Nomenclature[ edit ] NEMA receptacles, with their common US uses listed in purple text Most NEMA connectors are named following a simple alphanumeric code consisting of: a numeral preceding a hyphen, a numeral following the hyphen, and letters at the beginning and end of the code to indicate whether the connector is a locking type and whether it is a plug male connector or the corresponding receptacle female connector. 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". Twist-locking types are used for heavy industrial and commercial equipment, where increased protection against accidental disconnection is required.
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Nomenclature[ edit ] NEMA receptacles, with their common US uses listed in purple text Most NEMA connectors are named following a simple alphanumeric code consisting of: a numeral preceding a hyphen, a numeral following the hyphen, and letters at the beginning and end of the code to indicate whether the connector is a locking type and whether it is a plug male connector or the corresponding receptacle female connector.
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".
Twist-locking types are used for heavy industrial and commercial equipment, where increased protection against accidental disconnection is required. A connector with ground terminal is described as having more wires than poles, e.
A non-grounding device may be two-pole, two-wire; three-pole, three-wire; etc. The numeral following the hyphen is the current rating of the device in amperes. The LR, while sharing the same electrical rating, is a locking design that is not physically compatible with the straight-blade design.
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 , still in use in millions of buildings built before the s, and the three-pole and 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. 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. When the ground blade of a receptacle is on the bottom, the neutral blade is on the upper left and the hot blade is on the upper right. All descriptions below assume this orientation i. Since January 1, , all new power outlets are required to have a ground connection, using grounded receptacles typically R or R that accept both grounded and non-grounded plugs. 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. Polarized P plugs will not fit into unpolarized receptacles, which possess only narrow slots. Polarized P plugs will fit R 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 "3-prong" grounded P plug to be mated to a non-grounded R 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. The Japanese system incorporates stricter dimensional requirements for the plug housing, different marking requirements, and mandatory testing and approval by METI or JIS.
Newer NEMA plugs with wider faces middle have a safety advantage; plugs for electric toys right have noticeably wide faces. Although standards exist for , and , this series is obsolete, and only Hubbell still manufactures devices for repair purposes. According to NEMA, this is "reserved for future configurations," so no designs for this series exist and no devices have been manufactured. NEMA 4[ edit ] This series of devices is specified for 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. The neutral connection is the wider T-shaped slot on the lower right. The R receptacle has a T-shaped neutral hole, to accept both P and P plugs. An acceptable alternative version of the R receptacle has a rectangular slot that will only accept P plugs. The neutral blade on P 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. The R and R 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 as of November [update]. These prevent contact by objects like keys or paper clips inserted into the socket. 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. 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". The faceplate bonded onto the receptacle determines the final configuration of the receptacle.
The higher-current versions are rare, with twist-locking plugs such as L or direct wiring 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. The is also used on arc welders. NEMA 10[ edit ] The now- deprecated NEMA has a neutral pin at top of photo , but does not have a dedicated safety grounding pin NEMA 10 connectors are a now deprecated type that had formerly been popular in the United States for use with high-wattage electric clothes dryers , kitchen ranges , and other high-power equipment.
The older practice was common before the requirement of a separate safety ground was incorporated in the National Electrical Code. As commonly used, and 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 to the editions. Since North American dryers and ranges have certain components timers, lights, fans, etc. Although this is contrary to modern grounding practice, such " grandfathered " installations remain common in older homes in the United States.
Of the straight-blade NEMA 14 devices, only the and are in common use. The is used for electric clothes dryers, the is used for electric cooking ranges, and either may also be used for home charging of electric vehicles.
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. NEMA 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 device. According to NEMA, NEMA 16 straight-blade devices are "reserved for future configurations," so no designs for this series exist and no devices have been manufactured.
According to NEMA, NEMA 17 straight-blade devices are "reserved for future configurations," so no designs for this series exist and no devices have been manufactured.
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 amp devices specified and available for these applications. 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 amp devices specified and available for these applications. 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 amp devices specified and available for these applications. The center hole on the receptacle is not a contact.
The TTR receptacle is commonly available in nearly all RV parks in the United States and Canada, and all but the largest RVs manufactured since the s use this plug to connect to power feeds. 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 TTP plug on one side and a R or R receptacle on the other side.
Twist-locking connectors[ edit ] Twist-locking connectors were first invented by Harvey Hubbell III in 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. 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. Designs and devices for 15 amp devices L exist. Designs and devices for 20 amp devices L exist. LR receptacles are common at marinas that provide power to docked boats. They are also found on some RVs for connecting to shore power. 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.
The L6 connector does not provide a neutral connection. These connectors are thus found where industrial equipment or large power tools are commonplace. Typically, these connectors are found in commercial or industrial lighting circuits, especially where metal halide lamps are common.
IEC 60906-2 PDF
Maurn Museum of Plugs and Sockets: IEC standard household plug Archived from the original on It ensures that the protective-earth pin establishes contact before the line and neutral pins. From Iex, the free encyclopedia. They are nominally Old outlet and plug, Middle: The pins have a diameter of 4. The sockets are small enough that two can be installed in the space taken by a single Schuko or BS socket. South Africa and Brazil are the first countries in the world that have introduced the standard.
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