@JohnJayMack

I think is does need to be on both inverters. Most others for AC control need to be done that way.

If you have switched as a group on which I am sure you do, if it is loaded on the master, both will stay inverting anyway. I have not tried though so can't say for sure.

Did you know there is a warm up cool down function for the generator on the regular OS already?

Thank you for your answer @Alexandra. I am not running an ESS system and do not seem to have access to the Generator Warm up and Cool down functions. I asked about using an ESS system and was told that it was not advised. I called my supplier again today and their recommendation, based on the literature, is NOT to use the ESS functionality. Much of the literature that you suggested is around 5 years or so old and there may have been updates or improvements that I am not aware of.

Let me fully describe my system so that if I have missed something, a more informed suggestion can be made.

My system is installed in a motorhome. I have two Multiplus-II 24/3000/70-50 2 x 120 connected in parallel. This gives me a theoretical assist of 4800 watts. In addition to the two inverter/chargers, I have 1500 watts of solar controlled by a Victron MPPT 150/100 solar charge controller. I am using about 850 Ah at 24-volts lithium batteries that are charged by solar, the inverter/chargers and a few other charger options, all by Victron, for special circumstances. I am using the Cerbo GX and a Touch 50 to monitor and to control my system.

When I connect to shore power or to my generator, the connection goes through a dedicated smart transfer switch. This switch incorporates surge protection, high and low voltage monitoring, and if both shore power and generator are available, prioritizes the generator. To state the obvious, this is not a grid-tie system (I had a 13,200 watt grid tie system on my home that I sold when I retired.)

I designed and installed my system myself, seeking aid and advice from my Victron Dealer. When I asked about ESS, they advised against it.

In one of the documents that you referenced, https://www.victronenergy.com/live/ve.bus:manual_parallel_and_three_phase_systems, Under Assistants;

• If you are using a self-consumption assistant, such as ESS, Hub-1 to Hub-4, the assistant will need to be loaded into each unit in the system individually. ..............

With all the other Assistants: genset start/stop, relay locker etcetera, a unique configuration can be made in each unit.

The above seems to indicate that the relay assistant and general flag could be programmed individually on each inverter. But that would also imply that the inverters would automatically coordinate the Ignore AC 1 input function.

In this manual,

ESS design and installation manual

https://www.victronenergy.com/media/pg/Energy_Storage_System/en/index-en.html there is the following section:

When not to use ESS

• Off-grid systems - either with or without generator.

• Marine systems.

• Automotive systems.

• Inverter priority, also known as 'Intentional islanding“ or 'Ignore AC' input systems.

I saw somewhere in the manuals that there could be a short time when disconnecting from shore power that there could be "AC power still on the shore power connector." I am not sure that this applies to my installation because my system uses an external transfer switch to control which source of external power - shore or generator - is connected to the AC1 input.

One of the problems that I see with many answers is that the answers focus on the Quattro. The Multiplus II was designed, I believed, for the 50 amp RV market.

Hope this background helps. I am still looking for a more specific answer.