Talk:NEMA connector

Upside down 5-15

I'd question the rationale in the paragraph:

"It is customary in the U.S. to install 5-15 and 5-20 receptacles with the ground pin down. This is to ensure that a loose cord remains grounded even if its two prongs no longer contact the line voltage. As a safety measure, however, many receptacles are now installed "upside down" (with the ground pin up.) In the case of a metal object falling onto a dislodged cord, the foreign object is less likely to straddle two conductors, possibly avoiding a short circuit."

As I understand the practice, the goal is to make it less likely that a metal object falling between the plug and socket will touch the live blade without first touching the ground pin. A short circuit, which would trip the circuit breaker, is a more desirable outcome than a live bare metal object that someone might come in contact with. --agr 11:28, 14 June 2006 (UTC)

In every diagram of NEMA connectors I've seen, the ground pin is on the top. The NEMA standard document (available in PDF format here: http://www.nema.org/stds/wd6.cfm) shows the ground pin on top. Leviton has a nice diagram of all the pin configurations showing ground pins on top here: http://www.leviton.com/sections/techsupp/nema.htm

I agree that the reason for having the ground pin on top is to prevent conductive objects dropped between the plug and receptacle from contacting a live pin. The loose cord explanation for having the ground pin on the bottom doesn't entirely make sense, since the ground pin's primary purpose is to ground any internal shorts and trip the circuit breaker. With the plug loose enough so the live pins no longer contact, there will be no reason to protect against internal shorts, since there will be no internal voltage. The ground pin is longer so it is the first pin to contact, so any internal shorts will go directly to ground upon insertion. I believe, in all seriousness, that the reason it is customary in the U.S. to install these receptacles with the ground pin down is because people like to see the "smiley face". I don't know if the NEC specifies one way or the other. --Rich 02:35, 20 July 2006 (UTC)

I think a part of the reason the connectors are installed "ground pin down" is the mnemonic attraction: the earthed safety conductor faces the earth. I also wonder if there was a hang-over effect from the earlier ungrounded recepticles. That is, was it conventional to install these with neutral leftwards and hot rightwards? That would certainly explain keeping that convention when 5-15 connectors came around.

Atlant 11:35, 20 July 2006 (UTC)

If there is a reason for installing them ground down, I think it must be anthropomorphic. They look like faces. I'll admit that's why I prefer to install them that way. Rich is correct that the NEC does not specify.Yak99 00:10, 23 April 2007 (UTC)yak99

Could it be that the reason for the grounding pin down is that most (at least the ones that I have seen) is that the cord would be sticking up if the pin/hole was up instead of down. I looked at the cord for my computer and the cord comes out of the bottom of the plug if the grounding pin is at the bottom. Aa456 05:04, 15 October 2007 (UTC)

I'm not sure why, but it's common (at least in the Midwest) see the ground down in residential wiring, and the ground up in commercial wiring. Jayscore (talk) 02:05, 10 December 2007 (UTC)

I think the reason may be ergonomic. Try grabbing a plug with the ground pin up and typically it's not as comfortable as with the ground pin down and your thumb on the (typically) flat top of the plug.154.5.124.154 (talk) 20:37, 21 July 2009 (UTC)

The article says that it is customary to install these with the ground pin down, but all the pictures show the ground pin up. Either the pictures or the text ought to be changed. —Preceding unsigned comment added by 67.142.162.28 (talk) 23:28, 11 July 2010 (UTC)

6-20

"The 20 A plug has the neutral pin rotated 90 degrees, and the 6-20R receptacle may have a T-shaped hot hole, to accept both 6-15P and 6-20P plugs"

i didn't think american 240V wiring had a neutral so both holes are hot. Plugwash 02:13, 24 June 2006 (UTC)

Nearly all wiring has a neutral, without neutral, there is nothing reliable to refrence the 240 volts to. 48v 03:40, 11 July 2006 (UTC)

Ok i could have phrased that better, in US wiring 240V basically means both hots so in a socket that supplies only 240V (e.g. the nema 6 series we are discussing here) there won't be a neutral. Plugwash 20:43, 11 July 2006 (UTC)

So I presume that by 'both hots' you mean that there are two seperate 110 volt legs which makes plenty of sense. My question is this: what are the 110v legs refrenced to if there is not neutral?

