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My house is 54 y/o. Years ago the circuit panel was upgraded to all 20 amps with the exception of the AC and oven. I am adding a can light which uses 12 - 18 gauge wire. I chose 14 gauge. I am wanting to tie it in to the existing on/off switch which I believe may be wired with 12 gauge wire. Is it safe to tie in the 14 gauge to the 12?

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No, you may not use 14 gauge wire on a 20 amp circuit. You need to use 12 gauge wire.

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    I know it sounds silly since the lamp has small wire that you have to use such a large wire to make the connection but the lamp wiring is enclosed in the box and fixture.+ – Ed Beal Dec 18 '18 at 22:11
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Go for it, but you will need to change the breaker in that panel to 15A. Also put a tag on the #12 wire going to that breaker that says "#14 wire in circuit".

Also, any 20A receptacles on that circuit (Ms. Winky) must be changed to 15A receptacles (Ms. Horror).

Also, if the hardwired loads on that circuit total 7.5A or more, you cannot have any receptacles at all, or the loads must be changed to smaller draw loads.

Still want to do that?

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What does the switch currently switch? Were you going to do the splice at the existing light fixture or in the box itself (not sure why you'd do this, and you'll probably have space or missing neutral issues).

You should check the breaker that controls the switch's circuit. If it's 20A (likely with 12 gauge wire) and you want to continue with 14 gauge wire, you must verify your loads and downsize the breaker to 15A. You're probably better served just continuing with 12 gauge. If your existing wiring is aluminum, you must also splice to new copper wiring with a Al/Cu nut to avoid corrosion.

  • I want to wire it into the current light switch so it will come on at the same time as the existing light. Not from the 20 amp breaker to the light. It’s an add on. – Kem Dec 18 '18 at 22:05
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    Can you just tie into the existing light's box? You shouldn't need to modify the switch for this. I'd verify the conductor metal to know if you have to do a Al/Cu splice, and do the short run between the two lights with 12 AWG. – Steven Dec 18 '18 at 22:10
  • Not a good practice to downgrade a breaker, the next person sees the 12 in the panel and that huge disco ball keeps tripping the circuit so 12 is good for 20 and they upgrade the breaker. fire is the next possibility for not using 12 to the next fixture in the first place. – Ed Beal Dec 18 '18 at 22:18
  • These are all copper wires. – Kem Dec 18 '18 at 22:27

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