I am looking for an approved method to run class 1 low voltage wiring in a wall from jbox to jbox. What kind of cable and what kind of cable clamps are approved?

I have searched unsuccessfully for rated NM cable that contains just two 16 or 18ga. conductors. I've seen the MC luminary cable that contains two 14ga. conductors and two 16ga. low voltage wires, but this is a 3-way circuit so I need three 14ga. conductors. I would also rather not use MC cable unless it is my only option.

I did find a non-metallic wire sheath with a "UL Recognized" rating, so I could make my own cable from 16 ga. THHN wire, but would that be acceptable?

The rest of the installation is complete: there are 10 ceiling boxes connected by conduit, for dimmable LED lighting. I just need to run the wiring to the dimmer switches.

  • What voltage are you using?
    – bib
    Commented May 3, 2017 at 21:35
  • Do you mean something like Ethernet or HVAC controls?
    – brhans
    Commented May 3, 2017 at 21:38
  • This low voltage wiring is for the LED lighting dimmer controls, and it uses 0-10VDC.
    – user69083
    Commented May 4, 2017 at 15:42

2 Answers 2


Ok, Class 1 wiring systems NEC article 725.49 (A) sizes and use and (B) Insulation which give you approved insulation for sizes 18 and 16. If it is 16 or larger you need to use Article 310. I would forget the 16 and use 14 nm instead. If you decide on 18 or 16 the equivalent to thhn would be tffn. Or I would check with whomever the manufacturer is and find out what they suggest.

Hope this helps

  • OK, I could use 14-2 NM cable. I am just surprised there seems to be no code-approved class 1 method to run the 18ga. wires out through a knockout into the wall. i.e. cable clamps are not rated for individual 18ga. wires, and no mfr. makes cable with two 18ga. wires that is rated for class 1.
    – user69083
    Commented May 4, 2017 at 15:47

Simply use 14 gauge NM -- you can use any chapter 3 wiring method you wish for a class 1 control circuit. (If you were in conduit, there is a fill advantage to using thinner wire for control circuits, but that's not really a thing when you're using cable wiring methods.)

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