Is there an exception in the NEC for a low voltage wire to be terminated inside a 120V single gang electrical box? I thought the NEC allowed it as long as all the insulators on the wires were rated for the highest voltage in the enclosure. So if my 12VDC wire was rated for say 250V I would be good right?
I have a SM120X relay module connected to my smoke detector. It has a relay with isolated contacts where I want to connect a low voltage wire. The relay coil is powered by 120V.
Are there any markings I need to add to the low voltage conductors? I can see this would be dangerous if someone later connected these to high voltage not knowing where they are connected.
As long as the wire rating is rated for the highest voltage present you are fine.
I would not worry about what someone might do down the road. If they connect wires not knowing where they go or what they do it's their problem.
Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.
Answers based on the 2008 & 2011 NEC.