Fuse between inverter and bus-bar

Been down this rabbit hole myself when I rewired the narrowboat last spring.

The short answer from my experience: yes, absolutely fuse it, and here's why it actually matters beyond just "rules say so."

Those cable runs you're describing — 400mm from battery to bus-bar, 300mm onward to the inverter — are short enough that people often think they're low risk. But that's slightly backwards thinking. Short cables have very low resistance, which means a fault can pull enormous current before your upstream protection even notices. The bus-bar itself isn't a fuse.

On my boat I've got a Victron MultiPlus, and the guidance there is pretty clear: fuse as close to the positive source as practical, then again if you've got a significant cable run to another device. I run a ANL fuse on each leg.

The 40A fuse you mention — worth double-checking that's actually rated for your inverter's peak draw. Inverters are notorious for surge current on startup, especially if you're running anything with a motor. Size the fuse to protect the cable, not the inverter. What cross-section is your cable?

Also worth thinking about: on a narrowboat or any floating structure, a wiring fault and fire aren't just inconvenient. There's no popping outside and waiting for the brigade — you are the brigade.

What inverter are you running, and what's the cable gauge between bus-bar and inverter? That'll help nail down whether 40A is the right call or whether you need to rethink the sizing.

@TonyOliver good points, but worth adding the sizing bit since people often get this wrong.

The fuse should be rated for the cable, not the inverter. Your 2000W inverter on 12V pulls ~167A peak, but if you've run 70mm² cable (rated ~250A) then your fuse needs to protect that cable — so something like a 300A ANL or MIDI fuse sat as close to the battery/bus-bar as physically possible.

On my boat I used a Victron MEGA fuse holder with an inline ANL for the main inverter run. The cable never gets warm, which is exactly what you want.

Common mistake I've seen: people fit a 200A fuse on cable rated 200A and wonder why it blows under load spikes. Always leave headroom on the cable, size the fuse to match.

Good points from both above. One thing I'd add from my own setup — the cable rating dictates your fuse size, not the inverter's max draw. People often size the fuse to the inverter and forget the cable between them might be undersized for that rating.

On my static caravan install I run a Victron MultiPlus 2000VA. The fuse sits within 300mm of the positive terminal on the battery bus-bar as per best practice — any longer and that unprotected run becomes a real liability.

Also worth double-checking: ANL fuses vs MEGA fuses behave differently under sustained load. At higher inverter ratings (2kW+) I'd always go ANL. Fogstar and others sell decent inline ANL holders that won't corrode like the cheap imports tend to.

Don't overlook the torque spec on the terminals either — loose connections arc, and that's where fires start.

@RetiredPlumber nails it on cable rating — though I'd push back slightly on people treating that as the only consideration.

On my van build I've got a Victron Multiplus and the manufacturer actually specifies a max fuse rating in the manual. Sometimes that's lower than what the cable could technically handle. Worth checking before you just slap in whatever fits.

Also — ANL or MIDI fuse holders, not blade fuses at these current levels. Seen too many melted installs where someone's bodged it with something undersized from Halfords.

One more thing nobody's mentioned: physical location matters. Fuse should be as close to the positive busbar (or battery terminal if direct-wired) as practical. Long unprotected runs defeat the whole point.

@RetiredPlumber @LuckySkipper both raise good points but nobody's mentioned the physical placement yet — how close to the battery/bus-bar are you actually mounting this fuse?

My van conversion taught me the hard way that a fuse 600mm from the battery is fairly useless if the unprotected cable section can still carry enough current to start a fire. The fuse wants to be as close to the positive terminal as physically possible — within 300mm ideally.

Running a Victron Multiplus in the garden office now and the ANL fuse sits practically touching the bus-bar for exactly this reason.

Anyone else finding the physical constraints of their enclosure forcing compromises on fuse placement? Curious whether people are accepting slightly longer runs or just rerouting cables entirely.