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Old 03-20-2011, 01:10 AM   #1
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Checking to see if my calculations are right


If you were to strip the outer insulation off of Romex it would be considered similar to THHN as far as conduit fill is concerned? I looked all through 334 of the 08 code and there was mention of using EMT to protect a cable but nothing citing a table to reference that I saw.

Long story short I think I'm gonna use 3/4" EMT more or less to protect the wiring that is going to run along the furing strips (1.5" X 1.5") by our basement stairs to the relocated light switches. There are gonna be alot of things getting attached right in that area the wiring needs to go in(handrails, drywall, stair skirts, boiler hot water pipes, ect) and I just know with my luck I'll hit a piece of romex sure as anything even if I push it all the way against the wall and have the required 1 1/4 clearance per the code (Murphy lives here). Looking at Annex C in the 08 code book it's mentioning I can put nine 12 awg wires in a 1/2" conduit and 16 in a 3/4". Am I reading this right?

Also, do I have to do any derating on this? Being I'm running two runs of 12/3 wire through a conduit more than 24" long I think so. I have potentially depending on how I wire the circuit 4 or 6 current carrying conductors so I would derate it by 20% correct?

Circuit is only gonna a 15 amp circuit anyways but I'm running 12 awg because that is how the rest of the house was run so I just wanted to stay uniform not to mention my figuring is telling me 14 awg isn't gonna cut it.

I just wanna check and make sure I'm on target with my math on this. I'm amazing how little remodel jobs turn into major projects. Thanks guys.

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Old 03-20-2011, 04:53 AM   #2
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Checking to see if my calculations are right


In short leave the sheath on. No it is not the same a THHN

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Old 03-20-2011, 11:08 AM   #3
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Checking to see if my calculations are right


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In short leave the sheath on. No it is not the same a THHN
I know it's not, just for the sake of the conduit fill would it apply to the same table listing is what I was asking. So the rest of my figuring is solid? Thanks.
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Old 03-20-2011, 11:21 AM   #4
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Checking to see if my calculations are right


I guess you could use the cross section for figuring conduit size but not as actual conductors used in conduit. I would say that would be fine.

EDIT! Why use the cross section of the inner conductors of NM when you must use THHN or similar for the job. THHN and similar are listed in the code book. It looks like you plan to use NM anyway. Right?

Last edited by J. V.; 03-20-2011 at 11:43 AM.
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Old 03-20-2011, 03:14 PM   #5
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Checking to see if my calculations are right


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I guess you could use the cross section for figuring conduit size but not as actual conductors used in conduit. I would say that would be fine.

EDIT! Why use the cross section of the inner conductors of NM when you must use THHN or similar for the job. THHN and similar are listed in the code book. It looks like you plan to use NM anyway. Right?
I plan to only run the wires in the conduit for the duration needed to protect the wires from all the stuff that's gonna get driven into the walls. Thinking about using a product like this http://www.aifittings.com/c_3.htm#8600 .
Once I get the wire out of the concerned area I'll transition it back to plain old romex. I think this is legit per 334.15 (B) but just want to ensure I'm on track and maybe there is a better way to accomplish what I'm thinking about. Also looking at 300.4 (A) (1) appears to support my thinking but again just looking for.

Just so you know I'm not an electrican just a plain old home owner whom has some experience and formal training (albet 10-15 years ago) doing some electrical wiring while he was in the military but it wasn't a full time job, just an additional duty I would get tagged with every 3 or 4 months so I know my knowledge is far from complete and because I know this I ask questions .
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Old 03-20-2011, 04:17 PM   #6
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Checking to see if my calculations are right


you cannot strip the sheath from the NM and use it like that. If you want to transition for NM to THHN or some other similar individual conductor wire, you will have to set junction boxes and use real THHN or whatever and then convert back to NM when you want.

so, conduit fill is irrelevant since you are not allowed to do what you are suggesting. If you are going to do it, what difference does legal conduit fill make since it is illegal anyway?
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Old 03-20-2011, 09:30 PM   #7
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Checking to see if my calculations are right


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you cannot strip the sheath from the NM and use it like that. If you want to transition for NM to THHN or some other similar individual conductor wire, you will have to set junction boxes and use real THHN or whatever and then convert back to NM when you want.

so, conduit fill is irrelevant since you are not allowed to do what you are suggesting. If you are going to do it, what difference does legal conduit fill make since it is illegal anyway?
It's illegal to strip the jacket off romex in a conduit?

334.15 (C) lead me to believe that you can, but perhaps I'm misreading.

Thanks for your help and advice guys.
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Old 03-20-2011, 09:55 PM   #8
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Checking to see if my calculations are right


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It's illegal to strip the jacket off romex in a conduit?

334.15 (C) lead me to believe that you can, but perhaps I'm misreading.

Thanks for your help and advice guys.
are you talking about this statement:

the NM sheath shall extend through the conduit or tubing and into the outlet or device box not less than 1/4"?

Unless you have a different understanding of the word "through" than I do, that means the sheath must be on the cable that is in the conduit. You can only strip it where it goes into an outlet or device box.

Is that the section you were talking about?
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Old 03-21-2011, 12:38 AM   #9
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Checking to see if my calculations are right


Like I said leave the jacket on the romex and just sleeve it through the pipe no fittings needed(bushings a good idea)

how many runs of romex are we trying to get through this area? You should be able to get 2 in 1/2"EMT 3 or so in 3/4" I have never tried to see how many will fit in 1" but if it will fit (without going over board and using a come-a-long to get it in) it will be fine
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Last edited by Saturday Cowboy; 03-21-2011 at 12:41 AM.
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Old 03-21-2011, 12:39 AM   #10
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Checking to see if my calculations are right


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Like I said leave the jacket on the romex and just sleeve it through the pipe no fittings needed(bushings a good idea)
agreed except bushings required instead of just a good idea.

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