# NM or MC



## WronGun (Oct 18, 2013)

I’ve never used NM on any commercial job site other than temp power and lighting. 

Im a little confused as to when it is allowed.

I’m starting a large warehouse (steel beams and decking)

70% of the job I’ve designed to include EMT

but the other 30% is made up of wood framed bathrooms and offices that will be getting hard ceiling. It sure would make life easy if this portion can be done with NM. I’m just unsure on when it isn’t allowed. Obviously if it can be exposed to physical damage but it won’t be in these rooms. 


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## splatz (May 23, 2015)

It's based on the "building type" which is determined by the building code. If a building code expert (engineer, architect, inspector) signs / stamps documents showing the building type is III, IV, or V, then I guess I could determine if it might be suitable for romex. 

But I wouldn't. I have seen people get burned on this, and there's too much chance someone will successfully challenge it in the future, so I just wouldn't go there.


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## WronGun (Oct 18, 2013)

splatz said:


> It's based on the "building type" which is determined by the building code. If a building code expert (engineer, architect, inspector) signs / stamps documents showing the building type is III, IV, or V, then I guess I could determine if it might be suitable for romex.
> 
> But I wouldn't. I have seen people get burned on this, and there's too much chance someone will successfully challenge it in the future, so I just wouldn't go there.




Ya I was afraid of that. I’m not willing to chance it. 


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## splatz (May 23, 2015)

WronGun said:


> Ya I was afraid of that. I’m not willing to chance it.


It's one of those things where right or wrong, your fault or not, if something happens in the future, it will make a headache for you.


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## MikeFL (Apr 16, 2016)

IIRC the NEC states "...if the building is ALLOWED to be of Construction Type ...".

If you want to consider putting in NM, I suggest asking the architect of record, in a letter which cites ver batim the applicable NEC article, if the building is allowed to be built of Construction Type (whatever construction types it says) and saving his response in your file. It proves you were as diligent as can be and then there's what's known as "detrimental reliance" where you relied on the architect of record and it would (most likely) go against his E&O insurance if there were a claim.


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## WronGun (Oct 18, 2013)

MikeFL said:


> IIRC the NEC states "...if the building is ALLOWED to be of Construction Type ...".
> 
> If you want to consider putting in NM, I suggest asking the architect of record, in a letter which cites ver batim the applicable NEC article, if the building is allowed to be built of Construction Type (whatever construction types it says) and saving his response in your file. It proves you were as diligent as can be and then there's what's known as "detrimental reliance" where you relied on the architect of record and it would (most likely) go against his E&O insurance if there were a claim.




Good point , but we’ll have it whipped up in MC fast, so it may not be worth the hassle. 


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## MechanicalDVR (Dec 29, 2007)

WronGun said:


> Good point , *but we’ll have it whipped up in MC* fast, so it may not be worth the hassle.


I wouldn't have even bothered to waste time asking on this one.

I'm so used to MC that I've used it over NM many times.


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## nrp3 (Jan 24, 2009)

I think it’s worth asking the ahj for those areas. Worst they could say is no and you use MC. Not a big deal.


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## telsa (May 22, 2015)

NM is so different for the crew than MC that it usually does not pan out at all.

You end up losing out on your labor expense.

It's the TRANSITION that sucks down your labor. 

Do it and then you'll come to realize the truth of my post... between your tears.


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## WronGun (Oct 18, 2013)

I will call AHJ in morning. 

This question has come up numerous times and I never really understood the true answer. 

I remember only one situation when I was a second year apprentice where we wired all
The units in a tall apartment building in NM through metal studs. 

NM will absolutely save labor and material costs on this portion of the job AND it will be a much less PITA. 


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## matt1124 (Aug 23, 2011)

telsa said:


> NM is so different for the crew than MC that it usually does not pan out at all.
> 
> You end up losing out on your labor expense.
> 
> ...


Because the NM people don't have roto-splits or because the MC people don't know how to use a razor knife?


