National Electrical Code (NEC) Articles Governing Low Voltage and Communications Systems
The article map
Article 725 covers Class 1, Class 2, and Class 3 remote-control and signaling circuits. Article 760 covers fire alarm, Article 770 optical fiber, Article 800 communications, Article 820 coaxial/CATV, and Article 830 network-powered broadband. Chapter 3 supplies the wiring method; the article supplies the circuit and cable restrictions.
- Class 2/3 power sources must be listed and limited per Chapter 9 Tables 11(A) and 11(B); Class 1 circuits are not interchangeable with Class 2/3.
- 725.136 separation applies to Class 2/3; 760.130 applies to fire alarm; 800.133 applies to communications.
- 300.22 controls ducts and plenums. 110.3(B) requires listed equipment to be installed per its listing.
- Article 800 covers communications circuits, but coaxial CATV distribution is Article 820, not 800.
Worked example
A designer wants to install a 24 VAC Class 2 doorbell cable in the same EMT as 120 V control conductors. Article 725.136(A) prohibits Class 2/3 conductors in the same raceway with power conductors unless a barrier or specific exception applies. The correct fix is a separate raceway or a listed barrier; the fact that the conduit is grounded does not create permission.
Traps
Using Article 725 for fire alarm instead of 760; treating Article 800 as the article for coax; assuming all low-voltage cable is CL2; forgetting that Class 1 is governed by 725, not 800.