In the commissioning sequence, which test is performed immediately after the visual inspection?

• A. Insulation resistance test.
• B. RCD testing.
• C. Earth fault loop impedance testing.
• D. Functional testing.

Answer: (A)

Insulation resistance testing is done first to verify the insulation of all conductors before any power is applied. By using a megohmmeter to apply a high DC voltage with all loads disconnected, you check that there is no significant leakage path between live conductors or to earth. A high resistance value indicates the insulation is intact; a low value signals potential faults that must be addressed before energizing the installation. This step is performed immediately after the visual check because it screens for insulation problems that could pose shock hazards or cause damage once the system is powered. Tests that involve live current, like earth fault loop impedance checks, RCD tests, and functional testing, are saved for after insulation has been confirmed as acceptable.