Bad Wire NM / MC

[69gp]

Although the thread was closed about the bad NM cable I can add a little to this only about MC cable. We were doing an addition to a library that involved the contractor cutting through a granite and brick wall. A stairway and elevator was installed in a tower and we had to run several circuits between the existing building and the new tower. Everything was blue boarded and skim coated. Covered 100%. Devices and lights were installed and then we went to power the circuits up. POP, POP, POP all the circuits for the tower kept blowing. Check boxes and devices for signs of shorts and none could be found. All devices and splices were removed and when you tested between the black and white we had dead shorts. Thought that maybe the sheet rocker used some long screws. After removing some blue board there was no sign of screws in the cable. After looking at the cable you could see holes blown through the aluminum jacket.

What happened is when they assembled the cable they twisted the conductor to tight causing the black white and green conductors to short together. The best the manufacturer was going to do for me was to give me another 1000' real of 12-2 MC. Sorry to say i kinda blamed the hanger for using long screws.

 

[Sierrasparky]

Sounds like very poor quality assurance.
Kinda like the one who found a splice in a 1000' roll of 12-2 NM some time ago. Who would allow such. You cannot have a splice mid run of NM concealed.

 

[kwired]

I saw a piece of 6-3 NM cable that was "factory spliced".

It wasn't my install or my cable, but the guy that did find it brought it to a CEU class to show. He said there was an unusual bulge in the sheath that made him cut it open to check out what was going on there.

 

[480sparky]

I have seen two splices in the middle of the conductors in NM. Both times I found them while making up the panel.

I would strip the insulation off, and there would be two distinct colors of copper exposed. They were both cut flush and somehow brazed together. I wish now I had saved them, but I cut them off and let them fall to the floor.

Considering how much NM is in a house, compared to how much copper is actually exposed during the process, I have no doubt there's quite a few more out there that I've installed, just never discovered. I have, however, found a few open conductors in new NM installs. No doubt, it's possible that it's one of these factory connections that failed.

This is a listing issue with the manufacturer, though, and not an NEC splice that is required to be accessible. This is why I not not only meg, but ring out all new installations.

 

[69gp]

I have seen two splices in the middle of the conductors in NM. Both times I found them while making up the panel.

I would strip the insulation off, and there would be two distinct colors of copper exposed. They were both cut flush and somehow brazed together. I wish now I had saved them, but I cut them off and let them fall to the floor.

Considering how much NM is in a house, compared to how much copper is actually exposed during the process, I have no doubt there's quite a few more out there that I've installed, just never discovered. I have, however, found a few open conductors in new NM installs. No doubt, it's possible that it's one of these factory connections that failed.

This is a listing issue with the manufacturer, though, and not an NEC splice that is required to be accessible. This is why I not not only meg, but ring out all new installations.

We use to work in a factory that made cables and when they spliced a cable it was welded. Depending on the size of the wire they had a welder where each end of the wire would be clamped in and then positioned so that the ends were almost touching or butted together. Apply the current and the cable was welded. Some times a little filing was required to get the OD back to a normal size. The annealing done after is to make the wire soft again.

Check the process out.

https://www.youtube.com/watch?v=j_ECTjVYiSc

 

[mopowr steve]

I was one of the guys that found a "crimp on butt splice" in a section of 12/2/G NM-B and another time had a piece of 12/3/G that had the twisted conductors so tight it split the insulation on the conductors and shorted.
I sure hope Fire/EE investigators are aware of this practice from manufacturers as I could see an innocent someone getting into some big S if something goes bad especially if a life is lost!