Protection & residual current
Testing the RCD
Test button and instrument test at 0.5× and 5× the rated residual current
The RCD is the most important protection against electric shock, and it must be tested both functionally (test button) and with an instrument as part of the verification. The test documents that the device trips quickly enough in the event of a fault.
Function-test with the test button
Press the test button (T) on the device — it must trip. The test button only checks the mechanism and should be tested regularly in service, but it does not replace an instrument test of tripping current and time.
Prepare the instrument testing
Connect the RCD tester to an outlet on the circuit (line, neutral and PE must be present and correctly connected). Read the device's rated residual operating current I_ΔN — typically 30 mA for personal protection — before you choose test currents.
Typical I_ΔN30 mAMeasure at 0.5× rated tripping current
Pass a fault current of 0.5 × I_ΔN through the device. It must NOT trip — otherwise it is too sensitive and will cause nuisance tripping in operation. For a 30 mA RCD this corresponds to 15 mA.
0.5× (30 mA)15 mA — must not tripMeasure at rated tripping current and 5×
Then raise the fault current to I_ΔN and on to 5 × I_ΔN, and read the disconnection time. At 5 × I_ΔN the device must trip quickly. For a 30 mA RCD, 5× corresponds to 150 mA.
5× (30 mA)150 mA — must tripCompare with the disconnection times
Check the disconnection time against the requirements in DS/HD 60364-4-41: in a TN system the fault must be disconnected within 0.4 s at 230 V, in a TT system within 0.2 s. If the time exceeds the limit, the circuit does not meet the requirement for automatic disconnection.
TN system≤ 0.4 s (230 V)TT system≤ 0.2 sTest on both half-cycles
Repeat the measurement with the test current starting at both 0° and 180° of the sine wave. The tripping time can vary between the half-cycles, and the slowest value is the one that must meet the requirement.
Reconnect and record the results
Switch the breaker back on, and record the rated residual operating current, type and the measured disconnection times (at 0.5×, 1× and 5×) in the verification report. Failure to trip is a critical fault that must be rectified immediately.
An RCD that does not trip at 5× is dangerous — replace it before the installation is put into use.
Source
Based on DS/HD 60364-6 and DS/HD 60364-4-41 (disconnection times) and the trade's article »Verification«.