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Potential 'hot spot' in shop wiring during TIG weld

Gordon Heaton

Titanium
Joined
Feb 19, 2007
Location
St. George, Utah
Had another senior moment this morning & forgot to attach the ground clamp to the welding table/workbench. My table is on casters, all steel and has multiple 120V outlets around the perimeter which are supplied with a 12ga cord from the shop wall outlets. The welds (aluminum @ 150A) were short with a cool down in the middle for grinding out the backside. Welding went fine, and it was only while coiling up the leads I realized I hadn't attached the ground clamp. Thought about it for a few seconds, and sure enough the supply cord to the wall was rather warm the entire length! The current return had been through the 12ga ground to the regular shop wiring.

The big issue here is that there is, of necessity, no protection on the ground circuit, and had the welding been of longer duration or higher amperage the resulting damage could have been extensive. The welder is an HTP Invertig 221H inverter. It had never occurred to me that this could happen and it requires a shop-circuit grounded connection to the welded piece, but that could be as simple as a metal drill or grinder plugged in and laying on the welding table. Has anyone else had this experience?

edit: thinking it through a bit more, I guess the damage would have all been exterior in my case, since all my wiring is in EMT conduit and that is bonded with a #4 wire to the foundation ground. Therefore only the cord from bench to outlet was at risk. For buildings with in-the-wall Romex, though, it could at least melt nearby conductors and at worst start a fire.
 
Not an expert on this but I thought the output of welders are isolated from ground. Otherwise switching the polarity could be problematic. Was your ground lead connected to a grounded object by chance?

Bill
 
yeah I had the same experience a few months back but with a worse outcome.

Ground clamp was supposed to be clamped to the table but it had slipped off and I failed to notice. I had a 1x30” belt sander sitting on my welding bench plugged into a wall outlet.

I didn’t realize what was happening until after I completed the weld.

This was with an older L-Tec (esab) 250 tig unit running on AC.
I managed to fry both the sander and the welder. The welder was already acting up and approaching retirement but thats what did it in. If you tried to strike an arc on DC tig mode it seemed like the diodes had failed and would produce what appeared to be AC current. Evidently it didn’t like the welding current running through the ground.



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I had this happen years ago with a DC stick welder. My angle grinder was laying on top of the welder and plugged in. Its cord started smoking!. It's the kind of the thing where you can't believe it is happening, unless all the stuff I thought I knew about electrical circuits was baloney. Anyway, I reasoned there must have been something amiss in the welder. Sure enough, I took the cover off and discovered one of the heavy wires to the transformer, although insulation wrapped, was touching the case of the machine. Just had to bend it back away, and everything was fine.
 
Yes, happened to me. I had a rotary positioner on the bench doing TIG, the ground was connected to the bench but wasn't perfectly clean. The 120V cord to the wall outlet started smoking. The outlet was a bit melted and the box was hot. The welder was not grounded to anything except the power circuit so it must have fed back through the building circuits. There are SO many ways to go wrong...
 
I would be inclined to believe it was not the grounding wire getting the heat but the neutral (grounded wire) from imbalanced load. Do an ammeter test to know.
 
Not an expert on this but I thought the output of welders are isolated from ground. Otherwise switching the polarity could be problematic. Was your ground lead connected to a grounded object by chance? Bill

Howdy Bill,
Nope. The ground lead was hanging on the lead rack on the welding cart, 15ft away. I also thought the welding leads would be isolated, but maybe the inverter types are different?

I would be inclined to believe it was not the grounding wire getting the heat but the neutral (grounded wire) from imbalanced load. Do an ammeter test to know.

Not sure about this one, but I don't think so... I was getting the full 150A output at the torch, the welder function was completely normal, and the table is not connected in any way to 'neutral'. There was nothing plugged in to any outlet on the table. My service panel does not utilize neutral to ground bonding (yes, they do interact since the utility pole neutral runs to ground at the pole), and there is no direct neutral connection for the welder.

Thank you all for sharing similar experiences. Hope it can spare someone else the problem some time.
 