There is a neutral in the supply system just not at the socket, relative to neutral the two hots are the same magnitude but 180 degrees out of phase with each other, so equipment that needs 120V is connected between one hot and neutral (and uses a 1- or 5- series plug), equipment that needs 240V is connected between both hots and not connected to the neutral (and uses a 2- or 6- series plug) equipment that needs both (e.g. cookers, clothes driers etc) is connected to both the hots and the neutral (and uses a 10- or 14 series plug). Plugwash 23:24, 11 July 2006 (UTC)

Ahh. That makes much more sense. Thanks for explaining! 48v 23:45, 11 July 2006 (UTC)

Actually, that's not entirely accurate. There's no neutral in a 240V circuit. Two points of confusion: (1) the 240V are not relative to anything other than _each other_: they are 240V (RMS) apart from each other. (2) There is, however, a ground that is earth potential: one of the "hot" conductors is 120V "above" the ground and the other is 120V "below". The ground is not used in an ordinary 240V circuit except for safety. Some circuits, like a typical electric clothes dryer, require both 120V and 240V circuits; they will add a neutral line. To get their 240V circuit, they use only the two hot wires; to get their 120V, they use one of the hots and the neutral. So what's the difference between neutral and ground, you may ask? That's actually a good question, as the neutral is connected to the ground back at the main panel. The difference is that neutral is designed to carry the return current in a circuit, whereas the ground is not designed to carry current. In fact, in some places (unfinished basements, bathrooms, etc.) you are required to install a GFCI breaker, which will break the circuit as soon as it senses any current on the ground line. Fool4jesus (talk) 14:52, 26 February 2012 (UTC)

240v could easily be live-to-neutral in a commercial or industrial environment. This explanation is beyond the purview of this talk page, but I suggest looking at mains distribution articles (and wye and delta). 69.205.240.64 (talk) —Preceding undated comment added 02:33, 4 April 2011 (UTC).

Separate?

Many of these sections could be expanded into their own articles including common useages, regions, histories etc. Should we consider seperating this article into many smaller articles which would be easier to expand? 48v 03:40, 11 July 2006 (UTC)

The article isn't really big enough to need it yet but when it becomes so just split out long sections and replace them with a shorter summary and a main article link. Plugwash 21:05, 11 July 2006 (UTC)

Long winded

My word, this article does babble on. One picture would truly be worth 1000 words - we could then condense the text to "NEMA connectors use different combinations of pin widths, orientation, and dimensions to furnish connectors that are unique to a particular voltage, current capacity, and grounding system" or words to that effect. Put on my to-do list, I'm sure I can redraw from CEC and NEMA to save a ton of space here. --Wtshymanski 17:46, 21 July 2006 (UTC)

Hear, hear! [But I can't help noticing that it's been nine months since you wrote that. What's keepin' ya?  :-) ] 24.6.66.193 19:23, 18 April 2007 (UTC)

Busted. But I've been fighting off the kibibytes and remodelling a bathroom...it's been a busy year. --Wtshymanski 21:46, 18 April 2007 (UTC)

Just remember: Black goes to black, white to white, and always use GFCIs ;-).

Atlant 12:12, 19 April 2007 (UTC)

Hear, hear! DIAGRAM PLEASE! Here's an example of a good NEMA diagram. I'd add one myself but someone will probably beat me up with a copyright bat. --Goodmanj (talk) 20:52, 16 June 2009 (UTC)

nema 2 series dangerous.

it was claimed in domestic ac power plugs and sockets in content now moved to unusual and obsolete plugs and sockets that the 2- series connectors were dangerous. I can't see any danger in using them with 240V class 2 equipment other than the slight risk of connecting a 240V appliance to 120V (which would most likely just result in the appliance not working) would anyone like to comment on this? Plugwash 17:20, 15 September 2006 (UTC)

Are 5-15 connectors allowed on 20A circuits in the USA

if they are why do people bother with the 5-20 T slot in kitchens?

if they are not why is the 5-20 T slot (which also allows a normal domestic plug to be connected to a 20A circuit) allowed? Plugwash 11:51, 15 September 2006 (UTC)

Yes, 5-15 receptacles are allowed on 20 amp circuits. For example, most North American GFCI outlets use 5-15 pinning but are rated at "20A pass-through".

