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I'm looking to add some lights on motion detectors (un-switched) and security cameras under the eaves of our house. I know standard romex is often used in attics, but the soffits seem like they might be more exposed to weather. Our soffits are enclosed, like so: (picture from wikipedia.org) View of Soffit

So, do I need to protect any wires which reach into the soffit, such as would power the pictured light? Or should I use wire rated for exterior use? I'm also plotting some Cat 5e runs of a similar nature, should those be protected/exterior as well?

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I believe exterior grade wiring is more resistant to high moisture and UV degradation, which shouldn't be much of a concern for an attic or soffit space since it's sheltered. –  BMitch Aug 30 '12 at 1:58
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Regular NM is fine and meets NEC requirements. No need to use UF cable –  shirlock homes Aug 30 '12 at 9:36
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The cable is not the problem in this situation, it's all enclosed so there should be no problem using NM cable. You will want to make sure the junction box is weatherproof, and that all openings are sealed properly. Whenever I do cable runs in the rafters, I always add a drip loop before entering junction boxes. It's not specified in code, but if you get a leak in the roof you won't have to worry about water following the cable into the junction box. –  Tester101 Aug 30 '12 at 11:47
    
@Tester101 You always add value! –  bib Aug 31 '12 at 19:03
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2 Answers 2

up vote 5 down vote accepted

While soffits usually have some venting in them, the interior of soffits are interior spaces not much different from unfinished attics to which they connect. Attics do not require different wiring from other interior spaces, so it doesn't seem that soffits should either. While attics (and basements) may often be more humid than some other spaces in a wiring scheme, these do not pose significant problems for normal interior cabling and outlet boxes.

The fixture illustrated has a weatherseal around the base (as do all exterior fixtures) to keep water from infiltrating. On the other side of that seal, no liquid water should be present.

It seems likely that the same applies to CAT5e cabling. However, as has been discussed elsewhere, fire rating of low voltage cable is an issue. Use properly rated cable.

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I'm no expert, but I'd use internal rated cables. The exterior grade stuff isn't necessarily 'more weather resistant', but rather the interior stuff is safer in case of a fire (the insulation around the wires doesn't produce anything toxic when burned). Since it's under the roof, I'd want the same stuff that it's in my walls.

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