Electrical Troubleshooting Quiz

Strange things have been happening in the plant lately

Strange things have been happening in the plant lately. Rumors are circulating about sabotage and industrial spies. Many operators refuse to work at particular machines. Among the many complaints:

  • Three different drinking fountains routinely shock people.
  • Machines sometimes shut down in mid-run for no apparent reason.
  • Red (stopped) and green (running) lights are on simultaneously, though one's dimmer than the other.
Corporate issued a memo to "ground all of the machines." Your boss handed you the work order and wants you to start installing ground rods. How should you respond?

These are symptoms of circulating currents and differences of potential. Installing those ground rods is a waste of money and will delay an actual solution. When explaining this to your boss, use these facts:

  • Kirchhoff showed that electricity flows through all paths presented to it, dividing flow inversely proportionate to impedance.
  • "Ground" means "earth," [NEC Art. 100]. That's a high-impedance path to the source (electricity returns to its source — making a circuit).
  • You need a low impedance path.
Solve by inspecting your bonding system to ensure:
  1. Proper connection of the grounding strap on each distribution transformer.
  2. No L-G bonds on feeder (and branch) panels and circuits.
  3. Metallic raceway is electrically continuous.
  4. Panels and equipment housings are bonded per NEC Art. 250, Part V.
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