Welder Ground Lead

[jaggedben]

... Aside from this issue with the MC, have there been incidents? ...

Both Don and the magazine article have described other incidents.
It didn't take me long with google to find more, , including on this forum:
Welding currents go astray.
http://forums.mikeholt.com/showthread.php?t=158601
http://forums.mikeholt.com/showthread.php?t=169337

And while this MC arcing was not kosher, it also got noticed and fixed and no damage was done.

Um, how do you know that no damage was done?

There is always the possibility of something during construction causing fires or damage, but is this one of the ones that's been to blame?

Seems like the damage part is indisputable. Quantifying is something else, but it seems it happens.

Indiscriminately?

The same paths the welding current is taking is used for lightning strikes.

Um, no, I don't believe that is true. To my knowledge no designer of a lightning protection system would use electrical system conduits as part of the LPS. And it is also pretty irrelevant to compare a natural phenomenon over which we have relatively little control to a human initiated process over which we have a lot.

A good weldor makes good decisions about his work clamp, and like with most trades, a bad weldor is probably dangerous in far more concerning ways.

I can agree with that. I would probably put the OP example in the bad decisions camp though, if as was described they have their electrode at various locations up to 200ft away with no regard to moving the work lead clamp appropriately.

[FionaZuppa]

Um, no, I don't believe that is true. To my knowledge no designer of a lightning protection system would use electrical system conduits as part of the LPS. And it is also pretty irrelevant to compare a natural phenomenon over which we have relatively little control to a human initiated process over which we have a lot.

???
LPS is required to be tied to EGC....... and metal conduit is too. kinda inherent by the rules of NEC. thats not my view though on how LPS should be done.

[don_resqcapt19]

As both an electrician since 1998 and a weldor since childhood, I admit I am torn, and may not be presenting my case well.

I'm really trying to see IF there is a real problem with this beyond the "how dare they?" concern. I see a lot of disdain for the practice, but from us as electricians. Aside from this issue with the MC, have there been incidents? And while this MC arcing was not kosher, it also got noticed and fixed and no damage was done. There is always the possibility of something during construction causing fires or damage, but is this one of the ones that's been to blame?

I've posed the question on the forum at Miller Welding, where I've been a contributing member since its inception. My welding experiences are not usually on the kinds of jobs that posed the OP.

The cases I have worked on were where there was LFMC in part of the circuit that was carrying the welding current. In most cases it was just the LFMC and the wire in it that were damaged. In some cases, the internal EGC in the conduit also carried enough current to melt the insulation and make removal of the conductors impossible requiring conduit replacement. I don't think I have seen any issues where just the metal conduit itself was the welding current path, but I can see where it could be if someone had not tightened the couplings. Have also had to replace load cells where the load cells became part of the path because of the remote welding lead connection.

[jaggedben]

???
LPS is required to be tied to EGC....... and metal conduit is too. kinda inherent by the rules of NEC. thats not my view though on how LPS should be done.

To my knowledge the NFPA favors tying the LPS to the grounding electrode system, not the EGC per se. If done right, I believe there is no general reason why lightning current should be prone to travel on EGCs throughout the building. Lightning wants to go to ground, and the down conductors will hopefully carry it there without sending it onto EGCs and conduits that aren't in the path. Of course there are instances where makes its way where its not wanted, but I believe it's wrong as a general statement to say that significant lightning current routinely travels all over the electrical systems in buildings with well designed LPSs.

[mivey]

To my knowledge the NFPA favors tying the LPS to the grounding electrode system, not the EGC per se. If done right, I believe there is no general reason why lightning current should be prone to travel on EGCs throughout the building. Lightning wants to go to ground, and the down conductors will hopefully carry it there without sending it onto EGCs and conduits that aren't in the path. Of course there are instances where makes its way where its not wanted, but I believe it's wrong as a general statement to say that significant lightning current routinely travels all over the electrical systems in buildings with well designed LPSs.

That is a fair assessment.

[FionaZuppa]

did i miss something. doesnt the EGC have to tie to the GEC at some point?
once tied, 4 million volts travels everywhere, everything has some ohms

[mivey]

did i miss something. doesnt the EGC have to tie to the GEC at some point?
once tied, 4 million volts travels everywhere, everything has some ohms

That may be true to some degree but current and voltage have to be present to exchange energy. You can dump a bucket of water in a basin, but the water runs down the drain (the grounding electrode / electrode system). Other currents may be present if there are weak points (flashovers, other earth bonds, etc.)

[FionaZuppa]

That may be true to some degree but current and voltage have to be present to exchange energy. You can dump a bucket of water in a basin, but the water runs down the drain (the grounding electrode / electrode system). Other currents may be present if there are weak points (flashovers, other earth bonds, etc.)

4,000 amps to gec, 300 amps across egc
does it really matter how you dump your bucket?

[mivey]

4,000 amps to gec, 300 amps across egc
does it really matter how you dump your bucket?

Apparently. Lightning protection is standard for many apps.

[jaggedben]

I think the more general point is that lightning currents are not comparable to welding currents in either behavior or duration. It does not follow that the welding currents are safe because lightning currents may, in the odd circumstance, travel over the same metal without causing damage. And of course, sometimes lightning on EGCs does cause damage.