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Can I use URD aluminum 1/0, 1/0, 1/0, 4 wire to run a 100 amp subpanel approx. 60' away from my main box? I plan I running it through my attic which in Arizona can get very hot in summer time if there are temperature concerns with this type of wire. Thanks!

Here's the wire: https://www.amazon.com/dp/B0748B57B3/?coliid=I1882CE450GCTE&colid=1CFF7GENXIV3T&psc=1&ref_=lv_ov_lig_dp_it

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    Uh, are you planning to run it in conduit, as an exposed cable, or what? Also, is this subpanel in the same building, or in a detached outbuilding of some sort? Mar 23, 2020 at 23:12
  • How is your attic currently insulated? And would you be installing the wire on top of that insulation, or would it be possible to put it underneath?
    – Nate S.
    Aug 21, 2020 at 19:28

2 Answers 2

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Here is the UL standard summary for that type of cable:

https://standardscatalog.ul.com/standards/en/standard_854_12

It says:

1.2 These cables have insulation of solid, extruded dielectric material(s) that are for use in wet locations at 75°C (167°F) and lower temperatures. Cables that are marked with a conductor type that includes the letters "HH" have insulation that is for use in dry locations at temperatures as high as 90°C (194°F) as well as in wet locations at 75°C (167°F) and lower temperatures. Cables that are marked with a conductor type that includes "-2" have insulation that is for use in wet or dry locations at temperatures as high as 90°C (194°F).

So unless you attic is getting above 90C (which is REALLY hot!) you should be good.

Are you sure you need 1/0 here? That's a huge gauge for 100A. But yes, that will work.

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  • Yes, 1/0 is huge.
    – JACK
    Mar 23, 2020 at 23:08
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    Single-rated URD/USE cable isn't legal anywhere indoors...see NEC 338.12(B) Mar 23, 2020 at 23:15
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    You are oversimplifying how thermal ratings work. 90C ampacities assume the wire won't reach 90C in a 25C environment. Remember, thermal transfer is proportional to temperature difference, so a 90C wire will cool only half as well in an 80C attic as it will in a 70C attic. Thus, you must derate for environmental thermal, and that derate can get Very Ouchy. Also, 1/0 is only one size large of the normal #1 you use for 100A. (for feeder). If anything, I'm worried OP isn't derating enough. Mar 23, 2020 at 23:47
  • Wow I learn so much as I follow these comments. Adding a simple one here, most all of the time, the sub-panel wouldn't be drawing anywhere near the rated capacity, if anything at all. Unless this is a "grow operation" for weed, or some other continuous draw that would require derating, I think the OP would be fine, esp. considering the gauge of the wire proposed. Mar 24, 2020 at 0:57
  • @GeorgeAnderson the issue is that in Arizona, roofs really do get to 90C. And guess what the ampacity of 90C wire is at 90C... Zero. Mar 24, 2020 at 15:26
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The rate of chemical reactions is highly temperature dependent, so if you have a reaction that's already highly likely to happen - oxidation of aluminum - then making things hotter is the last thing you want. I'd say that the aluminum wire does not belong in hot Arizona attics, and due to ongoing climate change it soon won't belong in any attics in the US and the most populous areas of Canada as a matter of sound engineering, even if the codes may be lagging behind. Apart from everything else that's wrong with your choice of wire, the choice of material is the most problematic. Oxidation does matter even if there's no connections: aluminum wire can develop cross-sectional cracks that then oxidate, and said oxidation growth, in presence of even trace amount of water, produces a fulcrum "crack spreader" effect. In ideal installation conditions one could live happy with aluminum wire in a hot attic, but given the realities of retrofitting anything in an area that's too hot to comfortably work with - forget it. Use copper.

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  • We know how to make terminations work with aluminum, and that's the only place where oxidation is a serious concern. You fail to address the bigger problems here...anyway, this question needs a VTC for lack of followup from the OP, so that's what it'll get. Aug 21, 2020 at 22:52

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