Grounds

[orezok]

I got tired of pulling out an extension cord every time I needed to grind something on my welding table. I decided to add an outlet on the table. I extended a conduit to the table and made up a quad outlet.

But then I started thinking that the table is now grounded to the house circuit. The welder also grounds the table.

I was wondering if that 12GA ground wire will become a "heater" when I hit a piece of metal with 150 amps?

Has anyone had a problem with this?

 

[Shield Arc]

I had my table set up like that for a few years, until I made some changes. Never a problem, just keep your welding ground on the object you're welding, or like me 99% of the time I just clamp it to the table.

 

[boomer1025]

I got tired of pulling out an extension cord every time I needed to grind something on my welding table. I decided to add an outlet on the table. I extended a conduit to the table and made up a quad outlet.

But then I started thinking that the table is now grounded to the house circuit. The welder also grounds the table.

I was wondering if that 12GA ground wire will become a "heater" when I hit a piece of metal with 150 amps?

Has anyone had a problem with this?

Isolate the conduit from the welding table with a piece of heavy rubber/plastic or wood.

 

[orezok]

I'm not worried about the conduit, it can easily handle the amperage, it's the 12GA wire that worries me.

 

[dstig1]

Really? Steel is a much worse conductor than copper so will heat up a lot more with the same current flowing through it. Unless you were planning on huge conduit, I think you have that reversed.

In any case, it probably makes the most sense to just isolate the circuit and conduit from the table as previously noted. Use non-metallic conduit or Liquid-tite, perhaps and isolate the box as noted with a wood or plastic standoff so there is no contact.

I'm not sure if it would truly matter or not, but it seems a reasonable precaution....

 

[Shield Arc]

Take it from a guy who has burned up his share of electrical wiring when welding in factories. If your welding machine seems too cold, don't go turn it up, look and see if you attached the ground clamp first! :laughing:

 

[boomer1025]

I'm not worried about the conduit, it can easily handle the amperage, it's the 12GA wire that worries me.

If your putting a receptacle on the table, the ground wire for it runs back to the breaker box. Isolate the circuit and there shouldn't be any welding amperage bleeding back thru the circuit to the breaker box.

 

[orezok]

Really? Steel is a much worse conductor than copper so will heat up a lot more with the same current flowing through it. Unless you were planning on huge conduit, I think you have that reversed.

Exactly my point. The conduit due to it's cross section and high resistance will not be the problem. The 12 GA wire will.

Electricity like water takes the path of lease resistance.

 

[boomer1025]

Exactly my point. The conduit due to it's cross section and high resistance will not be the problem. The 12 GA wire will.

Electricity like water takes the path of lease resistance.

If you isolate the the circuit/conduit when you fasten it to the table. How is the welding current going to get to the 12ga wires ?? Take a short piece of heavy wall plastic pipe, split it and use it as a sleeve on the metal conduit where it fastens to the table. You now have an isolated circuit.

 

[orezok]

If you isolate the the circuit/conduit when you fasten it to the table. How is the welding current going to get to the 12ga wires ?? Take a short piece of heavy wall plastic pipe, split it and use it as a sleeve on the metal conduit where it fastens to the table. You now have an isolated circuit.

The conduit, the box and the 12GA ground wire are all bonded together.

 

[dstig1]

Exactly my point. The conduit due to it's cross section and high resistance will not be the problem. The 12 GA wire will.

Electricity like water takes the path of lease resistance.

You realize that is an oversimplification, don't you? The current will actually split between the conduit and the Cu wire, in inverse proportion to the resistance of each path. So much more current will go through the lower-resistance Cu, but the Steel conduit will still carry a significant current load. I'd have to look up resistance values and calculate it out to be exact.

 

[boomer1025]

You realize that is an oversimplification, don't you? The current will actually split between the conduit and the Cu wire, in inverse proportion to the resistance of each path. So much more current will go through the lower-resistance Cu, but the Steel conduit will still carry a significant current load. I'd have to look up resistance values and calculate it out to be exact.

There would be no welding current/voltage going back the conduit or the wiring if the conduit or box is isolated/insulated from the welding table.
Better yet, why not use plastic conduit & recp box.
No one said anything about a GFI Breaker yet as possibly a another option.

 

[dstig1]

There would be no welding current/voltage going back the conduit or the wiring if the conduit or box is isolated/insulated from the welding table.
Better yet, why not use plastic conduit & recp box.
No one said anything about a GFI Breaker yet as possibly a another option.

Well obviously... but he was talking about it being metal and connected to the table...in which case there certainly would be. I think it would make the most sense to isolate it and use non-conductive conduit.

 

[orezok]

Being a safety first type of guy, when I put electricity on a metal table I want that table to be grounded.

 

[dirt clod]

How would the welder ground feed back through building electrical? The welder has a transformer the secondary winding gets power from the primary winding via magnetic inductance. unless the circuit is completed between the two welder leads there is no flow of current. The circuit would not be completed from just one lead to building ground

 

[MikeD74T]

How would the welder ground feed back through building electrical? The welder has a transformer the secondary winding gets power from the primary winding via magnetic inductance. unless the circuit is completed between the two welder leads there is no flow of current. The circuit would not be completed from just one lead to building ground

If what you say was true I'd never been shocked while welding on the ground, but I have on many occasions even when my workpiece was on wooden horses.
I'd keep the utility circuit isolated from my bench. MikeD74T

 

[Oldtink]

dirt clod is exactly correct on this issue. The welding current from your power supply is only trying to get back to it's source. ie the other side of the transformer lead, or from - to +. It just can't go anywhere else by the laws of electrical circuits.
Want to prove it?
Touch the stinger (only) to the outer metal case of your welder with the return lead disconnected from the welding machine. Nothing!
Problems crop up here where the ground lead from the welder is disconnected from the weld met and is in contact with earth ground along with the weld met. Then it indeed will try to follow the building electrical system ground all the way back to the ground lead of the welder.
Hopefully there is enough resistance in the circuit you won't get an arc and start looking for the problem.....but it does happen.
That my friend is why attaching the ground lead from your welding machine to a good clean surface is so very important.

And for the love of live itself always ground electrical outlets and metal boxes.
more people are killed every year with 120VAC than any other voltage in this country. Besides that, it's a code violation not to have the receptacle grounded.
Been there done that........aint smart.