adapting 3-prong 220 6-50p to 30 amp RV

[Jim McGarvie]

One of our sons has a 3-prong 220 6-50p outlet in his shop, and a heavy duty extension cord he runs welders etc. from. He wants an adapter to plug into that cord that he can plug his motorhome cable into with a 50A/30A dog bone. ASSUMING for the sake of discussion (I will make sure he confirms) that his outlet is correctly wired (two 110V legs and ground, no neutral) and the extension cord is adequately sized, is there a way of doing what he wants? The only thing I can think of is for him to make an adapter that utilizes one of the 110V legs and the ground, and connects the ground to the neutral on the 30A RV receptacle.

But I'm not at all certain that is a good idea. Comments from someone more knowledgeable (which is probably most of you) are welcome!

Thanks.

Jim

[Dr4Film]

Is his RV 30 amp or 50 amp? Based on your post and mentioning the use of a 50-amp to 30-amp dog bone I am assuming that his RV is 30 amp.

I did something similar to use when visiting my brother in the Finger Lakes area at his farm except I wanted 50 amp versus 30 amp. He had a three-prong 40-amp welding outlet next to his service panel. I went to the local electrical supply store and purchased the same configuration plug that would go into his outlet, plus some 6-4 wire, a metal box and a 50-amp four prong RV receptacle. I used the two 120 VAC wires and the third wire as the neutral to wire from the receptacle to use for the 50-amp receptacle. Then the 4th wire I used for a ground connection at the panel. The panel had the neutral & ground bonded since it wasn't a sub-panel. It had its own direct service from a pole with a meter.

Worked like a charm until the adapter box got ripped off at a service shop in Orlando. Didn't realize it until I got to my brother's house once again and started looking for my adapter box, GONE!

So, the next day I went to the local electrical supply house and purchased everything I needed to have a 50-amp RV hookup located next to the electrical service panel. Now when I visit my brother, I don't have to be concerned about using any adapter box.

Edited June 21, 2022 by Dr4Film

[Jim McGarvie]

11 minutes ago, Dr4Film said:

Is his RV 30 amp or 50 amp? Based on your post and mentioning the use of a 50-amp to 30-amp dog bone I am assuming that his RV is 30 amp.

I did something similar to use when visiting my brother in the Finger Lakes area at his farm except I wanted 50 amp versus 30 amp. He had a three-prong 40-amp welding outlet next to his service panel. I went to the local electrical supply store and purchased the same configuration plug that would go into his outlet, plus some 6-4 wire, a metal box and a 50-amp four prong RV receptacle. I used the two 120 VAC wires and the neutral to wire from the receptacle to use for the 50-amp receptacle then used the 4th wire for a ground connection at the panel.

Worked like a charm until the adapter box got ripped off at a service shop in Orlando. Didn't realize it until I got to my brother's house once again and started looking for my adapter box, GONE!

So, the next day I went to the local electrical supply house and purchased everything I needed to have a 50-amp RV hookup located next to the electrical service panel. Now when I visit my brother, I don't have to be concerned about using any adapter box.

 

Thanks for the prompt reply, Richard. Maybe I didn't word it correctly, but his coach is 50A and the dog bone would allow it to plug into a 30A outlet. But I'm not sure that is germane to the issue.

I made an adapter similar to yours for a visit to a friend, but I decided it was more likely he would have another RV visitor than I would need the adapter elsewhere, so I left it with him.

Jim

[Dr4Film]

Well since his coach is a 50 amp then you DON'T want to use a 30 to 50 amp dog bone. You are better off making an adapter from the 40-amp receptacle to a RV 50 amp receptacle for him to plug into.

[waterskier_1]

Jim, hope you are doing well.  The only proper "NEC compliant" way is to run a neutral wire from his power panel to that welder outlet.  It is prohibited to tie the neutral to ground anywhere except at the entrance of the power to the power panel.  If you didn't have a neutral, it would allow voltage between legs to "float" based upon the current in each leg.  If only one A/C (for example) were turned on, you would have 15-20 Amps in one leg (for talking purposes, since without a neutral, you really don't have legs) which would cause the voltage on the opposite leg to rise, potentially to a dangerous (for the coach and electronics) level.  

That said, I do know some who either intentionally or out of ignorance, have tied a "false neutral" to the ground at the welder outlet, or a new parallel outlet, and it will work.  The danger comes when someone tries to service the system and doesn't know there is another ground on the neutral and that can cause voltage problems.  

  -Rick N.

[Jim McGarvie]

2 hours ago, waterskier_1 said:

Jim, hope you are doing well.  The only proper "NEC compliant" way is to run a neutral wire from his power panel to that welder outlet.  It is prohibited to tie the neutral to ground anywhere except at the entrance of the power to the power panel.  If you didn't have a neutral, it would allow voltage between legs to "float" based upon the current in each leg.  If only one A/C (for example) were turned on, you would have 15-20 Amps in one leg (for talking purposes, since without a neutral, you really don't have legs) which would cause the voltage on the opposite leg to rise, potentially to a dangerous (for the coach and electronics) level.  

That said, I do know some who either intentionally or out of ignorance, have tied a "false neutral" to the ground at the welder outlet, or a new parallel outlet, and it will work.  The danger comes when someone tries to service the system and doesn't know there is another ground on the neutral and that can cause voltage problems.  

  -Rick N.

Thanks Rick, we are doing great and hope you and your dad are as well.

And thanks for the info. Confirms my suspicions, and we don't want to mess with anything like that not recommended, even if it "might" work.

Jim