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NEMA connector: Difference between revisions

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In 1910, Hubbel worked on improving his popular flat blade design, filled {{US patent|1064833}} 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 {{US patent|1180648}}. The flat blade plug which in subsequent years evolved to become NEMA 1-15 was born.
{{Gallery|File:US_patent_774250,_fig_1.svg|{{US patent|774250}}, fig. 1, illustrating and lightbulb adaptor and attachable flat blade socket for it.|File:US Patent 1064833, fig 1 and 3.svg|{{US patent|1064833}}, fig. 1 and 3. First patent showing the parallel blades which became NEMA 1-15.|File:US_patent_1180648,_fig_4_and_5.svg|{{US patent|1180648}} fig. 4 and 5, showing a concept for polarized receptacle and plug.|File:|Write a caption here|File:|Write a caption here|title=Some of Hubbel's patents:|align=center|footer=|style=|state=|height=|width=|captionstyle=|alt3=|alt4=|alt5=|alt2=|alt1=|noborder=yes}}
 
==== Other American manufacturers ====
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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 1–151-15, still in use in millions of buildings built before the 1960s, and the three-pole 10-30 and 10–5010-50.
 
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.<ref name=WD6>{{Cite book|url=https://archive.org/details/NEMA-WD-6-2016/page/n24/mode/1up|access-date=2021-08-15|title=ANSI/NEMA WD 6-2016: Wiring Devices - Dimensional Specifications|publisher=National Electrical Manufacturer's Association|year=2016|pages=17}}</ref> Small specialized [[padlock]]s are available to fit these holes, allowing "[[Lockout-tagout|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. <ref> [https://patents.google.com/patent/US2664734 e.g., US Patent 2,664,734, H.McEneaney, issued January 5, 1954] </ref>
 
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'.<ref name="WD6"/>
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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. Neither NEMA nor the US [[National Electrical Code]] nor the [[Canadian Electrical Code]] specify a preferred orientation, but the [[National Electrical Contractors Association]]'s ''National Electrical Installation Standards'' (NECA 130–2010130-2010) specify that the preferred location of the ground is on top. 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.e., clockwise order is ground, neutral, hot for 120&nbsp;V receptacle versions; and counter-clockwise for plug versions).
 
===NEMA 1===
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===NEMA 2===
All NEMA 2 devices are two-wire non-grounding devices (hot-hot) rated for 250&nbsp;V maximum. Although standards exist for 2–152-15, 2-20 and 2-30, this series is obsolete, and only Hubbell still manufactures 2-20 devices (for repair purposes).<ref>{{cite web|url=http://ecatalog.bryant-electric.com/ProductInformation/ViewCatalogNoPDF.aspx?Dest=bryant-electric.com/ecatalog/a.pdf&Page=2|title=Hubbell catalog, NEMA 2|format=PDF}}</ref>
 
