If a metal box is being used, best practice is to insert a green grounding screw into the threaded hole in the back of the box or enclosure. The equipment-grounding wires then connect to the screw, making the metal box part of the grounding system.

If the multimeter reads the full voltage of the circuit (usually around 120V or 240V), the box is grounded. However, if the multimeter reads zero volts or close to it, the box is not grounded. Alternatively, you can use a voltage tester by touching one probe to the hot wire and the other probe to the metal box.

How to Test the Metal Box to See If It is Grounded Shut off the power for that room Pull off the outlet faceplate and then pull the outlet out of the wall Unscrew the wires so they are not attached to the outlet anymore Check that the positive and neutral wires are exposed and not touching anything. Turn back on the electricity for that room

The boxes, connectors, and conduits form a wire enclosure system called a raceway. A raceway is an enclosed conduit that forms a physical pathway for the electrical wiring to follow. In this way, the metal raceway acts in place of the grounding wire that is found in non-metallic cable.