Electrical Conduit in Pole Barn

[RichNJ]

Just finished my pole barn. It'll be used for tractor and other equipment storage. Spoke to the electrical inspector and he suggested using 1/2" EMT and 4" square boxes for lighting and outlets in the barn. After going to Home Depot I see there are other choices like metal watertight boxes and plastic watertight boxes.
Anyone have any suggestions or comments on which way to go.
1. 1/2" EMT and 4" square boxes.
2. 1/2" EMT and metal watertight.
3. 1/2" PVC conduit and PVC watertight boxes.

 

[cowboydoc]

If it was me I'd use the pvc pipe and boxes. If you get a short in the metal conduit or boxes in a metal barn you could electrify the whole building if it isn't grounded properly. I do that on any that I build and make sure that I have it ground with at least a 6' grounding rod.

 

[DocHeb]

PVC is nice since it doesn't corrode and is easy to cut, but is a bit more sensitive to impact. Also, once you assemble it with the adhesive, there's no going back to change something without trashing some components. You should plan your runs carefully since it's easy to get into a position where it's impossible to insert a length of conduit between the sockets of two fixed boxes. PVC has some flexibility that can help in that situation, but planning is better. Metal is a little harder to work with, but the choices of boxes and such is greater.

No matter which system you use, make sure you size the conduit appropriately. There are standards within the National Electric Code that limit the number and guage sizing of wire run through conduit.

 

[MikePA]

I had our barn wired by a licensed electrician and he ran the wire in gray PVC pipe where there might be a danger of the wire getting hit. Other places he just stapled it to the wooden beams.

All the boxes are metal and surfaced mounted. Ones exposed to the weather have the foam gasket and a cover. The lights in the stalls are mounted on the underside of the roof on a rafter. The bulbs have the clear glass what-cha-ma-callits as well as the metal guard around them. Ditto for the lights in the aisles. All the switches are the lever type with the foam gasket. Our horses love to use the boxes to scratch whatever itch they have. For the lights up on the rafters, I used the long lasting bulbs since the only way to reach them is with an extension ladder. The phone line comes in underground.

 

[RichNJ]

From the replies so far - PVC sounds like correct choice.
Installing a simple system in the barn looks easy. But don't know if there are any common mistakes to avoid.
For example -
When running conduit on a roof truss for lighting - Does the conduit have to be run on the bottom of the truss or can it be run on the side of the truss?
Can you bend PVC conduit or do you buy the pre-bent sections for that?

I have noticed that only 2 gang switch boxes are available. So If I need 3 switches I'll have to use (2) 2 gang boxes and wire them together via a small section of conduit.

I have the 1993 NEC book from when I wired the house and am familiar with the usual stuff but the conduit is new to me.
I already ran 100 ft of #2 copper from a subpanel box thru 1 1/4" PVC underground conduit into the barn and into a 100 amp breaker box.
There is 4 separate #2 wires - 2 for each 120V leg, 1 for ground and 1 for neutral. I color coded the neutral w/white electrical tape and the ground with green tape. Also put an 8 ft ground rod at the barn but it's not wired yet.

 

[Molerj]

Rich, I am not an electrician but have done alot of my own wiring. When I wired my pole
building, I used metal conduit & metal boxes. Not waterproof, but if you think you need
them go ahead. I used the conduit on all the places that were reachable, ie; the outlets &
switches. I stopped the conduit at the ceiling & just ran the wire out of the junction boxes
to the lights. Also It is a good idea to keep your outlet circuits & light circuits separate.
#12 wire to outlets with 20 amp. breaker & #14 to lights with 15 amp. breaker. Also you
have to buy the pre bent plastic 45's & 90's. I borrowed a bender for the metal conduit.
but you can buy pre bent metal ones for that too. You can buy 3 gang plastic switch boxes.

 

[JATO_RaT]

Rich, EMT or electrical metallic tubing is the best choice above ground. With a bender you can do just about any bend you want. Even someone who has never bent conduit before can be ok at it in a short period of time. PVC is great for underground, but every time you need a bend you either buy it or buy a warmer and make it. Its also much thicker and that means bigger notches if you put it in the stud walls (I realize you have a pole barn). I go with 1/2" EMt and 4 sq. boxes on everything. Use set screw connectors and couplings if weather is not a problem. They provide a better ground then compression particularly when the compression connectors are not tight. In the ground I use at least 3/4" PVC rigid, very rarely do I bother with 1/2". EMT by the very fact that it is metal provides the equipment ground you need. It is very easy to enusre that it is grounded properly. It also will be much neater in appearance then PVC. Offsets, 45 deg, 90 deg. are all a snap with EMT. Remember, all you get is 360 deg. of total bends before you need a junction box. In other words, once all the bends you make in a run add up to 360 degs., you must put a j-box like a 4 sq. IE>, after you bend 4 90 deg, you need a box. Avoid making that many because pulling the wire through after words can be difficult. Always pull the wire through after all the conduits in. Ground wire attached to the back of the 4 sq. in the ground screw hole is mandatory. Make it about 8" long and tie it to all the grounds if you run a separate ground. Outlet must also pigtail to this wire. Minimum wire is #12 it will be THHN either solid or stranded. Stranded pulls easier but in most cases needs a solid wire pigtail to tie into outlet or switch. If you have some questions, let me know. Rat..

 

[GlueGuy]

I'm with Rat on this one. General rule is to use metal anyplace above gound where there is danger of banging into it. In fact, code around here requires it. We switch from plastic to metal where you transition out of/into the ground. Plastic can be used above ground where it's behind walls, or otherwise protected.

The GlueGuy

 

[Phred]

Rich,

The other guys have pretty much summed it up but I will point out that the metal conduit is safer;

If you use romex or similar you have three wires; the black (the hot wire), the white (netrual which is the current return) and the green our bare copper ground. Now if all goes well you never use the green/bare wire. Its just there for safety sake to ground all the end fixtures and reduce the chance of a shock or fire. But what if a nail punctures the hot wire behind a wall? You can have a potential fire or shock hazard.
If the wire is in a metal conduit which has been properly installed the metal is grounded throughout your building. That same nail would short the hot wire to the grounded metal conduit and trip a breaker, thereby preventing a problem.
Also most folks would notice the nail was a bit harder to pound into the metal compared to the soft copper wire.
The conduit should all be connected to each other tightly so that any point on the conduit is connected electrically back to the breaker box, which is grounded. In addition, your green ground wire should be attached to each fixture box and gounded back at the breaker box. Therefore, the metal conduit is grounded at both ends.


The plastic stuff is non-conductive and therefore can't provide this extra safety feature. However, as the other guys have said, the plastic is water tight and the metal is not.
Therefore, the plastic is better for underground applications where water might get in to the metal.

Another issue is that the plastic is cheaper and easier to install.

Fred

 

[ddl]

Before you buy anything or take advise from anyone, contact your county and see if there is a wiring code they live with and the steps required to wire your building. We all have ideas and preferrences, but what counts is the law where you live. As long as you live there you may not follow the code but if you want to sell the place, you may spent a lot of money bringing the place up to code. Also remember that the NEC is the basic code not the safest code and remembeer it was written by firemen to provent fires. Contact your county offices and be sure!!

Dan L