Conduit fill question?

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  #1  
Old 03-03-11, 02:49 PM
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Conduit fill question?

NFPA no longer has online tables, I lucked out and found an old Ugly's Electrical Reference guide for NEC tables, circa 1987 in my closet LOL!

Anyway, do you count the egc's for each circuit in conduit fill calc or do they all count as one like in box fill calcs?

Also, when running thhn in conduit, do you use bare copper wire for egc or do you use thhn?
 
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Old 03-03-11, 03:05 PM
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each wire counts.i would run thhn for ground.
 
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Old 03-03-11, 03:42 PM
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With conduit fill each wire is counted. In box fill the EGCs are only counted once.

If you are using EMT or Rigid steel pipe, a ground is not required. (You may run one if you'd like) I would also recommend using green THHN for your ground.
 
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Old 03-03-11, 03:42 PM
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You count every wire in the pipe toward conduit fill, however you only need to run one ground wire per pipe, sized to match the largest hot wire in the pipe. If you're running metal pipe (EMT, IMC, RMC) the ground wire is not required if you use the proper conduit fittings and install them to mfr spec. I tend to think it's a good idea to pull in the ground wire unless you are quite confident in your conduit system.

You can use either green THHN or bare wire for the EGC, code doesn't care which.
 
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Old 03-03-11, 06:45 PM
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First, thanks! Let me run this scenario by you and see if I understand what you are all saying. I am installing 8 circuits along a shop wall, 1/2 are 20a 120v the other 1/2 20a 240v so they are all using 12/2. To complicate matters, 1/2 of the outlets will be on existing framing such that I will be able to pull nm from the attic above down the stud bay but the other 4 circuits will be on block wall so I will have to run conduit down the face. I was thinking of running nm to a junction in the attic and then coming down with conduit - if I read you right Ben, in that junction box I am able to join all the incoming nm grounds to just one ground that will go with the thhn down the conduit?

I am thinking about using a 4" square 2 1/8" with extension ring to get to 60ci to fit all that in.
 
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Old 03-04-11, 09:46 AM
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For four circuits all going to the same place I would not bother with the NM, although if you've already bought it there's no reason you can't use it as you suggest. An extra-deep box can't hurt -- go with 4-11/16" square if your supplier stocks them.

What I would do instead is run conduit straight from the panel and pull in continuous THHN conductors -- fewer splices, fewer hassles. If the attic is hard to get rigid conduit in you could use flexible metal conduit or ENT (flexible PVC) conduit which isn't much different than working Romex. You would then just need a transition fitting or condulet fitting to switch to the EMT pipe or sch. 40 PVC down the shop wall.

In either case, the conduit needs your eight circuit conductors and one ground. You can also pick up a booklet of wire marker stickers so you can know which neutral goes with which hot goes with which breaker #. If you pipe it all the way you can also use a rainbow of THHN colors for the hots to easily identify which ones are 120V, 240V, breaker number or whatever system you want to use.
 
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Old 03-04-11, 12:18 PM
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Food for thought. I have never used condulets before, from what I have seen I would probably need an lb style, are both ports threaded? Would i simply install a 3/4" emt connector to connect the emt and use the threaded side without the locknut, same for the liquidtite side? What nec rules apply to them for fill? If I go this route, I would need to bring over 12 thhn conductors plus ground (12g).

TIA
 
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Old 03-04-11, 02:21 PM
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Originally Posted by chopnhack View Post
are both ports threaded?
They can be, lots of different configurations out there. Or with PVC they are glue-in.

Would i simply install a 3/4" emt connector to connect the emt and use the threaded side without the locknut, same for the liquidtite side?
Yes. Liquidtight is an option too, but FMC (greenfield) or ENT (smurf tube) will be cheaper.

What nec rules apply to them for fill?
Same as the pipe going in, no splices in the condulet. They are pass-through only for making transitions in the conduit.

If I go this route, I would need to bring over 12 thhn conductors plus ground (12g).
In that case, run two conduits. There is a code limit called derating that kicks in with more than four circuits in a pipe. You don't want to have to worry about that.
 
