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Old 01-07-2018, 12:02 PM   #1
Skoolie
 
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Wiring before spray foam

Before I have the bus spray foamed...

I have not applied myself to understanding the electrical system of the bus yet (one step at a time) nor do I know much of house electrical systems. I will need to do that soon but before I insulate the cables in I have a few questions. I hope to repurpose some of the cables from unnecessary lights and things that are not needed for the bus with outlets and new lights. I am sure that I will need to change many of the fuses to be appropriate for the new uses but what about the cables themselves? Is there a standard gauge used throughout the bus that will work for 12v oulets and 12v fans or might some be to small? For 110v outlets, should I run new wiring now? I also want to change the function of some of the rear flashers to be turn signals and stop lights etc... should I do that now, pre-spray?

I will try to keep as much of the wiring out of the foam as possible running it above the windows behind an access panel but anything that goes to the lower wall, back wall, and the ceiling fan will end up buried in the foam within the electrical tubing.

Anything I should know? Tips that I haven't thought of? How much do I need to prep now before spraying? I suppose some string leads to feed wire in the future? Will the spray foam expand into the standard electrical tubing or pinch it? Is there a better electrical ducting system... redo with pvc or other solid duct... something without the side slit? Pull it all and route into the spray afterwards? If so, what about the parts where the wiring goes through metal framing? Just dig it out? I am only planning to spray the inch and a half depth of the original framing.

Thanks in advance for ideas and suggestions.
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Old 01-07-2018, 12:38 PM   #2
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I'd get the spray foam done before adding any wiring or plumbing. At some point in the future you are going to need access to those things.

Get the spray foam done then use a 1" grinder stone or cutter to cut channels for your conduit or Pex. That way it all sits on top of the foam right behind the wall panel, and you don't have to plan it all now. You'll want to change it even if you do plan it now, so you are going to have to cut away foam anyway.
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Old 01-07-2018, 12:45 PM   #3
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Lots of questions but good ones. Keep it a simple process though.

Make sure you have in your mind the electrical configuration that best suits your plans for use. Locate witches, receptacles for ease of use, for accessibilty if trouble develops later, best lighting effects etc.
Best to locate 110v entry on rear driver side directly into a main switch, breaker panel and for campground connection to keep the main cable as short as possible. Branch circuits can leave that area in the most direct fashion you can design/build and can be cut down on the number of runs by using multiconductor cable(s). You might need only 3-4 circuits depending on how the load is divided.
#14awg stranded would be my preferred choice but not as in extension cord type. Use pvc 3/4" conduit and an extra pull string inside for future additions. In these conduits, pull separate wires for hot, neutral, grd for the devices being fed and system ground, so yes, 2 greens.
This can all be ok in foam but keep the boxes covered for switches, lights, plugs. You have made it accessible at this point.
one circuit for fridge, one for lighting and some receptacles that are of low load items. At least one split receptacle for kitchen appliances and only use one at a time, not a coffeemaker and toaster together for example.
A/C, not sure about your needs and wants but if so, one dedicated 15 amp circuit wherever you intend to mount one.

DC.. a whole other kettle of fish due to your layout once again. yes, you can move existing around for best application for you. Keep it mostly at #12awg stranded for lights, dc outlets, grounding is SO critical to get right or a pita to troubleshoot for most anyone once covered up.

With both AC and DC, get it right and tested before even thinking foaming. Make sure you haven't forgotten something simple that will make for an amateur looking fix if you have to add later when interior is finished.
Probably missed something here so just ask. Just be very clear in your mind that the layout is what you want beforehand. Then foam

John
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Old 01-07-2018, 01:17 PM   #4
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Since we're on the subject of wiring I'm to the point where I'm making my AC ducts with the plan being to run my wiring inside the ducts. Some one mentioned to me that they thought the wires inside the ducts would affect airflow in a negative manner,,,Thoughts
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Old 01-07-2018, 01:28 PM   #5
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Tyania,

Take a look at my thread. I got my spray foam done this past fall. I ran hollow conduit lines as well as electrical lines for wiring up circuits. The bus's electrical system I made sure was solid and functioning before spray foaming. If there was any over-spray (and there was plenty of that) it would not adversely impact the 12 volt system. I secured the wiring, covered areas I didn't want spray foamed, taped other areas for construction (easier to remove the foam and tape underneath for a clean surface), and covered equipment such as heaters and duct work to prevent clogs.