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## Mulder (Sep 11, 2010)

telsa said:


> NM is so different for the crew than MC that it usually does not pan out at all.
> 
> You end up losing out on your labor expense.
> 
> ...


Unless you have a crew that is used to working with both NM and MC.


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## Cow (Jan 16, 2008)

We would most likely just use MC unless we were trying to be super competitive against another bidder then we might investigate if NM was allowed.


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## MTW (Aug 28, 2013)

WronGun said:


> I will call AHJ in morning.
> 
> This question has come up numerous times and I never really understood the true answer.
> 
> ...



Are you in Massachusetts by any chance?  It will surprise many people to know that Mass. has long relaxed the NM cable codes and still allows it above dropped ceilings to this day in "commercial" occupancies. The "tall building" rule throws people for a loop as well since Mass. removed the height restriction long ago.


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## WronGun (Oct 18, 2013)

MTW said:


> Are you in Massachusetts by any chance?  It will surprise many people to know that Mass. has long relaxed the NM cable codes and still allows it above dropped ceilings to this day in "commercial" occupancies. The "tall building" rule throws people for a loop as well since Mass. removed the height restriction long ago.




Yes MA


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## MTW (Aug 28, 2013)

If it were me, I would absolutely use NM cable if possible. If it's allowed by building type and enclosed in the walls, you're good to go. 

As for the transition, just use a 4" square with side bracket. I'm partial to the ones that don't have internal cable clamps.


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## macmikeman (Jan 23, 2007)

Near beaches nm is a way better method than conduit, mc, or any other metal wiring method. So in an area full of surfshops, dress and bikini stores, and the like , single level wood structures , I definitely slam in Romex wiring. And blue boxes to boot. Cowabunga.


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## splatz (May 23, 2015)

Measure and weigh the pros and cons, especially if it's something not seen very often, it isn't always easy swimming upstream. 

Romex saves a few bucks on materials and *maybe* some installation labor. Put an actual number to it though. 

First you have to determine the construction type and get iron clad documentation from a qualified expert with E&O insurance. You might have to pay for it if it's not in the existing drawings / documents. Put a number to the time and expense you'll incur here. 

Expect to be challenged by the customer as well as the inspector. I'd just raise the issue myself ASAP rather than waiting for them to bring it up. 

I am assuming you haven't done anything yet, make sure it's very clear in your proposal, include an attachment with the code reference and the documentation of the building type. Hand that to anyone that squawks. Put a number to the time you might spend explaining it. 

If it's work you've already won and in progress, and there's a formal submittal process, make sure what yo submit makes it clear that you're using NM and provide the attachment demonstrating it's compliant. If there's no submittal process, make a submittal anyway, i.e., inform the customer or GC you've done your homework, you saved them some money, you're using NM and it's legal, here's why, attach the attachment. Put a number to the time you spend having that conversation. 

Put a few dollars in to maybe some people thinking you're a corner cutter using NM in commercial eroding your reputation a bit. 

Put a couple bucks to the longshot that something will happen and someone will come after you for using NM. Could be something as minor as some rodent damage that wouldn't have happened if you had used MC like everyone else does. 

Is it still worth it? Around here, I'd think twice, because you just don't see NM in commercial unless the maintenance man did it. 

I definitely DO do a lot of things like this, where because I know my stuff I know a cheaper way THAT WILL PERFORM JUST AS WELL, and customers know I know how to save money, and that is a good reputation to have. But only if you're saving them real money, not if you're saving YOU a few bucks, because you knew a loophole and cut a corner.


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## MikeFL (Apr 16, 2016)

If the plans have a building code analysis on the front page (or any page) you should be able to rely on that.


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## Going_Commando (Oct 1, 2011)

MTW said:


> Are you in Massachusetts by any chance?  It will surprise many people to know that Mass. has long relaxed the NM cable codes and still allows it above dropped ceilings to this day in "commercial" occupancies. The "tall building" rule throws people for a loop as well since Mass. removed the height restriction long ago.


