Linking earth leads on plasma and mig?

[rtbcomp]

Still confused... I have an earth clamp bar on my welding bench, that I bung the welder return clamp onto (if I can't easily get it onto the piece being welded). The bench is on the ground, and has various other metal thingies lying on it, any of which might also be earthed through their metal case and to the power socket.

So the welding return lead/clamp is effectively at mains-earth potential. That must be the case for many people / instances, isn't it?

(in the above, I'm referring to the non-torch lead from the welder as the "return lead/clamp" to draw a distinction to mains "earth")

The problem occurs if you get a loop as per the diagrams above. If your bench and welder chassis are earthed there is no problem (top diagram) as long as the welding return isn't connected to the welder's case, as in diagram 2. If you get a loop some of the earth return current can find its way through the mains earth. How much depends on the relative impedance of the earth circuit and the welding return cable. If the earth clamp is doing its job you'll most likely be OK. In the worst case scenario (bottom diagram) you could end up with the all welding current going through the mains earth, which will burn it out.

This is what happened in the other post I mentioned.

https://www.mig-welding.co.uk/forum...wire-insulation-to-melt-in-wall-socket.69194/

https://www.mig-welding.co.uk/forum/threads/help-please-garage-electrics.45809/

 

[brightspark]

it can only happen if the circuit isn't rcd protected

 

[skotl]

The problem occurs if you get a loop as per the diagrams above. If your bench and welder chassis are earthed there is no problem (top diagram) as long as the welding return isn't connected to the welder's case, as in diagram 2. If you get a loop some of the earth return current can find its way through the mains earth. How much depends on the relative impedance of the earth circuit and the welding return cable. If the earth clamp is doing its job you'll most likely be OK. In the worst case scenario (bottom diagram) you could end up with the all welding current going through the mains earth, which will burn it out.

This is what happened in the other post I mentioned.

https://www.mig-welding.co.uk/forum...wire-insulation-to-melt-in-wall-socket.69194/

https://www.mig-welding.co.uk/forum/threads/help-please-garage-electrics.45809/

Gotcha - that's the bit I was missing, if the welder wasn't earthed

 

[rtbcomp]

it can only happen if the circuit isn't rcd protected

Have to disagree. Any rogue current is from the output of the welder, an RCD senses the difference between live & neutral currents in the mains input side. You'd have to use an earth-leakage trip on the mains plug of the welder.

 

[brightspark]

Have to disagree. Any rogue current is from the output of the welder, an RCD senses the difference between live & neutral currents in the mains input side. You'd have to use an earth-leakage trip on the mains plug of the welder.

true not thinking strait tired and tramadol cabbaging my brain wouldn't be any current imbalance