I'm not sure I understand the second half of your question, but I'll make some observations: You'd certainly want kitchen convenience outlets to accommodate 5-15 plugs because most of the loads in the North American world have that connector, even pretty hefty electric cooking loads like table-top broilers and big coffee makers. On the other hand, accommodating a 5-20 plug is a nice feature and cues the user that the circuit is a 20A circuit, even if there are very few domestic loads with a 5-20 plug. (I've only seen 5-20 plugs in industrial environments.) If I were to rewire my kitchen again, I'd probably install 5-20R T-slots for that reason.

Atlant 13:45, 15 September 2006 (UTC)

5-15 receptacles are allowed on 20A circuits as long as there is more than one receptacle on the circuit. In some jurisdictions, a 5-15 duplex counts as more than one receptacle, in others, not. Where I live, if you have just one receptacle on a circuit, it has to be a "single" receptacle, and it has to be a 5-20R. A 5-20R on a 15A circuit is not allowed anywhere.Yak99 00:14, 23 April 2007 (UTC)yak99

How are 5-20R receptacles able to carry more current than a 5-15R given that the dimensions of the "hot" blade (if im reading the article correctly) are identical ?

Type	Designation	Introduction	Neutral Width	Hot blade Width	Remarks
2 pin unpolorised	NEMA 1-15	19??	6.35 mm	6.35 mm	1/4 inch neutral blade
2 pin polorised	NEMA 1-15	1948	7.938 mm	6.35 mm	5/16 inch neutral blade
3 pin grounded	NEMA 5–15	1927 (mandatory 1962)	6.35 mm	6.35 mm	Only polorised with 3 pin plugs
3 pin polorised	NEMA 5–15	1948 (mandatory 1974)	7.938 mm	6.35 mm
3 pin 20 Amp	NEMA 5–20	19??	?	6.35 mm	Most recent standard -Transition ongoing.

82.132.139.217 (talk) 18:55, 22 December 2011 (UTC)

why do air conditioners get special treatment?

are they in some way more dangerous than other large portable loads (such as portable heaters) or is it just a case of them gaining more attention because there are in more common use. —The preceding unsigned comment was added by Plugwash (talk • contribs) .

Probably because they're inherently wet during operation (from condensate) and often wet from precipitation.

Atlant 23:04, 15 September 2006 (UTC)

Weird image...

Is there a reason the GFCI pic is a line drawing? I thought we only used them for sex acts? 68.39.174.238 20:21, 10 October 2006 (UTC)

Feel free to replace it with a photo provided the photo shows all the relavent features reasonablly well. Plugwash 20:00, 11 October 2006 (UTC)

Links to Diagrams

Given that the NEMA standard is available for free download, are the other links necessary? (Argument for: the NEMA link isn't a direct link; it requires that you agree with a simple license.)

Jordan Brown 08:13, 26 February 2007 (UTC)

Furthermore, it's a very large file that contains painstakingly intricate blueprint-style drawings intended for product designers. Simple, straightforward diagrams aimed at ordinary people would be preferable, such as the ones found here:

http://www.frentzandsons.com/Hardware%20References/twistlockplugandreceptacle.htm

http://www.frentzandsons.com/Hardware%20References/plugandreceptacleconfiguratio.htm

24.6.66.193 05:01, 21 April 2007 (UTC)

Bob Stein - VisiBone (talk) 18:00, 4 September 2009 (UTC) — I agree with the need for a comprehensive, basic diagram for users. Thanks, Jordan, for yours. Here's another great diagram that finally cleared up a lot of my confusion.

http://www.sheffield-pottery.com/Articles.asp?ID=127 (article with diagram)

http://www.sheffield-pottery.com/v/vspfiles/assets/images/nemaconnectors.jpg (diagram)

Here's Goodmanj's good diagram, copied from above (though missing NEMA 10):

http://www.nooutage.com/nema_configurations.htm (diagram and nomenclature)

like, NEMA10, eh???

