Technician A says that when making resistance measurements on a circuit, it is important to observe the correct polarity when connecting the test leads. Technician B says that resistance measurements should be made using a DVOM set to the Ohms scale. Who is right?

Technician A says that when making resistance measurements on a circuit, it is important to observe the correct polarity when connecting the test leads. Technician B says that resistance measurements should be made using a DVOM set to the Ohms scale. Who is right?

• A. A only
• B. B only
• C. Both A and B
• D. Neither A nor B

Answer: (B)

When measuring resistance, the meter uses a small internal current and measures the resulting voltage to calculate the resistance. Because resistance is a magnitude, swapping the leads just reverses the direction of current but doesn’t change the value shown. So observing a specific lead polarity isn’t needed for a valid resistance reading, as long as the circuit is de-energized and you’re using the Ohms function on the DVOM. This is why setting the meter to the Ohms scale is the essential step. Note that in-circuit readings can be affected by other paths, but that’s a separate consideration.

When measuring resistance, the meter uses a small internal current and measures the resulting voltage to calculate the resistance. Because resistance is a magnitude, swapping the leads just reverses the direction of current but doesn’t change the value shown. So observing a specific lead polarity isn’t needed for a valid resistance reading, as long as the circuit is de-energized and you’re using the Ohms function on the DVOM. This is why setting the meter to the Ohms scale is the essential step. Note that in-circuit readings can be affected by other paths, but that’s a separate consideration.