NM Cable Usage

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Cliff Brady

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We are doing electrical engineering for a residential house that they are turning into a commercial building. The house is a wood frame house and we are turning it into Use group B (office) type V construction. The building is currently wired throughout with NM Cable. They are wanting to switch out the 100 Amp panel for a 200 amp panel and pull a few new circuits for additional lighting and computer receptacles. There is a crawl space underneath and an unfinished attic. Can NM cable be used for the new circuits? We think the NM cable would be allowed in the walls but are not sure about the home runs that would be in the attic or crawl spaces. Would NM cable in an attic or crawl space be in violation of 334.10.3? Also, would we then need to change out all the NM Cable in the attic that is existing and rewire with EMT or MC?
 
Based on your description, the core answer to your question will be the local ordinances and practices for changing the use of an existing occupancy.

For the area I work in, the generalization is that if less than 50% of the wall surface is opened, on a room by room basis, the existing arrangement of wiring is "grandfathered", with certain caveats. Fix obvious hazards, remove or repair visible non-code installations and add such specific installations as listed in local ordinance. In cases I know of, this includes grandfathering original knob and tube.

In my area, there are numerous concentrations of business' centered on a crossroads that have expanded out into what was a residential neighborhood, by taking over existing dwellings, one at a time, and changing their certificate of occupancy, but not the construction type. The solutions are individual, and are worked out for each building with the various AHJs, the Fire Inspector, insurance underwriters and any other interested parties.

Talk with the local electrical inspector.
 
dcl34769 said:
What is the ceiling fire rating? If it is drywall the flash rating should be more than 15min. and nm would be perfectly acceptable.
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But above the ceiling is the attic. If the NM cable is just stapled to joists in the attic, that would be exposed, correct?
 
Someone please educate me on this.As a house with people sleeping in it and living 24-7 romex is plenty safe.But if we use this exact same building and remove the cooking and sleeping danger issue and change it to fully awake people for 40 to 50 hours per week it now needs a safer wiring system.Why ?
 
Jim W in Tampa said:
Someone please educate me on this.As a house with people sleeping in it and living 24-7 romex is plenty safe.But if we use this exact same building and remove the cooking and sleeping danger issue and change it to fully awake people for 40 to 50 hours per week it now needs a safer wiring system.Why ?
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I agree Jim, thats something I have noticed for a long time myself! I wish someone would or could explian this!
 
334.12 Uses Not Permitted.
(A) Types NM, NMC, and NMS. Types NM, NMC, and NMS cables shall not be used as follows:
(1) As open runs in dropped or suspended ceilings in other than one- and two-family and multifamily dwellings.

according to this if your building has drywall it is perfectly legal!
this is an addition to the 99' code cycle.

Cliff 334.10(A)(1) allows exposed runs
 
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The NEC would probably allow NM, but the AHJ may not. In my area some jurisdictions allow NM in commercial buildings and some do not. I recommend asking the building department for the city where the building is located.

Martin
 
celtic said:
Are you saying Romex is inferior or "unsafe"?
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It is not the most safe.If it was then why would it be limited in use ? Something is wrong when we use a system that would be unsafe in an office but fine if we live in it.Are we not at higher risk in homes ?
 
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