Is it OK to have the work clamp from two machines on the same part ?

[RichardH]

The work piece is not a shared "ground" in the same way that you would think of the ground in an electronic device.

Yeah, I think out of necessity welding leads are isolated, meaning there is only voltage potential between two leads from the same machine (and the clamp is really "return path" and not really "ground"). Witness the example here a few weeks back where the torch's lead got shorted to the case's ground (i.e., building ground) and created an unexpected current path through a nearby grinder. ;-)

[joshuab]

Yeah, I think out of necessity welding leads are isolated, meaning there is only voltage potential between two leads from the same machine (and the clamp is really "return path" and not really "ground"). Witness the example here a few weeks back where the torch's lead got shorted to the case's ground (i.e., building ground) and created an unexpected current path through a nearby grinder. ;-)

My understanding is that this is exactly right. Although people who really know about electricity cringe when I say it, it is kind of like each welder is sucking up only its own electricity, and one welder's ground clamp can't complete the circuit from another welder's stinger. It gets confusing because people are thinking about earth ground, and in that case, ground is ground, for many purposes. That's why I think we should all practice saying, "work clamp" instead of "ground".

[zoama]

My understanding is that this is exactly right. Although people who really know about electricity cringe when I say it, it is kind of like each welder is sucking up only its own electricity, and one welder's ground clamp can't complete the circuit from another welder's stinger. It gets confusing because people are thinking about earth ground, and in that case, ground is ground, for many purposes. That's why I think we should all practice saying, "work clamp" instead of "ground".

I mainly wondered if the HF from one machine could harm the other through it's work clamp on inverters.

[Rambozo]

About the only conceivable way you could blow something up is if two machines get into a loop. There are only a few ways I could see that happening. The first that comes to mind is that when stick welding you set the stinger down on the bench and accidentally knock the end of the stick into the MIG gun, TIG torch, etc. Not a likely scenario but possible. Because of diodes in the outputs I'm not even sure that would hurt anything, with DC, depending on polarity, not that I would try it. The other thing would be as you mentioned with TIG HF. If you left the TIG work clamp off, you could form some bizarre loopback if the TIG work clamp was grounding out on a cart and another machine's work clamp was on the table. HF always seems to find a way to get through to something, but it usually doesn't carry enough current to hurt things.