Welder return EGC issue

[chris kennedy]

I have an issue at a facility I'm fairly familiar with. I find a 480V welder that when in use fried the EGC contacts on 2 208V L15-20's where those two pieces of equipment sit on the same grounded welding platform.

Here is where I screwed up. I was measuring AC current (DC more appropriate?) on the EGC at the 480V welders safety switch. Was getting 13A on startup and 7A continuous while in duty. Had the welder change the return cable to one in better shape and clean contact surfaces and current dropped to under 3A.

Whats my next step here?

Thanks

 

[starbolin]

There has got to be two faults for the weld current to get on the equipment EGC. It should be a separately derived system where the only connection between the primary and the secondary is via a single point ground ( preferable back at the panel. )

First, the weld current must be creating a voltage differential across a metal surface in the work area. Your actions cleaning and replacing the return leg reduced this potential. Are they working on a metal table that has it's own EGC or a large workpiece where the weld return leg is the only ground? Continue to clean and bond any metal surfaces in the weld area. Lack of bonding on steel structures is a common omission in many weld areas I've worked.

Second, the voltage differectial must be appearing on the weld equipment EGC. This is very often the case. Sometimes it happens because someone was over-concerned with 'grounding' and bonded something to the supply side EGC that should have been bonded to the weld side EGC. Are the EGCs and the welding secondary separated inside the welding equipment? Are the power outlet EGCs separated from the weld platform? Are the welding equipment enclosures electrically separate from the weld platform?

The weld current polarity and cycle depends on what they are welding. If they are welding steel the current will usually be DC and if they are welding aluminum the current will be AC. With newer welders the AC frequency may be a square wave and the frequency may be as high as 400hz.

 

[chris kennedy]

Are they working on a metal table that has it's own EGC or a large workpiece where the weld return leg is the only ground?

Weld return only.

Second, the voltage differectial must be appearing on the weld equipment EGC. This is very often the case. Sometimes it happens because someone was over-concerned with 'grounding' and bonded something to the supply side EGC that should have been bonded to the weld side EGC. Are the EGCs and the welding secondary separated inside the welding equipment? Are the power outlet EGCs separated from the weld platform? Are the welding equipment enclosures electrically separate from the weld platform?

Couldn't open equipment as it was active.

The weld current polarity and cycle depends on what they are welding. If they are welding steel the current will usually be DC and if they are welding aluminum the current will be AC. With newer welders the AC frequency may be a square wave and the frequency may be as high as 400hz.

Welding Al.

 

[GoldDigger]

Make sure that the operator is connecting the return lead to the workpiece rather than the table if possible.
As stated, there will only be current on the supply EGC if there is an extra connection somehow from the table to building or earth ground, whether it is intentional or not.
Maybe to building steel or rebar in the floor?

 

[SceneryDriver]

Many older stick welders have a connection between the EGC from the line supply to the grounding lead on the welder supply; the low-voltage high-current supply isn't actually floating with respect to ground. It's annoying, and definitely leads to "objectionable current" on the EGC.

A guy I used to work with thought it was neat that he didn't have to hook up the ground clamp when he was welding on structural steel in the building. I told him that he'd start a fire or burn up a plug if he didn't use the ground lead. He seemed unconvinced. I sense there is much melting and burned power cable in his future.



SceneryDriver

 

[ptonsparky]

Many older stick welders have a connection between the EGC from the line supply to the grounding lead on the welder supply; the low-voltage high-current supply isn't actually floating with respect to ground. It's annoying, and definitely leads to "objectionable current" on the EGC.

A guy I used to work with thought it was neat that he didn't have to hook up the ground clamp when he was welding on structural steel in the building. I told him that he'd start a fire or burn up a plug if he didn't use the ground lead. He seemed unconvinced. I sense there is much melting and burned power cable in his future.



SceneryDriver

We made some suggestions as to welding practices when we noticed this procedure in a small industrial. We just said "Continue that practice and a "Taillight warranty" becomes active. They also had problems with bearing failures. For the most part they changed to GoldDiggers method.

 

[starbolin]

Many older stick welders have a connection between the EGC from the line supply to the grounding lead on the welder supply; the low-voltage high-current supply isn't actually floating with respect to ground. It's annoying, and definitely leads to "objectionable current" on the EGC.

...
SceneryDriver

Complete with the caution in the product 'manual' that to remove the strap was to risk injury or death!

 

[starbolin]

Weld return only.



Couldn't open equipment as it was active.



Welding Al.

