NM in EMT

[Elec83]

I just need to know if I am allowed to install 2 14-2 romex cables in 1/2” EMT as long as it is inside?

 

[infinity]

Probably not. You need to calculate the fill by using the width of each cable as if it were round.

 

[mopowr steve]

Ohhhhhhh, but you can have wire completely surrounded by insulation. Where’s the fill calculation for that?
It’s just a chase.
And that’s why nm-b uses 60* column for ampacity, cause it is often encapsulated with no free air space.

Easy, just want to ruffle feathers.

 

[infinity]

Ohhhhhhh, but you can have wire completely surrounded by insulation. Where’s the fill calculation for that?
It’s just a chase.
And that’s why nm-b uses 60* column for ampacity, cause it is often encapsulated with no free air space.

Easy, just want to ruffle feathers.

The fill limits for raceways are for protection of the conductors or cables from damage when they're installed.

 

[hillbilly1]

If it is used as a sleeve for protection, not a raceway, then I think the fill tables would not apply. If used as a raceway, then I think a inspector could kick it for the wire in the cable not being labeled with temp rating and such because the sheath should be removed past the transition fitting. I know of inspectors that kick mc cable for the same reason.

 

[480sparky]

If it is used as a sleeve for protection, not a raceway, then I think the fill tables would not apply. If used as a raceway, then I think a inspector could kick it for the wire in the cable not being labeled with temp rating and such because the sheath should be removed past the transition fitting. I know of inspectors that kick mc cable for the same reason.

I haven yet to see THHN marked with it's temperature rating. The fact that it's marked THHN tells the inspector it's 90°C. Same for NM. It's marked NM, so it's got 90°C conductors in it.

No mention of any 'transition fitting' was made by the OP, so we must assume the sheath is intact throughout the EMT.

 

[infinity]

I didn't see sleeve or removing the jacket in the OP so my response was based solely on him wanting to install (2)-14/2 cables in a 1/2" EMT. I didn't do the calculation but I'm pretty sure two cables won't fit per the NEC.

 

[flashlight]

Haven't tried it, but doesn't sound like they would fit very comfortably. Code or not I would use 3/4.

 

[mopowr steve]

(2 ) 14/2-g nm-b wires will fit in 1/2” EMT no problem, (2) 12/2-g nm-b wires still no problem. Get to 3 you might need a shoe horn and lube.

 

[flashlight]

OK, if they fit OK you woud still have to de-rate? More than 3 conductors. Unless it was not a raceway but a short protective sleeve?

 

[hillbilly1]

(2 ) 14/2-g nm-b wires will fit in 1/2” EMT no problem, (2) 12/2-g nm-b wires still no problem. Get to 3 you might need a shoe horn and lube.

I worked with one electrician years ago, when you would ask how many 3/0 would fit in a 2” conduit, he would say “How many do you need!” LOL!

 

[chrismarcellino]

Is this just a lone piece of EMT using to protect the NM, or does the EMT lead into a box or panelboard? If this is a protective sleeve for the demonstrable purpose of physical protection for exposed wiring only, then no fill restriction as long as the cabling isn't damaged (Chapter 9, Table 1, Note 2.) If this is a raceway, or is concealed, then the following fill calculations apply:

Longer OD of NM 14-2 is approx. 0.37" to 0.39" depending on brand. Using the worst case to determine total area as "for cables that have elliptical cross sections, the cross-sectional area calculation shall be based on using the major diameter of the ellipse" (Ch. 9 Note 9), then:

2 cables in 1/2" EMT gives 78.6% fill, which is more than the limit 31% for 2 cables/conductors (or even 60% if this was 24" or less of raceway). (Ch. 9, table 1.)

The smallest EMT that will be compliant for two NM 14-2 less than 24" in length is 3/4" and more than 24"in length is 1" diameter.

Options that would be compliant:
- A single NM in 14-2 EMT 1/2" gives 39% fill, which is less than the limit of 53% for a single cable, so you could put each in their own 1/2" EMT.
- Or just place a JB and splice (not strip) to THHN.
- Or use NM 14-2-2 which has a slightly smaller circular diameter of 0.35", and can be placed in 1/2" EMT.