===NEMA 3===
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===NEMA 5===
[[File:Domestic AC Type B USA.jpg|thumb|NEMA 5-15P plug and NEMA 5-15R receptacle (different scales, blade spacing is {{convert|0.5|in|mm|1}} for both.) Each receptacle also accepts an ungrounded plug, whether [[Electrical polarity|polarized or unpolarized]].|250x250px]][[File:American power socket.jpg|thumb|upright|Typical 5-15R residential receptacle]]
[[File:Electrical outlet with label.jpg|thumb|upright|5-20R T-slot receptacle mounted with the hole for the ground pin at the top. The neutral connection is the wider T-shaped slot on the right. ]]
All NEMA 5 devices are three-wire grounding devices (hot–neutral–ground) rated for 125&nbsp;V maximum, with the 5–155-15, 5-20 and 5-30 being grounded versions of the 1–151-15, 1-20 and 1-30, respectively. The addition is a {{convert|3/16|in|mm|1|adj=on}} diameter round or U-shaped ground pin, {{convert|1/8|in|mm|1|abbr=on}} longer than the power blades (so the device is grounded before the power is connected) and located from them by {{convert|1/4|in|mm|1|abbr=on}} edge-to-edge or {{convert|15/32|in|mm|1|abbr=on}} 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 {{convert|1/2|in|mm|1|abbr=on}} 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 {{convert|1|in|mm|1|abbr=on}} between power pins; 5-30 also has an L-shaped neutral blade.<ref>[http://lockingpowercords.com/topic/13-nema-locking-chart.aspx NEMA Locking Configuration Chart<!-- Bot generated title -->]</ref> These larger sizes are uncommon, as twist-locking plugs are generally used for high-current applications.
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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<ref>{{Citation |url = http://www.childoutletsafety.org/files/NEMA_TR_map_0726.pdf |title = Tamper-Resistant Receptacles — A Successful Adoption |access-date = 19 November 2013 |archive-url = https://web.archive.org/web/20131202225129/http://www.childoutletsafety.org/files/NEMA_TR_map_0726.pdf |archive-date = 2 December 2013 |url-status = dead }}</ref> and all of Canada, tamper-resistant receptacles are required in new residential construction {{as ofasof|November 2013|lc=y}}. These prevent contact by objects like keys or paper clips inserted into the socket.<ref>{{Citation |url = http://www.childoutletsafety.org/ |title = Child outlet safety |access-date = 21 January 2009 |archive-url = https://web.archive.org/web/20090122051010/http://www.childoutletsafety.org/ |archive-date = 22 January 2009 |url-status = dead }}</ref> 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.<ref>Drew Campbell ''Technical Film and Tv for Nontechnical People'', Skyhorse Publishing Inc., 2002 {{ISBN|1581159986}} Chapter 9</ref> (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)<ref name="tftv">{{cite book|last=Campbell|first=Drew|title=Technical Film and TV for Nontechnical People|publisher=Allworth|year=2002|page=133|isbn=1-58115-229-9|url=https://books.google.com/books?id=CARrSo742ycC|access-date=2010-02-16}}</ref> is called a "stinger".{{citation needed|date=November 2013}} Generally, [[lighting technician]]s use these extension cords to deliver power to lights rated at 2,000&nbsp;watts or less.<ref name="slth">{{cite book|last=Box|first=Harry C.|title=Set Lighting Technician's Handbook: Film Lighting Equipment, Practice, and Electrical Distribution|publisher=Focal|year=2003|edition=3rd|page=20|isbn=0-240-80495-3|url=https://books.google.com/books?id=EfUlyxSlBYMC|access-date=2010-02-16}}</ref>
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===NEMA 6===
All NEMA 6 devices are three-wire grounding devices (hot-hot-ground) used for 208 and 240&nbsp;V circuits and rated for 250&nbsp;V maximum, with the 6–156-15, 6-20 and 6-30 being grounding versions of the 2–152-15, 2-20 and 2-30, respectively. The 6-15 resembles the 5–155-15, but with collinear horizontal pins, spaced {{convert|23/32|in|mm|1|abbr=on}} center-to-center. The 20&nbsp;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&nbsp;A (and 5-50) receptacles look like bigger versions of the 5-15&nbsp;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.{{Citation needed|date = December 2013}}
NEMA 6 devices, while specified as 250&nbsp;V, may be used for either 208 or 240&nbsp;V circuits, generally depending on whether the building has a [[three-phase electric power|three-phase]] or [[split-phase electric power|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&nbsp;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 [[manual metal arc welding|arc welder]] also uses 6-50.<ref name="Lincoln">{{cite web |title=AC225 |url=https://www.lincolnelectric.com/assets/global/Products/K1170/e230.pdf |access-date=25 November 2019 |website=AC225 |publisher=Lincoln Electric}}</ref> Single-phase 6-50 is commonly used on farms for [[silo]] unloaders, and is used with a 6-gauge flexible power cord up to {{convert|200|ft|m|abbr=on}} long. The 6-50 receptacle charges electric vehicles at the same 32- or 40-ampere maximum from [[charging station]]s, on a short cord, as the more versatile 14–5014-50 with its fourth prong neutral not used currently for any electric vehicle charging purposes.<ref>{{Cite web |title=NEMA 6 50 vs 14 50 (Which Plug is Superior?) {{!}} |url=https://electriccarpledge.com/nema-6-50-vs-14-50/ |access-date=2023-06-21 |website=electriccarpledge.com |language=en-US}}</ref>
 
