You should have the welding earth/return as close the the point of work as possible , to prevent the current returning by the building earthing conductors, I cant remember the number of times I had to change cables because there was a bad connection in the return path, and all the return current going back through 6mm2 earth cable and melting the PVC off the cable , worse when its a 3 or 4 core flex
I aways thought that most electric welder's worked on around 36V DC, and you can get a shock from them if you are working in a damp or wet area,
Hi Poni,
The actual arc voltage when you are welding will be around the 18 to 40 volt mark, but the open circuit voltage will be a minimum 50V, but in the real world anything less than 80V, makes the set horrible to use, so that is the norm.. Pipe welding you want a good 90V due to the type of rods used..
Your burnt out cables....
Many years ago, the geniuses that designed welding sets decreed that the SECONDARY windings be bonded to the case of the machine and hence earth.
Now, off at a tangent a minute... The thing you are working on [we are talking large fabrications here] must be earthed to the frame of the building or other good earth with the "welding earth lead"
The idea is, to prevent a PD between the fabrication and anything else. Not just to protect against the welding voltage, but other electrical equipment might be in use too, and the lead to it, could get cut or squashed, whatever and liven up the fabrication.
Not only that, but say Bert Scroggins was drilling a hole with his class one Black and Decker. If the entire fabrication was not solidly earthed, he would not be too happy when the welder went to strike the arc either [for reasons i will explain in a second]
Back to welding....
What would happen then, if someone would forget to connect the "return lead" and start welding.
Now, remembering that the fabrication is solidly earthed, AND, that the welding set secondary windings were bonded to the case of the set [which was in turn earthed] what would happen, is that the entire welding current, [for manual processes could be up to about 600A] would wizz off to the "good earth" make its way to the MET, and then back through the wiring of the building back to the case of the welding set..
This, as you have seen! causes huge damage... Would not just be the supply to the set either.
Say Bert Scroggins had escaped being shocked [as he was hiding in the bog at the time] but had left his class one black and decker drill laying on the fabrication. The wiring to that could well act as a "parallel path" for the welding current too, and the wiring for it all the way back to the MET could be damaged too..
You will be glad to hear that this sort of welder is now obsolete, but i have seen a few still in use..
john..
