Grounding Welding Table - ????

[oldyellr]

The "ground" of the welding side of the circuit is distinctly different that the ground of the line voltage circuit

Okay, I'm learning something here. I just went out to the garage and checked my cheapie AC stick welder and sure enough, there's no continuity between the ground prong of the plug and the ground clamp. That puzzles me. Is there a specific reason for this? I can see where would be mandatory for an AC/DC welder, but I can't see a reason for it for AC.

Also, as Steave mentions, the welding and electrical circuit grounds are connected in industrial settings. Is there anything anywhere that says an AC welding table should not be connected to the building electrical ground and why?

 

[Steave]

Okay, I'm learning something here. I just went out to the garage and checked my cheapie AC stick welder and sure enough, there's no continuity between the ground prong of the plug and the ground clamp. That puzzles me. Is there a specific reason for this? I can see where would be mandatory for an AC/DC welder, but I can't see a reason for it for AC.


The welder has a transformer and the power used to strike an arc comes from that. The welding clamp /ground clamp" and the electrode/ "welding rod holder" are connected only to the secondary side of the transformer in the welder. If this makes any sense you got me beat but basically that's it. The cabinet of your welder should have continuity between it and the ground prong of the plug.:thumbsup:

 

[Rock knocker]

NEC 2008
630.15 Grounding of Welder Secondary Circuit
The secondary circuit conductors of an arc welder, consisting of the electrode conductor and the work conductor, shall not be considered as premises wiring for the purposes of applying Article 250

FPN: Connecting the welder secondary circuits to grounded objects can create parallel paths and can cause objectionable current over equipment grounding conductors.

 

[greasemonkeyok]

Let me see if I can say it in layman's terms. If the ground wire of the 110v circuit is connected to the metal welding table, and you have a electric drill plugged into that 110v circuit, then the current from welding circuit (secondary circuit coming out of the transformer) could be conducted into the case of the electric drill and bite your hand if you pick it up while welding, and your foot is touching some other ground (as in standing in water barefooted)?

 

[Rock knocker]

That would be possible. But I would think that is not why the NEC rules are such. I think the NEC is trying to prevent a scenerio where the typically high welding currents could enter and destroy the smaller line voltage wires. But your scenerio is quite possible.

So not to ridicule oldyeller, but ground is not ground. And ground is not ground in line voltage circuits where you have the grounded (neutral) conductor and the equipment grounding conductor

 

[greasemonkeyok]

Thanks. I was just trying to visualize the problem. Now I can substitute other things for the hand-to-foot part of the circuit.

I know GFI does not like it when you try to substitute one ground for another, but it probably doesn't take much current to trip a GFI.

 

[pat32rf]

I think a lot of the confusion is caused by referring to the negative welding terminal as "ground". It has no real relationship to the electrical ground in your building system. In most welding shops that I have worked in (as an electrician, I'm an amateur weldor) the welding tables are NOT permanently connected to the negative side of the welder. They may be bolted to a cable that comes from the welder, but weldors use both negative "ground" (straight polarity) and positive "ground" (reverse polarity) depending on the rod (job).
The welding tables might be permanently grounded to the electrical system (like if they have an electrical 110v box bolted to them).

 

[oldyellr]

Okay, so back to what I asked previously, is it actually "wrong" to have 110v receptacles mounted directly to a steel welding table, thus sharing the building's electrical ground with the welding ground? If so, how come welding can be done on steel structures in a building, where all the steel is connected together and grounded and shares the same ground with the building's electrical circuit?

 

[Rock knocker]

I give up

 

[oldyellr]

I give up

Are you implying that theoretically it's "wrong", but in practice it works okay, but you hesitate to condone it?

 

[mjncad]

Like I said originally (and someone ridiculed me), ground is ground.

I used to work with an electrical engineer who would give you a dissertation on why ground is not ground. From what he told me, grounding is a lot more complicated than just a spare wire to channel electrical energy safely to the earth in the event of a fault.

 

[Rock knocker]

Are you implying that theoretically it's "wrong", but in practice it works okay, but you hesitate to condone it?

