Temperature rating of NM-B cable

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Old 04-18-10, 07:47 AM
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Temperature rating of NM-B cable

What is the temperature rating of NM-B cable? Is it 90 deg. C? The reason I ask is that newer lighting fixtures require 90 deg. C wiring for the fixture. If you upgraded a ceiling fixture would you then have to run new wiring?

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Old 04-18-10, 08:51 AM
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I think I found the answer to my own question. See the link below:

http://www.nema.org/stds/eng-bulleti...oad/Bull92.pdf
 
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Old 04-18-10, 09:39 PM
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The ambient temperature rating of NM-B is 90 degree C. The rating of older NM cable is 60 degree C. Plain NM cannot be used with most newer light fixtures.
 
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Old 04-22-10, 03:23 PM
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Originally Posted by ibpooks View Post
Plain NM cannot be used with most newer light fixtures.
Plain NM wire meaning cloth NM, correct?

Lets say I have a friend , who used cloth NM wire with a new recessed fixture containing a CFL. How dangerous is this?
 
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Old 04-22-10, 03:35 PM
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Originally Posted by HansGruber View Post
with a new recessed fixture containing a CFL. How dangerous is this?
The CFL doesn't produce nearly as much heat as an incandescent bulb, so in this particular case it's not as big of an issue. It's a big deal if the CFL is replaced with an incandescent or halogen lamp.

What happens is that the excess heat bakes the insulation off the wires. In the best case, they short to the box and trip the breaker. In the worst case, they spark and start a fire in the ceiling. I have seen many light fixtures in which the wire insulation cracks off to dust in your hand as soon as you touch the wire. This is caused from using old wire or from using a bulb that exceeds the wattage rating of the fixture.

Actual Cloth NM with rubber insulation is at least 50-60 years old and tar-cloth NM with plastic insulation is at least 40 years old at this point, and I do not trust either for re-use. It should be left as-is or replaced if any new-work is done. This is mostly an issue of these materials having lost their flexibility so they cannot be manipulated very well (into and out of boxes, staples and clamps for example) without damaging the insulation. You have to treat it delicately when changing a box to not damage these old wires.
 
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