I found this one gang plastic nail-on box in the ceiling of a client’s basement. It has a type AC (BX) cable and a Romex cable spliced together. The Romex has a grounding conductor. BX cable normally uses its metal armor outer jacket as the ground. A BX cable should be spliced inside of a metal box so that the armor ground is carried over to the metal of the box. With a plastic box it is necessary to attach a BX connector with a metal grounding bushing onto the BX. A grounding conductor is then connected to the lug on the grounding bushing. This electrical box should also have a blank plastic cover on it.