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I am running wire for some recessed lights in my finished attic. It is a typical gable roof; the interior is plastered with 2x6 joists. Im curious to know if running Romex in the ceiling between the joists is ok. There is the occasional nail coming through the roof and wondering if this could be an issue. Also, if we ever put a new roof on the house, there could be a stray nail that nicks the Romex. The other alternative is Armored Cable which would be a huge pain...

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The National Electrical Code requires you to maintain 1 ¼" spacing back from the edges of framing members.

*300.4 Protection Against Physical Damage. Where sub- ject to physical damage, conductors, raceways, and cables shall be protected.

(A) Cables and Raceways Through Wood Members.

(1) Bored Holes. In both exposed and concealed locations, where a cable or raceway-type wiring method is installed through bored holes in joists, rafters, or wood members, holes shall be bored so that the edge of the hole is not less than 32 mm (1 ¼") from the nearest edge of the wood member. Where this distance cannot be maintained, the cable or raceway shall be protected from penetration by screws or nails by a steel plate(s) or bushing(s), at least 1.6 mm (1/16" in.) thick, and of appropriate length and width installed to cover the area of the wiring.

Exception No. 1: Steel plates shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing.

Exception No. 2: A listed and marked steel plate less than 1.6 mm (1/16" in.) thick that provides equal or better protec- tion against nail or screw penetration shall be permitted.

So if you drill through the center of your 2x6" rafters you are complying with the NEC.

However, if you are worried about future damage to your wiring from roofers, you could use armored cable. But if a responsible, licensed, insured roofer is hired they should use the proper length nails and there shouldn't be any threat to you cables.

If you really want to overbuild it use rigid pipe and wire and rest easy when the roofers come. 😉

  • The question was about wiring behind finished plaster on the walls, not subject to physical damage. – batsplatsterson Nov 18 '15 at 11:57
  • Uhh actually he said ceiling not walls and he is talking about wiring between the rafters so I assume he is removing some of the plaster to accomplish this. The code reference still stands you need to maintain a 1 ¼" clearance from the edge of the rafters even if you run parallel to them. – ArchonOSX Nov 18 '15 at 13:11
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    It's finished space, i don't think the walls would be finished but not the ceiling. Normally in "old work" you're fishing the walls, possibly making small holes in the plaster in places but not removing much. You don't have to secure the cable along the rafters if you're fishing it in finished walls / ceilings, certainly isn't subject to physical damage. – batsplatsterson Nov 18 '15 at 13:26
  • Ok yeah I see what you are saying. If he is fishing it then I don't why he's worried about roofing nails. But I guess he will have to figure that part out. – ArchonOSX Nov 18 '15 at 17:24
  • Actually thought of one more thing though. To get from the wall to the ceiling he will have to remove plaster at the top plate and drill through it. It sounds like it will be a lot of remodel unless he already has lights in the ceiling to run out of. – ArchonOSX Nov 21 '15 at 19:11
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You can argue that NM is less likely to get damaged in old work where you're fishing it unsupported behind an existing wall. Since it isn't stapled down inside the wall, a nail is more likely to push it around than penetrate it.

Personally I'd use MC cable for the reasons you mention. I think anyone would agree that there's less chance of dangerous arcing than with NM, even if it's a longshot with NM.

MC isn't really so hard to work with. Hardest part might be upgrading to metal boxes where it ties in to existing cabling, if you have plastic boxes.

There's always wiremold...

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When I add lights like this it depends on the insulation , if it is insulated and I have to remove plaster I will staple NM on the side in the middle of the rafters even older 2x4" construction this meets code if I have to drill I use the center in most cases or a steel plate to protect the wires if less than 1-1/4" from either edge of the 2x4 / 2x6 with the wires centered I have never put a nail through NM or been called back when contractors did the finish work for a dammaged wire. no insulation we usually punch holes and use old work boxes wire is free to move arround this is not as good of an install as the wire is not stapled and the boxes are only held in with "wings" to the sheetrock/ plaster but on remodels they have never red tagged a job like this

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unless he is talking about running romex above the trusses in between batting, like if the roof isnt sheeted, then as long as he nails it 1&1/4" away from any surface that will get nailed: use romex! i wouldn't even run mc cable up above the trusses, if that's even what he's talking about. who knows. i can't think of any reason whatsoever to use mc cable up there. mc cable isn't even rated for being subject to physical damage, like flex is.

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