Evaluating a kinked cable

dave11May 7, 2010

I took a close look for the first time at a cable running through the joists in my basement, which runs from the main to a garage subpanel. It's a 6/3 NM cable, length about forty feet. It's secure up in the joists, but I noticed one area that looks like it had been pretty badly kinked, then straightened. I assume it happened either before or during installation, because the cable doesn't have enough slack or play to have kinked after the install.

It's the only area like that. My question is what, if anything, to do about it. The cable sheath is intact, but the wire bundle underneath has a ridge in it that can be seen and felt.

The breaker on the main for this cable is 50 amp. Now, I never come close to that amperage in the garage. I have a large compressor, but wired for 240 it draws I think 18 amps. The lights when all on draw 3 amps. The receptacles can carry 20 amp, but they're not in use most of the time. The prior owner had a welder, which must have needed the extra amperage.

Given that my expected ampacity in the garage is way below the cables rating, am I being goofy by wondering about the kink in the cable?

And would simply touching the cable at the kinked area, after its under full load for say an hour, be a decent way to test if there's a problem? Obviously, if it warmer there, then there's a problem, but if it's the same temp, is there no problem?

I suppose the alternative is to cut out the kink and splice the ends, but I don't want to if it's not necessary.

Thanks for any input.

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The NEC says that bends in NM cable shall be made so that the cable is not damaged.

The NEC also says that the minimum inside radius of the curve for any bend shall be at least 5x that of the NM cable diameter.

For example, if the cable has a diameter of 1", the curvature of the bend can be no less than that of a circle created when the circle's radius is 5" (a 10" diameter circle).

That's a pretty shallow curve.

It is pretty obvious this cable assembly was bent far beyond that of its listing at some point.

And while the 'kink' itself may not pose overheating problems with normal current flow, damaged insulation on the individual conductors or frayed strands within the conductors can cause arcing under the right load conditions.

Arcing can cause a fire without ever tripping this feeder's breaker.

That is reason enough to change the feeder cable or remove the damaged area by splicing it.

But will it ever become a problem?

Chances are this feeder can function well and never cause any problems whatsoever.

But because it was overly bent, the chance for problems has increased manifold.

It's your call, but the prudent thing is to make the repair and sleep better at night.

    Bookmark   May 8, 2010 at 6:01AM
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