Creating RV adapter for welder receptacle

The friendliest place on the web for anyone with an RV or an interest in RVing!
If you have answers, please help by responding to the unanswered posts.

Back2PA

Well-known member
Joined
Jul 26, 2015
Posts
5,766
Considering contingency plans in the event I am unable or prefer not to go to my workamping job in a couple weeks at a private campground. Currently parked on in-laws' farm plugged in to 15A receptacle, which is working fine for basic battery charging etc. However circuit probably can't take microwave use, and AC usage this summer would be out of the question.

I believe I can get access to a welder receptacle in a farm shop, probably wired many years ago. I'm anticipating said receptacle has L1, L2 and common which I'm guessing is bonded to ground. I'm clear on the issues with two legs of 120V and 30 vs 50 amp RV plugs, and am tentatively planning on wiring a 50A RV receptacle. What I'm wondering about is the common/ground issue.

If I do find that the receptacle has no ground, and just L1, L2 & common, which of these setups is preferable?:

Option one:

Welder outlet --> 50A RV receptacle
L1 --> L1
L2 --> L2
Common --> Common
Common --> Ground

Or Option two:

Welder outlet --> 50A RV receptacle
L1 --> L1
L2 --> L2
Common --> Common
Ground rod --> Ground

I believe it's too far to the sub-panel to place the RV receptacle near there, but will check that and space to add a couple circuits
 

Isaac-1

Well-known member
Joined
Dec 3, 2016
Posts
4,700
Location
SW Louisiana
safer option 3

If it is 3 wires at 240V only and 50 amps, a safer option would be to convert it to 3 wires 120V at 50 amps, by moving one of the hots to neutral at the breaker box and then bridge L1 and L2 at the 4 wire 50 amp outlet to let you plug in your 50 amp RV cord and get power to both hot sides.  This would give you 6,000 watts total power to your RV at 120V only, instead of the normal 12,000 watts at 120/240 for a 50 amp RV hookup.  In effect this would be doing what a 30 amp RV to 50 amp RV dogbone does, just with 50 amps remaining available.

If this does not make sense, please ask for clarification before you try rewiring.
 

Back2PA

Well-known member
Joined
Jul 26, 2015
Posts
5,766
Isaac-1 said:
safer option 3

If it is 3 wires at 240V only and 50 amps, a safer option would be to convert it to 3 wires 120V at 50 amps, by moving one of the hots to neutral at the breaker box and then bridge L1 and L2 at the 4 wire 50 amp outlet to let you plug in your 50 amp RV cord and get power to both hot sides.  This would give you 6,000 watts total power to your RV at 120V only, instead of the normal 12,000 watts at 120/240 for a 50 amp RV hookup.  In effect this would be doing what a 30 amp RV to 50 amp RV dogbone does, just with 50 amps remaining available.

If this does not make sense, please ask for clarification before you try rewiring.

I understand where you're going here but that's not feasible as it compromises the welder receptacle which is still needed for farm use. Plus I'm giving up the opportunity to have the 12,000 watts available if I needed both ACs, etc

Are you suggesting your option 3 is "safer" to prevent a mis-wire thereby introducing 240 to the coach (which would be hard but not impossible to do with a 50 coach), or because options one or two which I suggested are unsafe from a wiring perspective?

Plus, I have to look, this may be an older "dryer plug" style receptacle, precluding using it directly anyway (although I could use a dogbone)
 

mel s

Well-known member
Joined
Apr 28, 2014
Posts
853
Back2PA said:
Considering contingency plans in the event I am unable or prefer not to go to my workamping job in a couple weeks at a private campground. Currently parked on in-laws' farm plugged in to 15A receptacle, which is working fine for basic battery charging etc. However circuit probably can't take microwave use, and AC usage this summer would be out of the question.

I believe I can get access to a welder receptacle in a farm shop, probably wired many years ago. I'm anticipating said receptacle has L1, L2 and common which I'm guessing is bonded to ground. I'm clear on the issues with two legs of 120V and 30 vs 50 amp RV plugs, and am tentatively planning on wiring a 50A RV receptacle. What I'm wondering about is the common/ground issue.

If I do find that the receptacle has no ground, and just L1, L2 & common, which of these setups is preferable?:

Option one:

Welder outlet --> 50A RV receptacle
L1 --> L1
L2 --> L2
Common --> Common
Common --> Ground

Or Option two:

Welder outlet --> 50A RV receptacle
L1 --> L1
L2 --> L2
Common --> Common
Ground rod --> Ground


I believe it's too far to the sub-panel to place the RV receptacle near there, but will check that and space to add a couple circuits

Back2PA
Aren't both of those options IDENTICAL.??


 

Isaac-1

Well-known member
Joined
Dec 3, 2016
Posts
4,700
Location
SW Louisiana
My concern is more about chance of electrocution, option one effectively removes the safety ground, so that one break of the neutral wire, or loose connection could kill someone.  Option 2 creates the potential for a ground loop, and the same thing, particularly bad if we are talking about a metal shed, as the potential for the walls of the shed is different than the wiring connected to the ground rod.
 

Back2PA

Well-known member
Joined
Jul 26, 2015
Posts
5,766
Isaac-1 said:
My concern is more about chance of electrocution, option one effectively removes the safety ground, so that one break of the neutral wire, or loose connection could kill someone.  Option 2 creates the potential for a ground loop, and the same thing, particularly bad if we are talking about a metal shed, as the potential for the walls of the shed is different than the wiring connected to the ground rod.

It is a metal shed. What if the ground rod is also grounded to the housing of the welder receptacle and/or the siding?
 

