What would be a suitable 800A rated fuse switch for the new 20kW Multiplus?

Interesting timing on this thread — I've been poking around the same rabbit hole since the 20kW Multiplus specs dropped.

At that current rating you're essentially in industrial switchgear territory rather than anything you'd normally find in the marine or motorhome catalogues. The Victron recommended ANL/MIDI fuse holders tap out well before 800A, so you're looking at busbar-mounted Class T fuses or proper DC breakers from the industrial side of things.

A few options worth investigating:

• Ferraz Shawmut / Mersen Class T fuses — widely used in EV and industrial DC applications, can handle the current, but you'll need a proper fuse holder to match
• ABB or Eaton DC isolators rated for high-current battery circuits — not cheap, but they're actually specced correctly
• Mega fuse blocks scaled up — some manufacturers do 500A+ versions but I've not personally verified anything at 800A

The combined fuse-switch in one unit at this rating is genuinely difficult to source in the UK without going bespoke or waiting on import lead times. Would be interested to know if anyone's actually commissioned one of these units yet and what their DNO/installer used.

My setup is only 5kW so I'm not in this bracket, but if I were scaling up I'd probably start with Bimble Solar or speak directly to a Victron distributor like Merlin Equipment — they tend to know what's actually available rather than what's just listed online.

Anyone gone down this route already?

@BrianBrown — you're not wrong about the industrial territory. Worth looking at the Eaton Bussmann NH/HRC fuse range — specifically the 800A NH3 series. Properly rated for DC bus applications if you spec the right voltage class, and you can get suitable switch-disconnectors to match from the likes of Socomec or Mersen (formerly Ferraz Shawmut).

The trap people fall into is grabbing an AC-rated fuse and assuming it'll handle DC — arc interruption characteristics are completely different and you'll have a very bad day.

I've been running a Socomec Fuserbloc on my much more modest setup and the build quality is solid. For 800A though you're looking at proper DIN-rail cabinet work, not a consumer enclosure. Budget accordingly — these bits aren't cheap but skimping at this current level is genuinely dangerous.

@WheresMeWires the Bussmann NH route is solid, but don't overlook Socomec's FUSE-SWITCH range — their INS-type disconnectors are specifically rated for DC battery applications up to 1000V, which matters enormously at these current levels where AC-rated switchgear can arc catastrophically on DC.

For 800A you're looking at the Socomec INS 1000 or similar. Yes, it's proper industrial kit and the price reflects that, but frankly at 20kW you're not in "pop down to CEF" territory anymore.

One critical point nobody's mentioned: verify the fuse's I²t clearing characteristics match what Victron actually specifies in their installation manual — a fuse that's technically 800A rated but clears too slowly under fault conditions is asking for a very exciting day in your battery shed.

Been down this rabbit hole for my shepherd's hut build (much smaller scale obvs) but the principle's the same — at 800A you really want something with a proper DC voltage rating, not just repurposed AC switchgear.

Worth checking out Victron's Lynx Distributor as a starting point for the busbar side, but for the actual fuse-switch at that current you're likely looking at Mersen (Ferraz Shawmut) — their GPV range is rated for high DC applications and used in industrial solar installs.

@TracyAllen the Socomec route is interesting — do you know if the INS range has adequate DC interrupt capacity at 48V or higher voltages? That's often where things get murky with switchgear that looks right on paper.

Great points from everyone here. One thing I'd add — at 800A you'll want to think carefully about your busbar arrangement and cable sizing leading up to the fuse switch itself. The fuse is only part of the story; the terminations and conductor cross-section need to handle fault current too, otherwise you're creating a weak point downstream of your protection device.

Also worth contacting Victron's UK distributors directly (Bimble, Merlin, etc.) — given the 20kW Multiplus is relatively new, they may already have recommended installation schematics that specify approved disconnection equipment. Saves reinventing the wheel.

@Gill1983 — good point about principles scaling up. The fundamentals don't change, just the consequences of getting it wrong become rather more dramatic! 😅