Hey guys thanks for the help on these little issues I
run into. I want to use NEC 300.3 (C)(1)
"Conductors of ac and dc circuits rated 600 volts ,nominal, or less, shall be permitted to occupy the same equipment wiring enclosure, cable, or raceway. all conductors shall have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure, cable or raceway."

The voltage is 120/240 a.c. and I want to install the start and alarm conductors in the same J-box box as the power. The alarm cable specified is rated for 300 v. dc.
300.3 (C)(1) only refers to the voltage rating so I'm thinking it's OK even though the alarm conductors are only rated for dc. Right?

Read Informational Note #1 .

Thanks Yoop. I did see that but the fact that the cable met the voltage requirement but was only rated for DC is what was throwing me off. I usually separate everything but when the GC stubbs the conduits out of the concrete wrong I end up having to make things work. I don't encounter much low voltage and Article 725 still confuses me. One of the things I don't understand is how to accurately classify the circuits when you don't know what the attributes of the power source are in the equipment that is powering them. Is there an easy way to determine that or is it involved?

What kind of alarm?

For this installation it was generator failure alarms.

725 breaks down each. Class 1/2/ & 3. Take a look.

Haha! Got it! I knew I somehow must be missing a step. Totally makes sense now.

Sometimes, that all it takes. Better to talk it out now then have something to smoke out later and get clarity later...