334.104 Conductors.
Code Change Summary: Revised code language on NM cables with control or signal circuits.
Since 1996, the NEC® has included type NMS (NM cable with an additional signal or communications circuit) in the Article for Nonmetallic Sheathed Cable (NM). The initial concept behind the proposal to include NMS back in 1996 was to address the need for a cable that could be used for both branch circuits and home automation.
Since the addition of NMS cable to the 1996 NEC®, no companies have come forward to create and certify such a cable through a testing lab. In the 2020 NEC®, the type NMS designation was removed altogether from Article 334, but new language was added in 334.104 to provide construction specifications for a similar cable type.
Currently there are companies manufacturing listed NM cables that incorporate both power and signal (see image). These listed cables comply with the conductor separation requirements in Article 725 for class 1, 2, and 3 remote control, signal and power limited circuits.
Below is a preview of the NEC®. See the actual NEC® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2020 NEC® edition of NFPA 70.
2017 Code Language:
334.104 Conductors. The 600-volt insulated conductors shall be sizes 14 AWG through 2 AWG copper conductors or sizes 12 AWG through 2 AWG aluminum or copper-clad aluminum conductors. The communications conductors shall comply with Part V of Article 800.
2020 Code Language:
334.104 Conductors. The 600-volt insulated power conductors shall be sizes 14 AWG through 2 AWG copper conductors or sizes 12 AWG through 2 AWG aluminum or copper-clad aluminum conductors. Control and signaling conductors shall be no smaller than 18 AWG copper.