Derating not an issue even above 24" for a typical branch circuit as you may derate the 90 deg column (Table 310.15(B)(3)(a)), and still end up above the 15 amps required of NM (or any wire of this gauge) for only 4 conductors assuming no elevate temperature derating is needed. Correct this must be a dry area/indoors, but cannot be embedded in a slab on or under grade even indoors IMHO in case that's where your conduit is.

The NM-in-EMT to NM transition requires a fitting on the end of the EMT (310.15(c)) to protect against abrasion and this must be accessible after installation whether sleeve or raceway.. 250.86 exception 2 permits you to not bond the transition end of the EMT conduit (which is also pertinent if just using the EMT as a protective sheath in which case neither end is bonded.) Please correct any typos/errors/different interpretations.

 

[Dennis Alwon]

OK, if they fit OK you woud still have to de-rate? More than 3 conductors. Unless it was not a raceway but a short protective sleeve?

It depends on the length of the sleeve. Look at note 2 in chapter 9 & 4

Notes to Tables
(1) See Informative Annex C for the maximum number of
conductors and fixture wires, all of the same size (total
cross-sectional area including insulation) permitted in
trade sizes of the applicable conduit or tubing.
(2) Table 1 applies only to complete conduit or tubing
systems and is not intended to apply to sections of
conduit or tubing used to protect exposed wiring from
physical damage.
(3) Equipment grounding or bonding conductors, where
installed, shall be included when calculating conduit or
tubing fill. The actual dimensions of the equipment
grounding or bonding conductor (insulated or bare)
shall be used in the calculation.
(4) Where conduit or tubing nipples having a maximum
length not to exceed 600 mm (24 in.) are installed
between boxes, cabinets, and similar enclosures, the
nipples shall be permitted to be filled to 60 percent of
their total cross-sectional area, and 310.15(B)(3)(a)
adjustment factors need not apply to this condition.

 

[McLintock]

I would cut the sheathing off and then run it into the EMT, NM does not pull well around 90s or offsets. Easiest thing to do is get some THHN off your truck and run it


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[infinity]

It depends on the length of the sleeve. Look at note 2 in chapter 9 & 4

So what would apply to a sleeve that is not a complete conduit system as mentioned in note #2?

 

[Dennis Alwon]

I would cut the sheathing off and then run it into the EMT, NM does not pull well around 90s or offsets. Easiest thing to do is get some THHN off your truck and run it


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That would not be compliant

 

[Dennis Alwon]

So what would apply to a sleeve that is not a complete conduit system as mentioned in note #2?

In terms of bundling then you are stuck with anything over 2' but for fill it is not clear and apparently any length could be used without fill being of concern, IMO.... Obviously I don't think that is the intent. One could argue that if the sleeve is not being used as protection at a certain spot of the run. But as I see it, a 10' stick of pvc stubbed up the wall in a basement from a receptacle has no fill requirements.

 

[infinity]

In terms of bundling then you are stuck with anything over 2' but for fill it is not clear and apparently any length could be used without fill being of concern, IMO.... Obviously I don't think that is the intent. One could argue that if the sleeve is not being used as protection at a certain spot of the run. But as I see it, a 10' stick of pvc stubbed up the wall in a basement from a receptacle has no fill requirements.

This is the part that is unclear to me when it comes to sleeves over 24". 310.15(B)(3) is for cable bundling when not in a raceway. Doesn't make any sense to me.

310.15(B)(3) Adjustment Factors.
(a) More than Three Current-Carrying Conductors. Where the number of current-carrying conductors in a raceway or cable
exceeds three, or where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(3)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

 

[LarryFine]

Forgive me if this is obvious, but the ideal solution is to transition from NM to THWN/etc. in a J-box connected to the EMT.

Did I overlook any explanation of either or both ends of how the EMT terminates, i.e., a box or panel?