Planning a new installation

Been through this exact planning phase myself before fitting my MultiPlus-II 48/5000/70 in the motorhome, and the wiring diagram stage is where most people make costly mistakes before a single cable is run.

The bit that catches people out with the 48/3000/35 specifically is the AC input current limit — that 35A figure is the charger rating, not the inverter output ceiling. If you're planning to use shore power or a generator as your AC-in source alongside solar buffering, you need to think carefully about how VE.Bus is going to arbitrate between them under varying load.

A few things worth pinning down before you commit to your cable runs:

• Battery cable lengths — keep them equal and as short as physically possible. Voltage drop at 48V hurts less than at 12V, but it still matters under high inverter load
• Are you running ESS or just Inverter/Charger mode? ESS with a grid meter changes everything about how the system responds
• CT clamp placement — if you're measuring grid input for self-consumption optimisation, where that clamp sits relative to your main incomer matters enormously
• Fogstar or similar LiFePO4? Make sure your BMS DVCC settings are properly configured in VEConfigure before you energise anything

The Victron documentation is genuinely excellent but it assumes a lot of background knowledge. The Victron Community is worth cross-referencing alongside here.

What's your battery bank setup and are you planning full ESS or standalone? That'll change the advice significantly.

MarshSoul | Posts: 847

@OffGridDoug absolutely right about the diagram stage being critical. One thing I'd add that catches people out specifically with the MultiPlus-II is planning your AC input/output routing before you touch the DC side. Getting your shore power, generator, and inverter outputs clearly mapped first saves an enormous amount of head-scratching later.

Also worth downloading Victron's VEConfigure tool early and having a play through the settings virtually — you'll spot potential conflicts in your setup before anything's physically connected. The transfer switch behaviour in particular can surprise people if they haven't thought through their load priorities beforehand.

What's your intended battery chemistry, Doug? That'll affect your charge profile settings considerably and is worth baking into the diagram at this stage rather than retrofitting later.

CaddyBuild | Posts: 1,203

@OffGridDoug and @MarshSoul both make solid points. One thing I'd flag that often gets overlooked at the diagram stage is labelling your cable runs with actual voltage drop calculations, not just wire sizes. I learned this the hard way on my first 48V build — the cable looked perfectly adequate on paper until I modelled a sustained load and realised I'd lose nearly 3% over the run to my consumer unit. Victron's own guidelines are fairly conservative for good reason. Spend an extra hour with a voltage drop calculator before you commit to conduit routes, especially if your inverter is mounted any distance from the battery bank. Saves a complete rewire later.

BreezyMechanic | Posts: 412

@OffGridDoug @MarshSoul @CaddyBuild — all solid points already covered, so I'll add the bit that nearly caught me out with my shepherd's hut build.

When I drew up my diagram for the Victron MultiPlus-II, I'd mapped everything beautifully on paper but completely forgot to account for cable derating once those runs are bundled together or passing through insulation. What looks fine at the planning stage can mean your cables are quietly running hotter than rated in reality.

Grab the Victron wiring unlimited guide — it's free and genuinely brilliant for this stage. Cross-reference everything against the actual installed environment, not just the cable's standalone rating.

Cost me a re-run of 35mm² twin when I caught it early. Far worse if you don't catch it at all.

LDVNomad | Posts: 34

Really useful thread — currently mid-planning on my LDV Transit conversion so this is exactly where I'm at.

Quick question for the group: I've been using a combination of a hand-drawn schematic and a spreadsheet to track cable sizing, but I keep second-guessing myself on voltage drop calculations across longer runs. Is there a go-to tool people are actually using for this? I've seen mentions of online calculators but nothing specific to 12/24/48V DC systems.

Also — @OffGridDoug did you find the Victron wiring diagrams on their website sufficient as a starting reference, or did you end up having to deviate significantly once the real-world constraints of the vehicle layout kicked in?