Fill calc doesn't seem right

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Old 04-07-06, 03:54 PM
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Fill calc doesn't seem right

I am using a fill calculation table from IOPath Software that seems to say that I can put up to 16 #12 AWG THHN at 75C through 3/4 " EMT. I have some flex conduit that is 3/4 and some other that is 1". I am pretty sure I cannot say flex is the same as EMT in fill calculations but 16 seems high for that much wire. What is the limit of #12 in a 3/4" and 1" and does an insulated ground wire count?
 
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Old 04-07-06, 04:13 PM
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What exactly is the flex in question?

Bottom line is 16- #12 THHN conductors in 3/4" EMT.
There are reasons you do not want to go that high though.

The ground counts as a conductor with regards to fill, but not with regard to derating. Only one ground is required per conduit and is based on the largest breaker/fuse of the circuit conductors in the conduit.
 
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Old 04-08-06, 08:54 PM
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Ground for conduit or circuits?

Thanks Speedy Petey for the reply. The flex is AL and will go from my main panel to a j-box in the attic. I am removing existing AL wiring and there are circuits that I want to change.

For example, one circuit goes to the living room and to the garage. I want one circuit for the living room so my plan is run romex to the jbox and then single insulated #12 wires through the conduit and into the panel. I assummed that each one of these circuits would need its own ground. Are you suggesting that I could tie all the grounds from each of the circuits (3 or 4 I think) into one at the jbox and then that one would go the main panel?
 
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Old 04-08-06, 09:03 PM
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You must have A (1) ground in each conduit,Sized to the largest ckt in the conduit. So you may run 1 ground up and suitably connect the others to it.

*tie all the grounds from each of the circuits (3 or 4 I think) into one*
 
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Old 04-09-06, 09:25 AM
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Originally Posted by Speedy Petey
Bottom line is 16- #12 THHN conductors in 3/4" EMT.
There are reasons you do not want to go that high though.
The main reason Petey is probably thinking of, is that once you have 10 current-carrying-conductors in a conduit, then you must derate them to 50% of their normal ampacity.

So a 90 #12 THHN would suddenly not be able to handle 20 amps anymore. There's more to it than that, but that's the short story on it.

If you can fish flex down to the panel, is there any chance of just fishing the romex straight to the panel, and ditching the j-box?
 
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Old 04-10-06, 09:23 AM
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Romex acceptable?

Thanks everyone for your help. Rocky Mountain's suggestion is what I wanted to do but somehow I got the impression from the code and this forum that plain romex wasn't going to give the required protection. The romex would run behind the sheetrock of a cathedral ceiling so there is a remote chance that someone could put a nail or something up there. If the nail pierces the romex, well, I see a problem.

That reminds of the whole discussion I have had about fishing new wire in a wall cavity. Normally in new construction the romex is supposed to be stapled or somehow secured in the middle of the wood framing, right? This makes sense to me because nails or something probably won't hit the romex since the romex is in the middle of the stud. On the other hand, after the sheetrock is up and wiring is added, a loose romex cable would just move if a nail or spinning drill bit struck it, wouldn't it?
 
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Old 04-10-06, 11:47 AM
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Originally Posted by Tyger52
plain romex wasn't going to give the required protection. The romex would run behind the sheetrock of a cathedral ceiling
Sheetrock on a finished wall is considered enough protection for NM-B (Romex). The only stipulation is that the Romex must go through the studs at a minimum depth of 1.25" from the face of the stud. Romex only needs additional protection where it could be stepped on, smashed, cut, etc like in an attic, garage or basement.

Normally in new construction the romex is supposed to be stapled or somehow secured in the middle of the wood framing, right?
Yes.

a loose romex cable would just move if a nail or spinning drill bit struck it, wouldn't it?
Pretty much yes, and that is why fishing of Romex cable is allowed inside finished walls without staples.
 
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Old 04-10-06, 02:38 PM
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Could he be wrong?

The whole reason I have a Jbox and am pulling wire through conduit above my ceiling instead of using Romex is that my electrician/neighbor told me that was how I should do it. There was existing flex 3/4" conduit that was empty and he suggested the jbox and using the conduit. The jbox is already there and only a few more circuits need to be run.

I could certainly fish the romex. As far as fishing, I am planning on pulling more 1" flex conduit for growth. We had to cut a hole in the ceiling sheetrock earlier to pull another section of 1.25" flex conduit, so as long as that is there, now seems like the time. Sound good?
 
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Old 04-10-06, 07:55 PM
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Tyger,
334.30(B) Unsupported Cables. Nonmetallic-sheathed cable shall be permitted to be unsupported where the cable:
(1) Is fished between access points through concealed spaces in finished buildings or structures and supporting is impracticable.
As for your last post, add flex for future runs to your heart's content. There are cheaper methods, if you're so inclined.
 
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