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How many 12/3 cables in 1/2" (trade) Greenfield?

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How many 12/3 cables in 1/2" (trade) Greenfield? blueman 09-02-2008
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Posted by blueman on September 2, 2008, 2:41 am


I am having difficulty understanding and applying the NEC tables I
have seen online to cables containing more than one conductor.

Is there any simple rule that says how many 12/3 Romex cables you can
put in flexible conduit (Greenfield)?

Specifically, what trade size flexible conduit would I need to carry 2
12/3 Romex cables? What size for 3 12/3 cables?

Thanks!

Posted by blueman on September 2, 2008, 2:50 am


OOPS - just to clarify I meant 12/2 (plus ground) not 12/3.
> I am having difficulty understanding and applying the NEC tables I
> have seen online to cables containing more than one conductor.
>
> Is there any simple rule that says how many 12/3 Romex cables you can
> put in flexible conduit (Greenfield)?
>
> Specifically, what trade size flexible conduit would I need to carry 2
> 12/3 Romex cables? What size for 3 12/3 cables?
>
> Thanks!

Posted by blueman on September 2, 2008, 3:02 am


The flexible metal conduit is only being used to "protect" the wires
in the vertical drop from their run along my basement ceiling joists to the
waist-level outlet boxes -- approximately 4 ft total length. The rest
of the run is pure Romex (and appropriate bushings are used to protect
the wire where it enters the flex conduit and where the flex conduit
attaches to the 4x4 outlet box).

Posted by John Grabowski on September 2, 2008, 7:26 am



> OOPS - just to clarify I meant 12/2 (plus ground) not 12/3.
>> I am having difficulty understanding and applying the NEC tables I
>> have seen online to cables containing more than one conductor.
>>
>> Is there any simple rule that says how many 12/3 Romex cables you can
>> put in flexible conduit (Greenfield)?
>>
>> Specifically, what trade size flexible conduit would I need to carry 2
>> 12/3 Romex cables? What size for 3 12/3 cables?
>>
>> Thanks!


I'm guessing that 3/4" for two and 1" for three 12/2's. Keep in mind that
the greenfield will need to be terminated at one end in a grounded metal box
as all metal conduit carrying live wires needs to be grounded.


Posted by on September 2, 2008, 11:00 am


On Tue, 2 Sep 2008 07:26:01 -0400, "John Grabowski"

>
>> OOPS - just to clarify I meant 12/2 (plus ground) not 12/3.
>>> I am having difficulty understanding and applying the NEC tables I
>>> have seen online to cables containing more than one conductor.
>>>
>>> Is there any simple rule that says how many 12/3 Romex cables you can
>>> put in flexible conduit (Greenfield)?
>>>
>>> Specifically, what trade size flexible conduit would I need to carry 2
>>> 12/3 Romex cables? What size for 3 12/3 cables?
>>>
>>> Thanks!
>
>
>I'm guessing that 3/4" for two and 1" for three 12/2's. Keep in mind that
>the greenfield will need to be terminated at one end in a grounded metal box
>as all metal conduit carrying live wires needs to be grounded.


You are probably guessing one size too small. When you use an oval
cable you need to calculate it as a circle the diameter of the widest
dimension.
They assume the cable may be twisted
Since a 12/2 is about .4" across the flat side it would look like a #1
single THHN conductor in your calculation. That means one in a 1/2",
one in a 3/4" and one in a 1" (table C3). You could surely get more in
there if you carefully stacked and taped them but it would not be code
compliant.

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