Does the Code allow metal cable tray without cover in plenum

[TMMB]

I'm asking about cable tray in Plenum, is it without cover or with cover, in light of NEC 300.22

and what kind of cables can be used above this cables


Please advise

 

[Smart $]

I'm asking about cable tray in Plenum, is it without cover or with cover, in light of NEC 300.22

and what kind of cables can be used above this cables


Please advise

If you literally mean a plenum, you cannot install cable tray within it. It is not a wiring method permitted in 300.22(B).

If you mean "Other Space Used for Environmental Air", such as above a suspended ceiling used for return air of an HVAC system, you can install solid bottom metal tray with solid metal covers. 300.22(C)(1) does not explicitly restrict cable types within the tray. However, Article 392 specifies permitted wiring methods therein.

 

[Strathead]

If you literally mean a plenum, you cannot install cable tray within it. It is not a wiring method permitted in 300.22(B).

If you mean "Other Space Used for Environmental Air", such as above a suspended ceiling used for return air of an HVAC system.

For all of the years I have been working in High rises and such, the space above a suspended ceiling used for return air is the very definition of an air plenum.

 

[TMMB]

in 300.22 C/1, Type MI cable, Type MC cable without an overall nonmetalic covering, Type AC cable or other factory assembled multiconductor control or power cable that is specifically listed for use within an air-handling space

what that mean in light of your above reply

regards

 

[david luchini]

For all of the years I have been working in High rises and such, the space above a suspended ceiling used for return air is the very definition of an air plenum.

See the Fine Print Note in section 300.22(C).

 

[Smart $]

in 300.22 C/1, Type MI cable, Type MC cable without an overall nonmetalic covering, Type AC cable or other factory assembled multiconductor control or power cable that is specifically listed for use within an air-handling space

what that mean in light of your above reply

regards

It means that you can run these types of cables "exposed" in "other spaces". Other types of cables and conductors have to be run inside a metallic wiring system (metal conduit, metal wireway, etc.).

IMO, you can install ladder type cable tray without cover and run any of the permitted-to-be-exposed (and permitted-to-be-in-tray) cable types. The AHJ may not be of the same opinion :blink:

 

[Smart $]

For all of the years I have been working in High rises and such, the space above a suspended ceiling used for return air is the very definition of an air plenum.

David points you to code text which states otherwise. The likely reason you [formerly] believed such is because "low voltage" cables run in this "other space" are likely required to be plenum rated.

 

[Strathead]

See the Fine Print Note in section 300.22(C).

"Air Plenum: Any space used to convey air in a building, furnace, or structure. The space above a suspended ceiling is often used as an air plenum. " from http://www.mascordefficientliving.com/content/faq-glossary.asp



or this "
a space, usually above a ceiling or below a floor, that can serve as a receiving chamber for air that has been heated or cooled to be distributed to inhabited areas." from http://dictionary.reference.com/browse/plenum

Seems like the code is being redundant, however your reference certainly absolves you of any redundancy.

 

[Smart $]

"Air Plenum: Any space used to convey air in a building, furnace, or structure. The space above a suspended ceiling is often used as an air plenum. " from http://www.mascordefficientliving.com/content/faq-glossary.asp



or this "
a space, usually above a ceiling or below a floor, that can serve as a receiving chamber for air that has been heated or cooled to be distributed to inhabited areas." from http://dictionary.reference.com/browse/plenum

Seems like the code is being redundant, however your reference certainly absolves you of any redundancy.

Definitions will vary. They are all derived from this one...

Plenum
(n.)
That state in which every part of space is supposed to be full of matter; -- opposed to vacuum.

Here are two more [pertinent] definitions...

1 a : a space or all space every part of which is full of matter b : an air-filled space in a structure especially : one that receives air from a blower for distribution (as in a ventilation system)

2. an enclosed space in which the air pressure is higher than outside

Note that by these definitions, a plenum can only be on the positive pressure side of the system. Return air is on the negative pressure side.

 

[david luchini]

"Air Plenum: Any space used to convey air in a building, furnace, or structure. The space above a suspended ceiling is often used as an air plenum. " from http://www.mascordefficientliving.com/content/faq-glossary.asp



or this "
a space, usually above a ceiling or below a floor, that can serve as a receiving chamber for air that has been heated or cooled to be distributed to inhabited areas." from http://dictionary.reference.com/browse/plenum

Seems like the code is being redundant, however your reference certainly absolves you of any redundancy.

The only definition that is relevant is this:

Article 100: Definitions

Plenum: A compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system.

 

[Strathead]

The only definition that is relevant is this:

Article 100: Definitions

Plenum: A compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system.

And since the ceiling space is a compartment and thec connection between the Air handler and the ceiling is duct, the ceiling space is used as a plenum in this case. The Code is redundant.

 

[david luchini]

And since the ceiling space is a compartment and thec connection between the Air handler and the ceiling is duct, the ceiling space is used as a plenum in this case. The Code is redundant.

The definition doesn't say anything about connection to the Air Handler.

There is no physical connection to the ceiling space by the air ducts. I most often see "plenum return" ceilings that simply have transfer grilles from ceiling compartment to ceiling compartment to facilitate the air movement back to an open ended duct. This does not meet the NEC definition of "plenum." And the FPN 300.22(C) makes it clear that these ceiling spaces are not regarded as "plenums" per the NEC definition.

 

[Wingrider]

We seem to get involved in 'What is a Plenum?' to define if we can run cable tray. The question was not to define Plenum, but define what can be run in a Plenum that has already been identified. From my experience (which may be short lived) the use of open cable tray is not a question, as I see it all the time, but what type of cable is in the tray. In a plenum, it must be plenum rated cable. If you have covered the cable tray, it is no longer part of the plenum, as it it sealed off from it. Then you can run any approved cable.