ECN Forum Forums Code Related Discussion NEC & other Code issues NM in Commercial Bldgs.

Type I and II have a higher fire resistant rating. There is a table in the '02 NEC as I recall, that give the fire rating and materials permitted for each Type of construction. Type I being the most fire resistant.

In a nutshell...

Types I and II are noncombustible (steel and concrete only). Type III is a limited amount of wood (such as masonry walls and wood trusses). Type IV is heavy timber (nearly nonexistent in most of the country). Type V is wood.

See Annex E in the back of the NEC.

When you do the math it turn out that when you factor in the labor and material for the wiring of a building the cost difference is about 20% less for NM cable. Now when it's a midrise or highrise building that's a fair piece of change. Also, NM cable is not usually the cause of fires. If NM cable causes fires more than other wiring methods maybe we shouldn't be wiring our homes with it. That's where we sleep DUH??

George Little,
That just material cost, what about the less time to in stall it too.

I'm not sure how many stories are required for a building to be considered a high rise, but under the IBC the tallest building that can be built using type III, IV, or V construction would be 5 stories. With a sprinkler system, that would increase to 6 stories. That is for an office building. With merchantile or residential occupancies, the limit would be 4 stories with a sprinkler increase to 5 stories. Those figures are for type III and IV. The limits for type V are less. Any buildings taller than these limits would need to be type I construction, which would prohibit the use of NM cable.

Other building codes will have story limits for type III, IV, and V construction in the same ball park.

Ryan,

If construction types One and Two are the least combustible why isn't NM cable permitted? I hope this isn't too dumb of a question. I've had difficulty understanding construction types as it applies to permisson to use NM cable since it was adopted by the NEC.

Frank

"One and Two are the least combustible why isn't NM cable permitted?" NM is combustable... In the sense of fire fuel and travel, and smoke load of a fire. Is my understanding of it... The NEC is written by the NFPA....

Do a little experiment:
Take a piece of NM, and a piece of MC 2' long, staple them to a wall verticaly, and apply a torch to them at the bottom. The one that wins the race to the top looses.

IMO the old "3 story rule" was much easier to interpet: (pre 2002 from the 99' NEC)

That was real simple..... 3 stories OK, 4 stories NOT OK. (Around here 4 stories also triggers the madatory installation of sprinklers.)

Localy NM is limited as follows with ammendments to the 2002 CEC/NEC:

So if you have (like often is the case here) commercial on the lower floors, and residential above. It would be MC and pipe on the commercial and common areas of that space, and possibly NM in the residential, depending on the other limits. The commercial portion of the building is one building type, the residential portion another. So often the buildings are concrete, steel studs, sprinklers and fire rated envelopes of the space. Often a concrete deck on top of it, then a wooden structure built on top of that for the residential portion.

I suppose one could build an airplane out of beer cans- but that's not really what the cans were intended for.

In a like manner, Romex was never intended for use in anything but the most simple of installations, such as homes were in the '30's.
(That's right- Romex dates from the '30's).

Let's keep in mind the DIS-advantages of using Romex:

- You're stuck with the provided colors. This becomes an issue with switch legs;

- You're stuck with the provided quantity of wires (so you get to carry multiple rolls);

- You're stuck with one wire size per cable. If your final location is one where you need different sizes, you get to pull multiple cables;

- You're limited to two cables (circuits) per connector; when entering a panel from the ends, you quickly run out of places to pu those connectors; and,

- Every cable has its' own ground wire. Panels get crowded pretty quickly!

I'm not trying to 'bash' the stuff; it's just that on the typical commercial or industrial job, I see nothing but MORE work using it rather than pipe.

Sure, running pipe takes more tools than a stapler and a pair of snips- but you are able to pull additional wires later (even replace a junction with a sub-panel if you desire), and get additional protection as well.

So types 111, 1V & V - NM is permitted? Meaning if there is wood construction NM is ok residential or commercial?