What is the procedure to test a ring final circuit for continuity and impedance during commissioning?

• A. Test continuous loop resistance by measuring between two end termination points; verify that both ring paths are intact and have same resistance within tolerance
• B. Measure insulation resistance between line and neutral only
• C. Check voltage drop under full load and ensure under 5%
• D. Use a megger between protective earth and neutral to confirm bonding

Answer: (A)

Testing a ring final circuit for continuity and impedance means confirming that both conductor paths around the ring are complete and present the expected, low loop impedance. You do this by performing a continuous loop resistance test: measure the resistance between the two end termination points for the live conductor, and do the same for the neutral conductor. If both readings are low and about the same, it shows both ring paths are intact and the overall loop impedance is within the required tolerance, so the protective device will operate correctly in fault conditions. If a path is broken or one path has significantly higher resistance, the loop resistance will be out of tolerance, indicating the ring is not properly continuous.

The other checks address different aspects. Insulation resistance between line and neutral tests isolation, not the continuity of the conductors around the ring. Voltage drop under full load assesses performance under load, not the physical continuity of the ring wires. A megger between protective earth and neutral checks bonding/insulation, not the ring’s loop continuity.