Thermostat wire

[geochurchi]

Hi All, if thermostat cable is rated at 300 volts, why can it not be pulled in the same conduit as the line voltage conductors?
Geo

 

[Little Bill]

Maybe because the line conductors are 600V?

 

[augie47]

Thermostat cable is not listed in 310.104 as one of the Chapter 3 wiring methods and Art 725 pretty much does not allow it, as a Class 2 or Class 3 circuit , to be installed in the same raceway power conductors.

 

[kwired]

Thermostat cable is not listed in 310.104 as one of the Chapter 3 wiring methods and Art 725 pretty much does not allow it, as a Class 2 or Class 3 circuit , to be installed in the same raceway power conductors.

That there.

A class 1 control circuit could be pulled in the raceway with power conductors, but "thermostat cable" is only rated for class 2 and 3, some other conductor type must be used if you do it.

 

[tom baker]

Please see the note to 300.3(C)
These are the code reasons, based on the low voltage side is not rated to handle line voltage if the Tstat and line voltage short in the j box or raceway
Plus HVAC equipment is designed so there is a separate terminal section for LV and Line Voltage.

There is a provision where you can take a class 2 (tsat) circuit and remark as class 1...and share the same raceway but all has to be a chapter 3 wiring method

 

[hbiss]

Wow! Three in one week. Go here- http://forums.mikeholt.com/showthread.php?t=189582
then follow the link to another thread there.

-Hal

 

[kwired]

Please see the note to 300.3(C)
These are the code reasons, based on the low voltage side is not rated to handle line voltage if the Tstat and line voltage short in the j box or raceway
Plus HVAC equipment is designed so there is a separate terminal section for LV and Line Voltage.

There is a provision where you can take a class 2 (tsat) circuit and remark as class 1...and share the same raceway but all has to be a chapter 3 wiring method

And when you do use such provision on say a typical HVAC control circuit - you must use all class 1 components. You can't just call it a class 1 circuit so that you can share raceway with power circuit. That class 1 wiring method must run all the way to thermostat, sensors, other devices and those devices must also be rated for class 1, this for the entire control circuit not just whatever segment you desire to be class 1. You can use transformers, relays, etc. to convert back to class 2 or 3 methods though.