NH just did silimar starting this year. The state passed an amendment waaay relaxing romex rules in commercial, so now it can be installed above drop ceilings and the like. We have just kept installing MC since there are more handy ways to hang it, and the sheath/insulation is so thin on new romex I really don't trust it above a commercial drop ceiling where rework and service gets done. The older stuff I would have no qualms installing (90s and earlier). Heck, the stuff with TW in it and the heavy sheath from the 70s I would argue is tougher than aluminum sheathed modern MC.


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## Signal1 (Feb 10, 2016)

If you do go with MC, go with the MCAP. You can make up your boxes faster than NM with that stuff.


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## MechanicalDVR (Dec 29, 2007)

matt1124 said:


> Because the NM people don't have roto-splits or because the MC people don't know how to use a razor knife?


I have always done most things in mc and have everything for that type install.

It's a new thing for me to have nm on my truck.


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## telsa (May 22, 2015)

I only ran one job that was a half-breed. I was astounded as to how much labor went into transitioning from MC to NM... if you hoped to meet Code. The materials savings didn't even remotely pay off. 

Unless the NM portion is seriously large, you won't win going that way.

Out my way, steel studs are EVERYWHERE. This means that you're in grommet city if you use NM. Suddenly NM doesn't look quite so appealing.

I'd change my tune IF a TON of wood stud construction was involved.


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## Going_Commando (Oct 1, 2011)

telsa said:


> I only ran one job that was a half-breed. I was astounded as to how much labor went into transitioning from MC to NM... if you hoped to meet Code. The materials savings didn't even remotely pay off.
> 
> Unless the NM portion is seriously large, you won't win going that way.
> 
> ...


Very valid point. NM with steel studs doesnt really save anything. Especially when you start messing with plastic boxes with self tapping screws. Those things are a gigantic pain in the ass and a 4 square bracket that snaps on to metal studs or a bracket with peanut screws slammed into it is waaaay faster. I'll never use those steel stud plastic boxes again and will just sling MC as its faster, and the grommets cancel out material cost savings between nm and mc. 

Wood studs are a completely different story and would use nm 9/10 times. I'm no stranger to romex racing, so labor with nm and nail-on boxes is way faster than mc and the material savings are real numbers.


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## cdslotz (Jun 10, 2008)

Do commercial jobs not have specs any more?

If this does...what do they say?


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## Math123 (Jun 16, 2018)

It's allowed, but to be honest, with my limited experience, every time I see an electrician running NM through metal studs idc how well he put grommets or bushings to protect it, he seems like a cheapo to me that might compromise quality for penny pinching. That's a first impression not knowing the electrician of course, one of my bosses has done it and he does quality work. Just in general I've only seen penny pinches doing it. Also at what point does factoring in the slow down of "softly or carefully" running the NM to make sure it doesn't get scraped or cut does your cost in labor and man power match or exceed the savings from using MC/AC. I am just a laborer I don't do math in terms of labor and material but even the bound to happen troubleshooting to correct issues or replace accidentally damaged runs seems to make it not worth it. (Labor costs) +( Quality and image of craftsmanship) + ( quality and durability of material) - rats or squirrels will get to it eventually I guarantee it - > $savings in material in my opinion. If I ever open shop I'll be able to find out for a fact.


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## sparkee13 (Aug 29, 2018)

telsa said:


> I only ran one job that was a half-breed. I was astounded as to how much labor went into transitioning from MC to NM... if you hoped to meet Code. The materials savings didn't even remotely pay off.
> 
> Unless the NM portion is seriously large, you won't win going that way.
> 
> ...


*

Unless the MC is coiled the wrong way 

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## catsparky1 (Sep 24, 2013)

If metal stud boys are not on it you punch lots of holes or wire goes up and down .


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## UnlimitedCurrent (Sep 14, 2018)

Cannot use NM in acoustic ceiling. Most commercial buildings use this ceiling at leat somewhere in the building.


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## UnlimitedCurrent (Sep 14, 2018)

In Pa we are still on 08 code. 334.12


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