Thermostat wire rating?

Status
Not open for further replies.

GG

Senior Member
Location
Ft.Worth, T.X.
Are thermostat wires rated class 1 power limited or class 2 and why? Someone was telling me that stat wires fall under both class 1 and 2?
 

raider1

Senior Member
Staff member
Location
Logan, Utah
T-stat wire is class 2 wiring.

Class 1 circuits must be wired using a Chapter 3 wiring method. (See 72546 2008 NEC)

Chris
 

raider1

Senior Member
Staff member
Location
Logan, Utah
Hey Greg,

The theory behind the difference of types of wiring for class 1 and class 2 or 3 circuits is that class 1 circuits can operate at up to 600 volts and not have power limitations.

Class 1 circuits include motor control circuit wiring. These circuits can be tapped off the the motor branch circuit and can be 480 volts. This is the reason that class 1 circuits must be wired with a chapter 3 wiring method.

Class 2 and Class 3 circuits are limited in voltage and power so the wiring method that can be employed don't need to have the same voltage ratings as the standard wiring methods in chapter 3.

As far as the exception that allows you to reclassify a class 2 or 3 circuit as a class 1 circuit and wiring it with a chapter 3 wiring method. The only thing I can think of is that with the higher rated wiring methods that you use it is less likely that you could have a fault and introduce a higher voltage into the class 2 or 3 circuit, but it is still possible.

Take a look at Chapter 9 Table 11(A) and 11(B) for the power source limitations of Class 2 and Class 3 circuits.

Hope this helps.

Chris
 

dcspector

Senior Member
Location
Burke, Virginia
Chris that helped alot. This has been the most confusing thing to me in the NEC. Thanks. I do not run into this problem here in DC very often, normally cut and dry as far as control wiring goes.
 

raider1

Senior Member
Staff member
Location
Logan, Utah
Chris that helped alot. This has been the most confusing thing to me in the NEC. Thanks.
Your very welcome.:)

I think alot of the confusion comes from the fact that a lot of people equate Class 1,2, and 3 systems with "low voltage" when in fact Class 1 circuits for the most part operate at nominal voltages up to 480 volts.

Chris
 

dcspector

Senior Member
Location
Burke, Virginia
Your very welcome.:)

I think alot of the confusion comes from the fact that a lot of people equate Class 1,2, and 3 systems with "low voltage" when in fact Class 1 circuits for the most part operate at nominal voltages up to 480 volts.

Chris
It is a tough one. I just need to open up my mind a bit. Thanks Chris. Does the MH book help with the understanding?
 
Status
Not open for further replies.
Top