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#98119 05/05/06 07:59 PM
Joined: Jan 2004
Posts: 1,507
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.

George Little
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#98120 05/05/06 09:50 PM
Joined: Aug 2003
Posts: 1,374
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.

Ryan Jackson,
Salt Lake City
#98121 05/07/06 09:51 PM
Joined: Jun 2003
Posts: 681
See Annex E in the back of the NEC.

Pierre Belarge
#98122 05/08/06 06:45 AM
Joined: Jan 2004
Posts: 1,507
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
#98123 05/08/06 10:15 AM
Joined: Aug 2001
Posts: 545
aldav53 Offline OP
George Little,
That just material cost, what about the less time to in stall it too.

The Golden Rule - "The man with the gold makes the rule"
#98124 05/09/06 10:56 AM
Joined: Aug 2003
Posts: 64
Now when it's a midrise or highrise building that's a fair piece of change.

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.

#98125 05/14/06 07:50 AM
Joined: Jul 2001
Posts: 311

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.


#98126 05/14/06 02:09 PM
Joined: May 2003
Posts: 2,876
e57 Offline
"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)
336-5. Uses Not Permitted
(a) Types NM, NMC, and NMS. Types NM, NMC, and NMS cables shall not be used in the following:
1. In any multifamily dwelling or other structure exceeding three floors above grade

For the purpose of this article, the first floor of a building shall be that floor that has 50 percent or more of the exterior wall surface area level with or above finished grade. One additional level that is the first level and not designed for human habitation and used only for vehicle parking, storage, or similar use shall be permitted.

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:
334.10. Uses permitted. Type NM, Type NMC, and Type NMS cables shall be permitted to be used in the following:

(1) One- and two-family dwellings,

(2) Multi-family dwellings permitted to be of Types III, IV, and V construction up to 4 stories in height except as prohibited by 334.12.

334.12(11). Add a new section as follows:

334.12(11). Uses not permitted

(11) In any nonresidential structure or occupancy.

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.

Mark Heller
"Well - I oughta....." -Jackie Gleason
#98127 05/14/06 03:09 PM
Joined: Jan 2005
Posts: 5,370
Likes: 1
Cat Servant
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.

#98128 05/16/06 08:01 PM
Joined: Aug 2001
Posts: 545
aldav53 Offline OP
So types 111, 1V & V - NM is permitted? Meaning if there is wood construction NM is ok residential or commercial?

The Golden Rule - "The man with the gold makes the rule"
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