Ceiling: Framing & Electrical Rough-in

[DeMac]

We've framed enough of the ceiling to install the overhead Electrical rough-in. The permanent wire structure is being used for our temporary lighting, while we build. I'll document our process in this thread.

I'll briefly cover the ceiling framing we chose. A simple process repeated often at skoolie.net, neither unique or complex.

Overhead Electrical Rough-in includes any overhead raceways & wiring.

Usually lighting, switchlegs, rooftop A/Cs, exaust fans, ceiling recepticals, smoke & CO2 detectors, sign or flood lights. Overhead often includes low voltage & communications, which I'll complete separately.

The high voltage wire methods used on Freddy D are commercial grade. Steel armored cable, steel boxes, steel fittings, steel supports.

 

[DeMac]

Tek Screws & Lumber

JakeSales.com has a large selection of fasteners.

This 270 ct box was about $50
Wood to Metal framing screws
#12 x 2-1/2" Reamer Tek Star/Torx T-30 Screw Head

Self-Drilling Wood to Metal Screws for Flatbeds, Trailers, or for Fastening Wood to Steel

To prevent lifting, the screws' tabs ream the wood to 7/16", then break away as they hit the steel. The tip drills the steel, then taps/threads the hole to 24 tpi. The countersink head design even cuts it's own recess. Speedy.

To stay perpendicular, we predrilled our wood framing with 3/8" pilot holes.

Ceiling framing lumber, two by three (1.5" x 2.5" actual) supported using two tek screws at each rib.

 

[DeMac]

After breaking a few screw tips. Even when using cutting oil, I found it better to drill, passing through the wood pilot holes, into steel rib using an 3/8" oiled cobalt bit, prior to driving in the tek screws.

The screws do well at self-tapping, only okay at self drilling. A partner w/ a sized length of 2x4 to hold the wood tight against the ceiling rib is required. Clamps are ok, but tough to align.

Make sure to size your screws to the thickness of your framing framing material.

 

[DeMac]

No jig or Craig tool

I don't have a Craig tool. I've had intentions of buying one for years. Maybe the price helps me forget.

My butt joints were completed while clamped. Predrilled (5/64"?), then toe-nailed using two 2-1/4" deck screws (also by Tek)

Blindside is toenailed, as well.

 

[DeMac]

Member Spacing

The center four framing members (three spaces) are 16"oc. The outside two are each spaced at 12"oc

I used string to find the center and measured off the string to each stud. Originally, I was transferring the string center onto the ribs with sharpie. Seemed harder to see the black.

 

[DeMac]

Center Six Feet

Center Six Feet complete. C-clamp still in place.

(where am I standing)

 

[DeMac]

Sliding Box Brackets

These telescopic brackets, with adjustable depth, are perfect for suspending mechanicals within the spray foam. (electric/data boxes & conduit, a/c condenser lines, pex, pvc & copper plumbing, propane gas, stereo speakers, etc)

Sliding Box Brackets are manufactured by nVent-Caddy, Erico, HoldRite, & others. They're available at electric supply, plumbing supply shops & big box stores, too.

Attached to & touching wood only, zero conduction. This is a 1.5" deep lighting box, same as the framing. With the 1.5" rib exposed, this allows for total of 3" spray in insulation. Ceiling down to 6ft, 4-1/2" already.

 

[DeMac]

Box Location, Alignment & Spacing

I never assume the wall is straight, floor level, or ceiling flat. Construction is string used for accurate & speedy box alignment.

The lighting boxes are spaced about 4 ft apart. Each centered and aligned over a particular work space. None are near the ribs, by design.

 

[DeMac]

Wire Selection

12/2 Solid Copper MC w/ Steel Armor & Polypropylene Wrap. 250ft / $175, red anti-shorts included. Available at Electric Supply Shops (big box stores typically carry Aluminum armor, aka: Armorlite).

12/2 is used throughout for 120v/20A circuits such as receptacles, small appliances & lighting.

Our bus roofs are very hot, increasing resistance. I use 20A rated wire but will de-rate the overhead circuits with 15A overcurrent protection devices. Both 20A rooftop AC circuits utilize 10/2, rated at 30A.