Isaac-1

Well-known member
Joined
Dec 3, 2016
Posts
4,700
Location
SW Louisiana
Well in the old days, many metal buildings used the metal frame of the building as the connection point for the safety ground.  I am not saying that it is up to code these days, but 50 years ago it was commonly done.
 

Back2PA

Well-known member
Joined
Jul 26, 2015
Posts
5,766
Isaac-1 said:
Well in the old days, many metal buildings used the metal frame of the building as the connection point for the safety ground.  I am not saying that it is up to code these days, but 50 years ago it was commonly done.

OK thx. I may not do this anyway, or I might luck out and it could be a modern 50A receptacle with proper ground (although I wasn't impressed with the sub-panel  :-\ )
 

Lou Schneider

Site Team
Joined
Mar 14, 2005
Posts
10,954
Besides grounding, the key issue is if the 240 volt outlet has sufficient neutral capacity (or any neutral at all) to support using it in the 120/240 volt configuration.  The neutral has to be able to carry actual current back to the power panel, not just provide a path to ground.

A 240 volt dryer outlet is a similar case.  One I thought about plugging my RV into only had two hot wires feeding it and relied on the metal conduit surrounding those wires to provide the safety ground.

It should be obvious a conduit run, with it's multitude of splices secured by spring tension or a single screw, would not be an adequate neutral capable of returning continuous current back to the power panel.

Neither is a ground rod sunk at a distance from the power panel ground.  You have the resistance of the earth between the two ground rods as part of the circuit and the resulting poor conductivity is why the power company runs a neutral conductor to the service entrance instead of just tying the neutral to the ground rod.

If the circuit doesn't have an adequate neutral, you'll be far better off installing one back to the neutral buss in the breaker panel, assuming there's one in the farm building panel.  As a temporary measure I wouldn't rule out running it out in the open if necessary.
 

Gary RV_Wizard

Site Team
Joined
Feb 2, 2005
Posts
73,959
Location
At our Silver Springs FL home
I'm anticipating said receptacle has L1, L2 and common which I'm guessing is bonded to ground.

I doubtful of that assumption - a typical older "welder outlet" will be two hots only and no neutral (common). The welder doesn't use any 120v so no need for a common neutral. It probably has a ground, either via the box & conduit or possibly a wire to some external ground. That type of outlet is not usable as a source for RV power.
 

Back2PA

Well-known member
Joined
Jul 26, 2015
Posts
5,766
Gary RV_Wizard said:
I doubtful of that assumption - a typical older "welder outlet" will be two hots only and no neutral (common). The welder doesn't use any 120v so no need for a common neutral. It probably has a ground, either via the box & conduit or possibly a wire to some external ground. That type of outlet is not usable as a source for RV power.


OK thx I'll have a close look this weekend. If possible I may have to just add a couple breakers to the box and run romex to the new RV box. Just working on contingency plans
 

cerd

Well-known member
Joined
May 29, 2018
Posts
621
Location
MN
Gary RV_Wizard said:
I doubtful of that assumption - a typical older "welder outlet" will be two hots only and no neutral (common). The welder doesn't use any 120v so no need for a common neutral. It probably has a ground, either via the box & conduit or possibly a wire to some external ground. That type of outlet is not usable as a source for RV power.

Agreed. A lot of modern welders still use this same configuration. Both of mine also use HHG configurations.

My vote is to either buy a generator or if the property owner is okay with it, hire an electrician to install an RV outlet.
 

solarman

Well-known member
Joined
Feb 8, 2018
Posts
459
Location
Texas
Gary RV_Wizard said:
I doubtful of that assumption - a typical older "welder outlet" will be two hots only and no neutral (common). The welder doesn't use any 120v so no need for a common neutral. It probably has a ground, either via the box & conduit or possibly a wire to some external ground. That type of outlet is not usable as a source for RV power.

I agree, this is the most likely case..

there are two ways to change this,

1. use an isolation transformer with 120/0/120 output and ground the center tap
2. spend considerably less and run a new line from the breaker box to a 50 A pedestal

 

Back2PA

Well-known member
Joined
Jul 26, 2015
Posts
5,766
solarman said:
I agree, this is the most likely case..

there are two ways to change this,

1. use an isolation transformer with 120/0/120 output and ground the center tap
2. spend considerably less and run a new line from the breaker box to a 50 A pedestal

I appreciate everyone's input. I was not aware how these welding receptacles were wired and so the questions. I have however installed 50A RV panels. It's not likely I will need this in any case (in the event I can't go to the planned campground in a week), but if so that's what I would do
 

John From Detroit

Well-known member
Joined
Apr 12, 2005
Posts
24,948
Location
Davison Michigan
A welder outlet is typically 3 wires HOT1 HOT2 (leg 1 and 2) and as Ground. the Ground wire is often smaller than the HOT wires there is no neutral and to convert it to an RV outlet you need to run a neutral (White) wire of at least the same gauge as the hot's.

Dryers, depending on the age of the install. may be 3 or 4 wire.

Electric Range is normally 4 wire And the neutral is same ga as the hot. (Ground may be smaller) Same for RV outlets.

There is no way to convert a 3-wire outlet to 4Wire RV use without running that added wire.
 

Lou Schneider

Site Team
Joined
Mar 14, 2005
Posts
10,954
The problem is a welding outlet is designed for a 220 - 240 volt load with nothing coming back down the (non-existant) neutral wire. An RV requires a neutral wire able to carry up to the full 50 amp rating of the main wires.

You can't use the ground wire as a neutral. It's designed only as a safety wire, to carry current just long enough to trip the breaker if there's a short to ground on the welder. One outlet I looked at used the metal conduit for the safety ground, obviously it couldn't be used as a neutral conductor.
 

Forum statistics

Threads
119,188
Posts
1,194,679
Members
123,979
Latest member
Thhr1127
Top Bottom