I have several project on my To-DO list that I am doing as I "move" from one section of my house to the next....However, I also have "full-house" projects, like running new wires.
I am currently working in my bedroom with exposed studs for another reason so I could take advantage of it and lay new cables that are 12/2....however, that room is on the same circuit as other bedrooms at 15Amps and with 14/2 wires running.
Eventually I will get to the other ones and upgrade the wires to 12/2 and link it all to a 20A breaker.

Assuming I will get to the other rooms in about 2 months - is it OK for me to simply add the larger gauge wire on the same circuit as the smaller gauge considering that throughout I am pulling 15Amps?

Thanks!

If not - I will of course just do the job at once by snaking the new wires behind the walls....something a bit more challenging than the current option.

PS: My main concern is code and regs...I don't believe there would be an actual safety issue...unlike if I were to put 14 on 20A

 

Yes, you can. Just be 100% sure all the 14/2 has been removed/disconnected before you change the breaker to 20 amps.