How to Find a Bad Electrical Ground


Electrical current flows by seeking the path of least resistance. Basic electrical principles dictate that ground should be this path of least resistance so current can flow smoothly through the circuit from the power source to ground. If grounding is not properly done, it interrupts this natural flow, creating stay voltages, electrical arching and interrupting normal circuit operation. For this reason, proper grounding is a must.

Things You'll Need

  • Electrical safety gloves
  • Ohmmeter
  • Conductive adhesive
  • Grounding straps
  • Screwdriver
  • Pliers

Finding the Grounding Points and Checking the Grounding Quality

  • Turn off all power to the electrical system and put on a pair of rubber gloves for safety.

  • Find all electrical grounding points for the system. A grounding point is defined as the point where a circuit is grounded, usually with a small metal grounding strap connecting the circuit to a metal floor or metal cabinet. For example, if you have a circuit board encased inside of a metal case, there is small metal ground strap connecting the circuit board to the metal casing. The metal case may be mounted in a metal cabinet where a metal grounding strap connects the case to the cabinet. The metal cabinet may be attached to a metal floor where the cabinet is bolted to the floor and the bolt serves as the ground point.

  • Visually check for frayed grounding straps. A grounding strap is a small metal strap connecting the electrical system to ground. One end of the strap is bolted to the electrical unit and the other end in bolted to ground. If a grounding strap is frayed, you have a bad ground. Replace it immediately. To replace it, use a screwdriver or pliers to unscrew the lug nuts, bolts or screws on both ends, remove the strap and replace it with a new one. Use the lug nuts, bolts or screws to attach the new strap in the same place where you removed the frayed one.

  • Measure the resistance at each electrical grounding point using an ohmmeter. Set your ohmmeter to the lowest possible setting, usually R x 100, so it can register low resistance. Place one ohmmeter lead on the unit and the other lead on the grounding point. For example, in the case where a metal cabinet is grounded to a metal floor, one lead will be on the cabinet and the other lead will be on the floor. Your resistance should be less than 1 ohm. If it is more than 1 ohm, you have a bad ground.

Fixing the Bad Ground

  • Unscrew and inspect the lug nuts or bolts mounting the grounding straps to the grounding point or bolting a rack to a floor.

  • Clean and remove all dirt or corrosion that may exist on or around the lug nuts or bolts and where the lug nuts or bolts connect to the metal surfaces.

  • Add conductive adhesive on and around the lug nuts and bolts and reattach the grounding straps.

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