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Ran 12/2 wire through an attic in July and learned what heat does to the insulation | Electricians - Librear

Ran 12/2 wire through an attic in July and learned what heat does to the insulation

Last summer I had to pull a new circuit in a house in Austin. Attic was probably 140 degrees. After about 20 minutes I noticed the Romex outer jacket felt sticky and soft. When I pushed it through a joist hole, the insulation kinda peeled back in a spot. I had to scrap that run and start over with a fresh roll. Anyone else had attic heat mess with cable like that?

3 comments

3 Comments

jamieh764mo ago

And actually that sticky feeling isn't just from heat, it's UV damage if that cable was sitting in direct sun before you pulled it. Romex is rated for 90 degrees Celsius but the sun bakes the outer jacket way worse than attic temps do. You might have been fine if you'd kept the roll in the shade until you used it.

richard_ramirez4mo ago

Idk I always thought it was just the heat that made that jacket get gummy but @jamieh76 you might be onto something with the UV thing. I had a roll of 12/2 sit in my truck bed for like two weeks one summer and the whole outer sheath got that weird tacky texture all the way through the roll. And that was just sitting in the sun, not even in an attic. So maybe it is more UV than I gave it credit for. Gonna keep my rolls in the shade from now on for sure.

ramirez.caleb4mo ago

Yeah but @jamieh76 I gotta push back a little on the 90 degree thing. Romex is rated for 90 degrees Celsius for the WIRE insulation inside the jacket, but the outer PVC jacket itself can start getting weird way before that. Direct sun exposure makes the outer jacket brittle and sticky way faster than just heat does, you're totally right there. But the UV thing is actually more about long term breakdown than just a few hours in the sun before you pull it. Ive seen rolls sit in a truck bed for a whole afternoon and they're fine to work with, just maybe a little soft. If it's actually sticky and gummy, that's usually from the jacket getting too hot during manufacturing or storage, not just a quick tan. Your point about keeping it in the shade is solid advice though, no argument there.