RCD problem that wasn't

I've noticed several threads recently where turning on VFD units has tripped the supply RCD. I too have had similar problems since first installing a VFD some years ago, recently this has seemed to become more of a problem.

I've just realised that since I replaced on old floodlamp fitting on the outside of the garage a few weeks ago, the problem has vanished. Now even my largest VFD doesn't trip the RCD when turned on.

I don't know if the issue was that the floodlamp was an open face type, or that the weather had got into the PIR motion detector housing.

Anyway - the learning (as I recall some have commented in other threads) is don't rush to blame either the VFD or the RCD, carefully check anything else fed from the same supply before buying a replacement RCD with different characteristic. In my case simply isolating the exterior lights at the MCB would likely have pointed to the cause a long time ago.

My brother had a similar problem when he had solar panels fitted. Occasionally the main RCD tripped, in the end it turned out to be a spider's nest in a light fitting in an outbuilding. Once you have something a bit leaky, it biases the RCD so a bit extra, such as from an inverter filter, can trip it.

Not neccessarily as the MCB in most cases is single pole and would only isolate the live, leaving the possibility of a neutral to earth leakage path which the RCD considers exactly the same as a live to earth leakage.