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Difficulty: EasyMultimeter: Resistance and Continuity

What critical safety precaution must always be taken before using a digital multimeter to measure the resistance of a component in an electrical circuit?

  1. A
    Keep the circuit energized so the ohmmeter can utilize the system's operating current
  2. Ensure all electrical power to the circuit is completely disconnected and de-energizedAnswer
  3. C
    Insert the black test lead into the high-amperage terminal port instead of the common port
  4. D
    Wrap the component terminals with electrical insulating tape before applying the test probes

Answer

Ensure all electrical power to the circuit is completely disconnected and de-energized
A multimeter's ohmmeter or continuity function operates by applying a small internal voltage from its own battery across the component leads and measuring the resulting current flow. If external power is present, the external voltage interferes with the measurement circuitry, causes invalid readings, and risks blowing internal protective fuses or damaging the instrument. Therefore, disconnecting and verifying zero power is the primary safety rule.

Step-by-Step Solution

1
Identify the operating principle of a multimeter set to measure resistance (Ω\Omega)
The meter outputs its own low internal DC voltage from an internal battery to pass a known test current through the component and calculate resistance via Ohm's Law (R=VIR = \frac{V}{I}).
Understanding how the meter measures resistance clarifies why external circuit power disrupts the measurement.
2
Determine the necessary condition of the circuit under test
The circuit must have zero external voltage and zero external current flow.
Any live voltage present on the test leads will alter the calculation, blow the meter's internal fuse, or pose an electrical hazard.

Key Concept

Multimeter Ohmmeter Safety and De-energization Requirement
Estimated Time:45s
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Topics

Multimeter: Resistance and Continuity

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