My apartment is supplied with 2 sources of electricity: the grid and a generator in the apartments premises. The change over is controlled by an ACCL. The apartment has an 25A ELCB/RCCB with 100mA sensitivity. The power to individual rooms is further protected by an MCB for each room.

When the generator is switched off, the RCD in the apartment trips. This does not happen when the grid fails, but happens every single time when the generator is switched off. The generator supplies electricity to some 200 other houses, and the RCD tripping issue occurs only at my apartment.

Tests I have done so far:

  1. Switched off the MCB for individual rooms one at time. I was trying to isolate if any specific MCB/room has a fault. The RCD failed every time.
  2. Switched off all unnecessary devices when running on generator. Every single device was turned off excluding my internet modem and wifi router. The RCD failed this time too.
  3. Used a multi-meter to check the voltage difference between neutral and earth. It is 0V when running on grid. It was 9V when running on generator. But when I tried to reproduce this for the apartment's maintenance manager, it turned out to be 0V.
  4. Replaced the ACCL and the RCD with new devices of same specification as earlier. The issue persists.

The maintenance manager recommends changing the RCD to a 300mA sensitivity. But I am not convinced without proving the source of the issue. What can cause such tripping? Are there any other tests I can conduct with simple instruments at home (multi-meter)?

  • \$\begingroup\$ Faulty RCD is my diagnosis. \$\endgroup\$
    – Andy aka
    Nov 22, 2020 at 12:02
  • \$\begingroup\$ @Andyaka I have replaced the RCD with a new one that has 100mA sensitivity. The issue persists. I have now updated the same in the description for my question above. \$\endgroup\$
    – Nikhil
    Nov 22, 2020 at 16:36
  • \$\begingroup\$ Well at least you have a spare that you can probably sell on to a neighbor \$\endgroup\$
    – Andy aka
    Nov 22, 2020 at 16:40
  • \$\begingroup\$ I have successfully mitigated this RCD nuisance tripping issue. Sharing some notes from the investigation, hopeful that it will help anyone else facing similar issues: nikhilapatil.medium.com/rcd-nuisance-tripping-5ca7432370e5 \$\endgroup\$
    – Nikhil
    Dec 21, 2020 at 4:25
  • \$\begingroup\$ Nikhil, if you found the problem (L3 Neutral ), why not leave your own answer below? \$\endgroup\$
    – Andy aka
    Dec 21, 2020 at 9:34

1 Answer 1


Short answer: I discovered that the neutral connection for one of the rooms had some fluctuating connectivity with earth. I have since disconnected the neutral from the neutral busbar and turned off the MCB for that room. This mitigated the RCCB tripping problem.

Long answer: https://nikhilapatil.medium.com/rcd-nuisance-tripping-5ca7432370e5


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