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#195703 08/18/10 10:36 PM
Joined: Aug 2007
Posts: 853
leland Offline OP

I've heard this but have never seen it in the 'book'.
My understanding is- Nm Just cannot RISE more than 3 floors.
Once a proper riser has been installed,NM can be on the 14th floor. so long as it is not above a dropped ceiling and the other such rules.

Guidance please.


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Joined: Aug 2001
Posts: 466
Likes: 1
The way I understood it if the building was over three floors NM could not be used. I think this has changed now if the building is sprinklered.

Jim M #195707 08/19/10 12:47 AM
Joined: Jul 2004
Posts: 9,936
Likes: 34
Basically the code removed the "3 floor" language from 334.12 but it still says type III IV and V construction so that puts you in table E2 and the floor limits start coming back depending on construction details.

Added for clarity

This is a building code restriction, not an NEC restriction. You could put RX in a 14 floor type III building if you had one but you can't build a 14 floor type III building.

There is an exception that allows RX in type I and II but it has to be in a raceway. I can't imagine why you would want to do that.

Last edited by gfretwell; 08/19/10 04:52 AM. Reason: additional info.

Greg Fretwell
Joined: Jun 2006
Posts: 613
In Canada NM is restricted to buildings of combustible contruction. The type of construction is mandated by the building code and that is 4 stories here. A 14 story building is not combustible construction and NM cables may not be used.
This is consistent with the intent in the NEC.
BC is in the process of increasing the height to 5 stories but so far no one is trying to build 5 story wood frame buildings.
A political move by the provincial government to increase the market for BC lumber. Frankly I think it is insane to go higher than 4 stories and 3 is still a hard building to escape in a fire if it is built out of combustible materials.
We have a 22 story concrete building that has had 3 or 4 fire in the suites without any secondary loss of life even from high floors There is a lot more time and ways out of non combustible buildings bur most fire departments cannot get ladders higher than 60 feet whis is around where a 5 story building roof would be.
Keep the NM cables out of high rises.

Joined: Jan 2005
Posts: 5,445
Likes: 3
Cat Servant
Code language finesse aside .... there were some interesting reasons for the restrictions we used to place on Romex.

Simply put, Romex was designed for simple residential applications, in places that had wood studs as the structure.

If you look into the limitations of wood framing, you learn that with balloon frame construction you can only go three floors tall; in a similar manner, simple cinder block can only go five floors tall. More than that, and the materials just aren't strong enough.

The former language in the NEC made it pretty clear that they were imagining Romex for this use alone. Why the code panels and listing groups didn't just explicitly sayso I have no idea. The manufacturer was certainly clear as to the intended market.

Now, all bets are off. From a code standpoint, I am hard pressed to deny the use of Romex anywhere. Ironically, the recent additional restrictions on Romex in 'damp' locations might have the effect of banning Romex from houses.

The whole world seems upside down!

Joined: Jul 2004
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First you have to figure out what "damp" means.
Article 100 blurs this

Location, Damp. Locations protected from weather and not subject to saturation with water or other liquids but subject to moderate degrees of moisture. Examples of such locations include partially protected locations under canopies, marquees, roofed open porches, and like locations, and interior locations subject to moderate degrees of moisture, such as some basements, some barns, and some cold-storage warehouses.

Location, Dry. A location not normally subject to dampness or wetness. A location classified as dry may be temporarily subject to dampness or wetness, as in the case of a building under construction.

I think you have to look at the issue. Will the kraft paper in the cable wick up water and deposit in a box?

I don't see a big deal with removing the "3 floor" language as long as they still say type III, IV and V.
The fire rating and sprinklers cover your fire concerns

Greg Fretwell
Joined: Feb 2002
Posts: 2,233
I thought that one main reason originally to limit RX wire was because if in a fire, the plastic on the RX would give off a toxic fume. So the wanted RX limited to smaller buildings to help get people out of a burning building and not having the people succumb to those fumes.

Joined: Jan 2004
Posts: 1,507
The State of Michigan has removed the limitation on use of NM cable in non-combustible construction as long as it is within the walls. It's hard to argue allowing smurf tubing in high rise buildings and not NM cable if we are talking about maintaining the wiring method for exiting the building or toxicity.

George Little
Joined: Jul 2004
Posts: 9,936
Likes: 34
The NRC says in type I and II the RX has to be in conduit but you are right, one of the conduits listed is Smurf.
I suppose they were thinking more about additional protection from damage.
Is that a regular 15 minute wall or a 1 hour wall?

Greg Fretwell

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