MultiPlus-II 2x120 - Load Shedding Via AC Out 2 and Contactor

Been mulling this over for my narrowboat refit and wondered if anyone here has gone down this route with a similar setup.

I'm looking at running a pair of Victron MultiPlus-II units and want to use AC Out 2 with a contactor for non-critical load shedding — things like the water heater and a secondary ring — so they drop off automatically when the inverter is working hard or shore power disappears.

A few questions I can't quite pin down:

• Has anyone actually wired a contactor into AC Out 2 on a MultiPlus-II in a UK 230V single-phase setup? I know AC Out 2 is relay-switched internally, but I want to confirm whether an external contactor adds any meaningful protection or if it's redundant.
• In VEConfigure, is the AC Out 2 behaviour tied purely to the presence of shore/grid input, or can you also trigger it via an assistant based on SOC or load thresholds?
• For a boat context, is there anything specific to BS EN ISO 13297 I should be aware of when using AC Out 2 as a shed circuit?

My shore power situation is a standard 16A blue CEE hookup on the marina, so nothing like the 50A American setups you see discussed elsewhere — but the principle of protecting the inverter from overload by shedding lower-priority loads feels just as relevant here.

Anyone running something similar on a boat or tiny house install? Curious whether the ESS assistant or the Generator Start/Stop assistant ends up being the better tool for managing this.

@KellyRobinson the contactor route is exactly what I did at the cabin when I wanted to protect the battery bank from the EV charger draining it overnight.

The key thing nobody tells you upfront — AC Out 2 drops the moment you go inverting, so if your narrowboat has any load you absolutely cannot interrupt mid-cycle (bilge pump, navigation lights), keep those firmly on AC Out 1.

I used a Victron Carlo Gavazzi meter on AC Out 2 with an ESS assistant running the logic. Set my SOC threshold at 40%, contactor opens, non-essential loads shed cleanly.

One gotcha: the contactor coil itself draws a tiny continuous current. Worth accounting for in your overall load calculations — sounds trivial until it isn't at 2am in January.

What battery chemistry are you running? That'll change where you want your shed threshold sitting.

@KellyRobinson AC Out 2 is the classic "non-essential loads" output — drops out automatically when you're on inverter only, which is exactly what you want for load shedding without faff.

Worth noting though, if you're running two MultiPlus-IIs you'll need to think carefully about whether they're in split-phase or parallel config, because that affects how AC Out 2 behaves across both units. Not identical to single-unit behaviour.

Also — the contactor @FormerCop77 mentioned — make sure it's rated for AC and not just DC. Sounds obvious but I've seen people get this wrong.

I'd have a poke through the VEConfigure assistant settings before committing to the wiring. The "AC Input current limiter" and the generator assist stuff can interact with AC Out 2 in slightly unexpected ways if you're not watching for it.

@KellyRobinson curious what you're using to trigger the contactor — are you pulling that signal from the Cerbo GX via a relay assistant, or going full DIY with something external?

I'm planning something similar for my static caravan setup and the bit that's making my head hurt is the priority logic when you've got solar, shore power and a generator all potentially fighting over who's in charge.

Has anyone written a decent Node-RED flow for this, or are we all just trusting Venus OS to behave itself like sensible adults? 🤔

Also — with two MultiPlus-II units in parallel, does the AC Out 2 contactor signal come from both units independently or does the master handle it? Feels like the sort of thing that ends in smoke if you get it wrong.

@KellyRobinson so hang on, you're running two MultiPlus-IIs on a narrowboat? Jealous doesn't cover it — my tiny house setup is crying in single-phase.

Genuine question though — are you planning to use VE.Bus System Configurator to parallel them or split-phase? Because the load shedding