This happens via capacitive coupling when you have an un-energized wire running next to an energized one and connect a high-impedance voltmeter. In your case, it would be from the switched wire running next to the hot wire.

How can earthing problems be corrected?

How to Fix Electrical Wiring in the Home With Electrical Ground…

  1. Shut off the main electrical power.
  2. Find the grounding rod driven into the ground. …
  3. Check the ground connection clamp. …
  4. Check the ground wire running to the copper or galvanized water service inside the house.

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