So, let me get this straight, the welding PSUs are on a grounded platform but the work is not on a grounded platform? This seems totally backwards to me. Though it is how I find many setups. Metal in the weld area needs to have a return to the welding PSU secondary return. Otherwise the return current will try to find it's way back through the supply EGC to the welder secondary. Which it should not be able to do. Or, perhaps, there is a voltage induced on local earth at the workpiece which is traveling back to supply ground via the work platform, the weld PSU cases and the weld PSU cords.

Another area that needs attention is the return leg to work connections. Everything you've described so far leads me to think this is a low budget operation. Are the weld return clamps made out of stamped steel or bronze? The free return clamps that the dealer throws in for free with the PSU purchase are worth exactly what you pay for them. An upgrade of the weld return clamps will further reduce induced voltages.

 

[chris kennedy]

They are welding on a big metal table that is welded to the ground platform, clamps are bronze. There is nothing low budget about these guys or their operation.

 

[GoldDigger]

They are welding on a big metal table that is welded to the ground platform, clamps are bronze. There is nothing low budget about these guys or their operation.

That sounds good, but it also have implies that the table is "grounded" as well as connected to the welder return wire. And that is what creates the parallel path which will carry greater current if the return connection is compromised for any reason.
1. Use a verrrry heavy bolted (not spring clamp) connection from the table to the welder return (not ground) terminal.
2. That way, if the return clamp on the workpiece has problems, the current will not be forced primarily onto the EGC. At least not to the same degree.
JMO.

 

[starbolin]

They are welding on a big metal table that is welded to the ground platform, clamps are bronze. There is nothing low budget about these guys or their operation.

My mistake.

I agree with GoldDigger there should be a heavy connection between the 'ground platform' and the welder return. I would mount the welder enclosures on plywood bases but that's just my preference. Some inspectors won't agree with me but having the welder enclosures siting on the grounded platform can create a path for the return current through the EGC, to the case, and back to the welder secondary. Other than that it is hard for me to see why the return current wants to go through the EGC. It's a mystery to me that, with a grounded work table, a grounded platform that there can be any residual voltage to drive current through the EGC system but yet that appears to be happening. There is somewhere a poor connection to the welder secondary return.

 

[chris kennedy]

My mistake.

I would mount the welder enclosures on plywood bases but that's just my preference.

It is mounted on plywood on a table isolated from the ground return. This has been operating with no issues for at least 2 years.

The following is a pic from yesterday. The welder is in center background, blue trap over it, its a Miller, didn't get the model number. The blue saw in the foreground is sitting metal to metal on the ground return path. This is the saw that started smoking. Again, 480V welder and 208V saw.

 

[cadpoint]

Raise the table onto isolation pads and the saw.

As is the 208 with ground - you can probable see welding voltage there.

It all might be a fluke, the band saw look old and could have just been age.

Everything gets energized when welding the anvil, the table, then the floor then the other
equipment on the steel floor. From what I see, maybe it's already isolated

I see no isolation with everything on a steel grate, if that's grounded also you've made everything
one and yes it will have no potential.

Since that's a higher model saw motor it had better motor parts that
all this have been working on for a while, and finally wore out.

They need to make or buy some gas tank straps.

 

[starbolin]

It is mounted on plywood on a table isolated from the ground return. This has been operating with no issues for at least 2 years.

The following is a pic from yesterday. The welder is in center background, blue trap over it, its a Miller, didn't get the model number. The blue saw in the foreground is sitting metal to metal on the ground return path. This is the saw that started smoking. Again, 480V welder and 208V saw.

The saw is a very nice Johnson. Built like a battleship. The welder is a Syncrowave. 250DX or 350LX. Can't tell from the picture. They are almost identical. With other electrical equipment on the weld platform there is no way to ensure, in every case, that welding current does not appear on their EGCs. Especially with TIG - the process they are using. The Sycrowave puts out a square wave with a DC component. In TIG mode it also outputs a continuous High Frequency current. Great for throwing hash about the room and arcing over miscellaneous wires.

When was the last time the spark-gaps were adjusted inside the welder? The HF circuits in those can output significant current.

 

[chris kennedy]

What are spark gaps?

 

[starbolin]

What are spark gaps?

I's a dohickey inside the welder used to generate the RF needed to maintain the arc for AC welding of aluminum. It's literally a gap between two carbon rods. It's the thing that makes the tell-tail little buzz from the PSU when welding aluminum.

There is an adjustment procedure in the welder manual. In some plants it is the electricians duty to periodically clean and adjust these. On some welders the gap hasn't been set in decades. A worn gap can cause higher than spec HF voltages which increases hash, harmonics, and increases the magnitude of undesirable currents. The gap on the Syncrowave is the only method of setting the HF amplitude.