Hypothetically...

A guy is building a welding table and wants to run a 25-30 foot 220V extension cord for a 50A welder so that it can be wheeled outside the garage during use. Let’s pretend he knows how to properly and safety wire this dedicated extension with all proper connections/strain reliefs. Is there any way, within code, to pull power from a single leg of the 50A circuit and break it off into 110V (20A) power? If a guy were to do this, I know that he will somehow need to limit this leg to 20 amps - would a 20A rated GFCI outlet be adequate? Or does there also need to be a 20A breaker/sub panel setup as well? Or is there something extremely unsafe about this that a guy might not be considering?

You might be asking “Why not two separate cords providing the necessary voltage and amp rating?”

Reason #1: running two dedicated cords (110 and 220) to a small welding table isn’t ideal. It adds to clutter. Just one more step in using this work surface. The 110 and 220 would never be used at the same time and always by the same guy. The 220 is strictly for the welder and the 110 is for a couple angle grinders.

Reason #2 & a possible irrational fear: A guy prefers that a 400 pound steel table be electrically grounded/bonded to the circuit so he doesn’t accidentally shock the bugeezes out of himself if things go sideways. The possibility of a burn hole or abrasion to wiring that goes unnoticed causing an electrified steel table isn’t something that’s preferred.

That said, there’s some mixed opinions and “I knew a guy” stories on the web about the possibility of a welder grounding to the home electrical circuit rather than back to a welder when you bond a circuit to the table. Because of this, some believe you should never bond an electrical circuit to welding table because you risk overloading a small ground wire, screwing up your electrical, or starting a fire. Still have no idea how much truth there is to this theory, but maybe it’s possible? So if a guy were set on bonding a circuit to the table, it seems that the 6 gauge wiring of a welder extension plugged into 6 gauge copper that travels a couple feet to a subpanel with a 2 gauge ground would reduce this risk compared to the 110 alternative.

Hope this makes sense. Any info or expertise is appreciated.

 

There was a post a few months ago where someone built a pretty swanky mobile welding table with multiple welders and tools all wired quite nicely and safely.

In a nutshell, you'd wire a 50A cord from the table to a subpanel mounted on/under the table. The subpanel would have a DP (240v) 50A breaker for the welder, and one or more 20A breakers to GFI receptacles. The panel would have a wire specifically bonded to the metal chassis for the ground (though the panel bolted to the metal, might be sufficient).

So yeah, definitely possible. Takes some planning, but definitely doable.


Here's the other thread:
Welding Cart build with attached sub panel.
Impressive cart!

 

Nominal voltages are 120/240 not 110/220.

Use 6-4 service cord (black-red-white-green) and terminate in a 60 amp breaker panel with breakers for the different welder and corresponding receptacles. Use a 14-50 plug on the other end of your cord. Twist Lock could be used to provide a more secure plug/receptacle connection.

The grounded breaker panel mounted to the steel table would provide your ground path.

 

The welder itself needs to be bonded to a ground return, so bonding the table with the same ground wire should not be a problem at least as I see it.
Bonding a second ground wire sized for the 20 amp circuit to the table is definitely bad because if the larger ground wire gets disconnected, then the second bond wire is inadequate if the 50A circuit has a fault to ground. A fire could then result.
You definitely need separate overcurrent protection for the 20A receptacle.

 

Thanks for the replies.
Zorfdt - you definitely answered my questions! I appreciate it!

I’ll definitely bond the subpanel to the frame. Planned on using twist locks.

120/240. Thanks for correcting.

Also, when people start talking about grounding the welder, it almost always gets confusing (maybe that’s just me?)... since there’s a ground clamp for the process of welding and a ground for the electrical supply to the welder, the term “ground” can be used in a couple different ways.

I plan on having a very substantial ground clamp solution for the welder. I want to make sure that the ground clamp is solid, protected, and has no possibility of causing issues with the welding process.

I‘m still not sure what to think about the idea of a welder inadvertently grounding to the household electrical. Again, hypothetically, if a guy were to drive a grounding rod into the ground, would an arc welder actually strike an arc to the rod? (...basically simulating that the welding ground clamp has somehow disconnected) Seems like it’d have to? Dumb question?

 

Hopefully this can answer some of your questions about grounding when using a welder:

https://www.lincolnelectric.com/en-u...ty-detail.aspx

 

The Lincoln link does tell a lot about the importance of grounding the welder frame to the electrical supply ground... or grounding to earth.

It also discusses the importance of having a good ground clamp for the welding circuit...

It mentions that an effective electrical ground (to the panel and grounding rod) prevents shock - but it seems like they're talking about the general purpose of a electrical ground with any equipment, right? Not necessarily that welding current could travel back to the panel.

Maybe I’m making too much of a deal out of nothing or maybe a not so hypothetical test is warranted.

 

Having a separate 120V cord to the dwelling with its own ground wire would definitely be more susceptible to having welding currents flow back to through the house wiring. If the welding table and work is grounded as recommended and the welding electrode is touched to the grounded metal housing of an electric tool (grinder, etc.), then you would get high current flowing through house ground circuits that would also likely blow the ground wire of the 120V cord.
Having a single ground wire connection to the building through the 50A cord and with a panel on the worktable as mentioned by Zorfdt would eliminate the possibility of high welding currents going through the home's ground wiring. Of course the cord on the tool could still blow from high currents through the ground connections on the cart. Perhaps a double insulated 2-wire grinder without a ground would be better in this situation, assuming that a suitable one is available.

Now if you wanted to prevent welding current from causing problems in the dwelling wiring no matter what crazy thing you did on or under the table, that's a different case. If you touched an energized welding electrode to one of the phases of the 240V circuit, the breaker would blow and protect as it normally does. The output circuit of the welder's step down transformer has a lower impedance than the house circuit and its open circuit voltage is also less. As a result the impedance of the home's wiring and connections to the power lines will limit the peak current before the breaker trips.
Now if you touched the energized welding electrode to the neutral then a high current would flow on the neutral of the 50A cord and though the house neutral wiring. It's likely that the equipment grounding conductors of the home would blow before the neutral does if the minimum required ground conductor gauge was used.

If you had a 240/120 volt transformer under the welding table to get the 120V then a neutral would not be required in the 50A cord and the situation above could not arise. Of course, you can always create all sorts of havoc on or below the welding table but it would be limited to that area. I'm certainly not saying such a transformer is really necessary, just mentioning some possible options.