50A single phase power connection

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JStan

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I am attempting to hook up a RV power connection plug from a three phase source. there is no neutral
wire running to the box. I have 208 between phases and 120 from each phase to ground.
The I am using # 6 wire for the L1 and L2, but the ground wire is only a # 12.
Is this ground wire big enough, and do I jumper the ground to the neutral on the plug?
Do I have the correct receptacle?
 
There is no neutral so there is no way to get 110 volts. You cannot used the ground as the neutral, this is illegal and very dangerous.
 
You need to run a neutral from the source to be code compliant. For 50 amp RV service, you should have two hot lines, a neutral, and a safety ground wired to a NEMA 14-50R outlet.
 
Dutch is correct however there are two different types of three phase sources of power, delta and wye. The wye has a neutral but the delta does not have a neutral.
 
Agree with Seilerbird. If you have a delta-configuration 3-phase (no neutral), you cannot supply a 50A RV outlet unless you run a neutral wire from the power source to the RV outlet.  You cannot use the ground, even if the wire is large enough (and #12 is NOT large enough anyway).

The RV expects 240v between L1 & L2 and 120v between L1-Neutral and L2-Neutral, plus a Ground as well.  Depending on the amp load in the two hot legs, the neutral may have to carry as much as 50A, so #12 wouldn't cut it anyway.
 
Tell us more about what you are trying to do and why, also what sort of RV is it.  There may be creative work around here.  I am thinking maybe a 208V to 120V lighting transformer feeding 50 amp 120V into a 120/240V 50 amp RV outlet, this would only supply 120V RV items at half the total watts of a normal 50 amp 120/240V RV hookup, but still more than a 120V 30 amp rv hookup, and should work if you have no 240V appliances onboard.

perhaps something similar to this https://www.ebay.com/itm/SQAURE-D-15T85HIS-U-15KVA-208Pri-208-120Sec-USED/282145940399
 
If you have 208 volts between the phases....A to B, A to C, and B to C, they you have a WYE connected output from the transformer that is feeding the box.  If this is the configuration, there SHOULD be a neutral wire associated with that output from the transformer feeding the box.  The actual neutral wire may not be in the box, but that may be because the box was originally used to feed a 3 phase WYE connected motor.  But, if the secondary (the leads that should be marked a, b, and c) of that transformer are in fact 208 volts from phase to phase, it is a WYE connection.  And if you are unfamiliar with electrical transformers or electrical in general, hire a qualified Electrician that knows the transformer configurations and how to hook things up. 
 
Why is it so hard for members to reply. It would be so helpful to know if the OP was helped.
To all members, please get back into your post and let us know if we were able to help you.
 
Rene T said:
Why is it so hard for members to reply. It would be so helpful to know if the OP was helped.
To all members, please get back into your post and let us know if we were able to help you.
:)) :)) :))


Those one post wonders seem to never come back especially if they don't get the answer they were looking for.
They fail to understand that we are looking out for their best interests and trying to keep them safe.

Failing to update us not only keeps us wondering what happened but is also doesn't help anyone else that has the same problem
or question and was hoping for an solution to their problem.

Is it time to attach a note when someone registers like:  IF you post a question and replies are received you are kindly asked
to reply whether or not it helped you.  Because this is an active forum a reply within 24-48 is requested if at all possible.
Your consideration is much appreciated - we hope you understand the benefit to others it can provide.
 
Ground (earth) and Neutral are the same electrical points.

Neutral and earth are connected together at the point of power generation... and at the output of each transformer in a transmission system.
Neutral and earth are also connected together at the breaker panel in a typical home installation.

https://electronics.stackexchange.com/questions/185028/what-is-the-difference-between-neutral-and-ground

 
TonyDtorch said:
Ground (earth) and Neutral are the same electrical points.

Neutral and earth are connected together at the point of power generation... and at the output of each transformer in a transmission system.
Neutral and earth are also connected together at the breaker panel in a typical home installation.

https://electronics.stackexchange.com/questions/185028/what-is-the-difference-between-neutral-and-ground

While your point is well taken, and technically correct, it would not apply to the OP's situation.  BONDING of the neutral and ground conductors is allowed only in the MAIN electrical panel in a residential service.

there are VERY GOOD REASONS that the NEC does not allow the ground conductor be used as a neutral. 
 
xrated said:
If you have 208 volts between the phases....A to B, A to C, and B to C, they you have a WYE connected output from the transformer that is feeding the box.  If this is the configuration, there SHOULD be a neutral wire associated with that output from the transformer feeding the box.  The actual neutral wire may not be in the box, but that may be because the box was originally used to feed a 3 phase WYE connected motor.  But, if the secondary (the leads that should be marked a, b, and c) of that transformer are in fact 208 volts from phase to phase, it is a WYE connection.  And if you are unfamiliar with electrical transformers or electrical in general, hire a qualified Electrician that knows the transformer configurations and how to hook things up.

