Inverters have a resistor or a thermistor in series with the input power to slow the rise of voltage across the main smoothing capacitor(s). The resistance value is usually between 20 and 50 Ohms, and it may be before or after the bridge rectifier. This soft-start or "precharge" resistor is bypassed by relay contacts after a short time delay. Your resistor could be short-circuit, or the relay that bypasses it may be stuck on, or driven on prematurely.
It could be my usage of RCB is incorrect.
After looking around, i found that in Netherlands we use breakers, and a maximum of 4 breakers is connected to a RCB.
The breaker is tripping (but I thought a RCB was a breaker) but the RCB to which this group/breaker is connected is not tripping.
Also I measure nu continuity between the ground wire and the phase or neutral wire.
Will swap out the resistor tomorrow, but I think I've already swapped it out when i did the transformer.
The old one looked a bit iffy (but it measured out ok) and I believe I swapped it for the one from the Transtig, but it could well be I put it back in after measuring.