Electrician tells me that you cannot mix 12AWT and 14AWT wires on the same circuit, according to code. I have run 12AWT on 15A circuit to avoid voltage, with 14AWT to individual light fixtures. I have also run 14AWT to light fixtures from receptacles on 20A circuit. Do I have to upgrade everything to 12AWT? What about pancake boxes, which AFAIK can only take 14/2?