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:
- 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.
- 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.
Something is wrong with the wiring to the ceiling fan or with the connections to the switch.
Possibly in between the last succesful test and the first unsuccessful use of that switch something has damaged the wiring (e.g. a nail into the wall? strain on the wires?)
I would isolate the circuit at the breaker box, test for voltage at the switch and then test the wires attached to the fan switch for unexpected continuity between live & neutral, live & earth. I'd then detach the switch from all wiring and test for continuity across it's contacts with the switch in each state.
Best Answer
Code considers areas normally dry to be ok for nm cable 334.10.A under your roof is one of those locations that Is not subject to dampness or wetness some jurisdictions consider a porch a damp location it usually depends on the roof type for example a normal 3 tab roof with tarpaper is considered a dry location, but a roof with corrugated plastic and even metal if not insulated is a damp location. If you use a GFCI in this location it needs to be WR weather rated the electronics are coated to protect them from moisture and they can not be located above 5’7” but they can be used to protect the load side. I would think as long as above 8’ exposed romex or NM cable would be allowed by your description soffits & normal roofing.
Updating because of change to thhn;
Where damp or wet THHN /THWN cable (almost all thhn is dual rated but thwn is the wet rating) needs to be used. Your circuit will need to be in conduit box to box 1/2” will be fine for your setup. All wiring methods below 8’ require protection but THHN requires conduit from start to finish.
The reason most home owners use UF and NM wiring methods is because 12&14 gauge circuits with thhn requires 3 different colors hot usually black, neutral usually white, and ground usually green. (Hot can be any color other than gray, white, green. Neutral can be white or gray , ground can be green or bare).
Home owners usually use pvc conduit as it is easy to cut and glue. From your box there can not be more than 360 degrees in bends or 4 90’s wire pulls get tough after 3. If you need more than 360 a conduit body is Normally installed I use a conduit body at a 90 in many cases called an LB, LR or LL the hole being back , right or left. There are also form C body’s that are inline , a box can also be used.
The one thing I see home owners do wrong in most cases is the wrong kind of box. Outside a bell box or weatherproof box is required unless recessed in the building structure.
The pvc conduit needs a strap within 3’ from the box and supports per table 352.30 1/2”-1” max space 3’
These are the additional things to think about but should get you on your way to a safe instal of your lights and receptacles.