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Posted By: renosteinke Receptacles: Check your assumptions! - 05/20/07 04:43 PM
Norcal sent in this pic of a receptacle he encountered:


[Linked Image]


This is the NEMA pattern used here:


[Linked Image]


Looks like 120v between neutral and ground .... gee, I wonder how that could have happened?

Remember this, the next time some fool insists that the neutral can't kill you. Or, wants to use the conduit as his 'neutral.' Or thinks bonding the neutral and ground (away from the main panel) is no big thing....

Posted By: 32VAC Re: Receptacles: Check your assumptions! - 05/20/07 10:05 PM
Just trying to work out the wiring of the socket:

Is it a 3 pole 3 wire NEMA 14-50 configuration that can supply either 240 or 120 volts at maximum 50 amps? (assuming the neutral is counted as a pole?)

I'm assuming that when wired correctly:
X-G=240V
Y-G=240V
X-Y=240V
X-W=120V
Y-W=120V
W-G=0V

Is it normal practice to run the 2 "hot" wires, a neutral & an earth from the board to the socket?
Posted By: renosteinke Re: Receptacles: Check your assumptions! - 05/20/07 11:08 PM
32, in the USA we create 240 by 'center tapping' a single transformer, and grounding that center tap.
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.

So, for this plug ... the X and Y are for your 'hot' wires. There should always be 240 between then.
The "W" is for 'white' ... the color of the neutral wire. Either 'hot' wire should read 120 to this point.

The "G" is the 'ground' wire, a separate conductor that is kept separate from all other conductors until you reach the main disconnect at the service entrance. Only at that point are the neutral and ground wire connected.

The neutral is used for carrying current all the time; the ground is used only if something breaks- and then only so that the breaker can trip.

There ought to be very, very little voltage measured between the neutral and ground. More than one or two volts, and you have an issue that you need to look into. Most often, these voltage reading are 'ghost' readings, caused by a 'dead' wire running next to a 'hot' wire.

The pic shows 120 between the neutral and ground. There are several things that might cause this ... all of them bad.
The neutral may be open. If that is the case, every neutral 'downstream' of the open connection is now a 'hot,' just waiting for a chance to zap you.
Someone may have mis-wired the receptacle, and one of the 'hot' sections is really the neutral. This means that any 120 load on this circuit will be treated to 240.
The receptacle might be used on the wrong type of system. For example, if used on a three phase system, with three 'hots' and no neutral. If so, again, any 120 load will be exposed to 208 volts.


Finally ... and this is the possibility that is most dangerous ... it is possible some clever sort downstream decided to use the pipe as a 'neutral' ... and the pipe is not bonded all the way back to the panel. If that is the case, the pipe is now 'hot,' just waiting to kill someone.
Posted By: 32VAC Re: Receptacles: Check your assumptions! - 05/21/07 12:14 AM
Is this pattern socket used for large items like stoves, ovens & clothes driers?

Posted By: renosteinke Re: Receptacles: Check your assumptions! - 05/21/07 12:33 AM
Good point, 32 .... I think this is the new pattern for stoves. (Water heaters are different).

In that case, the ground and the neutral are almost sure to be bonded at the appliance. Not correct, but still likely. If the ground path were intact, this would result in a dead short as soon as the thing was plugged in. If the ground path were not intact, the stove case would become "hot".
Posted By: NORCAL Re: Receptacles: Check your assumptions! - 05/21/07 12:45 AM
If you notice the "3 phase" symbol on the corner of the cover its being used as a 240 Volt welder receptacle.
Hey '32, in case you're interested, I have a list of (some) standard NEMA plug/receptacles on my Photobucket page:

NEMA Guide

The one in this photo is the 14-50R, 3-wire w/ Ground configuration, as you already pointed out. If you want to see the other two pages, let me know.

Ian A.
Posted By: renosteinke Re: Receptacles: Check your assumptions! - 05/21/07 01:08 AM
Thanks, Norcal. I had missed that marking ... A range recep used for three phase ... now I'm really getting worked up!

