Creating RV adapter for welder receptacle

[Back2PA]

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]

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]

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]

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]

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]

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 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 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]

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]

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]

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

 

[Rob&Deryl]

What Gary said.

 

[IBTripping]

Or, you can hire a master electrician to figure it out.

 

[cerd]

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]

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]

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

 

[Rene T]

This is a very serious question. To be honest, I am not so strong in matters that relate to welding. I just remember my father doing it when I was just a kid.

Welcome to the forum.
Just so everyone knows this is a 2 year old post

 

[John From Detroit]

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]

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.

 

[samSh]

hi everyone a newbie from Montreal