Safe measurement practice for resistors in-circuit Which single step is the most important to perform before measuring a resistor with a meter in a circuit?

Introduction / Context:
Measuring resistance is a routine task, but doing it incorrectly can damage the meter, disturb the circuit, or yield nonsense readings. The most crucial safety and accuracy rule is to ensure that no external voltage is present across the resistor under test.

Given Data / Assumptions:

• Digital or analog multimeter used for resistance measurement (ohmmeter function).
• The resistor may be in-circuit.
• We aim to prevent meter damage and false readings.

Concept / Approach:
Ohmmeters inject a small, known current and measure the resulting voltage to compute resistance. If the circuit is powered, external sources inject additional voltage/current that will corrupt the measurement and can harm the meter. Therefore, power must be removed, and ideally the resistor isolated from parallel paths if high accuracy is needed.

Step-by-Step Solution:
Turn off and disconnect the power source to the unit under test.Discharge capacitors to avoid stored energy affecting the meter.If precision is required, lift one resistor lead to eliminate parallel paths.Measure resistance using the ohmmeter; interpret values in Ω, kΩ, or MΩ as needed.

Verification / Alternative check:
Compare measured value to color code or schematic. If in-circuit reading differs significantly, isolate the component and remeasure.

Why Other Options Are Wrong:
Use highest scale: may reduce resolution and does not address safety.Keep leads short: helpful against noise, but secondary compared to de-energizing.Zero the meter: relevant for analog meters, but still less critical than removing power.

Common Pitfalls:
Forgetting to power down, measuring across energized nodes, or trusting in-circuit readings without considering parallel components.

Final Answer:
remove power from the circuit