nm-b in enclosed barn


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Old 11-11-14, 11:44 AM
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nm-b in enclosed barn

Will not have livestock now, but can't rule it out in the future.

Do I have to use conduit below 8'?
Will nm-b be appropriate?


Here is picture of barn
 
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Old 11-11-14, 11:50 AM
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How do you proposed to protect the cable?

Seems like you're going to need conduit.
 
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Old 11-11-14, 12:40 PM
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I don't know that it has to be protected in a detached structure. ..that's kind of what the question is
 
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Old 11-11-14, 12:47 PM
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I am not familiar with the NEC, but I would assume your barn would be considered a wet area and possibly even a hazardous area (combustible dust from feed?). I would also assume you would need water/dust tight conduit, boxes, fittings and fixtures.
Even if conduit is not required, do you trust that no mice will chew through your cables?
 
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Old 11-11-14, 08:28 PM
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At most I would consider the barn to be a damp area which would rule out NM.

What is the proposed usage of the barn? Where are you located?
 
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Old 11-11-14, 08:45 PM
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Basically it will be used as big garage. Tennessee.

I believe I can use exposed nm-b as long as it is not classified as an agricultural building..at least that is how I read it.

334.10(A) Type NM. Type NM cable shall be permitted as follows:*
(1) For both exposed and concealed work in normally dry locations except as prohibited in 334.10(3)*
 
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Old 11-11-14, 09:29 PM
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Type NM ALWAYS needs to be protected from physical damage. Normal wall coverings are sufficient so IF you want to have walls the NM will be acceptable. Otherwise I would strongly suggest using PVC conduit and individual conductors with type THHN/THWN insulation.
 
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Old 11-11-14, 09:34 PM
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And I think that is the crux of the issue. Whether staples to the 2x4s and not just hanging loose is "protected from damage." I have emt and metal boxes already so maybe I'll just do that the be safe I guess since nothing really defines protected.

I guess the inspector would determine based on his opinion
 
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Old 11-11-14, 09:40 PM
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Since you stated that it is possible that someday the building would be used for livestock the integrity of the equipment grounding system is paramount. Also, there is the problem of animal wastes being corrosive to EMT, those are the reasons why I recommend using PVC.
 
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Old 11-12-14, 03:38 AM
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Do yourself a big favor. Before you decide what to use for wiring check with your local codes office.

Also read up on the characteristics of NM compared to other materials. In the barn you will have corrosives, dampness and dust that will not be present in your home and just considering that the romex will not necessarily be subject to physical damage is not enough. As stated you will have rodents, corrosive gases (animal waist) and potential explosive dust (from hay etc). Do it right the first time and don't guess looking for the cheap way out. You may find shortly after you finish that you made a big mistake and if you spent a little more money you could have done it right the first time. Also be aware of your insurance needs. Wired wrong will the insurance company cover it if anything happens.
 
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Old 11-12-14, 04:40 AM
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Code enforcement is fairly lax in my part of tenn but we are not allowed exposed wire under 7' [?] if it's not enclosed by a wall covering [drywall, plywood, etc] it must be in conduit. Just stapling the wire to the studs isn't considered protection that would pass inspection.
 
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Old 11-12-14, 09:35 AM
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There are no electrical inspections in my county other than new living construction. I'll see what the insurance company has to say
 
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Old 11-13-14, 01:09 PM
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My understanding is that most (all?) barns require PVC conduit as a minimum. EMT isn't sealed and can let in dust, etc. I assume rigid conduit is allowable, but I don't know who would go to that trouble. If it's a garage, then any protection will work, whether it's wood arranged to protect the wires, plywood 'walls' or EMT.

If it were me, I would run PVC and THWN throughout. It's not that much harder nor that much more expensive, and allows future upgrades. It also protects you or a future owner if you do add livestock later. I also personally find NM (or UF) to look rather messy regardless of how careful you are stapling it.
 
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Old 11-13-14, 04:48 PM
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Anything running low enough for an animal to chew or kick I would do in rigid.
 
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Old 11-13-14, 07:34 PM
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I think EMT would be sufficient.
 
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Old 11-14-14, 08:01 AM
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If you plan on putting in a concrete floor and hold livestock in the building you need to install an equipotential ground plane, which basically means making sure all of the metal in the slab is bonded together and is bonded to the building ground.

All of the outlets need to be GFCI protected. NM really shouldn't be used in a livestock building, even if your inspectors aren't looking there. It's not the right material for the job. I would probably run EMT up in the ceiling and switch to rigid steel or sch 80 PVC drops for receptacles. An outdoor-rated panel wouldn't be a terrible idea either.
 
 

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