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How to Find and Test a Doorbell Transformer

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Doorbell Transformer Location
  • Doorbell transformers are usually located outside the home along the siding or on a wall in the garage.
  • They may also be fixed to a wall in the basement or closet near the front door or entryway.
  • If you don’t see it in any of these places, check the walls in the attic. It may be tucked behind the insulation.
  • For homes with visible doorbell wires, you may be able to trace them back to the location of the transformer.
Check the Doorbell Transformer Wiring
  • Before you run any voltage tests, check the doorbell transformer wiring and make sure it’s properly connected.
  • Cut the power by switching off the main breaker in your home.
  • Doorbell wire is usually 18-gauge and should be free of splices, tears and corrosion.
  • If the wire in your transformer appears worn or damaged, you’ll need to replace it.
Doorbell Transformer Voltage
  • Test the doorbell transformer voltage by setting the meter on your voltage tester to 25VAC (volts alternating current).
  • Measure the voltage on the transformer to see if it’s producing enough electricity. The voltage should be at or around 16.
  • If the voltage is too low, replace the transformer to repair your doorbell unit.