Inverter wiring

Been down this rabbit hole myself when wiring up the van — the shunt placement question trips up more people than you'd think, and getting it wrong means your battery monitor reads about as accurately as a Magic 8-Ball.

Quick breakdown of how I've got mine set up (Victron SmartShunt for reference):

• Positive goes battery positive → fuse/breaker → inverter positive ✅
• Negative goes inverter negative → shunt → battery negative ✅

The shunt needs to sit between the inverter (and all other loads/chargers) and the battery negative terminal — it's essentially counting every electron in and out. If you wire your inverter negative directly to the battery and bypass the shunt, your monitor won't see that current at all and you'll think you've got loads of juice left right up until the moment everything dies on the M5.

Also — and I cannot stress this enough — fuse that positive cable as close to the battery as humanly possible. A 2000W inverter can pull north of 160A at peak on a 12V system, so an appropriately rated ANL fuse inline is non-negotiable rather than optional. Fogstar and others sell decent inline fuse holders that won't cost a fortune.

What gauge cable are you running? That's the other classic gotcha — undersized cable on a 2000W inverter is basically a DIY hand warmer.

Anyone else got tips for tidy inverter installs? My narrowboat one looks like a spider had a breakdown, so genuinely asking for inspiration here.

@DevonNomad 100% this! Made that exact mistake on my narrowboat build 😅 Shunt must be on the negative side, last thing before the battery terminal — everything else (inverter, solar, charger, loads) connects on the "load" side of the shunt. That way your Victron BMV or whatever you're running actually sees all current flowing in and out.

Miss it by even one connection and your state-of-charge reading is basically fiction. Mine was showing 80% whilst the batteries were practically on their knees!

One tip — label both sides of the shunt clearly during the build. Future-you will be grateful when you're adding kit later 🔧

@PanelKate's narrowboat lesson is one most of us learn the hard way, isn't it.

What catches people out beyond shunt placement is cable sizing between battery and inverter. I've seen builds where someone's run 16mm² cable to a 2000W inverter and wondered why it keeps tripping under load. Voltage drop kills efficiency before the protection even kicks in.

My Victron MultiPlus 2 runs on 70mm² tinned copper, kept under 500mm each side — shorter the run, the better. Fogstar cells can deliver the current; don't let undersized cable be the bottleneck.

Also worth noting: both positive and negative cables should be fused/protected as close to the battery terminals as possible, not at the inverter end. A lot of forum diagrams show it wrong.

What inverter are you running, @DevonNomad? That'll determine your actual cable spec.

Beyond shunt placement, the one that bites people most often is cable sizing between the battery and inverter. Folks will spend hours agonising over fuse ratings then run undersized cable and wonder why their Victron Multiplus is throwing low-voltage warnings under load.

Voltage drop across a poorly sized run is brutal — especially if you've tucked the battery compartment a metre or two away from the inverter, which is common in static caravan conversions like mine. Even 0.5V drop at 200A makes your battery monitor and inverter disagree completely.

Rule of thumb I follow: calculate for peak inverter draw, not continuous. Then go one cable gauge higher than that calculation suggests. The marginal cost of thicker tinned copper is nothing compared to the headache of rewiring.

Torqued terminations matter too — a loose lug connection gets warm, then hot, then exciting.

Fused within 300mm of the battery positive terminal — non-negotiable, yet half the builds I've seen on here treat it as optional, which is how you get a motorhome-shaped bonfire.

@VanGill is right on cable sizing but the sneaky one nobody mentions is cable rating vs cable length: people buy 70mm² then run 4 metres of it and wonder why their Victron Multiplus droops under load — voltage drop compounds fast and your inverter starts doing weird things before it even trips.

Also worth flagging: tinned vs plain copper if you're in a damp environment. Narrowboats and motorhomes sitting outside all winter — plain copper lugs turn into green mush inside 18 months, ask me how I know.