Electrical backer board

I am getting ready to mount my electrical devices on a plywood backer board. I can't seem to clarify if code requires the plywood to be Fire-Resistant. My concern is that I'd rather not have a treated board in the van. Cost is minimally different at $60 vs. $30.

Thoughts on whether the plywood backer board for electrical devices needs to be Fire-Resistant or painted in an RV?

Thanks in advance,

Jack
Washington State

why not use UHMW plastic? Non conducting and can be screwed into easily

What are "electrical devices"?

I'm not aware of a restriction ... a bit of Googling coughed up:
=======quotes start=========
SECTION 603
COMBUSTIBLE MATERIAL IN TYPES I AND II CONSTRUCTION in the IBC to be able to understand what combustible materials are allowed in Type II construction
Type VB all combustible materials are permitted.
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Several occupancies require class B (flame spread 75 or less) wall finishes (IBC Table 803.11), especially in non-sprinklered buildings. Untreated plywood is class C (flame spread 76-200).
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It is up to the local authority what to require. The NEC only says that work be neat and workman like and that equipment be firmly attached to the surface to which it is mounted. It's generally understood that it's impossible to firmly mount anything to drywall, thus a more substantial surface is required. What that is is up to the local authority.

I've never heard of any requirement for color but I'm not too surprised. In particular if the panel is in public view I could see some requirement beyond unfinished plywood. A requirement such as it be painted, but a specific color is beyond typical requirements.
========end quotes=========

On the whole, most of the "treated" plywood is dealing more with the need to protect the backing board from moisture (such as mounting the board directly to masonry). There are fire-retardant paints you could apply instead of using treated board.
If you DO use treated fire-resistant board, then you cannot paint it. Some jurisdictions want 3/4" plywood if it's a panel backing. (thicker means it takes longer to burn enough to free the panel).
Normally i'd advise dropping in to a library and flipping through the electric code (and Seattle's tweaks thereto). But times ain't "normal" these days.

--dick
p.s. i thought i had an old (1995) copy of the NEC, but (a) i can't find it and (b) it's probably out-of-date in that aspect.

JustaGUy - I'm not excited about plastic to anchor potentially hot electrical devices.

Sprint2freedom - Electrical devices - Inverter, solar charger, busbars, fuses, switches, etc.

Autostaretx - I agree that the information is sparse. Even NFPA 1192 (2018) - Standard on Recreational Vehicles does not appear to address it, although they refer to too many other sources for me to verify all of them.

I think I will check with a local electrician to see what local code is for home and buildings.

Thanks everyone.

Jack

JIB said:

JustaGUy - I'm not excited about plastic to anchor potentially hot electrical devices.

Sprint2freedom - Electrical devices - Inverter, solar charger, busbars, fuses, switches, etc.

Autostaretx - I agree that the information is sparse. Even NFPA 1192 (2018) - Standard on Recreational Vehicles does not appear to address it, although they refer to too many other sources for me to verify all of them.

I think I will check with a local electrician to see what local code is for home and buildings.

Thanks everyone.

Jack

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UHMW plastic is ok. Google for the specs/properties. It is probably better than fire-resistant plywood.

If you are really concerned, or go the distance, mount all your equipment on a metal sheet, and have at least 1" of air space behind it.

I'm not sure what your concern is, but plastic burns as well or better than plywood. Yes it has more electrical insulating properties than plywood. I'm not aware of any RV codes. I am very familiar with Building and Electrical codes, and an inspector of each. What exactly are you trying to isolate, and from what? If heat is your concern, use metal. If conductivity is your concern, use plastic or PVC, or similar. Or combine for the best of both.

Who is doing the inspection that you have to pass code?

JIB said:

I am getting ready to mount my electrical devices on a plywood backer board. I can't seem to clarify if code requires the plywood to be Fire-Resistant. My concern is that I'd rather not have a treated board in the van. Cost is minimally different at $60 vs. $30.

Thoughts on whether the plywood backer board for electrical devices needs to be Fire-Resistant or painted in an RV?

Thanks in advance,

Jack
Washington State

Click to expand...

Our favorite material for electrical panels is expanded PVC (Celtec). Excellent screw holding, non-conductive, no finish needed and fire retardant. We make wall insert panels and recently started making panels with recessed boxes.

All the best,
Hein
DIYvan
541 490 5098


https://www.ebay.com/itm/132847848696


https://www.ebay.com/itm/133313028889

JUSTAGUY said:

https://millenniumalloys.ca/what-is-uhmw-plastic-and-what-is-it-used-for/

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Quoting from that page:
--quoth------------
However, the plastic would be considered flammable, but would be classified as HB on UL-1 (i.e. burning less than three inches in sixty seconds) and doesn’t have UL recognition.
---end quoth--------------------

Any plastic is a hydrocarbon chain. Even good old bakelite (the first man-made plastic) and phenolic (1960's favorite plastic for spark plug distributor caps), although normally highly resistant to "issues", can develop conductive "carbon traces" which then act as current paths for both electricity getting somewhere it shouldn't and/or a resistive (thus heating) path that eventually leads to heat damage of adjacent components (such as wire insulation or plastic cases).
Wood can exhibit the same characteristics.

