Plenum Space - Plenum rated cabled required when in a metal conduit?

[smalltime]

When running Class 2 / Class 3 / CM cable inside a metal conduit in an air return plenum above a suspended ceiling, is plenum rated cable required inside that metal conduit?

Here's what confuses me:
From my 2008 Handbook:
725.154(A) Plenums. Cables installed…shall be Type CL2P or CL3P. Listed wires and cables installed in compliance with 300.22 shall be permitted. Listed plenum signaling raceways shall be permitted to be installed in other spaces used for environmental air as described in 300.22(C). Only Type CL2P or CL3P cable shall be permitted to be installed in these raceways.

From Mike’s Understanding the NEC, 2008 edition:
725.154(A) Ducts, Plenums, and Other Space Used for Environmental Air.
Class 2 and Class 3 cables not identified as suitable for plenum use can be installed above a suspended ceiling or below a raised floor used for environmental air if the cable is installed in a metal raceway [300.22(C)(1)].

The text from my 2008 Handbook is very different from Mike's 2008 publication.

What am I missing here? Do I need plenum rated cable inside the metal conduit that's run in the plenum?

 

[suemarkp]

I think what you're missing is this:

Listed plenum signaling raceways shall be permitted to be installed in other spaces used for environmental air as described in 300.22(C). Only Type CL2P or CL3P cable shall be permitted to be installed in these raceways.

There must be something called a plenum signaling raceway. Personally, I have no idea what that product is. But I interpret the "Only Type CL2P..." clause to be modifying the previous sentence describing these plenum signaling raceways.

Section (B) also references "listed riser signaling raceways". Don't know why you'd want to use these if they don't get you out of the plenum cable requirement.

725.154(A) specifically says "Listed wires and cables installed in compliance with 300.22 shall be permitted."

 

[don_resqcapt19]

...There must be something called a plenum signaling raceway. ...

There is...it looks like smurf tube (Electrical Nonmetallic Tubing), but orange in color. I am sure it is made of a different material as smurf tube is not permitted in a plenum.

 

[fmtjfw]

There is...it looks like smurf tube (Electrical Nonmetallic Tubing), but orange in color. I am sure it is made of a different material as smurf tube is not permitted in a plenum.

Careful! Some plenum rated communications raceways are only plenum rated if the cables in them are also plenum rated. Look at the instructions and listing. Someone thought that we could put telco fiber in commo raceways in a place of assembly. NOPE

 

[don_resqcapt19]

Careful! Some plenum rated communications raceways are only plenum rated if the cables in them are also plenum rated. ...

Actually the code itself only permits the use of plenum rated cables in the plenum rated communications raceway.

 

[smalltime]

This is helping quite a bit. There is plenum communications raceway. A quick Google found this: http://www.cableorganizer.com/kwikpath/plenum-raceways.htm

Okay, so if I use a plenum communications raceway such as the stuff from the link, I need to also use plenum rated cable. Simple enough.

But this still doesn't answer the original question: When running Class 2 / Class 3 / CM cable inside a metal conduit in an air return plenum above a suspended ceiling, is plenum rated cable required inside that metal conduit?

Also - the other thing that I didn't note was the discrepancy between the text in the Handbook and the text in Mike's material.
Mike says, "Class 2 and Class 3 cables not identified as suitable for plenum use can be installed... if the cable is installed in a metal raceway [300.22(C)(1)]." but that text is not in my Handbook.

I'll admit [300.22(C)(1)] isn't the clearest paragraph I've read.

 

[fmtjfw]

This is helping quite a bit. There is plenum communications raceway. A quick Google found this: http://www.cableorganizer.com/kwikpath/plenum-raceways.htm

Okay, so if I use a plenum communications raceway such as the stuff from the link, I need to also use plenum rated cable. Simple enough.

But this still doesn't answer the original question: When running Class 2 / Class 3 / CM cable inside a metal conduit in an air return plenum above a suspended ceiling, is plenum rated cable required inside that metal conduit?

Also - the other thing that I didn't note was the discrepancy between the text in the Handbook and the text in Mike's material.
Mike says, "Class 2 and Class 3 cables not identified as suitable for plenum use can be installed... if the cable is installed in a metal raceway [300.22(C)(1)]." but that text is not in my Handbook.

I'll admit [300.22(C)(1)] isn't the clearest paragraph I've read.

300.22(C)(1) Wiring Methods. The wiring methods for such other space shall be limited to totally enclosed, nonventilated, insulated busway having no provisions for plug-in connections, Type MI cable, Type MC cable without an overall nonmetallic covering, Type AC cable, or other factory-assembled multiconductor control or power cable that is specifically listed for use within an air-handling space, or listed prefabricated cable assemblies of metallic manufactured wiring systems without nonmetallic sheath. Other types of cables, conductors, and raceways shall be permitted to be installed in electrical metallic tubing, flexible metallic tubing, intermediate metal conduit, rigid metal conduit without an overall nonmetallic covering, flexible metal conduit, or, where accessible, surface metal raceway or metal wireway with metal covers.

The way I understand 300.22(C)(1) is that any conductors are allowed in a metal conduit.
Since MC and AC cable are alllowed which contain THHN (more or less).
THHN conductors, NM, and UF cables are excluded from the plenum.
Once you enclose them in a metallic raceway they are acceptable.
Metallic conduit is a better containment than AC or MC sheath.

"other types" seems to cover "every other" to my way of thinking.

This is logic, not necessarily "code".