Re: low voltage in electrical box
...Try looking in NEC article 725.
Class 2 and 3 do not require a box for anything. I guess then that you can say that that's the code though I disagree that there is a "code for everything".
...I work mainly with fire alarm. We always make splices in a box even when running the wiring in cable.
The security and fire alarm trade have their own practices (just like the electrical and telecom trades do) and it is usual to make CL2 and CL3 splices in boxes even when cables are run open. This has nothing to do with the NEC, it's not required, it's just the way you guys normally do your work. Fire alarm will have other requirements (NFPA and local) outside of the NEC.