# code reference



## Dennis Alwon (May 9, 2009)

fes said:


> i guess i'm just missing it.........can someone point me in the right direction for a code reference that deals with low voltage (thermistat wire) being placed in the same conduit/flex as high voltage (120/240v).
> Thanks


300.3 (c)


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## BBQ (Nov 16, 2010)

In my opinion 300.3(C) is not really the correct reference, that has to do with conductors in general. That section makes it sound like it is allowed to mix circuits and it may be allowed .......... or it may not be allowed by other parts of the code depending on the nature of the circuits. 

As the OP is asking about thermostat wire I am going to assume they are class two conductors and that would make the 2008 NEC code reference 725.136 and that section prohibits Class 2 conductors with line voltage for most applications.

FES, what are the line voltage and low voltage conductors supplying?


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## don_resqcapt19 (Jul 18, 2010)

So many people look at 300.3(C) but fail to see the Informatational Note (Fine Print Note) that follows this section and refers you to 725.136(A).


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## Dennis Alwon (May 9, 2009)

BBQ said:


> In my opinion 300.3(C) is not really the correct reference, that has to do with conductors in general. That section makes it sound like it is allowed to mix circuits and it may be allowed .......... or it may not be allowed by other parts of the code depending on the nature of the circuits.
> 
> As the OP is asking about thermostat wire I am going to assume they are class two conductors and that would make the 2008 NEC code reference 725.136 and that section prohibits Class 2 conductors with line voltage for most applications.
> 
> FES, what are the line voltage and low voltage conductors supplying?


330.3(C) has an informational note about 725.136(A) and 690.4(B)


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## BBQ (Nov 16, 2010)

Dennis Alwon said:


> 330.3(C) has an informational note about 725.136(A) and 690.4(B)



Yes it does and most people skip right by it. (IMO)


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## MDShunk (Jan 7, 2007)

There's a few occasions where you can do that if the thermostat wire has 300 volt rated insulation (assuming 208). I forget what those instances are, but I've done it before.


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## user4818 (Jan 15, 2009)

IIRC if you do treat the entire circuit as line voltage (reclassify), you must do it with the whole circuit, not just the portion in the same raceway. This means you can't simply swap over to 18/2 stat wire once it leaves the whip. You'd have to use a "line voltage" wiring method for the whole control circuit.


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## BBQ (Nov 16, 2010)

MDShunk said:


> There's a few occasions where you can do that if the thermostat wire has 300 volt rated insulation (assuming 208). I forget what those instances are, but I've done it before.


Not if it is a Class 2 circuit.

If you can reclassify it per 725.130(A) Exception 2 and run the entire circuit in Class 1 wiring methods you could mix the conductors, but that T-87 at the far end of the circuit is going to have to mounted on a box to make it legal.


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## Dennis Alwon (May 9, 2009)

BBQ said:


> Not if it is a Class 2 circuit.
> 
> If you can reclassify it per 725.130(A) Exception 2 and run the entire circuit in Class 1 wiring methods you could mix the conductors, but that T-87 at the far end of the circuit is going to have to mounted on a box to make it legal.


So if there is a sticker I can remove the sticker???? 

My understanding is that the transformer determines the class. Is that correct-- also how is that determined- do you know?


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## 480sparky (Sep 20, 2007)

BBQ said:


> Yes it does and most people skip right by it. (IMO)



Then perhaps they should read 90.1(C).:whistling2:


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