# Electrical Metallic Tubing



## mam1869 (Dec 7, 2009)

Does anyone have any insight on whether the code prohibits NM-B wire to be run inside EMT?  I have heard conflicting arguments but I am not sure.  A contractor installed this in my unfinished basement and it did pass inspection.  Just trying to make sure it is ok.


----------



## raider1 (Dec 7, 2009)

Re: Electrical Metallic Tubing

NM cable is permitted to be installed in EMT.

Take a look at NEC sections 334.15(B) and 334.15©.

Make sure that the NM cable meets the conduit fill requirements of 358.22.

Chris


----------



## vegas paul (Dec 7, 2009)

Re: Electrical Metallic Tubing

Not sure what NM-B is, but per NEC 334.15 (B), NM, NMC and NMS are required to be protected from damage, and EMT is listed as one of the acceptable methods to accomplish this.  So, assuming you have NM, NMC, or NMS, in EMT installed in your basement, you should be ok (as long as the ampacitywas calculated correctly, EMT supported properly, etc.).


----------



## chris kennedy (Dec 7, 2009)

Re: Electrical Metallic Tubing

Also not prohibited by 334.12.


----------



## raider1 (Dec 7, 2009)

Re: Electrical Metallic Tubing

The -B designation on NM-B denotes that the NM cable is constructed with conductors that have 90 degree rated insulation in accordance with 334.112. There is a FPN to that section that has that information.

Here is what it says:



> 334.112 Insulation.The insulated power conductors shall be one of the types listed in Table 310.13(A) that are suitable for branch-circuit wiring or one that is identified for use in these cables. Conductor insulation shall be rated at 90°C (194°F).
> 
> FPN: Types NM, NMC, and NMS cable identified by the markings NM-B, NMC-B, and NMS-B meet this requirement.


Chris


----------



## vegas paul (Dec 7, 2009)

Re: Electrical Metallic Tubing

thanks raider1 - never saw that!


----------



## raider1 (Dec 7, 2009)

Re: Electrical Metallic Tubing

Your very welcome.

Chris


----------



## jar546 (Dec 7, 2009)

Re: Electrical Metallic Tubing

Is the emt inside or outside the structure?


----------



## mam1869 (Dec 7, 2009)

Re: Electrical Metallic Tubing

The EMT is in the unfinished portion of a basement... inside.

Why is chris kennedy saying 'Also not prohibited by 334.12.'?


----------



## chris kennedy (Dec 7, 2009)

Re: Electrical Metallic Tubing



			
				mam1869 said:
			
		

> The EMT is in the unfinished portion of a basement... inside.Why is chris kennedy saying 'Also not prohibited by 334.12.'?


Pointing out that NM can be installed in conduit in concealed work also.


----------



## mam1869 (Dec 7, 2009)

Re: Electrical Metallic Tubing

OK

Thanks Chris.


----------



##  (Dec 8, 2009)

Re: Electrical Metallic Tubing

A while back I raised this issue with the Chief Electrical Engineer of my AHJ.  My concerns are heat dissipation, conduit fill {no cross sectional area is listed in the code} and damage to the outer jacket from pulling it through conduit.  The CEE has contacted UL.  No answer yet.

I am not aware of any prohibition that has ever been in any code and the code has always allowed it "for protection".  That permission has been taken to mean that other than "for protection" it was not allowed.  We have allowed it for short sections such as passing through a rated wall in an attic but not as a general rule.  Since we work at the speed of government, it will be a while longer before I know more.

The added friction of the jacket makes the practice unlikely to catch on and so far it has seldom been an issue.


----------



## EPrice (Dec 8, 2009)

Re: Electrical Metallic Tubing

Since we're talking about EMT, I'll refer to Section 358.22, but other raceways have similar language.  358.22 specifically allows cables to be installed in EMT where not prohibited by the respective cable article.  As Chris Kennedy pointed out, it is not prohibited by the NM article.  Of course, it would not be allowed where the EMT is located in a wet or damp location, since NM is not permitted in a wet or damp location.

As for calculating conductor fill within the raceway, Note 9 found at the beginning of chapter 9 tell us how it is to be done.


----------



## raider1 (Dec 8, 2009)

Re: Electrical Metallic Tubing



> My concerns are heat dissipation, conduit fill {no cross sectional area is listed in the code} and damage to the outer jacket from pulling it through conduit.


Heat dissipation is no more of an issue with NM cable in a raceway then if I install NM cable buried in thermal insulation.

As for the conduit fill, Note 9 to Table 1 says that a multiconductor cable of two or more conductors shall be treated as a single conductor for calculating percentage conduit fill area. For cables that have elliptical cross sections, the cross-sectional area calculation shall be based on using the major diameter of the ellipse as a circle diameter.

If conduit fill is applied properly. then you should have no more problem with damage to the outer jacket then if you were pulling in single conductors.

Installing NM cable in raceways is not a common practice, but it does have it's applications.

Keep in mind though that if the raceway is in a damp or wet location then you can't install NM cable in those raceways.

Chris


----------

