NM in suspended ceilings - not!

[karl riley]

The prohibition of using NM in suspended ceilings in non-residential - 334.12(A)(1) - seems to be new for 2002.

Does anyone know the background of why this was put into the Code?

Karl

 

[don_resqcapt19]

Re: NM in suspended ceilings - not!

Karl,
This was part of the "trade-off" to eliminate the 3 story restriction.
Don

 

[Guest]

Re: NM in suspended ceilings - not!

Guessing here: It's hard to support properly and therefore was not supported properly? Lots of sharp edges in a suspended ceiling? Not plenum rated? As always, I'm interested in the real answer.

 

[iwire]

Re: NM in suspended ceilings - not!

Karl, I can not give you the background you are looking for but I can tell you that for us here in Massachusetts not much has changed, Mass. amended this article.

2002 NEC

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.

2002 Massachusetts Electric Code

334.12(1). Revise to read as follows:

In dropped or suspended ceilings in other than one- and two-family and multifamily dwellings, unless run so as to closely follow the surface of framing members, running boards, or the equivalent, or unless connected to luminaires (lighting fixtures) in accordance with 334.30(B)(2).

Bob

 

[ryan_618]

Re: NM in suspended ceilings - not!

Don nailed it right on the head. Reading the 2002 ROP it indeed was part of the "trade off".

 

[karl riley]

Re: NM in suspended ceilings - not!

Thanks for the info. The last job I did (as some of you remember) involved N/G faults in two NM circuits which ran from conduit-fed boxes in suspended ceilings in an office bldg. Of course the NM was grandfathered.

A local electrician has corrected the N/G accidental connections and the magnetic fields have returned to normal low values.

Karl

 

[pierre]

Re: NM in suspended ceilings - not!

I cannot remember what agency, but a smoke test was performed and in 5 minutes they could not see the exit signs. This made them change the nondwelling requirement.

Pierre

 

[bennie]

Re: NM in suspended ceilings - not!

Karl: What created the high magnetic fields? was the ground wire in a separate raceway? Was the conduit dividing the current to other paths?

 

[don_resqcapt19]

Re: NM in suspended ceilings - not!

The removal of the "3 story" limit was a very controversial issue for the 2002 code. It was rejected by the CMP at both the ROP and ROC stages, it was rejected by the body at the May meetiing, but the limit was removed from the code by the Standards Council when litigation was threatened by cable manufactures. This was code making by intimidation not, consensus!!
Don

 

[karl riley]

Re: NM in suspended ceilings - not!

Don, so they said you can sell NM cable to the third story but we are going to take it out of dropped ceilings in commercial. Wow. The deals!

Bennie, one of the NM circuits went to a recept that was tied into an abandoned circuit whose neutral was still connected at the panel. So it was a parallel path for the neutral going a different way back to the panel. Same efect as if it had been connected to an EGC from another circuit.

The second was a N/G connection at the end of a Romex. I am waiting to hear how that was done.

Karl

 

[brian john]

Re: NM in suspended ceilings - not!

Does anyone know the history of the 3-story rule? I know that sometime in the early 70’s NM was utilized in high-rise apartment buildings (at least in VA). Then the 3-story rule was passed and then underwent numerous changes with definitions of what a 3-story building is.

Curious why it was passed?