Sign up ×
Home Improvement Stack Exchange is a question and answer site for contractors and serious DIYers. It's 100% free, no registration required.

You guys are one of the best electrical help web-communities, so thanks for your time and efforts!

I am advising some homeowners who need to rewire their first floor on Long Beach Island, NJ after hurricane Sandy flooded the place. The house has a few complications. Wires need to be run along brick walls with no wire cavities inside framing to get to their destinations. In the past wires were routed through the crawl space which is a very damp space with an almost always wet rock floor and very little room to work. Electrical work was done poorly with unnecessary junction boxes. Everything metal had rust. That can all be fixed more easily because the subfloor is removed and the floor joists are exposed. Wires can be run along joist and over running boards with no junctions in the crawl space. There is no consensus in my research about using THWN wire for damp locations or just the regular Romex in a damp crawl space. My feeling was to put in the THWN for wet locations in all runs under the floor through the crawl space and up to the outlet boxes they feed since no one can complain about THWN being in parts of the run. There is a question in my mind whether the Romex feeding the crawl space THWN wire should not also be THWN since its paper wrapped grounding wire would be vulnerable to any water that climbed up the THWN wire running in the crawl space into the junction where the Romex feed the THWN.

The homeowners are worried about running any wires in the crawl space and wanted a way to keep all runs in the upper living area. The two complications are the brick walls running the length of the house and the fact that a very nice wood ceiling not so easily messed with is the only thing not ruined, plus it is a good idea not to drill holes through the main support beams in the ceiling/upper floor of this 100+ year old house. I suggested building a little soffit along the brick wall where they have a piece of wood trim anyway. The soffit will run the wires and be the trim. I cannot speak with confidence about the aesthetic result, but it should be fine if its done well. My electrical concern is the fire code parameters of the soffit for the wiring. The soffit will run three 12/2 wires and maybe one 14/2. The soffit will have an exterior measurement of 4 by 4" and the interior about 3 by 3". It will be made of wood that can either be painted of maybe left to stain. So it won't necessarily have drywall around it. They wanted the front to be removable--to unscrew so that if another flood damages the outlets the wires running to them can be removed and rerun more easily.

Does a soffit with three 12/2 wires and a 14/2 wire need to be of a certain cubic size that would be larger than the size I am suggesting (3 by 3 inches interior space)?

Does the soffit need to be dry-walled with the edges dry-walled to meed the fire blocking standards or can a wood soffit with seams where the edges meet satisfy the fire code burn rate for where wires are run?

Is there a preference to run wires in a soffit above verse a problematically wet crawl space difficult to get to and work in? And what sort of wire should be run? THWN?

share|improve this question
If you find yourself needing to run multiple cables from point A to point B, consider running 1 larger cable to a sub panel, then branch out as needed. – Jay Bazuzi May 27 '13 at 6:55
You might consider using PVC conduit and similar products that are more water resistant than steel in the crawlspace. Aesthetically I think running in the crawlspace is the best bet. You could also consider a conduit run in the soffit, with periodic drywall firebreaks inside. Generally horizontal soffits do not require firebreaks, as long as the soffit does not give fire a way to travel vertically, or pass thru a firebreak (wall). Your local building official will probably have an opinion and will be the final say on the matter. – mfarver May 27 '13 at 16:36

1 Answer 1

The crawl space case

Wiring in a crawl space (wet location) can be done successfully using a variety of means:

  • THWN (pretty much all building wire you buy at the borgs these days is both THHN and THWN) in either rigid metal conduit or schedule 40/80 PVC conduit
  • Type UF or NMC multiconductor cables, but not ordinary NM-B, or
  • Type MC cables rated for wet locations (i.e. those with an overall PVC jacket and THWN or XHHW-2 internal wires)

However, given the circumstances (i.e. the persistent wetness in the crawlspace), I'd be most comfortable with THWN in PVC and nonmetallic junction boxes down there, with the risers being THWN-in-PVC as well. The main downside, though, is that not only is this an expensive way to wire a house, most "wet location" electrical equipment will not survive being bathed in another storm surge!

Wiring in soffits

The soffit proposal is elegant; however, the main problem is going to be providing access to junction boxes -- you'll need to have blank plates interrupting the molding (preferably on the bottom of the soffit) in order to provide access to junctions:

314.29 Boxes, Conduit Bodies, and Handhole Enclosures to Be Accessible. Boxes, conduit bodies, and handhole enclosures shall be installed so that the wiring contained in them can be rendered accessible without removing any part of the building or structure or, in underground circuits, without excavating sidewalks, paving, earth, or other substance that is to be used to establish the finished grade.

Further more, you'd have to use an "old work" type of junction box in this application as you wouldn't have framing members inside the soffit to attach the boxes to. While the 3" by 3" soffit interior should be adequate for cabling, I would not use a conduit inside it due to the soffit interfering with conduit body access. I do not know of any fire code requirement for horizontal cable chases other than them requiring firestopping when they penetrate a firewall; however, as mfarver pointed out, your AHJ has the final say on that, and internal firebreaks in the chase would be wise.

Could a busway be the best way?

Another option for the soffit wiring case would be to use a plug-in, non-ventilated, totally enclosed busway system with branch circuit breakers at the outlet taps and type MC cable run exposed or NM run in surface raceways for the drops/horizontal runs to outlets and luminaires. While unusual for a residential application, plug-in busways offer a high degree of flexibility in layout, and can be subdivided so that branch circuits can be moved with only modest impacts on power to other parts of the house.

There are two drawbacks to this approach, other than it being relatively costly, though:

  1. A means of access into the soffit that does not damage the soffit would need to be provided: either the soffit side panel could have hinged access panels in it, or the screw system designed so that the side panel can be removed and replaced without causing any damage to it. See NEC 368.10(B) for details.
  2. You'd need to locate the branch circuit breakers at the tap-off points -- while this doesn't limit the height of the busway, as per NEC 368.17(C) and Point 1 in 240.21(A), there has to be some sort of rod, chain, or what-have-you attached to the breaker handle so that it can be operated from floor level.
share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.