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Old 03-04-11, 03:25 PM
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Awesome Ben, thanks for the info. Need to do some more planning. What method do you use to keep your runs organized, keep track of what circuit is what? I know you mentioned labels, but whats your method.
Thanks again
 
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Old 03-04-11, 05:25 PM
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To transition from EMT to flex I'd use a combination coupling like this

Halex

To transition from flex to PVC schedule 40, I'd simply use a straight flex connector to a PVC female threaded adapter like this

Amazon.com: Carlon E942D 1/2" Female Adapter Pvc Conduit Fitting: Industrial & Scientific

I see no need for a condulet
 
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Old 03-04-11, 05:44 PM
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Thanks Joe, thats what I was looking for, but those are not listed to be used with nm flex, which is what I am running. Do they make something like that for nm flex?
 
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Old 03-05-11, 06:36 AM
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The ENT fitting should be next to the rack of ENT. I have only seen coupling and terminal adapters.
 
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Old 03-05-11, 07:44 AM
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Originally Posted by chopnhack View Post
Thanks Joe, thats what I was looking for, but those are not listed to be used with nm flex, which is what I am running. Do they make something like that for nm flex?
Well, if I remember correctly, non metallic flex is made specifically to glue into regular PVC schedule 40 fittings. To join to PVC conduit, use a sch 40 coupling. To join to EMT, glue non metallic flex into a PVC female adapter and use a regular EMT box connector to join to EMT.
 
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Old 03-05-11, 02:57 PM
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That is creative! Thanks. I think that will work for the smooth wall liquidtite stuff, but the other ent (smurf blue stuff) that I have seen has a corrugated exterior. I did find this in the carlon catalog that seems to be exactly what I need in one shot.

 
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Old 03-05-11, 04:21 PM
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Originally Posted by chopnhack View Post
That is creative! Thanks. I think that will work for the smooth wall liquidtite stuff, but the other ent (smurf blue stuff) that I have seen has a corrugated exterior. I did find this in the carlon catalog that seems to be exactly what I need in one shot.

I haven't seen those. they might help you out. The liquid tight you are referring to is generically called Carflex. ENT (generically called smurftube) is what will glue inside sch 40 fittings. The Carflex might too, but I can't give you a definite answer on that. I recall that Carlon has always made a lot of nifty looking specialty items that are rarely stocked by distributors and must be ordered in full box quantities. Good luck.
 
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Old 03-05-11, 05:23 PM
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Very good information Joe. Thanks for clearing me up on those two products.
 
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Old 03-06-11, 06:38 AM
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Isn't smurftube real flimsy?
 
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Old 03-06-11, 08:25 AM
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ENT is not acceptacle in areas subject to physical damage. It has its usages and is easy to install.
 
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Old 03-06-11, 09:13 AM
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Originally Posted by Justin Smith View Post
Isn't smurftube real flimsy?
It's flimsy due to its construction, but relatively strong. Although I don't like to see it in a slab, I have seen it used. The biggest enemy to ENT or schedule 40 in a slab is destruction by buggies like this.

MQ Whiteman WBH-16E AWD Power Buggies. Contractors Direct.
 
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Old 03-08-11, 05:56 PM
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Really? How deep was it embedded?
 
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Old 03-08-11, 06:23 PM
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When I have seen ENT in a slab it was just laying on top of the rock and tied down with #9 tie wire and 1/2" EMT. After the pour it was probably embedded 4" deep in the slab. The problem is when the concrete laborers are running their buggies over it and anything else that is on top of the rock. In my opinion, the best to use in a slab is PVC that is buried under the rock to avoid the heavy buggies. Anything that gets broken during the pour is useless later when it is needed.
 
  #22  
Old 03-08-11, 06:32 PM
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1/2" emt = 1/2" rebar. I follow you now, I didn't realize they were breaking it during the pour
 
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Old 03-08-11, 06:44 PM
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Originally Posted by chopnhack View Post
1/2" emt = 1/2" rebar. I follow you now, I didn't realize they were breaking it during the pour
No, 1/2" EMT isn't rebar. In this case it was 1/2" thinwall conduit (EMT) cut and used as stakes to attach the ENT to. 1/2" EMT is commonly used as stakes in commercial work to tie conduits in place with tie wire before a pour.
 
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Old 03-08-11, 06:47 PM
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Gotcha, I thought they were tying it to the bar to keep it from floating off.
 
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