tinman13kup:
I do notice you only have L/N hooked up to the mains. The earth ground next to the N lug should be wired into the mains earth as well. A grounded 14ga pigtail will ensure polarity cannot be reversed(unless house wiring is bad).
i looked for the 14ga pigtail on google and i see it is a cable with a screw on one side. if i screw it on the wooden case, will it work as a ground?