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Islanding mode earthing requirements with PME supply to inverter in garage

I have the following situation, in my own house I might add:
TN-C-S single phase PME supply
50A B curve MCB in main distribution board feeds 10mm2 3C (one core used as CPC), SWA cable going to garage ~5m away from the house
In the detached garage there is a consumer unit feeding a 32A type B RCBO for an EV charger and a 32A type A rcbo for an inverter, both 30mA
EV charger has an open PEN detection relay
(I know about the selectivity issue here with the MCB but it's determined not a safety issue, short circuit unlikely. Sockets and lighting on separate 2.5mm supply)

Now the question is, if I want to enable the inverter to work in islanding mode, what earthing provisions do I need to add?
The house is detached and more than 30m away from other houses and metal street furniture
Ze from supply is 0.12 ohm, main fuse 100A
Inverter can perform N-E link and coordinate with changeover switch at incoming supply

Am I right in thinking that I should remain connected to supplies earth but add an earth rod? What impedance requirement should this earth rod have?
I think it's 200 ohm because the inverter is protected by a 30mA RCBO and in connected mode, the supply earth will be sufficient.
I also think the earth rod should be connected to the inverter directly (i.e. downsteam from the rcbo and not upstream) so that the RCD will be able to detect the leakage in islanding mode.

Thanks!

Parents
  • Realised this post was long winded but it’s missing some detail on the islanding circuit.

    The islanding / EPS output of the inverter goes to a 32A RCBO feeding socketed devices where short circuits are highly unlikely on 6mm2 cable.

    Overall, the proposed setup is:

    50A MCB -> 32A RCBO -> inverter (<200 ohm earth rod connects here) with contactor for N-E link-> 32A RCBO -> EPS/ islanding loads.

Reply
  • Realised this post was long winded but it’s missing some detail on the islanding circuit.

    The islanding / EPS output of the inverter goes to a 32A RCBO feeding socketed devices where short circuits are highly unlikely on 6mm2 cable.

    Overall, the proposed setup is:

    50A MCB -> 32A RCBO -> inverter (<200 ohm earth rod connects here) with contactor for N-E link-> 32A RCBO -> EPS/ islanding loads.

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