RCD-Testers can be used to check if the residual current device (RCD) of the installation is properly working. How to they do this?

I want to build my own RCD-tester. Which circuit can be used to generate a certain fault current? (e.g. 30mA AC or 30mA DC)?

  • \$\begingroup\$ RCDs are available in different versions for different purposes and standards. Building a tester with one that goes beyond what is already built in is not trivial. The simplest tester to determine whether an RCD is even able to trip is already built into the DUSPOL voltage tester. After pressing the button on the voltage tester, an increased measuring current will flow, which will trigger the RCD. \$\endgroup\$
    – arnisz
    Commented May 22, 2021 at 23:02

1 Answer 1


They contain a current source that is able to generate a current of any waveform and polarity between neutral an earth.

Cheaper ones may contain an array of resistors, those can only test AC and rectified AC fault currents.

If you have access to both sides of the RCD, the equipment can become a bit less complicated. Since then you don't need earth.

  • \$\begingroup\$ Thanks for the answer. Do you have a circuit diagram for the current source? \$\endgroup\$ Commented May 8, 2019 at 11:47
  • \$\begingroup\$ @MichaelH An arbitrary-waveform current source? That's a much more complex thing than you seem to think, and would require much more than a circuit diagram; there's software and pretty complex PCB layouts to work out too. Designing one would be a multi-month endeavour at minimum, and possibly multiple years of work. \$\endgroup\$
    – Hearth
    Commented May 8, 2019 at 13:40
  • \$\begingroup\$ @Hearth Okay thanks for the feedback! \$\endgroup\$ Commented May 8, 2019 at 14:07
  • \$\begingroup\$ @Hearth Yes. 2 years. \$\endgroup\$
    – Jeroen3
    Commented May 9, 2019 at 5:43
  • 1
    \$\begingroup\$ it is of critical importance WHEN the RCD triggers. The time component should not be forgotten! \$\endgroup\$
    – arnisz
    Commented May 22, 2021 at 23:04

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