There are round, square, rectangular, shallow, weatherproof, and extension boxes. Electrical boxes come in plastic and metal varieties. Plastic boxes are non-conductive and are relatively inexpensive. They come in different styles that either nail on or are the cut-in variety.

In general, it recommends plastic boxes for switches and receptacles and metal boxes for light fixtures. Metal boxes are required when the existing wiring in the home is metal clad cable and must be bonded to the ground wire.

Metal cable and conduit depend on the contact from its metal sheathing to the metal box to complete grounding. Even if the device does not complete the ground, Romex or NM wiring can always be used with metal electrical boxes by attaching the bare or green grounding wire to the box by a screw.