Cable requirements for use in a plenum

[badbob88]

I am in a petrochemical. facility and have a computer room that has a raised floor used to furnish cold air into the bottom of our DCS cabinets. There is cable tray under this floor for routing the cables into the same cabinets. What is the NEC requirement for cabling in this space. This computer room is not considered a occupied space. I contend the space under the floor is a plenum and that the cables should be plenum rated.

Bob

 

[Carultch]

I am in a petrochemical. facility and have a computer room that has a raised floor used to furnish cold air into the bottom of our DCS cabinets. There is cable tray under this floor for routing the cables into the same cabinets. What is the NEC requirement for cabling in this space. This computer room is not considered a occupied space. I contend the space under the floor is a plenum and that the cables should be plenum rated.

Bob

Cables cannot be used in physically constructed ducts or plenums, unless necessary for sensing/controlling the air. Such as fan wiring or a temperature probe, and even then, the length inside the ductwork would be minimal.

Plenum-rated cable is for use in a region of space in the building, above a suspended ceiling or below a raised floor, that is also part of the air handling space. Instead of being in physically constructed duct walls, the air is handled in a open region above or below a room. Plenum rated cable has a special insulation that has low smoke and low flame characteristics. I would also agree with you that the space below the raised floor, is also a plenum space, and therefore would require plenum rated cable. The occupancy shouldn't affect this requirement.

Here's Mike Holt's team discussing this:
https://www.youtube.com/watch?v=m45tigRxJj4

 

[Carultch]

I stand corrected. Per 645, if it is an "information technology equipment room", the rule doesn't apply.

 

[JFletcher]

Welcome to the forum

I am in a petrochemical. facility and have a computer room that has a raised floor used to furnish cold air into the bottom of our DCS cabinets. There is cable tray under this floor for routing the cables into the same cabinets. What is the NEC requirement for cabling in this space. This computer room is not considered a occupied space. I contend the space under the floor is a plenum and that the cables should be plenum rated.

Bob

IT rooms are required to have AC that is dedicated to that room; see 645.5(D)(4). The cables do not have to be plenum rated as it's not permissable in the first place to have underfloor ventilation serve the rest of the building w/o fire dampers (645.4(2)). It's not a plenum nor an air return space.

Chapter 645 deals with IT rooms.

 

[don_resqcapt19]

Note that Article 645 is an optional article.

Many IT rooms are not wired per this article as it is often more trouble that it is worth.

If you don't have all of the things required by 645.4, the article does not apply and all of the rules in Chapters 1-4 apply. If you comply with the requirements of 645.4, then and only then, you can use the relaxed wiring methods permitted in 645.