Hello,
I am trying to wire some new lights in my house. I currently have wiring of 12/3 going from my pannel to my basement. Can I use that wire to connect 14/2 in a junction box and run 14/2 to my lights and switches. There is currently a 30A breaker but I was going to replace it with a 15A double pull. I guess im asking is their a problem with abandoning the red wire and just using the white(common) and Black (hot) 12 guage to a junction box and connecting 14/2 to that for my power?
Thank you
Jeff

 

Do not mix wire gauges in the same branch circuit.

You definitely need to get the 30 amp breaker out of the 12 gauge circuit.

Use a 20 amp breaker with 12 gauge copper wire and a 15 amp breaker with 14 gauge wire.

 

Don't cut off the red wire at either end. Curl it up and push it to one side of the box.

It can be used in the future, together with the (same) white wire as a neutral. There are some esoteric rules but you can get another 20 amp branch circuit out of it as opposed to having to string a brand new cable.

If the branch circuit has any 14 gauge wire in it then the breaker is limited to 15 amps.

 

Time to start some controversy. I'm rather certain that you can use 14/2 in a 20amp circuit between the switch and the light fixture. The reason is that both the switch and the dedicated (light) outlet are incapable of utilizing more than 15 amps, so the switched wire in between doesn't need to be rated for higher use. I don't have my code book in front of me though, so I can't look that up right now.

I see a bigger issue though, having to do with those esoteric rules Allan mentioned. If you use the black and white wires to feed the light, the red must be disconnected at both ends and capped (one end being in the panel). Two hots sharing a neutral is a multiwire branch circuit. Those must be fed off double-pole breakers, which is annoying. More importantly, there's also a restriction on where the two hots can terminate. I can't look it up, but I don't think you could use the black to feed lights and the red to feed something else. Still, even if you are abandoning the red wire for now, leave it accessible. If you're not ripping a wire out of the building, it should be accessible.

Moderator Addendum: All general purpose 120 volt residential wiring must be at least the minimum size permitted for a breaker. If it is a 20 amp breaker you must use #12 minimum for all parts of the circuit, no exceptions, not even lighting.

 

Wrong. All wiring must be able to handle full amps of the breaker.

 

The wire size must match the breaker not just for the loads carried in the circuit but if there is a short the breaker must trip before the wire overheats and catches fire.

 

At one time this was a pretty common practice in residential wiring, but codes change and practices change with them.