Not at all. There is a world of difference between clamping on building steel and welding on a skyscraper, and the potential of welding loads frying the ground wire of a table hooked to 110v with SO cord.

And even on skyscrapers, the building steel doesn't act as ground. There is a uninterrupted ground path including the conduit and any Ufer grounds, and the building steel is bonded to that. But the steel beams are not intended to be a normal ground path for the line voltage, instead they are protected by the ground system. A crucial difference

 

[oldyellr]

Okay, so here is what the OP was asking:

I plan on putting several 110 Volt outlets on my welding table. Was thinking about using the table as a ground.

But since it is also the ground for the welder, there may be some kind of feed back into the 110V line and really screw things up.

Latest Idea - Isolate the table from the 110V LINE
Ground table to a real ground - As in mother earth.

Sure like to hear from some of you folks on the subject.

One part I don't quite understand is "using the table as a ground". Did he mean he was only going run the hot ad neutral from the electrical panel and depend on the table to provide ground through the receptacle boxes? That, of course, would be a no-no. I just assumed he would run hot, neutral and ground from the panel and mount the boxes to the steel bench, so that the bench is also grounded to the panel. He then asks if this isn't okay, should he isolate the boxes from the bench. Well, many power tools are now double insulated with only a 2-wire plug, but if the insulation did fail, would it be better if the tool shorted to the bench and blew a breaker, or not?

But getting back to the welder ground problem. The only way I can see wiring being fried if the bench and receptacles were grounded together is if you tried to weld something on the bench without the ground clamp being connected to the work or the bench, but touching some other part of the steel building structure. Then the return welding current would flow through the building to the panel and back through the receptacle ground wire to the bench and work, frying the ground wire.

 

[Rock knocker]

One part I don't quite understand is "using the table as a ground"

I assume that the OP means to attach the work clamp or the welding machine to the table.

But getting back to the welder ground problem. The only way I can see wiring being fried if the bench and receptacles were grounded together is if you tried to weld something on the bench without the ground clamp being connected to the work or the bench, but touching some other part of the steel building structure. Then the return welding current would flow through the building to the panel and back through the receptacle ground wire to the bench and work, frying the ground wire.

Bingo.

 

[Sberry]

Metal table will be grounded to Ground, as to the earth. - Chances are this is not needed???

This has nothing to do with it, by ground we are talking about aq wire connecting it to the electric system. Rock knocker, do not give up yet, dont quit 5 minutes before it happens, ha I could see this area needed work within a couple threads. I was at a residential the other day, the guy kept going on about where he added these rods, I finally said,,, forget the rod totally, its easy to see here that is confused with electrically grounded.

The only way I can see wiring being fried if the bench and receptacles were grounded together is if you tried to weld something on the bench without the ground clamp being connected to the work or the bench, but touching some other part of the steel building structure. Then the return welding current would flow through the building to the panel and back through the receptacle ground wire to the bench and work, frying the ground wire.

Yes, this is the potential problem.

 

[Sberry]

I remember way back in the day had a bench inside with electric circuit on it and the outside might have had one or just a grounded drill laying on it, was moving the welder work ground around, I actually figured it out when it didn't weld right, I don't recall burning something up but nice little arc strike on the tool case. The welder didn't move, sat on another wood bench so I bolted piece of welding lead between benches eventually splicing it to the machine leaving the lead available for jumping on machinery.

Today with steel building, common machine ground at the column, a quick connect bolted to it, use this lead for plasma, some stick but can go out the door or on the floor, if its more convenient, bench is grounded anhaveve a ground stinger, could swap it around, etc. The vise in the welding booth is cable connected to this common. Then a Y at the machine again, an electrode stinger hangs there to serve booth and benches and another one for remote on floor or outdoor. Never have to move thmachineses, could, disconnectsts and power, its already got a stinger, snatch up any one of the remote grounds etc.

I eleniated the pathway issue by grounding the bench via the welding ground and fed the 120 via 2 wire gfci Stand alone wire feeds we march the work cable around with the machine just like factory, they really dont seem to like ground loops anyway, hooking as close to the point of work or on the same bench via clamp or vise is best.