This article was posted before 01/01/2011 and is most likely outdated.

Low Voltage Cables and the NEC (9-28-2K)

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Mike, I am greatly appreciative of your outstanding dedication and contribution towards making our world an electrically safer place to live. I am relatively new as an electrical inspector (approx. 4 years).

I just finished reviewing your new publication titled "Low-Voltage and Limited-Energy Systems". I recently encountered some Audio/visual/sound system installations on our University of Arizona campus, which are highly suspected of non-conformance to minimum NEC requirements. I must admit my lack of familiarity with the Code related requirements. I am currently in the process of sorting through the true requirements related to the installations in question.

I have re-visited NEC Article 640 several times and I am still not confident with a clear understanding of the actual related Code requirements.

Q1. I have identified speaker wires installed in return air plenum space as not being plenum rated cable as addressed in NEC Section 640-3(b).

Mike's Comment: Class 2 or 3 cables used for sound systems can be installed in ducts, plenums, and other spaces used for environmental; if the cable is plenum rated (Type CL2P or CL3P), see 725-61(a).

Q2. Video camera power cords are routed through, and above lift-out ceilings. The camera cords are plug connected to receptacles in the plenum space. I have identified this as a violation of Sections 400-8(2) and 400-8(5).

Mike's Comment: You are correct, cords are not permitted to be installed in a plenum space, see 300-22(c).

Q3. My biggest problem is identifying the related Code requirement for supporting the speaker wires. The wires have been simply placed atop the lift-out ceiling panels. I'm assuming that I can stand on NEC Article 640-6.

Mike's Comment: Section 640-6 states that wiring must be neat and workmanlike manner and cables must be supported by the building structure in such a manner that the cable will not be damaged by normal building use. The fine print note identifies that one way to determine accepted industry practice is to refer to nationally recognized standards such Commercial Building Telecommunications Wiring Standard, ANSI/EIA/TIA 568-1991.

This standard identifies that a ceiling support wires may be used to mount appropriate cable fasteners loaded with multiple cables up to the total weight for which the fattener is approved. The T-bar rail of a suspended ceiling may also be used to mount appropriate cable fasteners loaded with cable up to a total weight of .45 lb/ft.

Q4. The loud speaker wiring above the ceiling contains open-air splices, which are not enclosed in boxes or fittings. According to your book (Page 25) this is not a Code violation.

Terry Sweet, University Of Arizona Senior Staff Technician
Facilities Management Technical Support Group

Mike's Comment: True, splices for low voltage wiring (class 2 and 3 circuits) are not required to be within an enclosure.