What is the typical sequence of testing when commissioning a new electrical installation?

• A. RCD testing, visual inspection, continuity and polarity tests, insulation resistance, earth fault loop impedance tests, and functional tests.
• B. Visual inspection, insulation resistance, continuity and polarity tests, earth fault loop impedance tests, RCD testing, and functional tests.
• C. Functional tests, visual inspection, insulation resistance, continuity and polarity tests, earth fault loop impedance tests, and RCD testing.
• D. Visual inspection, continuity and polarity tests, insulation resistance, RCD testing, earth fault loop impedance tests, and functional tests.

Answer: (B)

The main idea here is to build safety and reliability into the testing process by starting with the most fundamental checks and moving toward more specific protective-device tests. Visual inspection comes first to catch obvious defects or noncompliances before any energised testing. Once the system looks sound, insulation resistance testing checks that there are no insulation faults that could cause leakage or shock. After confirming insulation integrity, you verify wiring accuracy with continuity and polarity checks to ensure conductors are connected correctly and the earth path is continuous.

Next, earth fault loop impedance tests are done to confirm that, in the event of a fault, the protective device will trip quickly enough to protect people. With the loop impedance verified, RCD testing is performed to ensure residual current devices will trip properly when they should. Finally, functional tests check that all circuits and protections operate as intended under normal and fault conditions.

This sequence minimizes risk, ensures safety at each step, and provides a logical progression from basic integrity to final functional performance. Other sequences either skip or reorder these checks in ways that could mask faults or safety issues, such as testing protective devices before confirming the loop impedance or insulation integrity, or performing functional tests before basic electrical integrity is verified.