How much heat can NM take?


Old 07-31-06, 07:11 AM
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Join Date: Dec 2005
Posts: 257
How much heat can NM take?

I recently had to replace my dryer vent tube (electric dryer). My laundry room is an interior room of the house so the run is somewhat long; about 7 feet up the wall and 8 foot down a joist and out of the side of the house. The previous setup had been in place for about 20 years and used plastic, corrugated, flexible tubing. I replaced it with rigid aluminum tubing for better flow and safety (and holes in the tubing).

When I was replacing the tubing I noticed a wire (NM-grey) about a foot from the exterior wall going right through the path I needed to lay the tubing. I pushed the tubing through and used my hand to lift the wire over top of the tubing.

My question is: How much heat can the NM take? I'm not doing anything different that they had been doing for the past 20 years. I ran the dryer on high heat for 20 minutes and I could wrap my hand around the tubing without need to pull away. When I felt the tubing near the end or the run (closer to where the wire is) it was even cooler.

Is this OK? Thanks
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Old 07-31-06, 08:56 AM
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Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,537
Old NM is rated for 60 C (140 F). Newer NM-B is rated for 90 C (194 F). The important thing is to examine the cable. If the insulation or jacket is brittle and cracked or cracks off when you touch it, then the cable was overheated and needs to be replaced. If the insulation is intact and somewhat pliable, then you should be okay.
Old 07-31-06, 10:14 AM
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Join Date: Dec 2005
Posts: 257
It looked and felt OK when I examined it.


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