External CT on subgroup breaker instead of main grid connection — VEConfigure interpretation?

Been mulling this one over for a while and finally decided to post because I suspect others here have hit the same wall.

My static caravan setup runs a Victron MultiPlus-II GX 48/5000 alongside a small string inverter (roughly 2kW of panels on the roof). Everything — the Multi, the PV inverter, and all the caravan loads — feeds back to a single 32A breaker on a subgroup rather than having its own dedicated connection back to the main incomer. Running a fresh cable to the meter tails simply isn't practical on a static.

The question I keep circling is around CT clamp placement in VEConfigure. The docs seem to assume you'll always clamp to the main grid feed, measuring net import/export at the boundary point. But if your entire island — inverter, PV, and loads — lives behind a subgroup breaker, does clamping the CT on that subgroup actually give the MultiPlus meaningful data to work with for ESS/DESS logic? Or does it end up chasing its own tail, effectively measuring its own output and confusing the charge/discharge decisions?

I've had a read through the Victron ESS design guide and it's not entirely clear on this edge case. Some of the Venus OS community threads hint that the grid meter needs to "see" the inverter on one side and grid on the other — which wouldn't be true here.

Has anyone in a similar fixed-pitch or static setup managed to get sensible behaviour from this configuration? Curious whether a Victron ET340 or even a Carlo Gavazzi placed on the subgroup gave usable results, or whether it just falls apart in practice.

Hey @StormyMechanic, you've cut off mid-sentence there, mate — we're all left hanging! Finish your setup description and I reckon we can get you sorted.

That said, I've done something similar on a narrowboat install where the CT placement caused all sorts of confusion in VEConfigure. The key thing Victron's documentation doesn't spell out clearly enough is that the AC input current sensor must see the full grid import/export at the actual grid connection point, not downstream of any sub-distribution. If you put it on a subgroup breaker, the MultiPlus-II is essentially blind to loads on other circuits and will make poor or even dangerous charge/assist decisions.

Finish describing your wiring arrangement and I'll give you more specific advice. A rough single-line diagram would help enormously if you can sketch one up.

@StormyMechanic yes, finish that sentence before we all collectively expire from suspense! 😄

But jumping ahead anyway — if you're clipping the CT to a subgroup breaker rather than the main grid feed, VEConfigure will interpret everything through that CT's perspective only. The MultiPlus-II has no idea what's happening upstream. Effectively you're telling it "this IS the grid connection" — which works brilliantly for load-following a specific circuit, but your ESS assistant will make decisions based on that partial picture.

Classic gotcha: if your subgroup draws 2kW but the wider site is pulling 8kW from the grid, your battery may discharge thinking it's helping when it's barely touching the actual import.

Done something vaguely similar on my narrowboat isolating the inverter from the bow thruster circuit. The MultiPlus doesn't appreciate surprises from heavy motor loads it couldn't see coming.

@StormyMechanic whilst we await the rest of that sentence — classic cliffhanger energy — the short answer on CT placement is: VEConfigure absolutely supports a subgroup breaker CT rather than the main incomer, but your assistant mode selection in the MultiPlus-II needs to reflect what you're actually measuring, otherwise it'll attempt to zero out the wrong load and your grid feed-in limit becomes meaningless. Been there with my motorhome shore power setup using a Victron external sensor — cost me an afternoon of head-scratching before I realised the shore current limiter logic was fighting itself.

@StormyMechanic mate, the suspense is genuinely worse than waiting for a Victron firmware update to not brick something — finish the sentence or I'm claiming the post as performance art.

That said, on CT placement: putting your external CT on a subgroup breaker rather than the main grid feed will confuse the MultiPlus-II's ESS assistant something rotten — it'll only see load on that circuit, not total grid import/export, and your grid setpoint logic goes completely sideways. VEConfigure expects whole-house visibility unless you've specifically architected a partial-load assistant, which nobody actually has.

On my narrowboat I run the CT on the main shore power feed and it's the only sane option. Everything else is just teaching the Victron to lie to itself.