NEC 370.18(B) ruling on Cable Bus going through floors

[pennyarcade]

I have a question regarding NEC 370.18(B).

Can I run a cable bus system through a floor IF the penetration requires a firestop?

I can read the code both ways. One way I read it as firestop floors are exempt from the installation instructions outlined in NEC 370.18(B). The other way is that cable bus is ONLY permitted through floors when firestop is not required.

Any help would be greatly appreciated.

 

[charlie b]

What edition of the NEC are you using? I have 2008 and 2011 open at my desk, and neither one has an article 370.18. :?

 

[ron]

Maybe he meant

370.6(C) Through Dry Floors and Platforms. Except where firestops are required, cablebus shall be permitted to extend vertically through dry floors and platforms, provided the cablebus is totally enclosed at the point where it passes through the floor or platform and for a distance of 1.8 m (6 ft) above the floor or platform.

 

[charlie b]

If that is what you meant, then my answer is that your second interpretation is correct. I have never worked with cablebus myself. But from what I read in the definition, I infer that the interior of the enclosure is exposed to the air that surrounds the cablebus, at least in some portions of the run. I see the requirement that it be totally enclosed at the point it passes through a floor. So it must be able to be "not totally enclosed" in other areas. That tells me that it cannot serve as a fire barrier itself. Even if you put firestopping in the hole around the cablebus, as it passes through the floor, fire could go from floor to floor through the interior of the cable bus, starting at the point below where it becomes "totally enclosed" to the point 6 feet or more above the floor, at which point it is no longer "totally enclosed."

I forgot to mention this earlier, but welcome to the forum.

 

[pennyarcade]

for the 2014 NEC book, it is 370.18

I can understand why they have it written like this to prevent fire from transferring between walls and floors through the cable bus, but what happens if you have a cable bus filled with firestop? Here in Canada, I have seen installations where the cable bus is filled with an elastomeric compound, even inside the enclosure so that there are no air pockets. The cable bus filled with firestop gets certified here in Canada, even if the system goes through a fire rated wall.

In the end, it is up to the inspector to certify or not. Could anybody direct me to the proper resources to get a definitive answer?

 

[charlie b]

for the 2014 NEC book, it is 370.18

I have not yet bought that edition. Other than changing the article number, were there any changes to the way the article is written?

The cable bus filled with firestop gets certified here in Canada, even if the system goes through a fire rated wall.

Unless there are changes to the requirements in the 2014 edition, that would not be allowed in the US.

In the end, it is up to the inspector to certify or not. Could anybody direct me to the proper resources to get a definitive answer?

You have answered your own question. Contact the local authorities in the area in which you plan to do the installation.

 

[pennyarcade]

Nothing changed except for the numbering.

I've sent an inquiry to the NFPA to get more guidance. I'll post my findings here.