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SESK: Stuff Everyone Should Know · sesk.info/ham-ohmmeter-circuit-unpowered

What precaution should you take when measuring in-circuit resistance with an ohmmeter?

Make sure the circuit is not powered.

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  1. Make sure the circuit is grounded
  2. Make sure the circuit is not powered ✔
  3. Make sure the applied voltages are correct

Why: An ohmmeter supplies its own small current. Power in the circuit throws off the reading and can damage the meter.

Huh, didn't know that: Large capacitors can hold a charge after the power is off, so discharge them safely first.

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Rule one of measuring resistance: turn it off. Rule two: see rule one.
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References

Answer: Make sure the circuit is not powered. An ohmmeter supplies its own small current. Power in the circuit throws off the reading and can damage the meter.

  1. NCVEC 2026-2030 Technician Question Pool (February 19, 2026 errata) ncvec.org/downloads/2026-2030%20Technician%20Pool%20and%20Syllabus%20Public%20Release%20Feb%2019%202026.pdf
    B. Ensure that the circuit is not powered
    Checked 2026-10-09.

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