Different Voltages within Same Conduit

[jsinclair]

I have a dilemma here that I hope someone can help me out with. We have a 480v, 3 phase feed to a blower unit. This unit also requires (5) 24v control wires. The feeds and control wires originate from a control cabinent that is seperate from the blower unit. According to 2002 NEC Wiring Methods Section, conductors of the same voltage rating can occupy the same conduit. (Sorry I don't have my code book in front of me for proper reference.) Am I to take this as meaning that I can run a 480v feed through a conduit along with a 24v control bundle through the same conduit as long as the voltage rating on the wires are the same?? (We use 600v THHN, THWN, and MTW) I have always been taught to only run same voltages through the conduit. Can somebody help clear this confusion up.

 

[bphgravity]

Re: Different Voltages within Same Conduit

If your control power supply is listed as a class 1 supply, per 300.3(C)(1) and 725.26(B), they can share the same raceway. If the power supply for the control circuit is class 2 or 3, per 725.55 they will not be able to share the same raceway.

 

[don_resqcapt19]

Re: Different Voltages within Same Conduit

This sounds like HVAC equipment. Most HVAC control circuits are Article 725 Class 2 circuits.
Don

 

[tom baker]

Re: Different Voltages within Same Conduit

There is a new rule in the 2002 NEC that has been overlooked by most code authors, of course Mike Holt caught it! It allows a class 2 or 3 circuit to be reclassifed as class 1. Take a look at 725.52(A) ex no 2. This may be your way out.
I looked up the ROP and ROC on this change, it was changed as the same provison exists in Art 640.
By the way, Section 300.3(C)(1) is misstated more than any other code section on this forum. Thanks BP for your answer its 100% correct. The reason 300.3(C)(1) is mis-used is most of us are not familar with 90.3

 

[iwire]

Re: Different Voltages within Same Conduit

That's good, but once you do that the entire circuit will need to be treated as class 1 which really is article 300 wiring as per 725.25

 

[s wayne cook]

Re: Different Voltages within Same Conduit

Tom, If I understand you correctly, since the rules in 725 modify 300.3(C)(1), therein lies the rules of 90.3?

 

[s wayne cook]

Re: Different Voltages within Same Conduit

Mike Holts 99 Exam Prep Book has the following question...

Circuit conductors that operate at 277 volts(with 600 volt insulation) may occupy the same enclosure or raceway with 48 volt dc conductors that have an insulation rating of 300 volts. True or False?

His answer was "True".

Wouldn't 725-54(a)(1), [RE:1999 NEC], make the answer to this question "False"?

Wayne