This article was posted 11/30/2007 and is most likely outdated.

Article 725 Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits - 725.61
 

 
Subject - Article 725 Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits - 725.61
Based on - NEC - 2005 Edition

November 30, 2007
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Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits

725.61 Applications of Class 2 and Class 3 Cables

New sentence identifies the type of nonmetallic raceway containing Class 2 or Class 3 cables that is permitted in “other spaces used for environmental air.”

Class 2, Class 3, and PLTC cables must comply with the requirements of (A) through (H).
(A) Ducts, Plenums and Other Space Used for Environmental Air. Class 2 or Class 3 cables cannot be run in ducts or plenums, even if plenum rated [725.3(B)], but plenum-rated Class 2 or Class 3 cables can be installed above a suspended ceiling or below a raised floor that is used for environmental air. Figure 725-4

Listed plenum raceways can be installed above a suspended ceiling or below a raised floor used for environmental air [300.22(C)], but only if the cables contained in these raceways are plenum-rated Type CL2P, or CL3P. Figure 725-5

Author’s Comment: Nonplenum-rated Class 2 and Class 3 cables within electrical metallic tubing, as permitted by 300.22(C), can be installed above a suspended ceiling or below


Figure 725-4
(Click on image to enlarge)


Figure 725-5
(Click on image to enlarge)

     
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Comments

  • 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.

    John Williamson
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