Class 2 on Class 1 conductors

[marvintm]

I have been using the NEC for 20 some years now, but cannot find substantiation for what I believe to be a very typical requirement (and industry standard practice). I might be missing the forest for the trees.

Where (in NEC, UL, IBC) does it require that below 600 volts, electric light and power wiring or class 1 conductors (typically all THWN / THHN wire types ) must be in conduit? I am referring to 90% of all power wiring in a commercial building. I see where the NEC refers to ?when subject to physical damage?, but what about above drywall ceilings, or in block walls, ect.?
If someone can quote this requirement, in and of itself, my next question is already answered. If not... read on.

I have a situation where a contractor has run exposed conductors of common TFFN / THHN to serve a class 2 low voltage circuit, and in a non-environmental plenum to boot.

I know you are allowed to install a class 2 circuit as a class 1 circuit in some instances which dictates the use of 600 volt rated wire and installing as a class 1 installation. So using non class 2 conductors CLx does not seem to be in itself a violation...?

On the other hand, the section on Class 2 wiring does list a substitution path for CLx cables, and THHN is not on the list. With the above exception, I do not believe the absence of THHN on the list is a violation...?

I have even talked to engineers at wire manufacturers and they cannot put their finger on where the NEC requires conduit for conductors like this. They also do not believe that the UL listing of the wire requires use of a raceway (but they are not positive). I could see that with certain flame ratings, the installation of the wire could be restricted to some type of raceway.

I know that division 16 is typically specified to have everything in conduit with exceptions for class 2, but that isn't code, just industry practice.

Any thoughts?
UUGGGHHH...

 

[raider1]

Take a look at 300.3(A)

"Single conductors specified in Table 310.13 shall only be installed where part of a recognized wiring method of Chapter 3."

725.52(A) Allows class 2 and 3 circuits to be installed with Class 1 Methods and Materials. This section refers you to 725.25 which says that Class 1 circuits wiring method shall be installed in accordance with part 1 of Article 300 and the appropriate articles in Chapter 3.

Chris

 

[marvintm]

OK, were on the same track.

This keeps coming back to the methods of chapter 3, of which, nowhere does it require conduit that I can find. 300-3 states where multiple conductors of the same circuit exist, they must be run in the same raceway, ...cable,..ect., but it doesn't say they must be run in A raceway.

Keep going...... were not there yet.

 

[ryan_618]

300.3(A) requires that you use a wiring method. The wiring methods are from ARticles 320-390.

 

[marvintm]

So to recap,

Of the 40 some wiring methods listed in the Articles 320-390, none have been used in my example. While Class 2 low voltage installations are referred to chapter 7, that chapter lists CLass 2 low voltage cables that do not include THHN, MTW ect. Therefore, this cannot be considered a class 2 installation, and goes right back to a class 1 installation as listed in chapter 3 methods.

So the contractor has installed a class 2 circuit with unapproved materials, OR
he has installed a class 1 circuit using unapproved methods.

Thanks, thanks, thanks.
I really was missing the forest for the trees.

 

[raider1]

You are correct.

Basically you can use a class 2 rated cable or a wiring method recoginized in chapter three.

Chris

 

[hbiss]

I have a situation where a contractor has run exposed conductors of common TFFN / THHN to serve a class 2 low voltage circuit...

If I understand your question you are asking if TFFN / THHN used in a CL2 circuit and run as building wiring needs to be run in raceway rather than open.

In my opinion per Art 725, TFFN / THHN is not a listed CL2 wiring method. It is a class 1 wiring method (even though used for CL2) and as such must be installed per chapter 3.

-Hal