Clarifying breaker & wire size needed for AC-out on Multiplus UU 48/5000 120V

Been wrestling with a similar sizing question on my static caravan setup, so thought I'd start a thread as I can't find a definitive answer anywhere.

Running a Multiplus-II 48/5000 here in the UK (230V obviously, not the 120V version), and trying to nail down the correct cable and breaker sizing on the AC output side. Victron's documentation gives you a figure, but I've seen people on various forums go heavier "just to be safe" — which makes me wonder if there's something the docs aren't fully accounting for.

My caravan's potential loads aren't huge day-to-day, but I want headroom. The 5000 was a deliberate step up from the 3000 for exactly that reason — the 3000 felt like it'd be running close to its limits too often.

A few things I'm trying to clarify:

• Does the AC-out cable sizing need to account for full inverter rated output, or is it acceptable to size based on realistic peak loads?
• What breaker rating are people actually running between inverter AC-out and their consumer unit?
• Anyone using Fogstar or sourcing cable locally rather than paying Victron dealer prices?

I've got 10mm² copper on the AC side currently but wondering if that's adequate or if I should be looking at 16mm². Distances are fairly short — inverter to CU is maybe 1.5 metres.

Would be good to hear from anyone who's gone through this properly rather than just guessing. Static caravan installs seem underrepresented on here compared to narrowboats and vans.

@IanPearce56 UK 230V system so your AC-out is single phase — the 5000VA rating gives you roughly 21.7A continuous at 230V. Victron recommend a 32A breaker on the AC-out to handle brief surge currents without nuisance tripping.

For cable, I'd go 6mm² minimum for any reasonable run length. On my own Multiplus-II 48/3000 setup I used 6mm² throughout and it's been spot on. If your runs are longer than about 5-6 metres, worth bumping to 10mm² to keep voltage drop sensible.

Double-check your static caravan's consumer unit is rated for inverter use too — some older ones don't play nicely with the modified sine... actually Victron's pure sine so that's fine, ignore that!

@RetiredEngineer86 has the maths sorted, but here's what caught me out when I wired my shepherd's hut setup — the cable run length matters enormously for voltage drop.

My inverter is about 8 metres from the consumer unit and I initially thought 6mm² would be fine on paper, but after running the actual numbers I bumped up to 10mm² just to be safe. Glad I did, especially now I'm occasionally pulling decent loads.

Also worth flagging — your breaker needs to be rated for the cable, not the inverter output. Victron's own documentation recommends protecting the AC-out with a breaker sized to your cable rating. Don't just slap a 25A breaker on and assume you're covered because the 5000VA suggests ~21.7A.

What's your cable run distance, @IanPearce56?

Really useful thread this — exactly what I needed for my garden office build which I'm planning around a Multiplus-II 48/3000 (slightly smaller than yours @IanPearce56 but same principle applies I'd imagine).

Quick question though — does anyone know whether the AC-out breaker needs to be a specific type? I've seen mentions of needing a Type C MCB rather than Type B for inverter outputs due to the surge characteristics. Is that right, or am I overthinking it?

Also wondering about the cable run length — if you've got a longer run from the inverter to your consumer unit, does that change the wire sizing calculation significantly? My run would be around 8 metres which feels like it might push things compared to a super short install.

Good point from @VivaroNomad about the cabling catch — I'll add something that caught me out on the narrowboat install.

Victron's own documentation specifies a 32A breaker on AC-out for the 5000VA model, but the cable run length matters enormously. I initially spec'd 6mm² throughout, which was fine for short runs, but my longest circuit to the stern charging point pushed the voltage drop beyond acceptable limits under EV charging load.

Worth running your numbers through a proper volt-drop calculation — there are decent online tools, or just follow BS 7671 guidance. I ended up upsizing sections of that run to 10mm² to stay within the 3% tolerance.

Also worth noting: your breaker should be type C if you're running any inductive loads. Type B trips nuisance at startup on certain equipment.