By Appendix B of the Victron manual for this Multi, both AC-In and AC-Out both have a PE connection; AC-In to the source and AC-Out to the panel board and its PE bus. They both are connected to the case. Note also that Appendix B shows a case ground and the case ground has not been discussed by the OP.
The governing document for electrical systems on boats in the EU is ISO 13297 the source for this excerpt:
11.5 A separate DC equipotential conductor shall be connected from the metallic case or chassis of the inverter or inverter/charger to the main grounding/earthing point or its bus, and be of an amperage rating equal to the DC positive conductor. This conductor shall not be connected to the DC negative at the inverter or inverter/charger.
Regarding the nuisance tripping of the shore RCD:
As was discussed; there is a life safety requirement to bond neutral (N) and ground (PE) at all electrical sources that provide AC to a vessel. These sources include:
- Shore power: N/PE bond is at the shore side transformer providing power to the shore pedestal.
- Onboard generator
- Secondary of an isolation transformer
- Output of an inverter
- Output of an inverter/charger when inverting
From Mike D Dec 29: This is due to the protective sequencing of connecting the input L&N and then disconnecting the NE bridge on AC out. This leaves input N&E connected for a brief time - well sufficient to trip an RCD.
Victron inverter/chargers have two relays in the AC-In electrical path: an input relay and the N/PE relay. When shifting modes from pass through to inverting or from inverting to pass through, the two relays are controlled so that the required action of the N/PE relay has completed before the input relay is closed. This ensures that the shore side RCD will never sense an improper N/PE bond aboard.
From MikeD Dec 29: Those Galvanic isolator blocks are just big non polarised capacitors. Whilst the will stop DC, they wont, and aren’t designed to stop AC. So an AC leakage current can still flow through the hull to shoreside.
A galvanic isolator is designed to block galvanic current, hence the name, while still providing a path back to the shore power source for AC fault current. The galvanic current blocking is accomplished by two diodes in series pointing towards the vessel and two diodes in series pointing away from the vessel. Since diodes can be biased into conducting by low level AC, a capacitor is placed in parallel with the two pairs of diodes to provide a path for AC and to prevent the diodes from conducting.
Since a galvanic isolator is in the PE circuit, it is a life safety piece of equipment as the PE circuit must remain intact. Since diodes can fail in either shorted (loss of galvanic isolation) or open (loss of a path for fault current), galvanic isolators.
From ISO 13297: 6.9 When a galvanic isolator is fitted in the protective conductor, failure of the isolator shall not result in an open circuit.
In the USA, this requirement formerly met by either electronically monitoring the condition of the PE circuit or by use of “Fail Safe” galvanic isolator. With the advent of the requirement for RCD’s on shore power pedestals, the monitoring system has all but disappeared because this system momentarily connected PE > N and the RCD would trip so we must install Fail Safe GI’s.
If I was faced with this problem, I would:
- Install the PE connections as shown in the techdocs.
- Install a properly sized DC case ground for each Multi back to the main B- bus.
- Ensure that there are separate N busses; one for the non-inverter supplied loads and the other for the inverter supplied loads.
- Ensure by hand over hand or by ringing out that circuit discipline was maintained when the N from the two sets of loads were landed on a N bus. It will only take one conductor from an inverter supplied load landed on the N bus for the non-inverter supplied load to cause this issue.
