Per the nec, can I terminate conductors of different voltages, though both AC, in the same enclosure? For example; I'm installing a timer to control a few lighting circuits. The lights are 277v and the timer is 120v. I have a 2 pole 277v relay with a 120v coil which gets mounted to a junction box. Am I allowed to bring both voltages into the junction box in order to tie in the relay? What's the article # allowing or prohibiting?

Kal...
Take a look at NEC Article 300.3(C)(1)
The answer should be clear...

That was the only article I was able to find that mentioned it. I'm trying to clarify if that applies strictly to AC and DC circuits of different voltages, or also to two AC circuits of different voltages, because it says 'different systems'.

Kal...
The only restriction that is being made here is that all conductors shall have an insulation rating equal to at least the maximum circuit voltage applied to any conductor,. etc.
So AC, DC, 480V, 208V, 24v, as long as the insulation rating of all conductors is, in this case at least 600V.

Standard building wire is rated 600 volts, and that means both AC and DC.

The systems NEC is referring to is 120/240 V, 120/208 V, 277/ 480 volts, not AC or DC.

Hr has provided the correct section and advice.

Your good to go, and if anyone asks, cite that section of the NEC.

Thanks guys for the clarification. Appreciate it