Robolord
New member
- Location
- Salem, Utah, USA
Can NM wire be used , in a commercial building, above a grid ceiling? The grid ceiling is not being used as a return air plenum.
Use of NM wire
- Thread starter Robolord
- Start date
- Status
- Location
- Simi Valley, CA
NO
334.12(A)(2)
334.12(A)(2)
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
If the building is a classified as one that will allow NM you can run nm thru the walls but not above a dropped ceiling
mwm1752
Senior Member
- Location
- Aspen, Colo
If the drop ceiling has no access and a 15 min rating in a III, IV or V then its ok
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Not sure I agree with that. I don't see anything that mentions access and 334.12(A)(20 says prohibited exposed in dropped or suspended ceilings in other than one and two family dwelling.
I can see a dropped ceiling without access being a violation
- Location
- Illinois
- Occupation
- retired electrician
If the ceiling does not have access, the NM is not exposed and would be permitted.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Exposed to what? It is exposed in the ceiling it does not say it must be exposed to us or be viewable. My thinking is that a dropped area will allow fire to travel and the nm cable is toxic so it would not be allowed.
magoo5150
Member
- Location
- Mississippi
Thisis how I see it. No go in a dropped or suspended ceiling in other than dwelling.
- Location
- Illinois
- Occupation
- retired electrician
Did you read the definition that I posted? The definition in Article 100 is very clear that the wiring method is not exposed unless it is behind panels that are designed to be removed. A lay in ceiling panel is an example of a panel that is designed to be removed.
You have to remember there was no real reason for this rule. It was just part of the trade off from the opposing sides when the 3 story restriction was removed. It is only there to make it more difficult to use NM in commercial buildings. There was no real science or substantiation for the rule that restricts NM above drop or suspended ceilings.
While NM does give off toxic gasses when there is a fire, that also is not a real world issue...it is just something that sounds good in a substantiation. The amount of toxic gasses that are given off by things like NM, is so small when compared to the amount that is given off by the building finishes and furnishings. Also why would the gasses from the NM above the ceiling be a bigger deal than the gasses from the NM in the rest of the building?
romex jockey
Senior Member
- Location
- Vermont
- Occupation
- electrician
Thank you Don
Thank you Don
The phosgenes from the average couch is X100 toxic than RX....
~RJ~
Thank you Don
The phosgenes from the average couch is X100 toxic than RX....
~RJ~
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
That cuts if for me. I am never going to put a couch above a suspended ceiling.
(People who live in grass houses should not stow thrones.)
- Location
- Massachusetts
We would and have run NM above what we call 'Chicago Grid' which looks just like a suspended ceiling system except that instead of lay in tiles full size sheets of drywall get screwed to it.
No access, no chance of damage and no violation.
Sierrasparky
Senior Member
- Location
- USA
- Occupation
- Electrician ,contractor
We would and have run NM above what we call 'Chicago Grid' which looks just like a suspended ceiling system except that instead of lay in tiles full size sheets of drywall get screwed to it.
No access, no chance of damage and no violation.
I agree and this is not the classic definition of a drop or suspended ceiling.
Maybe the CMP is concerned that the dropped ceiling will be removed and leave the NM exposed. ?
Been a very popular thing the last 15 years.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
The whole thing makes no sense. So what if the nm is exposed in a dropped ceiling. Really how different is that then being installed in a dropped ceiling where there is no access. I don't get it... The only thing I can think of is that there is less chance of damage if there is no access.
mwm1752
Senior Member
- Location
- Aspen, Colo
Thats probably wht they defined non accessible is it is most likely the NM will not be damaged. Within the walls or ceiling is gennerally all that is behind the sheetrock , thought the definition needs no defending. a soffit is a good example of a dropped ceiling that has no access.
- Location
- Illinois
- Occupation
- retired electrician
It doesn't need to make sense...it is the NEC
Like I said in an earlier post, there is no technical reason for this rule...it was just part of the "politics" when the 3 story rule was removed from the code. Without this restriction, it is unlikely there would have been enough votes in the CMP to remove the 3 story rule.
- Location
- Simi Valley, CA
I believe that it has more to do with heat and rodent damage than damage by humans, but I've never seen the justification so I'm not sure. Also since they don't allow flexible cord in this same situation, I could see where it's not much of a stretch to get to NM cable.
Sierrasparky
Senior Member
- Location
- USA
- Occupation
- Electrician ,contractor
It doesn't need to make sense...it is the NEC
Like I said in an earlier post, there is no technical reason for this rule...it was just part of the "politics" when the 3 story rule was removed from the code. Without this restriction, it is unlikely there would have been enough votes in the CMP to remove the 3 story rule.
When did the 3 story rule go away? Kind of difficult to follow stuff that is removed. They book does not say " previously disallowed".
david
Senior Member
- Location
- Pennsylvania
It doesn't need to make sense...it is the NEC
Like I said in an earlier post, there is no technical reason for this rule...it was just part of the "politics" when the 3 story rule was removed from the code. Without this restriction, it is unlikely there would have been enough votes in the CMP to remove the 3 story rule.
Don, what year was that? (suspended ceilings)
I thought NM cable was disallowed before that trade off I thought the issue was physical damage in commercial ceilings.
I thought the trade off was concealing NM cable in floors walls and ceilings 15 min fire rating
mwm1752
Senior Member
- Location
- Aspen, Colo
NEC 2002 was the first cycle without 3 stories
- Status