EMT electrical conduit -- how many NM wires?

[TomR]

I have a dedicated 15-amp circuit in an unfinished basement that runs to an outlet on the wall for the sump pump. The wire/cable that goes to the outlet is white 14/2 NM-B w/ground. From the ceiling down to the outlet it is fed inside of metal EMT conduit. I assume that the metal conduit is

1/2-inch (the outside diameter of the conduit is about 3/4-inch).

I would like to add a pull string ceiling light above the sump pump for better lighting while working on the sump pump and/or the HVAC which is next to the sump pump.

What I am thinking of doing is getting power for the light from the outlet and running new 14/2 NM-B w/ground from the existing outlet back up through the same EMT metal conduit to the new ceiling light.

My main question is, is it okay to have two 14/2 NM-B w/ground cables inside a 1/2-inch EMT metal conduit?

[recyclebinned]

You can?t have any NM cable inside a conduit. It has to be single conductors.

[Nate Nagel]

I don't know the answer to that question as I'm used to seeing THHN instead... I'm assuming the reason for using NM is that the EMT just terminates at a bushing above the ceiling, and is only used for protection of the cable?

Is the recep in a 1900 (4" square) box or a handy box? If a 1900 box I would just get another stick of EMT and do it that way. (don't forget the bushing where the EMT terminates, to prevent chafing the NM.) If it is a handy box you probably don't have enough room in the box to legally add more conductors anyway, and should consider replacing it with a 1900 box.

nate

[RBM]

If you run NM inside of metallic conduit, the metal should terminate in you box using a proper fitting. At the other end of the conduit sleeve, there should either be a choke or a bushing on the end of the conduit and a staple into some framing near the end of the conduit. If you need more cable entries in the box, use additional sleeves

[gfretwell]

Wrong

334.15 Exposed Work. In exposed work, except as provided in 300.11(A), cable shall be installed as specified in 334.15(A) through (C).

(B) Protection from Physical Damage. Cable shall be protected from physical damage where necessary by rigid metal conduit, intermediate metal conduit, electrical metallic tubing, Schedule 80 PVC conduit, or other approved means.

[gfretwell]

The problem is conduit fill. You can't put that many NM cables in a

1/2" EMT

[Doug Miller]

[e-mail] wrote in news:64bcf2b4-d88f-4d98-8daf-383a8784b898 @googlegroups.com:

Absolute nonsense. NM cable is permitted inside conduit in any location where NM is permitted without conduit.

[Doug Miller]

"TomR" wrote in news:krpmvc$hde$ [e-mail]:

Probably not physically possible anyway... but no, not as far as I know.

[TomR]

Thanks. That's how the conduit and wiring is set up now -- with the right fittings clamps, etc.

Okay.

[TomR]

Thanks Doug, gfretwell, RBM, Nate, et al.

I have another option that I think will work. The existing 14/2 NM cable runs along the side of a ceiling joist close to where I want to put the new light. Most likely, I can just unstaple that cable and create enough slack to place a junction box in the circuit there and run the light from that junction box. Or, if that doesn't create enough slack, I could just use two junction boxes.

But, before doing that, I thought that I would check to see if I could do my original idea of having two NM cables in the one 1/2-inch metal conduit -- apparently not.

[trader4]

I ran two romex inside 1/2" liquidtight going to my furnace and it was an easy fit. I would think you could do the same with metal. think you'd get two inside metal as well.

[gfretwell]

You could get 2 in there if you aligned them perfectly and pulled them in together but it is still an over filled conduit. He also has another issue, the existing box is probably not big enough to terminate 2 cables.

[recyclebinned]

NEC Note 9 in the Chapter 9 tables says "A multi conductor cable of two or more conductors shall be treated as a s ingle conductor for calculating percentage fill area. For cables that have elliptical cross section, the cross section area calculation shall be base d on using the major diameter of the ellipse as a circle diameter".

[recyclebinned]

Even in that exception the conduit would have to be larger than ½? so a s not to exceed the fill capacity.

[Doug Miller]

[e-mail] wrote in news: [e-mail]:

How on earth did you manage to read that as prohibiting NM inside conduit?

[recyclebinned]

It exceeds 53% of the area for ½? conduit.

[Pete C.]

Probably not applicable in this case, but you are allowed to ignore conduit fill calculations for cases where the cables are passing through a short length of conduit sleeve. What was it, 24" length max?

[Doug Miller]

[e-mail] wrote in news:509607f9-50bb-4b4c-9ad7- [e-mail]:

All that proves is that _that_particular_combination_ can't be run in _that_particular_size_ of conduit.

You made the blanket claim that "You can't have any NM cable inside a conduit" -- which is complete and utter nonsense.

[Doug Miller]

"Pete C." wrote in news:51e0b891$0$51390$862e30e2 @ngroups.net:

It is 24" max, but you are *not* permitted to simply "ignore conduit fill calculations". Rather,

"where conduit or tubing nipples having a maximum length not to exceed 600 mm (24") are installed between boxes, cabinets, or similar enclosures, the nipples shall be permitted to be filled to 60 percent of their cross-sectional area ..." [2005 NEC, Chapter 9 Tables, Note 4]

[gfretwell]

Not true at all for a single 14-2 NM. A single conductor or cable can fill 53% of a raceway but when you get to two, that drops to 31%

Ok to make the math easier this is metric Using Southwire RX

width...........area

14-2 9mm ...63.6 mm2 12-2 10mm..78.5 mm2 14-3 7mm....38.5 mm2 12-3 8mm....50.24 mm2 10-3 9mm....63.6 mm2

From Table 4 Trade size..one wire 53%...2 wires 31%....3 or more 40%

1/2"EMT....104 mm2 ...........61mm2............78mm2 3/4"EMT....102 mm2 ...........106mm2...........137mm2 1" EMT......295 mm2 ...........172mm2...........222 mm2

Two 14-2 RX would need a 1" EMT to be legal.