Guys, does anyone have an NEC section or reliable source (pictures or videos would be awesome) of how to combine low voltage (12 or 14 VDC or VAC) and 120VAC or 240VAC in same enclosure?

I have this:


[Link: automationdirect.com]

It works great, but I had to place my 22/2 trigger wire (from Russound's C5 zone 15 trigger out) in the same space as 120VAC that's cutting power off to my Crown CDI1000.

Everything that I have even seen in the code or training stated not to mix low and line voltage.
Somewhere I seen 3 theories:
1. anything under 600VAC is considered low voltage. I always though it was 50.
2. as long as low voltage cable is rated higher than line voltage in that enclosure, we're fine. My line voltage is 120VAC -- the 22/2 is rated for 300V -- am I OK?
3. line and low voltage are mixed in all kinds of applications including HVAC systems (24VAC T-Stat wire into 120VAC furnace); washers/dryers (with LV relays activating motors/heaters) all in same enclosure; 3 phase motors (with their LV starters), etc.


So while this project is in my own house, I want to understand how to do this properly for when time comes to do this at a client's house.