Em wrote:
I added a light fixture to an existing 20A 12awg circuit, and didn't
realize I used 14awg romex until I was done. The new fixture wouldn't
overload even a 15A circuit, so a) are you gonna tell me I have to
fix my error and put in the larger cable, and b) why is that? Thanks

While replacing the cable would be good, it might be better to just swap
out the breaker.

--
Joseph Meehan

Dia 's Muire duit