I have installed a Victron Multiplus 2 C12/1600/70-16 230vac in a small caravan in New Zealand connected to a Victron 12.8 200Ah smart lithium battery and BMS. The multiplus 2 has the 16amp mains supply passing through the multiplus to supply power to the caravan. I have selected power assist and power control. The multiplus 2 controls the amount of power that can be drawn from the mains power and power assists if more if required it continues to provide power when the caravan is disconnected from the mains supply. The systems work well as expected.
My concern is that the multiplus 2 has only one relay to isolate the caravan from the mains supply and that the anti islanding does not meet the NZ regulations to prevent the caravan lead becoming live or power being sent into the grid in the event of the multiplus relay failing.
Does Victron have technology within these small inverters to prevent this situation to EVER occurring?
In general, unless you set up ESS, victron inverters will not inject power to the grid. The input will certainly not become live when unplugged, even when using ESS. It needs to detect a certain voltage for a certain period to allow connection.
I don’t think so, if the device is broken (relay failure or otherwise) there are always risks. This applies to any manufacturer and one or two relais.
If you do not need ESS functionality, don’t install the ESS assistant. But if you do, you will have to put a relay in front of the MP that can only switch on when an external power source is plugged in. For a 3 phase source with a 1 phase MP setup on L1, one of the other phases can be used (L2 or L3) but with a 1 phase source things get complicated: you either need a hardware switch detecting the insertion and removal of the plug (a) or an (certified, expensive) external electronic device detecting the direction of the power flow and ability to disconnect the MP (b).
And option (a) might not even suffice from an regulatory viewpoint as it will only isolate the RV power plug with the switch but would not work with an extension cable inserted.
No, I think it has 2 relays in series for this isolation. It would not be certified for ESS or parallel to mains operation without. My MP2 does a relay test for this function.
That is correct but due to the (small) delay that can occur between detecting Loss Of Mains (LOM) and disconnecting from mains, there is an unmitigated risk of having the ESS power the pins of the external (charge/shore) plug. And just for that reason it is officially not allowed/advised to rely on the MP’s internal LOM detection / anti-islanding for a mains power supply that can be disconnected, it is only certified for hardwired mains power.
Now for a 3-phase mains power installation, with only a single phase ESS installation, I would argue it to be an acceptable mitigation of that risk to use a (pre) relay activated by one of the other phases. When unplugging there is no delay in isolating the phase with the ESS on it.
For a single phase mains I’m not so sure a truly foolproof solution exists to have your cake and eat it too (as in have detachable mains and ESS).
Fails?
Assuming external L1, L2, L3 with MP on L1 and (pre) relay on L2.
A. If L1 fails MP will detect and disconnect internally.
B. If L2 fails pre relay will disconnect L1, L2 and L3, then see A.
C. If L3 fails nothing happens.
Either 3 ways, no external plug pins risk being (shortly) powered by the MP ESS
If there are actual 3-phase loads onboard, it might be wise to check for all phases to be available as well, and disable the pre relay when one or two are missing. But that is unrelated to the question whether ESS can be used in a situation with a (un)pluggable mains
I see your logic except that in some jurisdictions, a multi alone on a phase is not considered adequate. It must be a multi and a pre-relay. But I think this is for double protection.
Not sure what use case you have in mind. OP’s use case is a caravan, ours concerns electric boats with 3-phase shore power to charge the propulsion battery and a single phase MultiPlus II for AC onboard power with it’s own house battery. We are using a pre relay to make absolutely sure shore power can always be disconnected safely, even when using ESS functionality (for load balancing and charge scheduling foremost). The pre relay mitigates a small but present risk of the ESS feeding power back towards the (humanly reachable) L1 pin of the onboard shore power connector (that has the mechanical properties of a CEE plug, not a CEE receptacle). The reasoning is that I would not trust all skippers to never stick their fingers in the plug right after unplugging.