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RVing message boards => Tech Talk => Topic started by: JStan on February 03, 2018, 08:04:34 PM

Title: 50A single phase power connection
Post by: JStan on February 03, 2018, 08:04:34 PM
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?
Title: Re: 50A single phase power connection
Post by: SeilerBird on February 03, 2018, 08:17:36 PM
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.
Title: Re: 50A single phase power connection
Post by: NY_Dutch on February 03, 2018, 08:18:18 PM
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.
Title: Re: 50A single phase power connection
Post by: SeilerBird on February 03, 2018, 08:27:07 PM
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.
Title: Re: 50A single phase power connection
Post by: Gary RV_Wizard on February 04, 2018, 10:06:57 AM
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.
Title: Re: 50A single phase power connection
Post by: Isaac-1 on February 04, 2018, 03:04:31 PM
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
Title: Re: 50A single phase power connection
Post by: xrated on February 04, 2018, 04:36:05 PM
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. 
Title: Re: 50A single phase power connection
Post by: Rene T on February 09, 2018, 02:28:45 PM
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.
Title: Re: 50A single phase power connection
Post by: RedandSilver on February 09, 2018, 03:05:15 PM
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.
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Title: Re: 50A single phase power connection
Post by: TonyDtorch on February 09, 2018, 04:10:53 PM
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