 

[DeMac]

Boxes then Holes

Before we open the wire roll, I walk though with a drill, pulling an imaginary wire from box to box & drilling holes where they're needed.

Metal in the eye is no joke. Wear glasses.

For a tight fitting 7/8" bushing, I use a 1/2" hole-saw, then usinh a step bit / unibit I ream it to 13/16". Use lube. Test fit bushing until it goes in. (Gudentiche.)

Trade size half inch. Actual size 13/16"od, designed for 7/8" hole

Cable protection. Snap-in bushing aka push-in bushing. (Adding another hole.)

Yes, that's cutting oil dripping. I also test fitment as I ream. Very tight with locking clips. If it were not so tight, I'd use adheasive.

 

[DeMac]

Cable Straps & Protection

NEC 300.4 Protection against physical damage
(For Non-Metalic Sheathed Cable - NMC)
(d) ...cable or raceway shall be installed and supported so that the nearest outside surface of the cable or raceway is not less than 1-1/4 in. (31.8 mm) from the nearest edge of the framing member where nails or screws are likely to penetrate.

Please reference the NEC 300-4

The cable is supported using CS8-12 cable straps (by Erico, Nvent, Caddy) to hold the cable away from the stud and mid-depth into the sprayfoam.

12/2 Solid Copper MC w/ Steel Armor (not Armorlite) is quite stiff, aiding bends when hand forming a gap as I cross the steel ribs.

Zero metal to rib/shell contact. No brackets overlapping rib screws. Nothing flopping around nor pulled taunt. Redundant strapping and cable ties.

Note: RV walls, ceilings, & floors are too thin to use NMC & still adhear to the minimum requirements of residential construction. RV exceptions are there for the NRVIA inspector.

(...more to come later... )

 

[DeMac]

Forward Lighting

120v stair/egress lighting, front ac circuits & switchlegs. Also, routed local dc terminations to this access point.

Forward bulkhead: Strapped both existing dc wirelooms & new ac cable. Secured to framing using Mounting-Head Cable-Ties. All terminations routed to either (L) or (R) access points.

Wide view. Additional lighting boxes to the right & left. At the top of the photo, you can see the box for the front rooftop AC (future use).

 

[DeMac]

Hatch Bezel and Framing Thickness

Rearward view of the same front, rooftop ac box in the previous post.

Side Note:
Even after adding 1-1/2" of framing, there's still about 3/8" of overlap between the inner & outer trim pieces of the hatch. I was skeptical beforehand.

(front facing)
Here again the mc wire, where crossing perpendicular over top, is screwed to the framing members using Mounting-Head Cable Ties

 

[DeMac]

Installation Details

*1/2" Snap-in bushing
*MC wire protectors, anti-shorts

Mechanical mc connector, anti-short and ground screw.

I prefer hand drivers when securing cable connectors. Power drivers inevitably guillotine the cable & cause hidden shorts.

 

[DeMac]

More Lighting

Staggered lighting over dual countertops, same equidistant spacing on both sides. Tight spacing between mc supports, redundantly secured.

Provide ample cable length for alterations in lighting layout & fixture product selection by forming wide radius bends and supporting mc to the adjacent rafter, mounting-head cable ties over the top.

Center of the bus, main panel location and five switchlegs (two in 12/3) all in one stud bay (wall cavity)

 

[DeMac]

Rear Lighting & Rooftop AC

I used 10/2 mc (30A rated) for the roofrop heat, a/c, dehumidifier.

Note the cable arching under the ribs.

Rear bench & emergency egress lighting.

 

[bridg73988]

Nice work! (That's an understatement) I appreciate the craftsmanship and attention to detail where safety is concerned. Last thing any of us needs to do is burn down a rig because of shotty electrical work. You have already helped me out with a wall framing issue recently and I will be starting on my ceiling next weekend so this thread gets an automatic subscribe from me. Thanks for taking the time to document and post with such great detail.

 

[Rucker]

Beautiful exposition. This is how we should all work.

 

[TheHubbardBus]

Great stuff, DeMac! Thanks for sharing.

 

[DeMac]

Thank you, all. I appreciate each of your feedback.