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-   -   A case of different wire sizes.... (http://www.diychatroom.com/f18/case-different-wire-sizes-10892/)

BigJimmy 08-21-2007 12:02 PM

A case of different wire sizes....
 
Ok, here's one for consideration:

I installed a number of fluorescent lights in my basement recently. I designed the conduit system to carry additional conductors for the purposes of recircuiting the 1st floor. All circuits involved are 15A however I ran 12awg. wire in most instances to account for the derating requirements found in 310.15.(B).(2)(a). When it came to making the connections to the fixtures, I had a bunch of scrap 14awg. wire lying around and I figured I'd simply use that to make the connections from the nearby 4sq. boxes to the fixtures themselves. Inspector came by and took exception to this. I argued that these conductors are no more than extensions of the fixture wires which are 18awg., the only reason for the 12awg. was due to derating and finally that the OCB size was 15A. He didn't agree.

Any thoughts?

Stubbie 08-21-2007 01:55 PM

If you ran individual 14 awg wires then you are in violation and the inspector is right. 14 awg thhn is no allowed outside of conduit or enclosures, boxes etc... and is not a classified fixture wire rated 105C. It doesnt originate in the fixture therefore it cannot be a fixture wire. However if you ran to the fixtures with some flex conduit and ran the 14 awg thru that then you would be compliant. The most common application is to run fixture whips of metal flex from the jb to the light.

Stubbie

BigJimmy 08-21-2007 02:48 PM

Quote:

Originally Posted by Stubbie (Post 58778)
If you ran individual 14 awg wires then you are in violation and the inspector is right. 14 awg thhn is no allowed outside of conduit or enclosures, boxes etc... and is not a classified fixture wire rated 105C. It doesnt originate in the fixture therefore it cannot be a fixture wire. However if you ran to the fixtures with some flex conduit and ran the 14 awg thru that then you would be compliant. The most common application is to run fixture whips of metal flex from the jb to the light.

Stubbie

No, no, I didn't run them outside of the raceway system! In close proximity to each fixture, there is a 4-sq. box. Each fixture is connected to the box with a length of conduit or an offset nipple. I don't disagree with you a bit that THHN is not fixture wire. The inspectors gripe is that it's 12awg. to the box and then a length of 14 to the fixture. The only reason that I used the 12 is due to derating. I argue that 2 single conductor 14's from the box into the fixture are not subject to the same derating conditions.

Stubbie 08-21-2007 03:58 PM

Ok... I misunderstood. As for derating you would need to have 10 conductors (you don't count grounds) whether 14 or 12 awg, in the conduit before the deration would drop below the rated ampacity of the copper wire. That being said I can see no violation in what you did, in fact it is quite common to downsize the wire to the fixture when not using it as the junction point in commercial applications. As long as the ocpd remains 15 amps for the smallest wire being used I would say the inspector is overly cautious.

Stubbie


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