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number of wires in 3/4 inch conduit
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| 2 quick questions:
How many insulated No. 12 conductors are allowed in a 3/4 inch conduit
Right now there are 3 No. 12 conductors and I was hoping I could get 3
more in there. I understand that a 40% fill is allowed.
Second question
My goal is that I am running a dedicated 110 circuit. Is it allowable
to only run two conductors and "borrow" the ground from another run that
will be in the same junction box?
Thanks in advance!
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| Member, Takoma Park Volunteer Fire Department 2006-03-21, 1:21 pm |
| cdoc wrote:
> 2 quick questions:
> How many insulated No. 12 conductors are allowed in a 3/4 inch conduit
> Right now there are 3 No. 12 conductors and I was hoping I could get 3
> more in there. I understand that a 40% fill is allowed.
>
Which type of conduit do you have the answers vary with the actual
inside diameter of the conduit that you are using.
> Second question
> My goal is that I am running a dedicated 110 circuit. Is it allowable
> to only run two conductors and "borrow" the ground from another run that
> will be in the same junction box?
>
Each raceway need only have one Equipment Grounding Conductor (EGC) so
if you're not using the raceway itself as the EGC then you run one EGC
that is sized for the highest ampacity over current protective device
that supplies conductors in that raceway. There is no benefit to
running an additional EGC unless you need an isolated EGC for that
circuit.
> Thanks in advance!
You're Welcome
--
Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
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| newsman 2006-03-21, 2:21 pm |
| Most types of conduit can legally acommodate 6 no. 12 conductors; you'd
have to look-up your specific type in a code or other reference book.
Two other points: 1. If you have more than 3 current-carrying wires in
a conduit, you have to derate the ampacity of the wires. See the code
for how much; it depends on exactly how many current-carrying wires
there are. Once you do this, you may find that the original 12 ga.
wires are now too small. There are some ins and outs of this rule
involving shared neutrals and travelers that may allow you to avoid
derating. 2. All the wires in a conduit are supposed to be pulled at
one time, so the correct way is to pull-out the existing wires, add the
new wires to the bundle, and pull the entire group into the conduit.
This provision gets ignored a lot, but it's the legally correct way.
cdoc wrote:
> 2 quick questions:
> How many insulated No. 12 conductors are allowed in a 3/4 inch conduit
> Right now there are 3 No. 12 conductors and I was hoping I could get 3
> more in there. I understand that a 40% fill is allowed.
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| gfretwell@aol.com 2006-03-21, 3:21 pm |
| On Tue, 21 Mar 2006 06:23:56 -0600, cdoc <cdoc@msoms.com> wrote:
>2 quick questions:
>How many insulated No. 12 conductors are allowed in a 3/4 inch conduit
>Right now there are 3 No. 12 conductors and I was hoping I could get 3
>more in there. I understand that a 40% fill is allowed.
Assuming EMT and THHNN/THWN the number is 16. Different types of
conduit and wire will change this a little. If you are talking about
cables in conduit (two 12/2 romex) you may be full.
>Second question
>My goal is that I am running a dedicated 110 circuit. Is it allowable
>to only run two conductors and "borrow" the ground from another run that
>will be in the same junction box?
>
OK as long as it is big enough for the largest breaker involved
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| gfretwell@aol.com 2006-03-21, 3:21 pm |
| On Tue, 21 Mar 2006 06:23:56 -0600, cdoc <cdoc@msoms.com> wrote:
Derating was mentioned. As long as these are all modern THHN/THWN
conductors (90c rated) derating doesn't really become a factor until
you get 9 current carrying conductors if there are no other problems,
like high ambient heat. You don't count grounds for derating
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| Thanks to all!
Very well covered. Indeed it is EMT and THHNN/THWN.
cdoc wrote:
> 2 quick questions:
> How many insulated No. 12 conductors are allowed in a 3/4 inch conduit
> Right now there are 3 No. 12 conductors and I was hoping I could get 3
> more in there. I understand that a 40% fill is allowed.
>
> Second question
> My goal is that I am running a dedicated 110 circuit. Is it allowable
> to only run two conductors and "borrow" the ground from another run that
> will be in the same junction box?
>
> Thanks in advance!
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| electrician@electrician.com 2006-03-21, 7:21 pm |
| My calculators at http://www.electrician.com will provide the answers
you are looking for. I have a raceway fill calculator and wire size
and ampacity calculators that follow the 2005 NEC Table 310.16 and
accompanying sections. I have been working on these all winter and am
anxious to see that they are used.
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| Beachcomber 2006-03-22, 1:21 am |
| On Tue, 21 Mar 2006 06:23:56 -0600, cdoc <cdoc@msoms.com> wrote:
>2 quick questions:
>How many insulated No. 12 conductors are allowed in a 3/4 inch conduit
>Right now there are 3 No. 12 conductors and I was hoping I could get 3
>more in there. I understand that a 40% fill is allowed.
>
>Second question
>My goal is that I am running a dedicated 110 circuit. Is it allowable
>to only run two conductors and "borrow" the ground from another run that
>will be in the same junction box?
>
>Thanks in advance!
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