"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."

Um, so were they ever permitted? or were they not? It's got to be one or the other, eh? --carlb 05:24, 6 March 2007 (UTC)

FWIW, I don't remember ever seeing a NEMA 10 plug or receptacle (Montreal, QC). I remember from around the mid-late 1980's when the landlord of the apartment that I was living in did some electrical upgrades and one of them was adding a NEMA 14-50 plug/receptacle for the stove which was previously hard wired into the wall. --Aa456 00:33, 24 September 2007 (UTC)

terminology

Perhaps a brief discussion about the meaning of words like "plug" "socket" "receptacle" "connector" etc. It seems different words are being used to describe similar things, and the same word used to describe different things. So, first off, these words need to be defined, and a standard usage needs to be adopted so as to not be so confusing. 143.127.3.10 21:08, 5 June 2007 (UTC)

Globalize tag?

In what way does this need a "worldwide view". As an article about a specific electrical code element, I fail to see how that tag is relevant. The intro notes that these plugs are used in countries other than the US. Pjbflynn 00:22, 19 June 2007 (UTC)

The beginning mentions other countries that use it, but the rest of the article only discusses the US and Canada.--Jorfer 23:55, 19 June 2007 (UTC)

Frequency?

Shouldn't it say something somewhere about how many hertz these plugs are generally used with? Especially since this is not the same as other plugs (I'm pretty sure NEMA connector are usually used with 60 hertz, in contrast with the 50 hertz of European models). I don't feel that I really know enough about this though to edit the article. 209.176.79.34 (talk) 18:04, 8 January 2008 (UTC)

Whoops, wasn't signed in. The above is me. Crito2161 (talk) 18:05, 8 January 2008 (UTC)

I wouldn't argue too strenuously, but my feeling is that it doesn't need to be in this article. The frequencies used in different markets are discussed in mains electricity, which is linked at the top of this article. Here is my basic argument against inclusion: For each connector type, we talk about the voltage and current it's used for. We do this for two reasons: (1) The connectors are deliberately different, so that you cannot connect devices in a hazardous way. Plugging a 120 V appliance into a 240 outlet would be hazardous, and a home in North America (for example) can have both 120 V and 240 V outlets, so preventing this confusion is important. (2) The connectors actually have to be designed differently, depending on the current they handle. The 50 A receptacle has to be made more robust than a 15 A receptacle, so that it doesn't catch fire. But frequency has neither of these concerns. If you're in a 60 Hz country, you're getting 60 Hz electricity no matter what outlet you plug into. And any 60 Hz receptacle would be physically capable of handling 50 Hz power, or vice-versa—we're not talking about RF or microwave frequencies where it's a critical design parameter. So basically, the situation is that NEMA connectors are used in the same places that the electricity is 60 Hz, but neither fact has anything directly to do with the other. -- Coneslayer (talk) 18:56, 8 January 2008 (UTC)

In Canadian homes the only 220 or 240 V outlets are those for the electric laundry dryer and the kitchen stove (range) which both require a spcial oulet (not the same for them both) so the possibilety to plug a 110 V appliance in a 240 V outlet are all but nill. Peter Horn 20:30, 10 June 2009 (UTC)

Safety comparison

Could somebody who understands this stuff include a safety features section similar to a Schuko#Safety_features and Europlug#Design_considerations? And compare the NEMA std with Schuko, europlug and others? --Jirka6 (talk) 16:54, 31 March 2008 (UTC)

