Houston we have a problem.....Melted insulation on NM sheath

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77401

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South of the Border in Houston, Texas


OK, I found this at a customers. The breaker kept tripping & she kept resetting it till it would not reset any longer. About every 18" I found a complete melt thru on the hot wire. Problem was traced back to a Keyless pull chain in a closet, ground wire had come into contact with the hot screw.

So why do you think the damage got this bad?
How much longer till full ignition?
 
Re: Houston we have a problem.....Melted insulation on NM sh

Re: Houston we have a problem.....Melted insulation on NM sh

77401 said:
The breaker kept tripping & she kept resetting it till it would not reset any longer.
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Wow! :shock:

To get that much heat going from current that is tripping the breaker, suggests to me that your client was standing at the panel and resetting the breaker over, and over, and over. . .I can imagine a relentless determination to get the power back on. :roll:

Thank goodness the breaker failed open, before enough thermal energy was released in the hot spots to cause ignition.
 
Re: Houston we have a problem.....Melted insulation on NM sh

Re: Houston we have a problem.....Melted insulation on NM sh

77401 said:
So why do you think the damage got this bad?
Click to expand...

Seriously? Schizophrenia. One of the clinical symptoms is repeating an action multiple times expecting a different result even when there never is one.

77401 said:
How much longer till full ignition?
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Probably never on a 120V branch unless that cable was in contact with something highly flamable. Not enough energy to sustain the arc.
 
Although I think AFCI is a good idea, a GFCI breaker or upstream recepticle would have tripped on this one too since it was clearly arcing to the gnd wire.

And can anyone explain to me why GFI breakers are more expensive than an AFCI that is a lot more involved and expensive to manufacture?

Seriously, that.is.whacked.
 
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Seriously? Schizophrenia. One of the clinical symptoms is repeating an action multiple times expecting a different result even when there never is one.
Click to expand...
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Is this what you mean?zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz :p :p
 
Until you can overcome stupidity I don't think anything will completely solve problems like this. I had a similar burned wire at an apartment complex. They had a small gym in the basement of the office building. After a pipe burst and flooded the basement the maintenance men brought in several dehumidifiers and plugged them into receptacles that were all on one 15 Amp. Circuit. Naturally the breaker tripped so they moved the hot conductor to one leg of a 40 Amp. breaker. Now the breaker didn't trip but the wire burned. I pull in two 20 Amp. circuits because one of the maintenance men told me that even before that they had the the #14 conductor landed on a 30 Amp. single pole breaker to run the fitness equipment. To make a long story short , the management at the apartments only wanted one circuit repaired so they could continue to try and burn the building down ( it worked before so why change anything ).
 
jwelectric said:
THANK GOD the NFPA is mandating Arc-Fault on ALL 125 volt circuits.

An Arc-Fault would not let this happen.

Another good point for the Arc-Fault
:)
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Yeah right......

Perhaps you should say an arc fault breaker is not supposed to let this happen. ;)
 
jwelectric said:
THANK GOD the NFPA is mandating Arc-Fault on ALL 125 volt circuits.

An Arc-Fault would not let this happen.

Another good point for the Arc-Fault
:)
Click to expand...

HUH?

77401 said:
ground wire had come into contact with the hot screw.
Click to expand...


Why didn't the CB trip?
Oh, that's right it DID...until it also became a casualty.

How does a CB doing it's job - until it expired - become less safe than an AFCI?
 
77401 said:


OK, I found this at a customers. The breaker kept tripping & she kept resetting it till it would not reset any longer. About every 18" I found a complete melt thru on the hot wire. Problem was traced back to a Keyless pull chain in a closet, ground wire had come into contact with the hot screw.

So why do you think the damage got this bad?
How much longer till full ignition?
Click to expand...

I think the ground wire wasn't in 'full' contact for quite some time, thus the serious over heating, and despite what your post says I think it was the current on the bare ground that burned the sheathing.
 
Sparky your right!
It did look like a light contact. Not a dead short. No telling why it happend as the fixture had been there for some time.
I would agree on your assesment of the ground carrying some of the current.

Another thing that was weird, is the burns were about 6" long, but only melted thru the outer covering every 2 feet or so.
 
Seen this before... The melting at intervals.

Haven't given it much tought till now, putting 2+2 together from other experiances and your describtion.

Exp. #1
Starting large motors under high LRA on SOJ, the cords would flex, and twist.

Exp. #2-500+ hearing a dead short in conduit rattle.

Exp. #3 Internet video of high voltage fault via junkie climbing a pole, lines flexed at fault.

Exp. #4 High LRA on elevator start that would rattle and flex conduit.

Seen something like this on romex years ago.....

Your describtion of wacko hammering the breaker with ~10000 amps with a over heated ground wire that flexed like a snake in the same pattern everytime she did it. The wire was the close to the same tempature* over the whole length, but the portion you are seeing is where it flexed outward. You may find that it alternated sides if run flat....

FYI, 3, and 4 wire conductors in cables, and MC/AC are transposed clock-wise, and high loads on clockwise systems will twist and bind the conductors closer together. Put in counter clock-wise system they will twist the other way and push apart.

*Another element also related to the flexing, that can contribute to the effect is that the higher magnetic flux created during the short will match up at different parts of the conductors and vary due to the total length of the circuit. Current flowing one way, and then returning the other, the hotter portions of the cable is where the effect was highest during the repeated shorts.

So you wave warned this nut-bag not to do this again? IMO an AF breaker would have done the same with the same treatment being applied by same woman.
 
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