by comparing the current going out on the live connector to the current returning on the neutral, and will disconnect the circuit if the difference exceeds 4-6 milliamps. They are cheaper than GFCI circuit breakers and can be wired to feed additional "downstream" outlets so that putting one GFCI receptacle in a circuit will protect all the plugs, lights and switches downstream from it. They are also recommended for power tool outlets and locations where children might insert metal objects in the sockets.
[edit] Leak current detection and interruption (LCDI) plugs
Because portable air conditioners have caused many electrical fires, those sold in the United States now must have Leak Current Detection and Interruption (LCDI) plugs. The cords have a fine wire mesh around the conductors and circuitry to detect any current leaking from the conductors to the mesh, which would happen if the cord was damaged or frayed. These could be NEMA 5-15, 5-20, 6-15, 6-20 or 6-30 plugs depending on the air conditioner. The plug is equipped with "Test" and "Reset" buttons on the housing.
[edit] NEMA TT-30
NEMA TT-30 is a 30A 125 volt recreational vehicle standard which may also be known as RV 30. It is frequently (and sometimes disastrously) confused for a NEMA 10-30. The RV receptacle is common in nearly all RV parks in the United States and Canada, and all but the largest RVs manufactured in the last 30 years use this plug. The hot and neutral blades are angled at 90 degrees to each other, similar to NEMA 10 devices. The plug is slightly smaller than a NEMA 10 but larger than ordinary 5-15 plugs. The ground pin, however, is a U-shape, like those on straight-blade NEMA grounding devices. Due to the appearance of this plug, many people assume that it is to be wired for 240V. This is not the case! This is a 120V device. Adapters exist with the TT-30 plug on one side and a 5-15 or 5-20 plug on the other side.
[edit] External links
- Georgia State University - Physics Department - Household Wiring ~ Polarized Receptacles (diagram)
- E Technologies - Receptacles (socket configurations)
- NoOutage.com - NEMA Configurations (socket configurations)
- Power Cabling - NEMA Configurations (socket configurations)
- Stay Online - NEMA Plug & Receptacle Configurations Reference Chart (Straight Blade) (socket configurations)
- System Connection - Power Cord NEMA Mold Chart (socket configurations)
