Re: Welding Cable
Agreeing with both Don & Dereck I would like to relate the following, in addition to what was said; some real world advise.
In our main facility, we have a number of 250A, 480Y/277V 3 ph lighting panelboards. A few years ago, when these panels and feeders were replaced, engineering specs called out for feeder conductors, and of course pipe, to be sized in accordance to limit voltage drop to 3%. This was for the run from the unit-substation's distribution to the panel. Some feeders actually became 2 sets of 500kcmil CU in 4" c. The difficulty arose in the fact that the lighting panel boards were not increased in size physically to allow for the larger and more numerous cables; it remained 225A. Even though these were custom made stainless steel panel boards, and contained the main, and distribution breakers, they also had internal heaters with full sized Honeywell controls; there was not much additional space. What the contractor had done was to bring both of the conduits and conductor sets into the panel board. Another factor was the frame size of the main, [in this case], molded case switch. It did not allow for the termination of 2 sets of 500 kcmil. Let's face it, with all of the conduits, these main feeders, and the branch circuitry, there was little room.
What the contractor had done to terminate these oversized main feeders, was to install a distribution block with short sections of welding cable between the block and the main. I will not comment about inspection or follow-up; it was just installed that way.
Over the next 20 months, we lost 80% of the mains devices, not because of the double sets of oversized cables, per se, but due to the welding cable, which was just terminated in the screw lugs of the mains thermal cycling and failing. Lugs just vaporized.
We had to go back in each and every case, and re-work the feeds so that the double conduits with oversized cables terminated outside of the panel board, and then brought down a single set of 300kcmil; the largest conductor approved for the new mains & lugs.
I would have never thought that the real thermal failure & damage would have been caused by the improper termination of the welding cable in the mechanical lug. By the way, the panelboards were only loaded to about 55% and were always on.
This cost us a few hundred thousand dollars to repair, and countless hours of preparation and inconvenience to execute. I guess if I have a point,,,,don't use the welding cable. And if you must use a highly flexible connection, make sure that you use the proper terminations.
