plenum ceiings

[copper chopper]

is it true that any octagon or 4 inch square that has mounting holes already in it from the manufacture, and is installed in a plenum ceiling is not rated for use in that zone??? has anyone heard of this??

 

[walkerj]

Not true

 

[don_resqcapt19]

There is no such thing as a metallic "plenum" box unless you are in Chicago. There is a requirement for boxes without holes in return air ceilings in Chicago.

 

[capybara]

300.22C3 requires metal boxes or NM boxes listed for use within an AH space......

 

[don_resqcapt19]

300.22C3 requires metal boxes or NM boxes listed for use within an AH space......

But, there is no special requirement for a metal box in a "other space used for envriomental air", only the non-metallic box has to be listed for use in that space.

 

[copper chopper]

I was just wondering, the other day I was looking thru a raco catalog and wondered what the astrik was for next to some of there boxes and it said listed for plenum use. so i noticed that all of them had no holes in them.. thanks for your input...

 

[capybara]

Yes, I see that in the Raco box catalog
http://www.hubbellcatalog.com/raco/RACO_part_search.asp?SRCH=plenum&go.x=10&go.y=3
but as Don said, there is no special NEC requirements for metal boxes, only for NM boxes.
of course it maybe one of those "Chicago specs" things

 

[m sleem]

I heared but i can't adress now, the code requires solid bottom+solid cover for boxes that located in plenum ceiling.

Actually, i would think there is a solid reason, during the fire case where cable burns and emitts the smoke, the smoke will flow in HVAC ducts.

 

[cowboyjwc]

I heared but i can't adress now, the code requires solid bottom+solid cover for boxes that located in plenum ceiling.

Actually, i would think there is a solid reason, during the fire case where cable burns and emitts the smoke, the smoke will flow in HVAC ducts.

Well in that case you wouldn't be able to use Flex either since the smoke would escape from it as well.

 

[don_resqcapt19]

I heared but i can't adress now, the code requires solid bottom+solid cover for boxes that located in plenum ceiling.

Actually, i would think there is a solid reason, during the fire case where cable burns and emitts the smoke, the smoke will flow in HVAC ducts.

Please cite the code section that says this.

 

[m sleem]

Well in that case you wouldn't be able to use Flex either since the smoke would escape from it as well.

I'm not sure what do you mean by flex. but if you mean the flex non-metallic conduit, i would think this type of conduit is not permitted to be used in plenum ceiling....!!!!

 

[m sleem]

Please cite the code section that says this.

See 300.22(c)(1) & 300.22(c)(2)(b).

I'm not 100% sure, perhaps it is near to my opinion.

 

[iwire]

I'm not sure what do you mean by flex. but if you mean the flex non-metallic conduit, i would think this type of conduit is not permitted to be used in plenum ceiling....!!!!

Flex, as in Flexible Metal Conduit.

 

[m sleem]

Flex, as in Flexible Metal Conduit.

Well, please see 300.22(b).

.......The connectors used with flexible metal conduit
shall effectively close any openings in
the connection. Equipment and devices shall be permitted
within such ducts only if necessary for the direct action
upon, or sensing of, the contained air. Where equipment or
devices are installed and illumination is necessary to facilitate
maintenance and repair, enclosed gasketed-type luminaires
shall be permitted.

 

[don_resqcapt19]

See 300.22(c)(1) & 300.22(c)(2)(b).

I'm not 100% sure, perhaps it is near to my opinion.

There is nothing in those sections that say you have to use a metallic box without holes. 300.22(C)(2)(b) applies to cable tray only. It does not apply to boxes used with cables or raceways.

 

[don_resqcapt19]

Well, please see 300.22(b).

A "plenum" ceiling is a 300.22(C) space, not a 300.22(B) space.

 

[m sleem]

There is nothing in those sections that say you have to use a metallic box without holes. 300.22(C)(2)(b) applies to cable tray only. It does not apply to boxes used with cables or raceways.

Yes,you are right.

May be i'm not familiar with cable box. Initially i was thinking there is no difference between cable tray and cable box.

 

[m sleem]

A "plenum" ceiling is a 300.22(C) space, not a 300.22(B) space.

I'm confused, if the flex shall effectively closed where located in non-plenum ceiling, i would think it should be in plenum as well.

From the beginning, i mean the cables that laid directly in cable tray without any tube (I'M NOT SURE THIS APPLICATION IS PERMITTED OR NOT AS PER NEC).

If permitted, don't you think this tray or box has to be non-ventilated where located in plenum?

 

[iwire]

Enclosed cable tray

Open cable tray

Boxes like we are talking about

 

[m sleem]

Many thanks, very helpful.