NM cable in EMT-EC mag article

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tom baker

tom baker

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Did anyone see the article on the last page of Electrical Contractor magazine? Author implied that when using EMT to protect NM cable from damage that said EMT would have to be limited to 1o feet. We have had this discussion before and there seemed to be a general agreement that the distance is not limited.
 
Re: NM cable in EMT-EC mag article

Tom
If I remember right someone contacted NFPA to get a formal interpretation on this and the reply from NFPA was one length of conduit, or 10'.
I'll try to find the thread.
 
Re: NM cable in EMT-EC mag article

EMT as a complete system (grounded, connectors, boxes, etc) would be unlimited. As a protective ungrounded sleeve, then 10' was the NFPA interpretation.
 
Re: NM cable in EMT-EC mag article

Please understand that the NFPA is just an opinion the same as everyone who posts on this site. If you want an official interpretation, a formal request must be submitted to the NFPA and it will go to the panel members for their votes. It must be framed in such a way that a yes or no answer may be given.

With all that said, it is the words that are printed in the Code that determine your answer, not someone else's opinion. Answers to the questions "How far is near?", "How much force will produce physical damage?", "How much strength is required for a through the roof raceway to accept a 125', #2 Al. triplex final span?" are all subject to interpretation or the result of proper engineering. The NFPA is not magic and neither is anyone else. The bottom line is that the AHJ has the final word; therefore, the AHJ is always correct. :D
 
Re: NM cable in EMT-EC mag article

Tom: One of the people that sits on the Utah IAEI board with me is on the CMP for the cable wiring method articles. He told us the other day there is a tentative amendment being entertained to allow NM cable to be installed in a complete system of EMT. It appears as though it will probably pass.

If it does pass, I could see no reason to limit the length for the purposes of protecting the conductors.
 
Re: NM cable in EMT-EC mag article

Ryan, what prohibits NM from being shoved through EMT systems today (not short lengths for protection)?

I use it frequently that way for convenience if doing a solo pull and have never had inspection problems. The fill/volume charts explicitly mention cable assembly and tell how to size oval assemblies accordingly.
 
Re: NM cable in EMT-EC mag article

See 334.112 - NM conductors must be of a type in the 310 list.

Now look at the second sentence of 310.13. This allows anything in the list to be used in a chapter 3 wiring method - like EMT. If NM were allowed to have some sort of oddball insulation not in the 310 list, then I could see your point, but its construction requirements force it to have a normal insulation.

One can also argue that the inside of EMT is a "normally dry" location - or at least should be :D

[ January 22, 2004, 07:22 PM: Message edited by: tonyi ]
 
Re: NM cable in EMT-EC mag article

I also saw the article and I noted that the author said one of the problems was that the NM cable had to be clamped where it entered the box and that this was impossible with the EMT.
Recently there was a thread discusing the legitamacy of installing a Romex connector backwards, i.e. with the screws on the inside of the box.
If so, the connector could be installed with the pipe threads going out thru the 7/8" hole. A 1/2" rigid coupling would be screwed onto these threads. Then an EMT connector would be screwed into the other end of the coupling and the EMT attached. The Romex would be fed into the box and the small screws tightened thus securing it.
[It may be necessary to insert a locknut between the Romex connector and the coupling.]
Does this pass muster?
~Peter
 
Re: NM cable in EMT-EC mag article

Ok,I had an issue in 2000 .A split service on a 2 story home so we set the service with a 200 amp disc. 4/0 SER from the panel to the disconnect.A block home so we exited the soffit and sleeved pvc to the disc all good so far right !!!! NOT.inspector said no way the ser isn`t supported inside the pipe as required to be supported unless there was a connector to transition into pipe as a raceway if not, it is still to be supported as if run exposed.This came up today and I thought I would put it out there.....
 
Re: NM cable in EMT-EC mag article

Allen i have done that before and see nothing wrong with it.Seems he is pushing this a bit far.Just where does he think that cable will go ?
 
Re: NM cable in EMT-EC mag article

Peter, 334.30(B)(1) allows for NM to be unsupported between fished access points.

I would argue that since you have to fish NM through the raceway, and the only access is through the EMT (or whatever raceway) connectors in the boxs/panels, that those connectors qualify as "access points" - therefore no additional support is required ;)

This same argument would apply to the sleeved SE scenario mentioned above since the SE article references 334.30 for support issues.

[ January 22, 2004, 10:33 PM: Message edited by: tonyi ]
 
Re: NM cable in EMT-EC mag article

Tonyi

When you fish cable through a wall you still support it to the box. 'Fished' through a raceway how do you support it to the box?

I was the person who emailed the NFPA for an informal discussion on the length of conductor for 'physical protection'. The response was less than one length of conduit. My understanding of the issue of not permitting the installation of a cable assembly in a raceway is, it was a mistake between the two different CMPs, they were not aware of the changes being made in the language change for the 2002 cycle.

Another thought of installing NM cable in a raceway is the bending radius of the NM cable.

Charlie - I concur with your post - it is well worded :)

Pierre
 
Re: NM cable in EMT-EC mag article

Pierre, Chapter 9, notes 5 and 9 both explicitly mention explicitly multi conductor cables and note 9 mentions eliptical cables and how to size them (particularly relevant for NM)

If it were not the intent that cable assembly be allowed in raceway, what would be the purpose of this chapter 9 language?

I contend that NM through raceway is no longer a "NM cabling system", it becomes a raceway cabling system that is secured/supported per that raceway's article.
 
Re: NM cable in EMT-EC mag article

How it is done in the Columbus area.

I will use the following example:

A pipedown (emt or pvc) used to protect nm wire to a metal box.

Pipe has male ends with bushings on both ends of it. The pipe is secured to the wall. Just before the box the nm exits the pipedown. A c-500 or a plastic connector is installed in the box to "secure" the nm.

Why? Because the nm could be pulled out of the box if it is not secure.

I know you are going to ask who would pull on the wire. Think of this:

NM's last "support" is where it goes through a floor joist. Joe homeowner hangs laundry on the nm, and don't tell me you have never seen this done. The nm could be pulled against the box tripping the breaker. When this happened the egc is broken. Joe homeowner resets this breaker and now the box and pipedown are "hot".

Little Janie comes by and toughes the box.

Mike P.
 
Re: NM cable in EMT-EC mag article

If one is running a length of metallic raceway more than 24 inches, how does one bond the metallic raceway?

I am not saying that a cable or wiring assembly is not permitted to be installed in a raceway, I am asking how it is installed and does it meet code as far as conduit fill, bending radius, bonding, and other applicable code requirements.

For instance, if you are installing 14/2 NM cable, what is the minimum size EMT that would be required? Lets say there are two 90s and an offset in the run.


358.2
This definition states that EMT is for the 'protection and routing of conductors and cables'.

Pierre
 
Re: NM cable in EMT-EC mag article

A single 14-2 or 14-3 is comfortable in 1/2" EMT in terms of fill. The EMT can't be bent tight enough to cause any issues - however a 90 degree pull elbow could. I see this more of an application issue than a code issue though.
 
Re: NM cable in EMT-EC mag article

Pierre: bonding of the raceway is not required when used for physical protection. See 250.86 Ex 2.
Note the exception refers to "short sections" it could be argued that a short section is anything less than 10 ft. That comments takes me back to my orginal post.
 
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