Low and high voltage in the same conduit

[Flawild]

I’m getting mixed answers maybe you guys can help? I have 120 V lighting system in a commercial building that is going to have 0 to 10v dimming capabilities. My question is on running the 0 to 10 V wires in with the 120 V switch legs. I would obviously use 600 V rated wire probably an 18 gauge THHN. What do you guys think?

 

[infinity]

It is permitted if the Class 2 wiring can be reclassified as Class 1. Here's a document from Lutron:

http://www.lutron.com/TechnicalDocumentLibrary/048-162.pdf

Welcome to the Forum.

 

[don_resqcapt19]

I’m getting mixed answers maybe you guys can help? I have 120 V lighting system in a commercial building that is going to have 0 to 10v dimming capabilities. My question is on running the 0 to 10 V wires in with the 120 V switch legs. I would obviously use 600 V rated wire probably an 18 gauge THHN. What do you guys think?

THHN is not one of the permitted wiring types for a Class 1 circuit. See 725.49(B).

 

[infinity]

Also THHN does not come in #18 AWG. It would likely be TFFN or equivalent which is what we use.

 

[Flawild]

Or id use #14

 

[infinity]

Or id use #14

What insulation type, did you see what Don posted in post #3?

 

[hbiss]

THHN is not one of the permitted wiring types for a Class 1 circuit. See 725.49(B).

My 725.49(B) says nothing of the kind. But we are getting off the subject here.

... I have 120 V lighting system in a commercial building that is going to have 0 to 10v dimming capabilities. My question is on running the 0 to 10 V wires in with the 120 V switch legs. I would obviously use 600 V rated wire probably an 18 gauge THHN. What do you guys think?

This question is getting as old as which way to install a receptacle, ground up or down.

Reclassifying the CL2 to CL1: many times that is not possible because it requires the low voltage devices in the dimming circuit to be capable of handling the line voltage should a fault occur. Unless specifically allowed in the documentation (like that Lutron system above) you can't do it.

I won't go into the reasons why the LV can't be run with the line voltage, that's been covered ad nausium. Suffice it to say that your options are running a separate wire (which can be cheap thermostat wire) for the dimming or using Luminary cable, which is an MC type cable that has 18GA gray/purple conductors separated from the white/black line conductors.

-Hal

 

[oldsparky52]

My 725.49(B) says nothing of the kind.

I had to go read that section and came away with the same thought.

 

[roger]

My 725.49(B) says nothing of the kind. But we are getting off the subject here.
-Hal

I had to go read that section and came away with the same thought.

What does your 725.49(B) say?

725.49
(B) Insulation. Insulation on conductors shall be rated for
600 volts. Conductors larger than 16 AWG shall comply with
Article 310. Conductors in sizes 18 AWG and 16 AWG shall
be Type FFH-2, KF-2, KFF-2, PAF, PAFF, PF, PFF, PGF,
PGFF, PTF, PTFF, RFH-2, RFHH-2, RFHH-3, SF-2, SFF-2,
TF, TFF, TFFN, TFN, ZF, or ZFF. Conductors with other
types and thicknesses of insulation shall be permitted if listed
for Class 1 circuit use.

No mention of THHN in 18 and 16.

Roger

 

[infinity]

Or id use #14

Yes you could, disregard my question in post #6 the section Don posted is for #18 and #16 conductors. If using #14 then THHN is permitted.

 

[oldsparky52]

What does your 725.49(B) say?

No mention of THHN in 18 and 16.

Roger

I am of the understanding that THHN is not manufactured in sizes smaller than #14. The substitution of TFFN (which is mentioned) is what we did for conductors smaller than #14.

 

[roger]

I am of the understanding that THHN is not manufactured in sizes smaller than #14. The substitution of TFFN (which is mentioned) is what we did for conductors smaller than #14.

I agree and always used TFF or TFFN too, the point was the code section does not include THHN for smaller conductors.

Roger

 

[oldsparky52]

I agree and always used TFF or TFFN too, the point was the code section does not include THHN for smaller conductors.

Roger

I was making the point that of course that code section would not include THHN conductors (16 & 18) because they don't exist.

 

[Flawild]

Thanks for the info, above ceilings im going to use the mc cable with the 0-10 wire built in. But in exposed areas we hve to run EMt and some of the fixtures from The factory come with proprietary boxes that only have single 1/2 inch knockout in them and no room for others knockouts. So if I can’t pull some kind of control wires for the 0 to 10 in with the 120 I don’t know what to do? I’ll give the inspector a call tomorrow see what he says

 

[roger]

So if I can’t pull some kind of control wires for the 0 to 10 in with the 120 I don’t know what to do? I’ll give the inspector a call tomorrow see what he says

You can. You can use one of the conductor types in 725.49(B) or do as you mentioned and use a # 14 THWN.

Roger

 

[hbiss]

Sometimes you gotta do what you gotta do. In this case I would look at pulling 18/2 tray cable in the conduit for the LV along with the line voltage THHN conductors. That's exactly what some of the luminary cable manufactures do with their MC. Type TC is 600V, can be run in raceway and is a separate listed cable. So no worries about running it next to line voltage. That's about as compliant as you can get without the pitfalls of reclassifying. I can't see any AHJ having a problem with it.

-Hal

 

[infinity]

Sometimes you gotta do what you gotta do. In this case I would look at pulling 18/2 tray cable in the conduit for the LV along with the line voltage THHN conductors. That's exactly what some of the luminary cable manufactures do with their MC. Type TC is 600V, can be run in raceway and is a separate listed cable. So no worries about running it next to line voltage. That's about as compliant as you can get without the pitfalls of reclassifying. I can't see any AHJ having a problem with it.

Although what you've proposed would be almost identical to a cable manufactured that way I don't see how it's code compliant in a raceway with power conductors.

 

[hbiss]

Although what you've proposed would be almost identical to a cable manufactured that way I don't see how it's code compliant in a raceway with power conductors.

Yeah, I know and we've talked about "rolling your own" before. But the more I think about it I can't see why it wouldn't be. The LV is separated from the line voltage conductors in it's own listed 600V cable assembly.

I might be missing something but I'm not seeing anything that would prohibit it.

-Hal

 

[GoldDigger]

Yeah, I know and we've talked about "rolling your own" before. But the more I think about it I can't see why it wouldn't be. The LV is separated from the line voltage conductors in it's own listed 600V cable assembly.

I might be missing something but I'm not seeing anything that would prohibit it.

-Hal

I think the distinction between wire and cable (even a single conductor cable) decides the issue.

 

[hbiss]

I think the distinction between wire and cable (even a single conductor cable) decides the issue.

And that's something that is often confused in discussions like this.

-Hal