Using Multiplus-ii 5000 in 240V split-phase grid-tied ESS setup

DIY
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I want to map out a schematic for a dual inverter system for split-phase 240V using Multiplus-ii 5000/48v in a grid-tied North America setup using the existing panel with a 200 amp service and all loads connected to the existing breakers. This would be a non-solar setup (for now…) I would want to connect the inverters to the existing panel with a dual-gang breaker and then put a current clamp on for each leg of the split-phase of the Grid main’s 200A 4/0 wires that come into the panel. The Multiplus-ii would be setup in grid-tied ESS mode and configured to charge the battery and discharge the battery back to the grid to offset time-of-use billing. The goal would be never sending energy back to the grid, but nulling out the grid use to near zero during the peaks. I believe in this case you can use the current clamp port built into the Multiplus-ii and put it on the mains. What current clamp would you use for the 200A capable mains?

In the case when the home load is exceeding the capacity of the inverter, the grid would just make up the difference past the capacity of the inverter. I believe all that is needed in for this to work is to connect the Grid to the input AC port and then the output AC ports would be not used.

Anyone have any reasons why this won’t work?

What happens in this setup during a power outage? I think I’d rather figure out how to connect the whole panel to the output of the inverter rather than to guess which circuits I’d want to stub out during a grid failure. I’d rather have a manual disconnect or main panel lockout breaker based transfer switch to deal with a power outage rather than re-route a subset of (critical loads) to the output of the multiplus-iis secondary AC outputs. During a power failure, I’d like to run all the lights, the dryer, the oven, the car charger, the heat pumps, the space heaters… all off the inverter, just not all at the same time, and I’ll manage it myself with the manual transfer switch.

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The NEC has a rule called the 120% rule which will limit the size of the dual-gang breaker to 40A (if I recall correctly) to prevent the busbars in the existing panel from overloading and melting. You should research that before starting.

Victron has these CTs available for the MultiPlus-II, you would need two of the less-accurate 400A version.
Compatible current transformers:

  • CRT12XXXXXX: Current Transformer 100A:50mA for MultiPlus-II Wire-end (available in 1.5 and 20m cable length).
  • CTR140050100: Current Transformer 400A:50mA for MultiPlus-II (10m) Wire-end (the current sensor wiring can be extended up to 20m using 0.75mm² wire).
  • CRT11XXXXXXX: Current Transformer 100A:50mA for MultiPlus-II Jack connector (for older MultiPlus-II units, available in 1.5 or 20m length).

For my setup, I use a Carlo Gavazzi EM530 Energy Meter connected to 5A CTs found on amazon with a 40:1 ratio to handle up to 200A (200A:5A)

You need to ensure that your power company and AHJ will approve the Victron gear, it will likely need to be UL 1741 listed. Grid-parallel Victron installations in the US are limited by lack of grid-code support. Depending where you live, do not underestimate the administrative hurdles. There are no UL 1741-SA or -SB certificates for Victron.

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The problem with this approach is that you cannot predict when a power failure is going to occur. So if you are exceeding the power available from the inverters when the grid goes down, the inverters could instantly overload and shut down (depending on the overload).

Then you will have to manually intervene, turning off breakers you don’t want, and potentially restarting the Multiplus-iIs. Perhaps you can live with that inconvenience, especially if it rarely happens.

I ended up with two critical load sub-panels, leaving only HVAC and the kitchen range in the main panel.

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Victron just posted UL 1741 (2nd edition) certs in Jan 2025. Does that change anything? https://www.victronenergy.com/upload/documents/Certificate-UL-1741-and-CSA-C22.2-MultiPlus-II-48V-5kVA-120V.pdf

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Yes it does help, but it depends on jurisdiction.
UL 1741 is the minimum level of certification accepted by most AHJs, which is presumably why Victron is investing in that certificate.

But places like California have lists of approved equipment, and Victron isn’t on it (iirc).

It does not help with ESS, however, as 1741-SA and -SB are required for many jurisdictions.
Victron will need to support a new Grid Code called 1741-SA for that to be legal.

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Interesting system. I assume that you do not feed back into the grid when your production exceeds your system needs, correct?

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Yes, since I have no production, I’d just be banking the time of use utility power at night to ride through the peaks during the day. If the load ever exceeds my capacity, grid helps out.

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Thanks for the response and posting this. I am very interested in a dual Multiplus II 48v split phase system with panels and batteries that does not feed back into the grid. Not clear at all to me where the line is that causes concern for the public energy providers. Clearly feeding excess power back into the grid is a problem that would draw scrutiny. But what about configuring for no power feeding back into the public grid? Doesn’t UL1741 specify that the approved units have the capacity to be configured for no power feeding back within acceptable limits?

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The only way to 100% guarantee no feedback to the grid is to never install the ESS Assistant, and to never enable PowerAssist.

Both of these features would put the Multiplus in parallel with the grid, making them grid-interactive, and potentially causing power to feed back to the grid when large loads are shut off.

This approach means the system will operate in one of two modes (there is no middle ground):

(1) The system is connected to the grid, passing through power to loads on AC-Out and optionally recharging the batteries. If PV is also available, it can only be used to charge the batteries, and cannot provide power to loads. UPS mode ensures that the inverter will switch over to battery when grid power is lost.

or (2) The system is running on PV and batteries to provide power to loads connected to the AC-Outputs. Grid is disconnected using the “Ignore AC Input” flag. PV Power not consumed by the loads must be stored in the battery. Once it is full, the PV must throttle back.

Some NodeRED or scripts will be needed to automatically switch between modes based on battery State of Charge. This approach will require daily battery charging and re-charging cycles.

UL1741 merely guarantees that the inverter will disconnect from the grid when the frequency is out of spec or the grid goes down. “Within acceptable limits” means 2 seconds, I believe.

UL1741SA and SB address grid-interactive behavior that ESS Assistant would need to meet.

The public energy providers own their networks, and are legally allowed to impose restrictions on grid-interactive devices. The alternate approach I described above avoids the issue by making the Multiplus essentially a large UPS system with no grid interactive behavior.

If your energy provider were to allow you to use Victron gear with ESS, you will probably get a net metering agreement which explicitly allows grid feedback, and a utility meter that reads import and export. It can’t hurt to ask them them and find out what equipment they will allow.

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