Permitted use of NM cables in commercial building

Status
Not open for further replies.
K

KhanhNg

Member
First, I would like to thank all who contribute to this thread.

I am a code inspector. I want to know what you think about whether NM cables are permitted to be installed in a Type V (wood structure) commercial building in according to NEC 334.10 (3)

Taken from the NEC

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

(3) Other structures permitted to be of type III, IV, and V construction except as prohibited in 334.12. Cables shall be concealed within walls, floor, or ceilings that provide a thermal barrier of material that has at least a 15-minute finish rating as identified in listings of fire-rated assemblies.

To me, this is very clear-cut. There is no other way to interpret this any other way. NM cables are permitted to be installed in a Type V commercial building (for example), only if it is concealed in a stud/ceiling space (or any other space) with min 1/2" sheetrock or other finish material with equivalent 15-minute fire rating. If NM cables are installed in accessible attic space, then this is clearly a violation of conditional use as permitted by NEC 334.10 (3).

Please respond with your opinions regarding this section. I have a hard time convincing someone who would not allow a can light fixture to be installed above an hydrotub, but think I need common sense in applying this section. :-?

Thanks for your input.
Mike
 
Last edited:
Seems clear cut to me. :smile:
My land. It's even permitted in a type 5 assembly occupancy where fire separations are not required. Sounds like somebody bashing NM-B again.
 
Yup,. you seemed to have nailed it. I think the some get confused with the "attic" space ,.. a look at the definition of concealed helps a bit.

Concealed Rendered inaccessible by the structure or finish of the building.....
Click to expand...
 
I was not going to post this but ,... it is bugging me ,.. it almost seems as if there is no finish rating for ceilings:-?


95. What does a 15-minute finish rating mean when applied to 518.4(C)? Does the 15-minute
finish rating only apply to wood construction? Do the walls, floors and ceilings all need the 15-
minute finish rating before ENT or RNC can be used?


Panel Response: See the FPN for definition of Finish rating found below 518.4 which is
extracted from the UL Fire Resistance Directory Category BXUZ
Definition:
A finish rating is established for assemblies containing combustible (wood) supports. The finish
rating is defined as the time at which the wood stud or wood joist reaches an average temperature
rise of 250?F or an individual temperature rise of 325?F as measured on the plane of the wood
nearest the fire. A finish rating is not intended to represent a rating for a membrane ceiling. The
requirements for finish ratings are not included in
ANSI/UL 263.
The test wall is a 10 x 10 wood frame with thermocouples between the wood studs and gypboard
It applies to wood frame construction only.
The 250 deg. is the average of all TC?s and 325 deg. is spot temperature reading. The Finish
Rating is the time elapsed once fire is applied to reach the required temperatures indicated and in
the location of the test wall.
Yes, only to wood frame construction.
The finish rating would be required on the wall membranes that protect the ENT or RNC wiring
method, regardless of orientation.

Click to expand...
 
I'm in the middle of doing a commerical job now, office building, all wood framing... I was considering the NM-B only between outlets and feeding them w/ MC (drop ceiling & open attic), but then I realized that I would have to order the material for both romex & mc. I just ran mc everywhere and didn't worry about it.





Click It
 
ceb58 said:
They are talking commercial setting not residential.
Click to expand...


Yeh, I got that. Having never used NM in commercial building I guess I never realized it couldn't be run in an attic.

I have seen NM in several attics of commercial buildings, though.:confused:
 
I once told an electrical inspector I would give him $100.00 if he could show me the word "commercial" in the NEC. The type of construction, environment of wiring,etc. affects what wiring method can be used, not whether its commercial or residential
 
frogneck77 said:
I once told an electrical inspector I would give him $100.00 if he could show me the word "commercial" in the NEC. The type of construction, environment of wiring,etc. affects what wiring method can be used, not whether its commercial or residential
Click to expand...



Article 511 Commercial Garages

210.8(B)
(2) Commercial and institutional kitchens

220.56
It shall be permissible to calculate the load for commercial

225.7(C)
other commercial or public buildings where the luminaires


There's plenty more. Do I get the Ben Franklin?:grin:
 
wirebender said:
Article 511 Commercial Garages

210.8(B)
(2) Commercial and institutional kitchens

220.56
It shall be permissible to calculate the load for commercial

225.7(C)
other commercial or public buildings where the luminaires


There's plenty more. Do I get the Ben Franklin?:grin:
Click to expand...
I should have said in regards to type of wire required. Have I been wrong all these years? Will you take a George Washington?
 
iwire said:
NM can even be used in Type I and II construction if the building could have been of type III, IV or V.
Click to expand...


Just remember that local laws may not permit some of the installation types that the NEC permits.


As Bob has pointed out, sometimes we need to slow down our reading process to fully comprehend the actual wording of the NEC.


Or
Maybe we just need to get up earlier in the morning. ;)
 
iwire said:
NM can even be used in Type I and II construction if the building could have been of type III, IV or V.
Click to expand...

I absolutely agree. Practically, the installer has to follow the plan, or have the electrical engineer and architect revise the plan to allow NM use. Thank you Bob for pointing that out.
 
I posted my own thread titled "wire/Wire type" about this same issue. I can't believe I found your thread. Everyone commented that its up to the officials and all these other reasons. I read the same thing in the book
Thanks alot
 
What about the situation where theres gypsum on the Ceiling rafters and then a drop ceiling, I've run into a few of these ... wheres that put on in the Class of structure ?
 
wirebender said:
You mean we can't install NM in an attic? :confused:
Click to expand...
I too am missing the section that prohibits NM cable in attics, commercial or residential not withstanding. 324.23 imposes limitations and installation requirements for NM in an accessible attic. With a 15 min fire rated ceiling per 334.10(3) would not the use of NM cable in the attic be acceptable?

HME
 
Status
Not open for further replies.
Top