How would you ground/bond this?

[travish]

We are building a resistance welding machine here at work, It has 3 welding transformers that are each on casters so they roll to change for different product widths. My question is specifically from the cabinet to the welder. There is no means for grounding the transformers inside the x-formers. I ran liquidtite from the panel to each x-former with only the phase conductors inside, because there is only 2 lugs inside the x-former.

can I run one ground wire from the cabinet to the frame of the machine and then ground each x-former to the frame of the machine, or do I need to run 3 ground wires and land each on the corresponding welder frame?

Thanks
Travis

 

[erickench]

In accordance with NEC 250.118(6) the LFMC cannot be used as an EGC if the length exceeds 6 ft. You might be better off running one ground wire from the cabinet to the frame and then grounding the transformers to the frame. Since these transformers are separately derived I would look at NEC 250.30.

 

[travish]

yea I knew that the liquidtite could not be my ground, My opinion is I grounded the frame of the machine with 1/0 copper, OCD is 400a. The frame is welded 4" sq tubing, it is not a bolted connenction where paint may interfere with the connection. A bonding wire (1/0) from each weld station to the frame, to me is ok to provide the fault current path. But I wrestle with the fact that the ground wire is not technically run with the phase conductors though it is laying beside them.

 

[augie47]

I would say your thoughts are in-line with NEC requirements. Your 1/0 bond may well provide an adequate path, but 300.3(B) would require the equipment ground to be routed with your phase conductors.

 

[TimK]

Weld???

Weld???

I can understand the need to ground the frame, but why would you need to bond across the welds? Also, and this might be an assumption, but if the transformer is bolted to the frame is that not an approved electrical connection?

 

[travish]

I was just saying that the main machine frame is welded together, which is a better connection than a bolted connection which depends on surface contact, bolt tension and all the paint being removed.

I am not bonding around the weld joint of the frame, I am needing to ground the frame that the welding transformer is on. It rolls left and right to accomadate differnt width parts that we are going to weld/make for production parts. it is bolted to the main machine when you get it to the correct width, look at the 2nd picture, the 3 units with wheels are the welders. so I need a ground wire for this.

A bonding jumper from each welder to the frame, I guess isn't really run "with the ungrounded conductors"

I think I am being to picky, I am trying to put a distance on "ran with the phase conductors". If it was a 18 inch wide cable tray with three 400a feeders in it and ran 1 ground wire in the cable tray, the ground couldn't be right beside all 3 feeders it can only be beside 1 or 2 feeders. I am worrying about a distance of 10ft under a machine where there is 4ft from the ground wire to the phase conductors, It is almost that much distance/seperation in large service entrance panels.

some times it is almost a curse to feel like you have to do everything as close to perfect as you can.