Mixing wire gauge- 10 and 12 gauge

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Old 09-26-15, 07:53 PM
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Mixing wire gauge- 10 and 12 gauge

I am happy to have found this forum- reading old posts has really helped me get this project moving.

I am installing recessed lights in my basement to replace some very dim (and kind of ugly) wall sconces. They are on a 15 amp circuit, which someone wired (to the switch and from the switch to the sconces) with 10 gauge wire.

If I'm reading the instructions right, the biggest wire recommended for my cans is 12 gauge. Can I use 12 gauge on this circuit? If so, where do I switch the gauge? I'm not really keen on going all the way back to the switch, can I just attach 12 gauge wire to the existing 10 gauge coming off the switch and then attach the 12 gauge to the cans?

Thanks for any help you can provide!
 
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Old 09-26-15, 08:03 PM
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If the #10 does not exceed the box fill of the junction box on the light #10 is fine. Measure the cubic inches of the junction box attached to the light and tell us the number of wires in the box.

One thought: Is the #10 copper or aluminum?
 
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Old 09-26-15, 08:56 PM
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A 15 amp circuit can use #14 .
 
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Old 09-27-15, 05:29 AM
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You can switch gauge anywhere but if you switch gauge halfway between the light and the switch then you will have to put another junction box, with an exposed cover, there.

The chances are high that the little junction box that comes with the can light will not hold a set of 10 gauge wires coming in and another set of wires continuing on to the next can light.

Ten gauge copper wire can handle up to 30 amps but once you put ordinary lights and/or receptacles on the circuit, the circuit is limited to 20 amps or less. Once you put 14 gauge wire on the circuit including on any sub-branch, the entire circuit is limited to a 15 amp breaker.

In a general sense, mixing wire gauges is allowable although usually it is overkill. But in some cases notably involving long distances, mixing gauges may be needed.
 

Last edited by AllanJ; 09-27-15 at 06:06 AM.
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Old 09-27-15, 12:17 PM
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The box is about 1.5 x 3 x 5, so 22.5 cu in. It has these little four-holed Orange plastic connectors where you just strip the end of the wire and poke it in the hole, I am not sure how to tell if they can handle 10 gauge.

Thanks so much for your assistance!
 
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Old 09-27-15, 12:43 PM
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Do you have aluminum wiring?
 
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Old 09-27-15, 01:03 PM
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Oops, forgot that question. It's copper.
 
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Old 09-27-15, 01:43 PM
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I am not sure how to tell if they can handle 10 gauge
Unlikely they will since the Manufacturer said #12 max.
The box is about 1.5 x 3 x 5, so 22.5 cu in.
If I did the causation correctly you need about 10 cubic inches for four #10 so you are okay with fill but I wouldn't try to work with #10 if you can easily replace it. #14 will be a lot easier to work with. I'd start at the switch with #14. It will even make doing the switch a bit easier.
 

Last edited by ray2047; 09-27-15 at 02:08 PM.
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Old 09-27-15, 05:31 PM
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It may be semantics, but from Post 1: "If I'm reading the instructions right, the biggest wire recommended for my cans is 12 gauge."

Taking the fixture manufacturer's written 'recommendations' as installation instructions, I would say that #10 is NOT allowed the fixture.


110.3(B) Installation and Use. Listed or labeled equipment
shall be installed and used in accordance with any instructions
included in the listing or labeling. (NFPA 70 - 2014)
 
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Old 09-28-15, 11:36 AM
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Make sure that the circuit breaker that protects this circuit is rated for the lowest amperage wire in the circuit. If you mix #10, #12 and #14 wire in a circuit, you will need to protect the circuit with a 15 amp breaker.
 
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Old 09-28-15, 01:39 PM
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Taking the fixture manufacturer's written 'recommendations' as installation instructions, I would say that #10 is NOT allowed the fixture.

110.3(B) Installation and Use. Listed or labeled equipment
shall be installed and used in accordance with any instructions
included in the listing or labeling. (NFPA 70 - 2014)
The key word as I see it is
the biggest wire recommended for my cans is 12 gauge.
recommended. It doesn't say maximum allowed. As I wrote before I think #12 is the maximum size wire the push connectors will accept.

As I wrote though if possible run #14 from the switxh to make things easy and then interpretation is a moot point.
 
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Old 09-28-15, 01:57 PM
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The integral box clamps and push in connectors are probably only rated for #14 or #12, so you may need to use other KOs, clamps and wire nuts, but there is no problem using the #10 so long as the box has adequate cubic inches.
 
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Old 09-29-15, 07:51 PM
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Ok, I figured out how to get back to the switch and run #14 from there, and the circuit has a 15 amp breaker so I should be good to go, right? Thanks for all the help!
 
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Old 09-29-15, 08:11 PM
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Yes, good to go. .
 
 

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