Is this legal for the NEC?

[letterman]

I built a leanto on the front of my pole barn. It's 3 sided, so the horses can get shelter when the weather is nasty. At the last minute I decided to add a light. That required getting the cable (NM Romex) thru the wall from inside the barn. This left me two options.

1. Drill a home thru the top 2x6, and thru the pole barn steel siding.
2. Run the cable thru one of the ribs on the underside of the roof steel.

I chose the second option for two reasons. First, it was less work, since there is a rib every 10 inches, so there were plenty to choose from. Secondly, drilling thru steel siding is going to leave a sharp edge on the steel where the cable runs, which could eventually puncture the cable.

As far as safety, I think I chose the right way, but is it legal acording to the NEC?

(I'm not too worried about this, it wont be inspected, I'm just curious).

Thanks

[RBM]

Agricultural buildings require wiring equipment to keep dust and moisture out. UF cable or NMC is OK but NM is not permitted

[gfretwell]

I will assume the "Romex" is type UF and agree your idea is OK. If it went through a bored hole in steek it would nee additional protection pipe or something (meaning a listed raceway used as a sleeve). You have the serious danger identified, a cable rubbing on a sharp edge.

[RBM]

Any building that you would call "Barn" is considered an agricultural building by the NEC. To be NEC compliant, you can not use type "NM" cable

[RBM]

I feel your pain!!! I've been in the electrical contracting business for over 35 years, and I'm still asking the same questions you are. I believe the main concern in agricultural buildings is combustible dust. They make a tight fitting gland connector to use with UF that would prevent dust from entering boxes and fittings

[John Grabowski]

My town has quite a few farms and stables. It amazes me what these farmers do when they wire up things themselves. I saw a dog kennel and stable wired up with lamp cord a few years ago. Just last week I got a call about converting a private in-ground pool to a public pool so the farmer could have a camp for kids in the summer. In NJ an electrician must certify a public pool every five years. I go to look at the pool and see that the pump wiring is fed underground with Romex inside of greenfield. There were junction boxes every 50' or so that were actually indoor metal time clock enclosures. No greenfield connectors were used. No grounding. No pool bonding. They will need to spend several thousand dollars to make the pool safe and compliant.

[RBM]

You've got the picture. Another thing to consider regarding NEC rules, is that they consider how the next guy may use your barn

[John]

Thank all of you for a great discussion.

John

[Wayne Whitney]

Another thing is that NEC Article 334 requires that when NM is used outside of a dwelling unit, it needs to be covered by a 15 minute (fire) finish like drywall. So that includes barns and detached garages.

Cheers, Wayne

[dpb]

While "basically" UF is similar to NM, it isn't the same as either (or it wouldn't have a different designation). The "C" is for corrosive/wet environment which the Code considers any barn to be, by definition.

That's the reason for the proscription against NM.

...

That is true for haymows and other areas for grain and similar storage, true. It is not the reason for a livestock barn, however. They are, in general, damp if not actually wet and the animal byproducts are quite corrosive even in vapors as well as in the solid and liquid forms. Hence, since the Code is written to cover all uses from the casual pleasure horse barn of OP to the full-fledged production milking parlor or farrowing house, it is written for the conditions that may be expected in a "working" barn.

--

[Tom Horne]

No sir the main concern in stock barns is that the environment is inherently damp and corrosive because of the inevitable constant presence of animal urine. If the man has been in the horse care business for long he has already seen how fast any steel that is not galvanized of otherwise corrosion protected will rust in a stock barn. The paper filler used in Type NM cable will wick moisture into electrical boxes and accelerate the corrosion of ordinary switches and receptacles housed in them. Type NMC cable on the other hand is called barn cable by those of us who go back far enough in the craft to remember the use of that marking by manufacturers before the Type NMC cable class was identified as a standard cable type. It is much the same way some manufacturers now mark type AC cable that also has an insulated green grounding conductor in it HFC meaning Health Facilities Cable. But search far and wide you will not yet find that classification in the UL building materials list or other listings of electrical materials because as yet that marking is not yet accepted by the consensus code making and standards bodies. Ordinary electrical materials are generally unsuitable for use in stock barns because in order to keep the installation safe for humans and animals for the entire useful life of the building materials, including cable, that is suitable for damp and corrosive locations must be used.

[Tom Horne]

Actually Wayne you have that backwards. The building code requires the fifteen minute rated noncombustible finish in multiple dwellings and several other occupancy classifications because the smoke contributed rating of such cable is too high for buildings with lots of people at risk. There is no such requirement in single family homes or stock barns except in a few locations like San Fransisco.

San Fransisco's precautions regarding stables come from a fire that occurred decades ago in a stable in Golden Gate park. There were dozens of horses trapped by the fire and citizens could hear their death screams for many blocks away. The sense of horror that instilled in the public there at that time caused the city to require all horse barns in the city limits to be protected by automatic fire sprinklers. As far as I know there is no such requirement for sprinkler protection in single family homes or even multiple family dwellings in that city to this day. Maybe if dying people would scream as loud as a horse does... but I digress.

[Wayne Whitney]

Exercepts from Paragraphs 334.10 and 334.12 of the 2008 NEC (same as

2005 NEC):

334.12 Uses Not Permitted. (A) Types NM, NMC, and NMS. Types NM, NMC, and NMS cables shall not be permitted as follows: (1) In any dwelling or structure not specifically permitted in

334.10(1), (2), and (3).

334.10 Uses Permitted. Type NM, Type NMC, and Type NMS cables shall be permitted to be used in the following: (1) One- and two-family dwellings. (2) Multifamily dwellings permitted to be of Types III, IV, and V construction except as prohibited in 334.12. (3) Other structures permitted to be of Types III, IV, and V construction except as prohibitied in 334.12. Cables shall be concealed withing walls, floors, or ceilings that provide a thermal barrier of material that has at least a 15-minute finish rating as identified in listings of fire-rated assemblies.

So the NEC doesn't have any requirements about finish rating for NM cable used in dwellings, although the building code probably does. However, outside of dwellings, 334.10(3) of the NEC requires that NM cable be covered with a 15-minute finish rating. So if you want to use NM cable in your barn, you need to cover it with drywall or 1x boards, just like you need to cover plastic foam insulation. The same goes for a residential detached garage, a commercial building, etc.

I believe this requirement is fairly new and is a replacement for a requirement limiting NM cable to structure of 3 stories or less. I guess both the manufacturers and the responsible NEC committee felt this was an acceptable trade off. I'm not 100% sure about this history, though.

Cheers, Wayne