Area surrounding chimney as raceway

[jaselectricman]

I have encountered several times where people have used the area surrounding a chimney as a raceway to run type NM cable. Is this practical considering the temperature in that area? What would be practical to use as a derating temperature when doing this? There is nothing in the code that explicitly prohibits using this space as a raceway.
Does anyone have an opinion on this?

 

[iwire]

Re: Area surrounding chimney as raceway

This is a common practice when trying to fish from basement to attic.

If I use 12/2 NM as an example, 12 AWG is rated 30 amps in 310.16 (forget about 240.4(D) for now) now apply the temperature correction factors from 310.16 to 30 amps and you will find you can run the 12 AWG through ambient temperatures of 132 to 140F and still end up with an ampacity of 21.3 amps.

30 amps x.71 temperature correction factor = 21.3 amps at 132 to 140F

You could go further if you use 240.4(B) which allows the use of the next higher standard overcurrent device rating.

30 amps x .58 temperature correction factor = 17.4 amps at 141 to 158F and you could still use a 20 amp breaker.

210.4 Protection of Conductors.

(B) Devices Rated 800 Amperes or Less. The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used, provided all of the following conditions are met:
(1) The conductors being protected are not part of a multioutlet branch circuit supplying receptacles for cord-and-plug-connected portable loads.
(2) The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).
(3) The next higher standard rating selected does not exceed 800 amperes.

I would not think the temperature around a chimney would be higher than 158F.

 

[jtb]

Re: Area surrounding chimney as raceway

I always ran UF if against masonry though. Any code refs allowing/ not allowing NM here?

 

[iwire]

Re: Area surrounding chimney as raceway

334.10 Uses Permitted.

(A) Type NM. Type NM cable shall be permitted as follows:

(2) To be installed or fished in air voids in masonry block or tile walls

If you can fish it inside block why not beside a chimney.