Calculating NM volume in EMT

[myemail63114]

Using the major diameter of 12/2 w/G to calculate area (d=.437, A = .152) you can only fit one cable in 1/2 EMT (A= .161 @ 53% fill rate) and even 3/4 EMT is not adequate for (2) 12/2 w/G at 31% fill rate. How do you take into account the elliptical shape of NM cable, surely the ability of the cables to nest on their flat sides would greatly decrease the cumulative cable area. Otherwise each 12/2 NM takes up .1520 area in a raceway???

 

[xformer]

Using the major diameter of 12/2 w/G to calculate area (d=.437, A = .152) you can only fit one cable in 1/2 EMT (A= .161 @ 53% fill rate) and even 3/4 EMT is not adequate for (2) 12/2 w/G at 31% fill rate. How do you take into account the elliptical shape of NM cable, surely the ability of the cables to nest on their flat sides would greatly decrease the cumulative cable area. Otherwise each 12/2 NM takes up .1520 area in a raceway???

IMHO.. I would read the notes to Chapter 9 tables... especially note 9

 

[fmtjfw]

Using the major diameter of 12/2 w/G to calculate area (d=.437, A = .152) you can only fit one cable in 1/2 EMT (A= .161 @ 53% fill rate) and even 3/4 EMT is not adequate for (2) 12/2 w/G at 31% fill rate. How do you take into account the elliptical shape of NM cable, surely the ability of the cables to nest on their flat sides would greatly decrease the cumulative cable area. Otherwise each 12/2 NM takes up .1520 area in a raceway???

It is probably not a good idea to assume that the flat cables (with semicircular sides) will nest. It is likely they will twist. This is why you treat their maximum dimension as the diameter of an equivalent circular cable for conduit fill purposes.

If you tape them together to force them to nest, then you are going to have a very difficult time getting the assemblage to bend around bends.

 

[myemail63114]

Additional Information

Additional Information

The application is a conduit drop in basement for GFCI. No problem with one NM down to GFCI terminating there, but what if I want to add cable up and out for additional locations downstream of GFCI? Used 3/4 EMT in past but two 12/2 NM /w/G technically exceeds volume...stripping insulation off not an option I assume???

 

[xformer]

The application is a conduit drop in basement for GFCI. No problem with one NM down to GFCI terminating there, but what if I want to add cable up and out for additional locations downstream of GFCI? Used 3/4 EMT in past but two 12/2 NM /w/G technically exceeds volume...stripping insulation off not an option I assume???

That is an engineering issue and not a NEC issue...

If one is planning on making such an install, then size the pipe down to the receptacle for 2 NM cables..

 

[readydave8]

junction box at top & thhn down to recep?

 

[Dennis Alwon]

It is very different if the conduit is a sleeve or if it is part of the entire run. If you sleeve it down the wall then Note 2 to the table 1 in chapter 9 exempts compliance with fill.

 

[Nom Deplume]

Just use two 1/2" EMT and be done with it.

 

[Smart $]

The application is a conduit drop in basement for GFCI. No problem with one NM down to GFCI terminating there, but what if I want to add cable up and out for additional locations downstream of GFCI? Used 3/4 EMT in past but two 12/2 NM /w/G technically exceeds volume...stripping insulation off not an option I assume???

Get some 12/2/2 NM-B.

Southwire lists 12/2 CU-NM-B dimensions as 410?179mils.... 12/2/2 CU-NM-B dimensions as 381mils.

You can fit more conductors in lesser fill space.

 

[mopowr steve]

It is very different if the conduit is a sleeve or if it is part of the entire run. If you sleeve it down the wall then Note 2 to the table 1 in chapter 9 exempts compliance with fill.

I agree with Dennis,
I run 2 - 12/2/G NM all the time with no problem for basement recepts in 1/2" EMT with throat bushing on top. Also NEC states that the jacket must still extend into box a 1/4". I believe that this requirement was put in around the 2008 Code cycle before that I could get 3- 12/2/G
in but it had to be stripped and jacket would have to be 1/4" into the conduit stub.