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How to Ground a Metal Electrical Box

Robert Sylvus

An electrical system's ground wire connects all of the system's metal parts to earth, which prevents electrical shocks and fires. When a home uses metal electrical boxes to hold switches or outlets, the metal box must connect to ground. If one of the live wires in a metal box without ground came loose and touched the box, the box itself would become part of the live circuit. If an unsuspecting user touched that live box, he would also become part of the circuit. If the metal box is grounded, the ground wire becomes part of the circuit instead.

Metal electrical boxes must connect to a ground source for safety.
  1. Turn off the electricity to the service panel at the "Main" panel box, found outside next to the electric meter. Flip the switch labeled "Main" to the off position. The service panel, located inside, contains the circuit breakers.

  2. Examine the wire feeding electricity to the metal electrical box from the service panel, called the feed wire. Modern homes use a wire set with a ground wire included. The ground wire either comes without insulation or with green-colored insulation.

  3. Remove the service panel's cover with a flat-head screwdriver. Most service panels use four slotted screws to hold the panel's cover in place. The large wires, usually 6-gauge or larger, from the main panel enter the service panel. One of the large wires connects to the ground lug, located on a bus mounted to the service panel's housing. All of the electrical system's ground wires connect to the ground bus, which has green-colored locking screws.

  4. Run an insulated ground wire from the service panel to the metal electrical box, if the feed wire does not contain a ground wire. Cut the wire to length with wire cutters. Push one end of the ground wire into the service panel and the other into the metal electrical box.

  5. Use wire strippers to remove 1/2 inch from the insulating covering from each end of the ground wire, if needed.

  6. Push the bare end of the ground wire into one of the service panel's bus holes and tighten the bus's locking screw with a flat-head screwdriver. The holes on the side of the bus hold wires and the screws that penetrate the top of the bus hold the wire in its respective hole. Adjust the ground wire so that it does not touch anything in the service panel.

  7. Loosen the metal electrical box's green screw with the flat-head screwdriver. The green screw spins into the metal box's housing.

  8. Bend the ground wire around the metal electrical box's ground screw. Tighten the ground screw with the flat-head screwdriver.