Replies

1. 
   DanH | Mar 16, 2007 05:44am | #1

   Barns can be tricky. Wiring must be protected from damage, but in livestock barns steel conduit cannot be used as the grounding means (though it may be used for wiring protection).

   If not a livestock barn it gets simpler.

   So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
1. 
   cap | Mar 16, 2007 07:10am | #2

   When you say "steel conduit cannot be used as a grounding means", are you saying that there is a Code requirement prohibiting use as the EGC?  If so, what's the ref?

   Not that a backup ground isn't a good idea: I've always insisted on running an insulated EGC on EMT when I wire a horse barn.  I've lost a couple of bids because of it, but I won't cut corners on safety.

   Cliff

1. 
   DanH | Mar 16, 2007 01:38pm | #3

   That's my understanding. Due to the corrosive nature of the stuff on the floor. Can't quote you chapter and verse, though.
   So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin

1. 
   BryanSayer | Mar 16, 2007 04:44pm | #4

   I think Dan is right, but it might not be an NEC thing. I know in Columbus they do not allow the conduit to be the ground, though any metal does have to be bonded to a ground. I guess the reason is that someone might come along and put in a plastic box, thus breaking the continuity of the conduit.

2. 
   cap | Mar 16, 2007 07:28pm | #6

   I agree, it's not a good idea.  But I always infer that "can't" has a Code prohibition behind it, whereas "shouldn't" implies it's not a good practice/design.  I just wondered if I'd missed some aspect of the Code on this issue.

   I think the only Code pertinent to the situation--and this is indirect--is 110.3(B), equipment must be installed per the listing instructions, and 110.12, installation shall be done in a neat and workmanlike manner. 

   Per their listing, EMT systems don't need an EGC.  And if the EMT is run in the right locations (NOT in the stalls) and fastened well--more than Code minimum--you could probably omit the additional grounding conductor and have little chance of damage to the pipe causing a break in the grounding path.  But like I said, I insist in running the grounding wire.  It adds significanty to the job cost; not only the cost of the wire, it's also the labor in pulling and all the splicing and terminating.

   Anyway, to the original poster, one thing to consider is that a livestock barn can be a damp and corrosive environment--the ammonia from the manure can chew up steel over time. 

   For horse barns, I prefer to run free condictors in Sched 80 PVC.  I enclose the conduit it in stout two-by-four chases up to 8 to 10 feet from the floor to protect it from damage.  This is an installation that'll last 20 to 30 years.  Many clients want the "look" of EMT in horse barns made of steel--the galvanized conduit matches the galv sheetmetal inside the barn.  I advise them that the EMT may corrode in 5-10 years and require replacement.

   There's other options--heavywall steel conduit or medium wall steel conduit.  I've never had anyone take my suggestion of using medium wall or heavywall; the cost put 'em off, and I wasn't disappointed.  Hand bending IMC, even a half-inch, is a real workout.  And then there's the threading...aargh!  How about using compression fittings for IMC, you ask?  Well, compresssion fittings put you right back to a risk of losing your grounding path due to damage.

   Good luck to the OP.

   Cliff

1. 
   Stuart | Mar 16, 2007 08:31pm | #7

   Cliff -

   I'm an electrical engineer who does a lot of design work on wastewater treatment plants.  In the Class 1, Division 1 hazardous rated areas of the plants we've typically specified vinyl coated rigid steel conduit (the primary manufacturer is Robroy) because even galvanized rigid will rot out in a few years from the sewer gases, but that stuff is insanely expensive.  Recently, the local electricians have suggested using aluminum conduit instead, and it seems to be working out well - it's a lot cheaper and easier to install, and it seems pretty resistant to the corrosive atmosphere.

   It's still going to be more expensive than PVC or EMT, but it may be worth considering for use in barns or other locations where it has to stand up to corrosion as well as wear and tear from animals.

2. 
   cap | Mar 16, 2007 08:48pm | #8

   Stuart,

   Thanks, yes, I'm aware of PVC-coated heavywall.  Never installed any of it. 

   I understand that you need bender shoes designed for it; using standard shoes on a 555 or other power bender will damage the coating.  I figure if I ever get client with a budget that would allow PVC-coated heavywall, I'll use IMC instead.  And maybe have it silver plated for corrosion resistance...!

   Most horse barns here in California are well-ventilated year-round, what with the mild climate.  So ammonia doesn't get anywhere near the concentrations it would in  your application.

   Now, about that aluminum conduit--just curious, do you specify a separate EGC?  I've heard that the impedance of Al pipe in long runs can necessitate a copper grounding conductor.

   Cliff 

3. 
   Stuart | Mar 16, 2007 09:03pm | #9

   Yes, I always spec a separate EGC...it seems like everything I work on has conduits transitioning back and forth from PVC to rigid to EMT to aluminum to who knows what, so it's easier to always include one.  As a result I haven't really ever looked into the impedance issues with aluminum conduit.

2. 
   bhackford | Mar 16, 2007 09:43pm | #10

   No livestock.  Still no exposed 12/2nm, so plastic conduit for everything right? 

2. 
   BossHog | Mar 16, 2007 05:16pm | #5

   "Exposed 12/2 nm wire is not going to work staple horizatially to the back of board and batten siding right?"

   Well, it's worked in our barn for 50 years, so it must be O.K.

   (-:

   Based on the rather poor condition of the fixtures and wiring in our barn, I've venture to guess that it should be taken much more seriously than it when our barn was wired.

   Fixtures are sort of exposed to the weather, unless the barn is 100% enclosed. So outdoor type fixtures are probably a good idea.

   Conduit is also a good idea, as you WILL have rats and mice around.

   Certainly make sure that the fixtures are out of the way where they can't get hit by equipment, or by someone moving a ladder around. (Don't ask how I know)

   Murphy's law says that if you're gonna break a light bulb in the barn, it will be while it's dark out and you really NEED the light.

   (-:

   Never underestimate the value of attacking your fans. I've met some Green Day fans who could do with having a little sense knocked into them. [John Dobbin]