Afaict they don't really have any, if you partially insert an american plug you can easilly touch the live pins. I guess the americans think (rightly or wrongly) that the lower voltage means such features are not required. Plugwash (talk) 18:23, 22 January 2009 (UTC)

Compatibility

Can American NEMA plugs be plugged int Japanese outlets (and vice versa) & the appliance run without any problems? 68.14.147.200 (talk) 04:49, 10 May 2008 (UTC)

Afaict (i'm not american or japanese so this is from information I have picked up on line) the answer is usually yes but there are a few potential issues

1: a lot of japanese sockets will only accept the plugs with two narrow blades, not the ones with a wider blade used for polarisation:

2: the japanese voltage is a bit lower which may cause problems for some applicances

3: half of japan uses 50hz, some american appliances may not like the lower frequency

4: if you are planning to sell something the safety standards are different which could potentially bring up legal issues. This isn't really an issue if it's only for your own use though.

-- Plugwash (talk) 18:40, 22 January 2009 (UTC)

Historicals

Lots of practical info here, but very little historical data or other social/soft stuff. Anyone care to add it in? —Preceding unsigned comment added by 67.81.164.24 (talk) 02:53, 24 October 2008 (UTC)

(years later) A perennial problem. Everybody has the current catalog and code book, nobody has any historical documents. It's like everythign was given to us by flying saucer. --Wtshymanski (talk) 16:39, 19 January 2012 (UTC)

Ground fault circuit interrupter (GFCI) receptacles

Re NEMA connector#Ground fault circuit interrupter (GFCI) receptacles^{[citation needed]}. The requirement(s) for their use, especially in bathrooms, is (are) to be found in the national building codes of Canada and the US, in the provincial and state building codes as well as in the city and municipal building codes. The rub is that these codes do not appear to be available for a gratis consultation but must be ordered on line for the payment of serious money. Try to google National Building Code of Canada & see what it gets you. have fun... Peter Horn 20:44, 10 June 2009 (UTC)

Python?

During my searching, I've seen "python", "python plug" and "python connector" mentioned multiple times. Are these NEMA connectors also called "python plugs"? That seemed kinda odd to me. 188.192.118.79 (talk) 03:23, 12 February 2010 (UTC)

Python is a brand name for a series of plugs and connectors (the female version of a plug you'd find on an extension cord for example) manufactured by Leviton. You attach them to the cord yourself. The name "python" probably comes from that they hinge open like clams and the two screws that hold the thing together look like fangs. --Marc Kupper|talk 06:59, 9 October 2010 (UTC)

NEMA 2-20 fitting NEMA 5-20 & 6-20?

I don't think that's correct. The pin orientation would allow it if the spacing was the same, but according to the standard, the pins in a NEMA 2-20 connector are farther apart (.844 in center to center) than the those in a NEMA 5-20 or NEMA 6-20 (.609 in center to center). Carolina wren (talk) 06:29, 28 May 2010 (UTC)

1-15 Plug Picture

A_plug.jpg

The current picture for the 1-15 plug, A_plug.jpg (at right) - which lists itself as a "Type A" connector and not a NEMA 1-15P, does not appear to be a NEMA1-15P. I believe that NEMA plugs in this series all have circular holes in them to be grabbed by the socket. Can someone confirm? tonsofpcs _(Talk) 02:41, 4 April 2011 (UTC)

Why do you believe that? The NEMA standard WD 1 is availble for free download. It says the holes in the ends of the blades are optional, but if present, have to meet specified dimensions. You can't have a receptacle that relies on an optional feature of a plug. --Wtshymanski (talk) 02:50, 4 April 2011 (UTC)

dead link

http://www.cpsc.gov/CPSCPUB/PUBS/099.pdf should be updated (this is the correct link) for the GFCI fct sheet. All I see is reflist2 and cant change it. —Preceding unsigned comment added by 198.169.188.226 (talk) 13:14, 20 May 2011 (UTC)

Y Done Updated in the "Special safety features" section [1] --Tothwolf (talk) 02:55, 21 May 2011 (UTC)