{{gallery|width=150 |height=150|align=center|lines=3
|File:Nema 6-15.svg|NEMA 6-15 (Green "U"-shaped contact is ground.)
|File:Silo - 50A power socket for silo unloader.jpg|NEMA 6-50 with dustproof flexible shroud, used on a farm [[silo]] unloader
}}
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All NEMA 14 devices offer two hots, a neutral, and a ground, allowing for both 120 and 240&nbsp;V when supplied by [[Split-phase electric power|split-phase power]], or 120 and 208&nbsp;V if the supply is [[three-phase electric power|three-phase]]. The 14-30 has a rating of 30&nbsp;A, and an L-shaped neutral blade. The 14-50 has a rating of 50&nbsp;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 park]]s, since they are used for "[[Shorepower|shore power]]" connections of larger [[recreational vehicle]]s. Also, it was formerly common to connect [[mobile home]]s to utility power via a 14-50 device. Newer applications include [[Tesla, Inc.|Tesla]]'s Mobile Connector for vehicle charging, which formally recommended the installation of a 14-50 receptacle for home use.<ref>{{cite web |title=TeslaMotors.com: Go Electric - Ready, Set, Charge |url=http://www.teslamotors.com/goelectric#charging |publisher=Tesla Motors, Inc. |access-date=7 June 2013 |url-status=dead |archive-url=https://web.archive.org/web/20130620090910/http://www.teslamotors.com/goelectric#charging |archive-date=20 June 2013 }}</ref> The 6-50 is a smaller size receptacle that charges at the same 32- or 40-ampere maximum from electric vehicle [[charging station]]s as this more versatile 14–5014-50 with its fourth prong neutral not used currently for any electric vehicle charging purposes.<ref name=":0">{{Cite web |date=June 24, 2021 |title=Home EV charging: How to know which plug type is right for you |url=https://www.enelxway.com/us/en/resources/blog/home-ev-charging-how-to-know-which-plug-type-is-right-for-you}}</ref>
 
{{gallery|width=150 |height=150|align=center|lines=3
|File:220sb.svg|NEMA 14-30 and 14-50 receptacles
|File:NEMA 14-30 Dryer Receptacle.jpg|NEMA 14-30 clothes dryer receptacle and plug
|File:NEMA 14-50 outlet.jpg|A NEMA 14-50 supplying 12&nbsp;[[kilowatts|kW]] (9.6&nbsp;kW sustained) on a 240&nbsp;V circuit to recharge an [[Electric vehicle|EV]]}}
 
===NEMA 15===
NEMA 15 are three-pole and ground connectors (phase A, phase B, phase C, ground) rated for 208&nbsp;V. Intended for delta three-phase circuits with ground and no neutral. The straight blades all carry one of the three phases.{{citation neededcn|date=October 2021}}
 
===NEMA 20===
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.{{citation neededcn|date=March 2021}}
 
===NEMA 21===
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.{{citation neededcn|date=March 2021}}
 
===NEMA 22===
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.{{citation neededcn|date=March 2021}}
 
===NEMA 23===
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.{{citation neededcn|date=March 2021}}
 
===NEMA 24===
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===NEMA TT-30===
[[File:NEMA TT-30.png|thumb|upright|NEMA TT-30 plug and receptacle. (The center hole on the receptacle is not a contact.)]]
The NEMA TT-30 (TT stands for [[travel trailer|Travel Trailer]]) connector is a 120&nbsp;V 30&nbsp;A [[recreational vehicle]] standard (hot-neutral-ground), also known as ''RV 30''. The TT-30R receptacle is commonly available in nearly all [[RV park]]s in the United States and Canada, and all but the largest RVs manufactured since the 1970s use this plug to connect to power feeds.{{citation neededcn|date=October 2023}}
 
