What about plenum rated cable in HVAC equipment? e.g. Mounting a temperature sensors in the air stream or some other sensor. Can we run plenum rated cable to that sensor in the equipment?

With reference to Figure 725-4, there is a callout indicating that "Plenum rated...cables are not permitted in a plenum..."

Please refer to Question 7 in the “Focus on the Code Questions for CMP-3” article at the following link on the WWW.IAEI.ORG website.

http://www.iaei.org/subscriber/foc/cmp3.htm

NEC 2008 725.154(A) specifically states that "Cables installed in ducts, plenums, and other spaces used for environmental air shall be Type CL2P or CL3P." As an example, NEC 2008 760.154(A) for Fire Alarm Systems and NEC 2008 800.154(A) for Communication Circuits also have similar language.

In addition to being approved for installation in “Other Space Used for Environmental Air” (the typical air-handling space above a suspended ceiling), isn’t ‘plenum-rated’ cable also approved for use in “Ducts or Plenums Used for Environmental Air” (barring any other specific prohibition in the NEC)?

Admittedly, this topic can be confusing because of the careful tracking that one needs to do in the NEC.

I would agree with the IAEI article – the rules in Chapter 7 supplement or modify the general rules in Chapter 3 (either to be less restrictive or more restrictive).

I am open to any comments.