24VDC control and power in same cable and NEC 725?

[HenryOhm]

Sorry, this is probably a bit obtuse. I have a multi-conductor 600V rated cable running from a switchboard to an excitation panel. The cable uses only four of the 14AWG wires in it for switching a relay in the panel and two other feedback contacts to the switchboard, numerous other spares in the cable. We are replacing an analog voltage regulator in the panel for a digital one that needs 24VDC power at all times.

Is it OK to run the power for this in the same cable? The existing relay coil consumes a whopping 1.2W @ 24VDC, so carrying hardly any current and the feedback contacts are probably driving similarly sized interposing relays. I can't foresee any significant buck or spike that the power cable might see from the switching on the other four conductors? The cable run is no more than 200ft. All the 24V ultimately comes from the same large battery bank.

Where I guess I'm a bit unclear is regarding any code issues requiring separation. I'm especially unclear on NEC 725.26(2002), now NEC 725.48 (2011), i.e. "Class 1 circuits and power supply circuits shall be permitted to occupy the same cable, enclosure, or raceway only where the equipment powered is functionally associated."

Thanks in advance for any and all help!

 

[dpc]

In general, it is allowed by the NEC as long as wire is insulated for the highest voltage present. If the low voltage circuit is being treated as a Power-limited circuit, then it's not OK, and I believe that is what you are seeing in Article 725, but I don't have an NEC here and I don't feel like looking it up on-line.