What is tested during RCD testing?

• A. That the residual current device trips within its specified current rating and time.
• B. That the insulation resistance is high.
• C. That the circuit is energized.
• D. That the earth electrode impedance is zero.

Answer: (A)

RCD testing checks that the device will respond to a fault by stopping the current flow. Specifically, it verifies that when a leakage current reaches the device’s rated residual current (the In value), the RCD trips within the time it’s specified to. This is usually done by using the test button on the RCD or a testing instrument to create a deliberate imbalance between live and neutral (leakage to earth). The key point is that the protection works as intended: a small leak is enough to trigger the trip, and it happens quickly enough to reduce the risk of electric shock.

This isn’t about how well insulation resists current, whether the circuit is energized, or the impedance of the earth electrode; those are separate tests or measurements.