Low and high voltage in the same conduit

Flawild

Member
Location
Florida
Occupation
Electrician
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?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
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).
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
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
 

roger

Moderator
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Location
Fl
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Electrician
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
 

roger

Moderator
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Location
Fl
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Electrician
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
 

Flawild

Member
Location
Florida
Occupation
Electrician
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

Moderator
Staff member
Location
Fl
Occupation
Electrician
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

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
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

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
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

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
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

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