A megger will be used to check an in-service cable. The Electrician MUST be sure that the circuit is:

• A. Energized
• B. De-energized and locked tagged and tested
• C. Grounded
• D. Under load

Answer: (B)

The main idea is that insulation resistance testing with a megger must be done on a circuit that is completely isolated from the power supply. A megger applies a high DC voltage to the insulation to measure leakage current, and this test is valid only when there is no live voltage that could interfere with the reading or cause a hazardous condition.

That’s why the correct approach is to ensure the circuit is de-energized, locked out, and tagged, and verified as zero-volt before starting the test. De-energizing removes the live source, locking and tagging prevents accidental re-energization, and a test verifies there is no voltage present at the test points. This creates a safe environment and yields an accurate insulation resistance reading.

Why the other options aren’t suitable: testing while energized is dangerous and would defeat the purpose of measuring insulation resistance since the live supply can contaminate the reading and create a safety risk. Grounded or under-load conditions do not provide the necessary isolation and would again distort the measurement and introduce hazards.