Mix #14 and #12 wire on 15 amp circuit?

Is there any problem using #12 wire to add lighting only (no receptacles) to an existing 15 amp circuit (that has both lighting and receptacles), which obviously uses #14 wire? I recall an electrician once telling me you should not mix wire because of "feedback", but I did not understand what he was referring to. Any information would be appreciated.

 

You are allowed by code to do this.

However, I would not.

If you do this the danger is that someone later may see the number 12 wire and think that it is a 20 amp circuit, without bothering to look at the breaker.

Thinking it is a 20 amp circuit they may replace the fuse with a 20 amp fuse, which would not be good.

Or they might extend the circuit thinking it has enough power for their needs and realize too late that it does not, or they might not even realize it and try to hook up a large appliance that needs a 20 amp circuit.

Spend the money and buy the proper size wire.

 

But other than the confusion issue that Bob cites, there is no immediate hazard. There is no "feedback" issue.

I hope that anyone who would be tempted to change the fuse or breaker would notice that the wire at the box is #14, or that anyone who went to extend it would notice that the breaker he turned off says "15" on it. But anything can happen to people who don't pay attention. We just hope that not too many of those people are doing electrical work.

 

if the distance is short there is no major benefit to running 12 guage wire. Otherewise I agree with John that it's up to the person doing the wiring to realize that it's a 15 Amp circuit. You could tag the wire in the panel as 15 Amp only to help avoid any later confusion.

 

I decided to proceed and tag the wire as suggested in a couple of places to try to prevent confusion in the future. I do appreciate the concern, though, because I once bought a house where a basement remodeler mixed #12 wire with existing 15 amp circuits that initially confused me as to what I was dealing with.

Thanks for everyone's input.