A customer in the UK with a Grid-Tied ESS installation is reporting intermittent tripping of the RCD located at the main consumer unit and a sub-board, between the grid and the Multiplus-II AC Input. The property uses a PME Earth connection at the transformer in the street. The AC Output is in use for two LED lighting circuits (probably SELV). I believe the RCD is a standard AC type 30mA.
This system had been operating correctly for years with a 5kVA Multiplus (not -II) which was replaced recently with the Multi-II 5kVA. The nuisance tripping is intermittent; sometimes every day, sometimes every few days. The customer has not noticed any pattern as of yet, other than it often occurs when the Multi is switched on (and goes into Inverter mode presumably). The Multi is on Firmware 467.
UK Country Code (G98/99) is setup, and this prevents toggling the Ground Relay (I think it is default off with this code?).
I've browsed Wiring Unlimited and other questions here to ascertain the reason but still coming up short. I realise cumulative leakage may be a likely cause, but the only circuits appear to be LED lighting on the AC Output. Earth Loop Impedance tests have been carried out by an electrician on site on the AC Output (UPS circuits) while in Pass-through Mode, and the results were fine.
The Multiplus was moved to a different sub-board (with its own RCD using an isolated Ground Rod) to try and prevent this, yet the system still tripped that RCD, which would seem to narrow down the issue to the Multi or the UPS circuits.
We are attempting to isolate the UPS circuits (and bypass the Multi and sub-board) as well as leaving the unit switched off for a few days, to see if the nuisance tripping continues. After that we'll try swapping the Multi.
Seems like quite a common question! I was wondering if anyone has any further thoughts on investigating this? Thanks