When i'm building for myself (versus trying to satisfy "regulations" or "code"), i'm perfectly happy to use wood (there's a reason the term "breadboard" exists in electronics). I'd say that i prefer wood (or plastic) over metal, since a "dropped wire" won't cause sparks when it hits the back plate. But i also try to follow "good practice" techniques: put a "vertical wall" (barrier) between the low voltage and high voltage areas... again to contain things from one side accidentally getting into the other. Space things out ... don't try to squeeze components as tightly as (might be) physically possible. Air flow keeps things cooler, so things that do release heat (such as the tiny resistance inherent in devices) don't damage near-by objects during normal operation. Space also helps if something does fail in a "spectacular" fashion (sparks, small flames). Anchor and pre-bend wiring so that cables are not mechanically stressing their terminations.

--dick

Thank you all for the input and insight! I can't find any stated specifications or requirements for the backer board, beyond "Good Judgement" even in the NFPA 1192 specification and several of the documents it references.

I am going to proceed with standard plywood as it will do the job at a reasonable cost. Some of the plastics look good, but UHMW is going to be very expensive, as my panel is fairly big to accommodate all of the devices.

Thank you again,

Jack

JIB said:

...

I am going to proceed with standard plywood as it will do the job at a reasonable cost. ...

Click to expand...

Plywood is a good choice. I've seen it used for many electrical installations. I assume that your electrical components will be a basic surface mount, not recessed.

For some assurance as to flame resistance take a propane torch and direct it at the flat surface of a piece of your plywood. It will char after a time, but it won't burst into flame right away unless you direct the flame at an edge.

vic

If things go bad enough that you painted plywood backing board is going to catch fire, your plywood backing board catching fire is probably the least of your worries at that point.

A 1/4" cement tile backer board gives you a flame resistant surface over your ply backing.

Dirt cheap, about $10 for a 3'x5' sheet.

You have to fasten your components THROUGH it as it will not hold fasteners for the long haul

Shawn182 said:

If things go bad enough that you painted plywood backing board is going to catch fire, your plywood backing board catching fire is probably the least of your worries at that point.

Click to expand...

Well said. I agree 100% FWIW.

So many of these things get overthunk.

vic

hein said:

Our favorite material for electrical panels is expanded PVC (Celtec). Excellent screw holding, non-conductive, no finish needed and fire retardant. We make wall insert panels and recently started making panels with recessed boxes.

All the best,
Hein
DIYvan
541 490 5098

Click to expand...

I can vouch for expanded PVC sometimes called foam PVC. It is lightweight, inexpensive, holds screws very well, is dielectric and self extinguishing. I've tested that myself by creating a fabric and glue fire onto of a sheet of expanded PVC with a pretty serious fire that smothering would not extinguish had to use a fire extinguisher to extinguish--the expanded PVC did not even show a melt or burn of any kind. Wood is NOT used as a substrate for electrical mounts due to the fact that it IS electrically conductive, especially when wet, does swell and absorb moisture, and is NOT self-extinguishing. Other plastics as mentioned also work well, and nearly all circuit boards and electrical systems are mounted to various types of plastics. Wood is a terrible choice as an electrical insulator as it is not. Why ladders went to fiberglass because wood conducts electricity. For your safety, do not use wood to mount electrical components if you want the mount to electrically insulate. Also, wood sawdust is highly explosive, not flammable, explosive. So any sawdust is a human health risk and an extreme explosion risk. Keep that away from electrical systems.

kcshoots said:

I can vouch for expanded PVC sometimes called foam PVC. It is lightweight, inexpensive, holds screws very well, is dielectric and self extinguishing. I've tested that myself by creating a fabric and glue fire onto of a sheet of expanded PVC with a pretty serious fire that smothering would not extinguish had to use a fire extinguisher to extinguish--the expanded PVC did not even show a melt or burn of any kind. Wood is NOT used as a substrate for electrical mounts due to the fact that it IS electrically conductive, especially when wet, does swell and absorb moisture, and is NOT self-extinguishing. Other plastics as mentioned also work well, and nearly all circuit boards and electrical systems are mounted to various types of plastics. Wood is a terrible choice as an electrical insulator as it is not. Why ladders went to fiberglass because wood conducts electricity. For your safety, do not use wood to mount electrical components if you want the mount to electrically insulate. Also, wood sawdust is highly explosive, not flammable, explosive. So any sawdust is a human health risk and an extreme explosion risk. Keep that away from electrical systems.

Click to expand...

Ladders went to fiberglass over wood for durability. Aluminum ladders also replaced wood ladders. (Not that I recommend using an aluminum ladder around electricity.)

This isn't a 480 volt distribution panel. It's a van conversion.

The electrical power components in some RV trailers are mounted on and even recessed in particle board.

Carry on.

vic

kcshoots said:

I can vouch for expanded PVC sometimes called foam PVC. It is lightweight, inexpensive, holds screws very well, is dielectric and self extinguishing. I've tested that myself by creating a fabric and glue fire onto of a sheet of expanded PVC with a pretty serious fire that smothering would not extinguish had to use a fire extinguisher to extinguish--the expanded PVC did not even show a melt or burn of any kind. Wood is NOT used as a substrate for electrical mounts due to the fact that it IS electrically conductive, especially when wet, does swell and absorb moisture, and is NOT self-extinguishing. Other plastics as mentioned also work well, and nearly all circuit boards and electrical systems are mounted to various types of plastics. Wood is a terrible choice as an electrical insulator as it is not. Why ladders went to fiberglass because wood conducts electricity. For your safety, do not use wood to mount electrical components if you want the mount to electrically insulate. Also, wood sawdust is highly explosive, not flammable, explosive. So any sawdust is a human health risk and an extreme explosion risk. Keep that away from electrical systems.

Click to expand...

what thickness should the Expanded PVC sheet be?