I wonder if the folks at DarwinAwards let you make reservations?
Posted By: EV607797 Re: Receptacles: Check your assumptions! - 05/21/07 04:29 AM
32V:

Here in the US, residential electric hot water heaters are hard-wired using a 30 amp, 240 volt circuit. There is no plug/cord connection required. It's just two wires (one from each end of the transformer to derive 240 volts) and a ground (or earth) wire. In some juridictions, a disconnect switch might be required within sight of the water heater. Commercial installations can vary greatly, but are usually three-phase services.

Electric furnaces may require multiple circuits or simply use just one large circuit. These too are wired directly, though there may be a requirement for a disconnect switch to be located within sight if the circuit breaker(s) feeding the unit are not within sight. We do have some exceptions where padlock attachments for these breakers are considered an alternative to a separate disconnect at the furnace. In my home, the furnace is fed by a single 80 amp, 240 volt breaker with a padlock attachment in the main panel.

Outdoor air condintioning compressor units or heat pumps always require a disconnect switch within sight, but like water heaters, usually only require a 2-wire 240 volt circuit that is hard-wired. These can range from 20 to 60 amp loads, depending upon the size of the units.

Electric stoves that incorporate the cook top and oven in one appliance, (referred to as ranges in the US) utilize a NEMA 14-50 receptacle, or "socket".

When a separate electric cook top and oven are installed, they are generally hard-wired with no plug/socket connection. Some local codes may require these installations to be done differently.

Electric clothes dryers, the current requirement is for a NEMA 14-30 receptacle (socket) and matching cord. Dryers are always required to be plug (socket) and cord connected since they are portable appliances.

There was a time when the "earth" or "ground" wire and the "neutral" were permitted to use the same wire, resulting in just a three-wire connection for these appliances. This lasted for at least 50 years and I really don't know why it was deemed to be dangerous all of a sudden.

Electric ranges and dryers have certain components, like clocks, lights and motors that operate on 120 volts. For this reason, the new standards require that an insulated neutral wire be provided to these appliances.

Sharing the ground (earth) and neutral for minor 120 volt requirements is no longer permitted.
Posted By: BrianP Re: Receptacles: Check your assumptions! - 05/22/07 07:44 PM
This is a 120/208 Y at 50A? I'm looking at the NEMA patterns, and I don't see any for this. The 15-50R is probably the closest, but that is for 250V, not 120/208.
Posted By: Rewired Re: Receptacles: Check your assumptions! - 05/22/07 10:16 PM
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
Posted By: classicsat Re: Receptacles: Check your assumptions! - 05/22/07 10:50 PM
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.
Posted By: electure Re: Receptacles: Check your assumptions! - 05/23/07 12:26 AM
Quote
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.

Posted By: mikesh Re: Receptacles: Check your assumptions! - 05/24/07 04:43 PM
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.

Posted By: renosteinke Re: Receptacles: Check your assumptions! - 05/24/07 07:57 PM
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!
Posted By: pauluk Re: Receptacles: Check your assumptions! - 05/26/07 12:31 PM
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.

Posted By: pauluk Re: Receptacles: Check your assumptions! - 05/28/07 12:19 PM
Originally Posted by Theelectrikid
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.
Posted By: mikesh Re: Receptacles: Check your assumptions! - 05/29/07 04:37 PM
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.
Posted By: testguy Re: Receptacles: Check your assumptions! - 06/14/07 03:22 PM
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
Posted By: winnie Re: Receptacles: Check your assumptions! - 06/15/07 02:16 PM
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
Posted By: BrianP Re: Receptacles: Check your assumptions! - 06/15/07 03:13 PM
Take a look at this post showing the panel that feeds this receptacle: https://www.electrical-contractor.n...showflat/Number/164033/page/1#Post164033

It sounds like this probably is a 240V delta.
Posted By: NORCAL Re: Receptacles: Check your assumptions! - 06/16/07 12:21 AM
It is 240 Volt 3 phase......
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