In article , Just Joshin wrote:
On Mon, 26 Mar 2007 11:01:56 -0600, Chris Friesen
wrote:

Em wrote:
I added 14-gauge (15A) romex cable to a circuit that had 12-gauge (20A)
wire, indicating I had made a mistake, but it turns out to be a 15A breaker
on the circuit with 12-gauge wire. Is that OK/safe? I don't have to correct
my mistake, right? Thanks

Correct. However, if the #12 wire goes to the panel you may end up
confusing the next person looking at the electrical system--they may
assume that since it's #12 wire its safe to put a 20A breaker on the
circuit, not realizing that the circuit includes some #14..

Chris

Some AHJ would have you lable the circuit 15amp only.

I have before seen a municipality's code webpage saying that it is
against code to have a branch circuit having wires differing in allowed
breaker amps. However, I did not find it clear whether that was NEC or a
local building code.

If you have mixed size wiring in a branch circuit, I would equalize it
if possible. If not, I would have visible tags everywhere the larger
wiring would be seen saying that the branch circuit is a mixed wire size
circuit and what the breaker amps should be - and hope the home inspector
does not see that being a problem when you sell the house.

Personally, I think there should be no permanently installed wiring
thinner than 12 in a house, as common as 20 amp breakers and fuses are.

- Don Klipstein )