Could you clarify the underlined remark?  It sounds like you repeated something incorrectly (from the first sentence).  It all sounds correct though, except...that line highlighted.
 
The primary side of the transformer that is fed from whatever power company/utility, would likely be marked as phase A, phase B, and phase C (Capital letters).  The secondary side of the transformer, the side that the OP says that there is 208VAC phase to phase, would likely be marked...phase a, phase b, and phase c......all small letters.  I've seen different markings on transformers also.  The letter "H", as in H1, H2, and H3 for the primary side of the transformer.  Then the letter "X" for the secondary side...X1, X2, and X3.  On a WYE connected system the neutral is of course going to be marked "N".

Normally, the phase markings are going to be the A,B,C nomenclature, and where they land the wire, (in this case...a three phase transformer), will be labelled "H" for the primary side and "X" for the secondary side.

Hope that clears it up for you.
 
It?s been my experience that the feed to the transformer would be phased ?A,B &C?
Assume for a minute the primary into transformer is 600V (could be 575 whatever), the transformer is wound 600/120/208V, delta primary!wye secondary.
The primary conductors would land on H1, H2 and H3. No neutral on primary side.  The secondary conductors would also be refered to as phases A,B and C but they would land on X1, X2 and X3.
A neutral should be carried from the X0 point to lower voltage panel/load. It is in the transformer where the grounding is done. Ground is connected to X0 and case in transformer and other end of ground conductor is terminated at building ground or there are other acceptable places this can be connected.
Thats the way it?s done up here in the north.
Hope this helps a bit to clarify.
 
Even if the OP didn't come back, I still  find the thought process interesting.  And I am always impressed by the depth of knowledge of our members. 

It's true, some new posters are only interested if they get a favorable response that confirms what they want to do. If not they are off to some other forum to answer shop.  Either way, I still think it's a learning experience for us readers. Feel to continue to post.......
 
SeilerBird said:
Just because he did not post a second time does not mean he did not read the responses.

Check his profile. He hasn't been back, at least not logged in under his username.
 
Bob T said:
It’s been my experience that the feed to the transformer would be phased “A,B &C”
Assume for a minute the primary into transformer is 600V (could be 575 whatever), the transformer is wound 600/120/208V, delta primary!wye secondary.
The primary conductors would land on H1, H2 and H3. No neutral on primary side.  The secondary conductors would also be refered to as phases A,B and C but they would land on X1, X2 and X3.
A neutral should be carried from the X0 point to lower voltage panel/load. It is in the transformer where the grounding is done. Ground is connected to X0 and case in transformer and other end of ground conductor is terminated at building ground or there are other acceptable places this can be connected.
Thats the way it’s done up here in the north.
Hope this helps a bit to clarify.

In your scenario, you are assuming a Delta/Wye configuration.  There are Delta/Delta, Delta/WYE, WYE/WYE, WYE/Delta, and other less used configurations......which are almost endless (not really, but there are a bunch).  The point that I was trying to make is that the O.P. stated that he had 208VAC from phase to phase.....which is indicative of a WYE configuration, not DELTA.  The other point that I was trying to make is that he appears to have NOT found the neutral wire in his box, which would allow him to get 120VAC from any one of the phases...A, B, or C..and the neutral.  I also pointed out, since I don't know what the 208VAC 3 phase power was originally used for, that it might have been to supply 3 phase power (208VAC to a smallish 3 phase motor that was hooked up for low voltage, as opposed to a more common 3 phase 480VAC.  Almost all modern day 3 phase motors, especially of the smaller H.P. variety are capable of being connected for "Low or High" voltage.....with low being 208 and high being 480.

And, on a side note, the primary side of the transformer is almost certainly not 600V or 575.  The utilities that bring power into commercial businesses are generally 6900-7200VAC.  In our plant (which is very old), the utilities bring in 161,000 VAC and several large transformers around the plant step that down to a very common 13.8Kv.  13.8Kv is the distribution lines that are all over the plant and feed various transformers via LBS's, fuse cutouts, etc.  That 13.8Kv is than stepped down again, depending on the need, to 2300VAC, 4160VAC and a few....very few, 600VAC transformers.  The 2300 and 4160 transformers then step down again to other needed voltages......480VAC is the most common, but there are plenty of  208/120VAC WYE connected transformers too.

So, there you have it......electricity in a nutshell! 
 

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