The appearance of this plug is sometimes confused with a NEMA 10 connector, rated for 240&nbsp;V, but the NEMA TT-30 is a 120&nbsp;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.{{citation neededcn|date=October 2023}}
 
==Twist-locking connectors==
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==Additional safety features==
[[File:NEMA 5 correctly installed commercially.png|thumb|left|A North American NEMA-5 receptacle halfway through a corrective re-installation. The fluorescent green spacers, which firmly attach the receptacle to the metallic sub-structure, are made necessary by using {{convert|5/8|in|mm|abbr=on}} drywall instead of {{convert|1/2|in|mm|abbr=on}}, or by slightly -misplaced device box housings.]]
 
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.<ref>{{cite web|url=http://www.hubbell-wiring.com/Press/pdfs/HS127.pdf |title=Tamper Resistant Receptacles: The New Standard of Electrical Safety |publisher=Hubbell Wiring Systems |access-date=18 October 2009 |url-status=dead |archive-url=https://web.archive.org/web/20110712230338/http://www.hubbell-wiring.com/Press/pdfs/HS127.pdf |archive-date=12 July 2011 }}</ref>
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===Leak-current detection and interruption (LCDI) cordsets===
Damaged power cords of portable air conditioners have caused many electrical fires, and about 350 deaths per year.{{citation needed|date=October 2020}} To combat this, the 2017 NEC<ref name="EZ-pdh">{{cite web |title=2017-NEC-Significant-Code-Changes-Part-2 |url=https://cdn.ez-pdh.com/course-material/EE1002-2017-NEC-Significant-Code-Changes-Part-2.pdf |website=cdn.ez-pdh.com |publisher=EZ-pdh |access-date=18 October 2020}}</ref> 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 5–155-15, 5-20, 6–156-15, 6-20, or 6-30 plugs, depending on the air conditioner design, and are typically molded-on designs.
 
==Color code==
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However, although colors are not standardized by NEMA, some industries utilize colors for certain applications, following [[de facto standard]]s:
*A receptacle with a green dot is a so-called "hospital grade" device; The primary reason to use a hospital-grade receptacle at a patient bed location is to ensure that a receptacle with a greater contact tension is provided to minimize possibilities that an attachment plug supplying medical or life support equipment may be disconnected because the attachment plug slipped out of the receptacle. Also such devices are tested to survive harder use while limiting electrical leakage, compared to wiring devices intended for residential or commercial purposes.{{citation neededcn|date=October 2023}}
*Per UL Standard ANSI/UL 498, a receptacle (any color) with an orange triangle, is an [[isolated ground]] (IG) device, where the grounding pin of the receptacle is connected to ground independently of the frame of the receptacle and wiring outlet box. This is also a requirement of the National Electrical Code (NFPA 70), Article 406. While neither UL nor the CSA require the face of the receptacle to be a specific color, most IG receptacles are orange.<ref>{{cite web|url=https://www.nema.org/Standards/Pages/Application-Guide-for-Isolated-Ground-Wiring-Devices.aspx|title=Application Guide for Isolated Ground Wiring Devices|last=NEMA|website=www.nema.org|access-date=2016-03-26}}</ref>
*A blue receptacle may indicate built-in [[surge suppressor]]s.{{citation neededcn|date=October 2023}}
*A red receptacle may indicate a special-service outlet such as one connected to an [[Emergency power system|emergency standby power source]]. The ''Canadian Electrical Code'' requires that "essential" receptacles in hospitals, connected to emergency power systems, must be red.<ref>{{cite book |date=2015 |title=C22.1-15—Canadian Electrical Code, Part I: Safety Standard for Electrical Installations |publisher=Canadian Standards Association |edition=23rd |isbn=978-1-77139-718-6 |page=Rule 24–106(6) |no-pp=y}}</ref>
*At least one manufacturer makes a yellow receptacle, which identifies it as [[corrosion|corrosion-resistant]].{{citation neededcn|date=October 2023}}
 
==Break-away tabs==
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