Q. Can a stranded 12 AWG wire be placed under the screws for receptacles and switches?

A. Conductor terminations must comply with manufacturer’s instructions as required by 110.3(B). For example, if the instructions for the device state “Suitable for 18-2 AWG Solid,” then only solid conductors are permitted. If the instructions do not specify "solid" such as, “Suitable for 18 - 12 AWG,” then either solid or stranded conductors can be used with the terminating device.