My father-in-law is a builder. He has put in 20 amp and 15 amp breakers, and ran 12-2 as the home runs to the switch's and the first plug to make them hot. He then ran 14-2 to feed the rest of the plugs, lights, and ceiling fans.
Is it okay that he used different gauge wires on the same circuit?
Best Answer
It is fine for the 15 amp circuits, but not for the 20 amp circuits.
The National Electrical Code requires circuits protected by a 20 amp circuit breaker to use #12 AWG copper wire throughout the circuit.
The National Electrical Code allows circuits protected by a 15 amp circuit breaker to use #12 AWG copper wire but #14 AWG wire cannot be protected by anything larger than a 15 amp breaker for power and lighting.
Regardless of where it is in the circuit, even if it is after the first receptacle, #14 wire cannot be used on a power or lighting circuit protected by a 20 amp breaker.
The following are pertinent excerpts from articles of the National Electrical Code:
The #14 wire that is installed on 20 amp circuits would need to be replaced with #12 or the breaker on that circuit needs to be replaced by a 15 amp breaker.
Usually, 20 amp circuits are used for receptacle circuits and 15 amp circuits are used for lighting circuits.
Good luck!