How hot is too hot

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jxofaltrds

jxofaltrds

Inspector Mike®
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Mike P. Columbus Ohio
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ESI, PI, RBO
Working on a job where the furnace did not shut off.

Temperatures in the house were high enough to melt candles (6") to nothing, plastic blinds fell off the walls, tub surround seperated from the wall, etc.

2 days later the walls were still warm to the tough.

I feel that the older 60C wiring might have been damaged.

My problem is how to prove my opinion.

PS no fire only heat.

Mike P.

It's been a while
 
If you are concerned enough, try to propose to the owner a megger test. They may not go for the whole house, so propose a section of the house, and try to perform this test where you feel the heat was at its highest temperature.
 
60?C equals 140?F. It would have to be hotter than that in the room to reach that temp in the walls where the wiring is. Did it really get that hot? Just asking.
 
electricman2 said:
60?C equals 140?F. It would have to be hotter than that in the room to reach that temp in the walls where the wiring is. Did it really get that hot? Just asking.
Click to expand...

I was thinking the same thing! The walls should have kept the wires from reaching that high of a temperature.

FWIW: My sauna reaches 160?F and the wiring inside the sauna wallis not an issue. It is romex!
 
Working on a job where the furnace did not shut off.

Temperatures in the house were high enough to melt candles (6") to nothing, plastic blinds fell off the walls, tub surround seperated from the wall, etc.

Tough to believe. That would have to be a hell of a heating system unless it was 100 degrees outside!

-Hal
 
Re: How hot is too hot

jxofaltrds said:
I feel that the older 60C wiring might have been damaged.
Click to expand...
I think it should be fine. The 60C wires are not rated for 60C. They are rated for a 60C rise in temperature (due to I2R heating from current flow), and based on an ambient of 30C. So they are rated to handle a continuous (i.e., for years and years) temperature of 90C (194F). This event will not have caused the wires to get that hot, and to stay that hot long enough to have damaged them.
 
Charlie,

Would you explain how 60C wire is not rated for 60C? Table 310.13 lists TW wire with a Maximum Operating Temperature of 60C. That doesn't sound to me like a temp rise.

Also, the correction factors at the bottom of Table 310-16 show a 60C conductor at an ambient temp of 60C having no allowable correction factor. Again, that's not a 60C rise, but rather an ambient temperature.

My understanding is that if a 60C wire is in an ambient temp of 60C, its allowable ampacity is 0 amps because any IR2 heating from current will exceed the rated operating temp.

Bryce
 
You have a good point. I had not looked at 310.16 from that perspective before. The term "maximum operating temperature" is not defined in the NEC. But if I were to be allowed to suggest a definition, I would say it means "ambient temperature plus temperature rise from I2R heating." So I suspect you may be right. :oops:

Anyone out there have any facts to offer? If not, opinions would also be welcome. :?
 
Re: How hot is too hot

charlie b said:
jxofaltrds said:
I feel that the older 60C wiring might have been damaged.
Click to expand...
They are rated for a 60C rise in temperature (due to I2R heating from current flow), and based on an ambient of 30C.
Click to expand...

Are you sure Charlie? The heading in table 310.13 says "Maximum Operating Temperature". I take this to mean including ambient, not degrees rise above ambient.

sorry Charlie. Didn't see your reply when I posted.
 
OK. I stand corrected. I should say I sit corrected, as I cannot type while standing. :roll:

Many thanks to Bryce, John, and Brad.
 
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