Did same as Mud once also. Did not have ground clamp on work table but the rotary positioner was being used. After a while we were smelling burning plastic and the green ground wire was melting. The little ground wire (16ga?) on the positioner was taking full weld current. Not much we were just doing thin wall SS tubes. Figured out the ground lead is electrically connected to the input power ground and it was being sent all through the building, up the input power of 220 back to sub-panel and then down the 110 circuit to the positioner that was sitting on work table.
Just thinking about this, I should be able to set the machine on a steel table and weld on that same table without hooking up the ground lead?
 
Shed next to mine managed to run weld current thru the telephone system.(pre mobile era),somke pouring out everywhere.The guy was a frootloop,always drilling into his leg or hand ,or cutting bits off with a bandsaw.
 
Stray welding currents lead to all kinds of disasters. In one case our welder was going along doing flux core on a large weldment. He did not realize that the ground clamp had fallen off. He had been using the crane to turn the item and had left the chain sling draped over what he was welding. The current travelled up the chain through the hook, up the cable through the winch overhead and back to the welding machine. The chain had turned blue before it was discovered. The chain had to be discarded. The crane still worked.
Theoretically welding current should not reach electrical grounds but it happens all the time.
I remember introducing welding theory to a group of grade tens in a Prairie town. A little voice at the back says, " No wonder my uncle is always replacing the bearings on his swather." The uncle was just attaching the ground lead anywhere on the swather frame not realizing he was sending current through bearings.
 
I was using a friend's 1980's vintage 415V stick welder last month: a CIG "Contractor" which I think is a licensed version of a Lincoln design. It struck a few sparks without the ground clamp connected and turned out to have a 30 ohm short to earth on the secondary winding. No amount of cleaning of the transformer windings would eliminate the partial short so it had to be scrapped. As far as a modern inverter goes I would have thought they'd also be isolated as they have a high frequency ferrite transformer at the heart of their design.

The old "Contractor" welder got replaced: I had a couple of the stationary non wheeled versions bought at an auction so we swapped the leads over and used it, internally it's a much beefier transformer than the wheeled version of the same name.
 
Stray welding currents lead to all kinds of disasters. In one case our welder was going along doing flux core on a large weldment. He did not realize that the ground clamp had fallen off. He had been using the crane to turn the item and had left the chain sling draped over what he was welding. The current travelled up the chain through the hook, up the cable through the winch overhead and back to the welding machine. The chain had turned blue before it was discovered. The chain had to be discarded. The crane still worked.
Theoretically welding current should not reach electrical grounds but it happens all the time.
I remember introducing welding theory to a group of grade tens in a Prairie town. A little voice at the back says, " No wonder my uncle is always replacing the bearings on his swather." The uncle was just attaching the ground lead anywhere on the swather frame not realizing he was sending current through bearings.

Strangely enough, my shop made welding positioner carries full welding current through ball bearings with never a problem. I built the thing with old, used bearings from the local motor rewind shop. They are often doing bearing changes just as part of motor maintenance, so they are not all necessarily bad bearings.

I figured at the time that I'd just get a couple of 'new ones' from them once in a while, but it's been years now, and the thing rolls over just fine. Maybe 'run-in' bearings make better contact?
 
Something isn't adding up here and there should be isolation. Perhaps there is an internal short, or maybe the manufacturer is cutting corners but every machine I have owned had isolation and I've owned a lot of welding machines. Come to think of it most machines I've wired had the ground direct to chassis purely as a safety. If I had a machine that wasn't isolated and wanted to keep it I would float it on an isolation transformer.
 
Years ago someone I knew, now deceased was welding with the ground off, I don't remember the details but he told me he was working on a big weldment. He said he thought he smelled something but did not see anything. Well he had a fire going in the wall that got into the roof. a passerby came in and said there was smoke coming out of the roof. He went out to look, by then flames were through the roof. By the time the fire brigade showed up the whole thing was involved. A total loss in the end. The fire investigator was the one that spotted the ground lead hanging on the hook on the welder.
 








 
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