Mixed voltage in conduit

[krussell@scs-usa.com]

Ok,

You have conduit run with 6 conductors (THHN stranded 600 V wire). The client wants to use 4 conductors for 120 volt circuit and 2 conductors for 24 Volt AC control wire (let?s say to energize a 24 volt holding coil on a contactor)

Guy #1 says ?you can?t run low voltage and 120 volts in the same pipe. 24 volts is a class 2 circuit and can?t be run with a class 1 circuit?

Guy # 2 says ?the wire is rated for a class 1 circuit and the conductors are pulled, we don?t have a problem. Wire it up and its fine.? He does agree if it was a class 2 wire such as thermostat wire it would be unacceptable but it clearly is not, so you are fine.

Guy #1 state the 24 volt control transformer is a Class 2 transformer so it is a class 2 circuit, regardless of wire type and rating and can?t be mixed with class 1.
Who is correct?

Expanding this.

The customer wants to pull a Belden Shielded cable (9418) http://www.belden.com/techdatas/metric/9418.pdf cable in the same conduit. It is intended to be used for a 4-20 mA signal intended modulate a VFD.
Is it allowed in the same conduit?

 

[iwire]

OK I will give this a try

If it is a class 2 circuit, and it is if it is supplied from a class 2 source, you cannot run it with power and lighting conductors.

BUT,

Not all 24 volt circuits are class 2, the class has to do with the power available more than the voltage. For instance, 6 volts DC from a emergency battery unit to a remote head would not be class 2 even at 6 volts.


Furthermore the code allows a class 2 circuit to be reclassified if you treat the entire circuit as class 1. This could be difficult.

725.130 Wiring Methods and Materials on Load Side of
the Class 2 or Class 3 Power Source.

(A) Class 1 Wiring Methods and Materials. Installation
shall be in accordance with 725.46.

Exception No. 1: The derating factors given in 310.15(B)
(2)(a) shall not apply.

Exception No. 2: Class 2 and Class 3 circuits shall be
permitted to be reclassified and installed as Class 1 circuits
if the Class 2 and Class 3 markings required in 725.124 are
eliminated and the entire circuit is installed using the wiring
methods and materials in accordance with Part II,
Class 1 circuits.

 

[OTT2]

I would say see 725.133