The end result was awesome. The closed cell spray really insulates well. I'm very happy with the end result. I'm adding a second layer of insulation, but it's the hard board insulation to where I can run extra electrical lines and what not as I need. The end result is a bus with an R-value in the low 20s or so. Most conventional homes don't have that much R-value, so I'm delighted to be that much further ahead.

Plumbing is not the issue so much as planning the electrical system. The 120 volt system is the big concern. Be sure you know where the refrigerator, stove/oven, microwave (IF you want one - we don't due to cancer concerns), washer, dryer, lights, fans, A/C, computer(s), monitors, printers, televisions, and other appliances are located and the wiring to properly, and SAFELY plug them in is mapped out and well planned for. After that is figured out, prepare the masking and covering accordingly. Spray foaming after al that goes really FAST!!! About four hours or so later, and YOU are DONE!!! The foam will react with the metal and get fairly warm. You definitely do NOT want to touch the areas being sprayed for several minutes (I personally recommend 15 minutes). The fumes are also potent and WILL take your breath away if you do not have a respirator with new, clean filters. I could explain the chemical reactions within your lung tissue, but this is a bus building site, not a medical analysis site. Open all windows/doors after spraying is completed. Let those fumes dissipate before working on the bus. My bus took about three days to really air out before I could get in there and get working again.

Hope these experiences I had help you with your project.

You'll enjoy the results!

M
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Old 01-07-2018, 01:36 PM   #6
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Wire insulation is rated on among other things it's ability to allow a certain maximum amperage to flow in the wire it protects. Temperature plays a role in that ability. Placing wire in a conduit decreases the ability of the wire to shed heat caused by current flow. This can lead to insulation failure etc. Check the wire mfg's specs as they apply to your planned configuration and you'll be good to go. Jack
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Old 01-07-2018, 01:47 PM   #7
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That's a good point, Jack. To extend it a little further, I've wondered what happens when wire is embedded directly into sprayed foam without any conduit at all. Surely that keeps the wire a little warmer still? My thought is that, at least if there's a conduit, there could possibly be a little convective cooling as the hot air inside the conduit finds its way out. When a wire is fully embedded in foam there definitely won't be any such air movement.

I'd suggest to somehow keep all wires from being directly foamed into place. For wires that aren't yet installed it's easy to just place conduit; for those already in place like the bus body/chassis systems.. I guess they could be disconnected and fed through a conduit, or maybe the split loom tubing would do well enough to keep the foam at bay without having to disconnect any wires.
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Old 01-07-2018, 02:10 PM   #8
Skoolie
 
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Quote:
Originally Posted by family wagon View Post
...maybe the split loom tubing would do well enough to keep the foam at bay without having to disconnect any wires.
I wonder the same. Anyone foamed with the split loom tubing? Did the insulation get in there?
I like the neatness and future access of a solid conduit but I am curious... that and not sure how good I am going to be at taking the wiring apart to pass through the conduit. Label, label, label, i guess.
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Old 01-07-2018, 03:05 PM   #9
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Quote:
Originally Posted by Stu & Filo. T View Post
Since we're on the subject of wiring I'm to the point where I'm making my AC ducts with the plan being to run my wiring inside the ducts. Some one mentioned to me that they thought the wires inside the ducts would affect airflow in a negative manner,,,Thoughts
The only problem I know with it is that buy international construction code it has to be in a fire rated conduit. In building construction.
It is done all the time but is usually limited to more like having to cross the air plenum of the unit.
There is no problem with running it within the ductwork but I would still put it in a conduit to protect it from the edges at the turns.
There is also plenum rated thermostat cable out there that is fire rated for that purpose but to me it still needs protected from rubbing at the turns or any rub points and running EMT conduit to pull your voltage as you do your ductwork is simpler than the ductwork.
I would hate for you to get done and not be able to get insurance or have an accident and get denied because of something simple like this.
Also don't run the thermostat or low voltage cable along side or inside the same conduit as the higher voltage power wires. There have been issues with the higher voltage cross feeding into the lower voltage cable.
Hope this helps.
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Old 01-07-2018, 04:43 PM   #10
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Quote:
Originally Posted by Stu & Filo. T View Post
Since we're on the subject of wiring I'm to the point where I'm making my AC ducts with the plan being to run my wiring inside the ducts. Some one mentioned to me that they thought the wires inside the ducts would affect airflow in a negative manner,,,Thoughts
Someday you will want access. That goes for everything unless you can pull it out without hindrance and repull but do yourself a favour for all the time it takes to do it right.

Dust collector also.

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