How to Ground a Sub Panel Box

All electrical boxes and circuits need some type of grounding.

A sub-panel usually is controlled by a 240-volt breaker in the main panel.A sub-panel usually is controlled by a 240-volt breaker in the main panel.
Main service panels are grounded back to the utility grid and also to a ground rod pushed into the ground near where the electric service enters the building. Sub-panels are grounded back to the main service panel through the wiring that feeds power to the sub-panel from the main service panel. This grounding gives a second level of safety against electric shock in the event of a short circuit in the wiring leading from the sub-panel.

Shut off the breaker in the main service panel that feeds power to the sub-panel. Use a screwdriver to remove the screws that hold the cover onto the sub-panel and set the cover aside. Locate the incoming wire from the main panel.

Remove 12 inches of the outer coating from the wire with wire strippers to expose the four wires inside. Separate the four wires. There will be one black, one red, one white and one bare or green wire.

Move the bare or green wire away from the other three wires. This wire is the ground wire. If it is a green wire, remove one inch of coating from the end of the wire. If it is bare, there is no coating to remove.

Insert the end of the ground wire into one of the screws on the ground bar. The ground bar will look like a row of screws in a bar that is not one of the neutral bars along the edge of the sub-panel box. Tighten the screw with a screwdriver.

Return to the main panel and make sure that this wire is attached to the neutral bus inside the main panel. If it is not, turn off the main breaker and insert the end of the wire under one of the screws on the neutral bus and tighten the screw with a screwdriver.

Turn the main breaker back on. The sub-panel is now grounded. If you have not completed the installation of the sub-panel, leave the cover off until you are finished. Do not turn on the breaker that drives the sub-panel until you have finished the installation and the cover is in place on the sub-panel.

Things You Will Need

  • Screwdriver
  • Wire strippers

Warning

  • Always make sure that the breaker controlling a sub-panel is off before working on the wiring within the sub-panel.

About the Author

Allen Teal was first published in 2002 in the "Adult Teacher" and "Adult Student" books for the Assemblies of God Sunday School department. He has also been published on various websites. He received an Associate of Arts in business from Mineral Area College in Park Hills, Mo.