I cant find this in the NEC.
Is there a reference in the NEC to separate 24vdc and 120 vac into their own conduits?

Try Article 725. 2005 NEC
725.26
725.41
725.55
Depending on the class of the 24volt.

Thanks for the quick feedback.
Unfortunately I only have the 2008 NEC and 725.26 / 725.55 are no longer listed.

2008 NEC Article 725
725.48
725.136
Try thoses
Also read Article 725 Definitions for
Classes 1,2,3.

Thanks.
It looks like the answer is yes it is acceptable for our situation.

Sorting out when it's Ok and when it isn't seems an interesting subject.

Can you provide a few more project details that describe the application?

Thanks

A rigid coduit connects a control panel with a metering device.
The device uses 120VAC for control power and has a contact that will have 24vdc going through it and used back at the control panel as an input to a PLC.

Since these circuits are functionally related, even if the 24 vdc is class 2 or class 3, you could take advantage of exception #2 to 725.130(A) and also apply 725.48(B)(1) and run the 24 vdc as a class 1 circuit.

Shop_Test - As I understand it the two could in certain applications be serving the same device and be combined, but the NEC calls out certain separation devices and or distance that must be maintained between the conductors?

Tom- In the case of wiring as a Class 1 circuit (upgrade the wiring), NEC2005 725.27(A) would require 18 or 16 AWG and 725.27(B) would require 600 volt rated insulation of specific types?

Am I barking up the right tree?

Same temperature rating, your good. Personally, I always separate power from control. Regardless of the situation. Just my way.