Class 2 wiring ampacities for lighting systems

Is there a table showing the ampacities of various sizes of class 2 wiring? Table 402.5 has ampacities for fixture wire (down to 18 gauge). I have run some 16 gauge for some LED lighting but am curious as to whether or not the NEC has a minimum required size for Class 2 lighting systems under 30 volts and what current it can carry. 725.179(H) shows a minimum 18 gauge for class 3 but I can't find anything for class 2. I've seen guys pull 20 gauge stat wire off their trucks for low voltage lights and want to know if that is allowable.
 

augie47

Moderator
Staff member
Location
Tennessee
my opinion would be, if its a lighting system operating at 30 volts or less, Art 411 would apply and the conductors used would need to be part of the factory assembly of listed parts and covered by the listing and only the manufacturer supplied cable should be used.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
my opinion would be, if its a lighting system operating at 30 volts or less, Art 411 would apply and the conductors used would need to be part of the factory assembly of listed parts and covered by the listing and only the manufacturer supplied cable should be used.
Don't give lighting manufactures the opportunity to charge double for CL2 cable Gus.:happysad:
 

augie47

Moderator
Staff member
Location
Tennessee
Don't give lighting manufactures the opportunity to charge double for CL2 cable Gus.:happysad:
You would think as short as it is, Art 411 would be an easy read. To me it is not.
If one chooses to use a Class 2 wiring method, Art 411 refers you to the even more confusing Art 725 where it appears one would need a CL2X or CL3X cable.
After an hour of searching, I am at a loss as to ampacities
 
Thanks for your time and input, gentlemen. Section 725.43 says maximum 7 amps for 18 gauge Class 1 wiring. Section 240.4(D) says the same, but that doesn't nail down a Class 2 application. Perhaps Augie is right with first post, but then 725.130(B) seems to indicate it is OK to run other wire as long as it is listed appropriately. I'm running a 16 gauge CL3R sound cable for some tape light and won't load it past 6 amps. I'm beginning to understand why a class 2 stat wire is a default solution...it is hard to pin this down.
 

kwired

Electron manager
Location
NE Nebraska
What are the limitations of your power supply? Chapter 9 tables 11(A) and 11(B) give you limitations for power supplies.

Just looking at requirements for inherently limited supply sources, one should not need much larger then 18 AWG (maybe just pushing into needing at least 16 AWG if it meets maximum values listed in those tables, even if using to short circuit the source, as it shouldn't put out enough current to overheat the conductor.
 
The power supply will be Class 2 and so will not exceed 100 watts and about 8 amps if 12 volts, so I agree I will be safe with 16-18awg. What I am curious about is if I had a load of just a few feet of LED tape light drawing perhaps 30-40 watts would it be permissible to run smaller than 18 gauge. I see nothing in the code about a minimum required wire size or the ampacity of such. I'll agree that 18 gauge minimum might be a default answer but what's to prevent someone from using a 20 or 22 gauge class 2 stat wire? I'd like to do a tutorial on this at a local college because I think there is a lot of misunderstanding on this topic, and there are more and more of these systems in use. Trouble is I can't figure it all out myself with code references to back me up. Thanks for the input, this is a great forum and I wish I knew about it sooner.
 

kwired

Electron manager
Location
NE Nebraska
The power supply will be Class 2 and so will not exceed 100 watts and about 8 amps if 12 volts, so I agree I will be safe with 16-18awg. What I am curious about is if I had a load of just a few feet of LED tape light drawing perhaps 30-40 watts would it be permissible to run smaller than 18 gauge. I see nothing in the code about a minimum required wire size or the ampacity of such. I'll agree that 18 gauge minimum might be a default answer but what's to prevent someone from using a 20 or 22 gauge class 2 stat wire? I'd like to do a tutorial on this at a local college because I think there is a lot of misunderstanding on this topic, and there are more and more of these systems in use. Trouble is I can't figure it all out myself with code references to back me up. Thanks for the input, this is a great forum and I wish I knew about it sooner.
How much current can the source put out and for how long - if short circuited needs consideration to answer your question IMO. If source can't put out enough current to overheat a specific size conductor then there shouldn't be any problem with using that size conductor, it is inherently protected by the limitation of the supply.
 
True, I am using all class 2 supplies so there shouldn't be any risk of ignition or shock with a failure because of limitation of supply as you said. I still wish there were a guide to the ampacity of a 20 or 22 awg wire so it could be matched with a small load for design purposes.
 
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