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Joined: Jan 2006
Posts: 558
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Reno: I know of a mushroom farm around here that used that very same receptacle, in that very same type of box, WIRED the very same way ( to a 120 / 208 3-phase supply) to power these portable manure conveyors, BUT the really scary thing is the receptacles were OUTDOORS exposed to the elements.. not weatherproof in the least!
Did I get you worked up a bit more? LOL
O ya I think the darwin people do make reservations!
A.D
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Joined: Nov 2002
Posts: 456
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That pattern is used for 50A 120/240 appliances such ranges. Typically not wall ovens or cooktops, as they are hard wired. Dryers use a similar patter, but have an L shaped neutral.
FWIW, we've used the 14/50 and 14/30 for years in Canada, and TMK should be what was installed in mobile homes and condos/apartments in the USA, since they are supplied as sub-panels where ground and neutral must be separate.
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Joined: Dec 2000
Posts: 4,294
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The 15-50R is probably the closest, but that is for 250V, not 120/208. The NEMA 15-50R would be the correct choice for a 50 Amp 208 Volt 3Ø 3 Wire circuit as well.
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Joined: Jun 2006
Posts: 613
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renosteinke said: "What that means is that there is 240 between the 'ends' of the transformer, and only 120 between either end, and the center. This grounded center tap becomes the neutral.
Since the transformer is center tapped, the "120" from either half is exactly out of time with the 120 from the other half."
Reno:
The last thing you say in your explanation is the two Hot conductors are out of time. Do you mean out of phase? I think they are in phase. or do you mean they are vectoraly opposed? I would agree with that.
A scope across the 2 120 volts of a single phase transformer will show the voltage rise and fall in phase. both potentials are equal and in phase. The vector sums are opposite. An in balance load from center to A or center to B would add to zero in the same time.
The receptacle looks like a 14-50R with the x and y transposed as for a plug in the drawing.
It has never been allowed to use the neutral to bond an appliance here in Canuk land and many a US citizen has had to change the cord on their appliances when emigrating. I understand that in the project to harmonize electrical standards in North America that the US removed the ok to bond with the neutral and Canadians gave up the requirement for fuse protecting each element and the 120 volt outlets on ranges disappeared with it too.
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Joined: Jan 2005
Posts: 5,445 Likes: 3
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I did not want to use the term 'phase,' as both hots are derived from the same phase of the PoCo feed. I suppose you could say that they were 180 degrees out of phase ... but aren't we making a distinction without a difference.
What dose matter is that everyone understand that the voltages, at the same instant, are exactly the same ... and exactly opposite each other. If one is +120, the other is -120 ...etc. They have to be, as they are 'sections' of the same impulse from the primary side of the transformer.
BTW, I wondered what happened to those receptacles!
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Joined: Aug 2001
Posts: 7,520
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It's probably just as well we don't use this sort of configuration in Britain, judging by the mess that some people can make with a simple 3-wire (hot/neutral/ground) hookup.
Then again, if some of the past stories on ECN about range/dryer hookups are anything to go by, simply having the system around probably doesn't help the uninitiated either -- 4-wire cords with neutral-ground bond still in place on the appliance, etc.
We do have some 1-ph 3-wire local distribution in the U.K., but it's 240/480V, with a normal residential supply still being just 2-wires tapped from neutral and one "outer," so the average person wouldn't know about it anyway.
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Joined: Aug 2001
Posts: 7,520
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I have a list of (some) standard NEMA plug/receptacles on my Photobucket page: NEMA Guide I just noticed that there's a misprint on that chart. Row 14 is shown as 3-ph 600V when it should be 1-ph 125/250V.
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Joined: Jun 2006
Posts: 613
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Reno
14-50r is the current 125/250 volt configuration for domestic ranges in Canada and are typically installed in 120/240 and 120/208 circuits fed from 8/3.
I like the +120 and -120 volt to explain the single phase transformer. I can see you clearly do understand it just caught the time thing and got onto that.
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Joined: Jun 2007
Posts: 7
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Since the outlet is labeled 3 phase; what you may be looking at is a 240 volt, 3 phase, Delta, 4 wire (center tap of one winding is neutral). I just ran into this a couple weeks ago. I agree; this is wrong receptacle for this application. What you may have is: Assuming G is neutral: 1. X to W = 240V 2. W to Y = 240V 3. X to Y = 240V 4. W to G = 120V 5. Then either X or Y to G = 120V 6. Then the other one in #5 above to G = 208V (wild leg) Look at this website for more http://en.wikipedia.org/wiki/Split_phase
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Joined: Sep 2003
Posts: 650
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The meter was reading 120V between the W pin and the ground pin, and the box is labeled 3 phase.
My guess is that this is a 208/120 wye service, and that from any of the X, Y, or W pins to ground you would see 120V, and from any X,Y, W pair 208V.
This is not necessarily a code violation. The receptacle is rated for the voltage and current. As I recall, code does not require that _standard_ receptacle patterns be used, and the 'non-interchangeable' requirement is by premises. If NEMA 14-30 receptacles are used exclusively for 3 phase receptacles at a given plant, and never also used as single phase receptacles, then this isn't a violation...even though the _standard_ would limit 14-30 receptacles to having a grounded neutral on the W pin, and say that you should use NEMA 15-30 receptacles for this application. See 406.3(F)
IMHO sticking with standard receptacle patterns is a very good design practise.
-Jon
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Posts: 57
Joined: August 2003
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