Anyone else using their van setup as a home backup during power cuts?

Since finishing my van build last spring I've been wondering whether to wire it up properly as an emergency backup for the house. Running a Victron MultiPlus 12/3000 in the van at the moment alongside a 200Ah Fogstar Drift LiFePO4 — more than enough to cover the basics if the grid goes down.

My thinking is a simple changeover switch at the consumer unit so I can plug the van in via a long shore power lead and have it supply a few key circuits — fridge, router, a couple of lights. Nothing fancy, no whole-house stuff. Realistically I'd only need 300–400W sustained so the battery should last a fair while overnight.

Has anyone actually done this rather than just thought about it? Mainly wondering about the safest way to handle the changeover without risking back-feed onto the street, and whether a proper interlocked switch is overkill for occasional use or just the sensible route. Also curious whether a qualified sparky needs to be involved for something like this or if it falls outside notifiable work.

@VanKev interesting timing on this thread — I've been thinking about the same thing but for a narrowboat rather than a van. The principle's similar though isn't it?

My main concern is the transfer switch side of things. If you're feeding back into the house consumer unit you need a proper changeover switch to isolate from the grid, otherwise you're backfeeding into the DNO network which is obviously a massive no.

Has anyone done this with a Victron MultiPlus specifically? I know it has the transfer relay built in but I'm not sure whether that's sufficient for a semi-permanent house backup arrangement or whether you'd still need an external changeover.

Also wondering about cable runs — how far is your van parked from the house typically? I'm thinking about what gauge cable you'd need to avoid volt drop over any decent distance.

Done exactly this with my van setup during a few outages last winter.

Biggest practical issue is transfer switching — you don't want mains and inverter fighting each other. If you're running a Victron MultiPlus already, look into their transfer switch relay or grab a proper changeover switch (Lewden do decent ones). Don't just bodge it with a standard extension lead.

For the actual connection, a decent 16A or 32A commando socket on the house wall makes it clean and repeatable. Run the van up alongside, plug in, flip the changeover, sorted.

@FinnTaylor78 same principle applies on a narrowboat but mind your cable run length — voltage drop becomes an issue fast at 12V over longer distances. Worth upsizing to 24V if you're not already.

One thing people underestimate: runtime. Know your house loads before you commit to powering much beyond the essentials.

@VanKev worth noting that running a 12V MultiPlus as whole-house backup puts serious strain on your battery bank due to the high inverter draw at 12V — you're looking at enormous cable runs and potential voltage sag under load.

If you're seriously committed to this use case long-term, a 24V or 48V rebuild pays dividends massively. My shepherd's hut runs a Victron MultiPlus-II 48/3000 precisely because I wanted genuine flexibility between site and property backup without the cabling headaches.

Also consider your DNO obligations — if you're in any way feeding back towards the grid incidentally during a cut, you need proper isolation. @RayWatson81 is right about transfer switching being the critical bit. A Victron AutoTransfer Switch or a proper manual changeover (Lewden make decent ones available UK-wide) keeps you compliant and safe.

@BatteryBarry makes a good point about the 12V strain — have you considered just stepping up to a 24V bank if you're going to do this regularly?

I've got a static caravan setup running 24V Fogstar Drift cells and the difference in cable losses versus my old 12V van build was immediately obvious.

Genuine question for the thread though — what are people actually powering during these cutouts? If it's just the fridge, a few lights and phone charging, does it even need to be wired in properly or is a decent extension lead from the van sufficient for most use cases?

I ask because I keep overthinking a "proper" solution when realistically a UK power cut lasts what, 2-4 hours at most half the time?

@BatteryBarry raises a valid point about the 12V MultiPlus — the cable runs and connector ratings become critical at those current levels. I'd seriously consider whether upgrading to a 24V or 48V system before attempting whole-house backup is worthwhile; halves or quarters your cable losses immediately.

One thing nobody's mentioned yet: islanding protection. If your van is backfeeding the house during a grid outage, you need to ensure you're not inadvertently energising the street-side of your meter. A proper changeover switch (or a Victron transfer switch wired correctly) is non-negotiable here — it's a legal requirement, not just best practice. DNO engineers working on "dead" lines won't thank you otherwise.

I've run my motorhome Victron setup as house backup twice now. Works well for essentials, but I deliberately shed non-critical loads to protect the Fogstar lithium bank.

@VanKev this is basically what I've been pondering for my static caravan setup, so watching this thread closely 👀

Genuine question nobody's answered yet though — what's your plan for the transfer switch side of things? Presumably you'd need something to isolate grid before the van's MultiPlus starts backfeeding, otherwise you're essentially a hazard to any DNO engineer working on the street during a cut.

Also curious whether you'd park the van permanently for this role or actually want to keep using it? Because those are pretty different wiring solutions. A dedicated cable reel to the house vs a proper weatherproof hookup point changes the whole conversation.

I'm half-tempted to do something similar myself with a Fogstar battery bank but the "bodge it temporarily" vs "do it properly with an MCS-compliant install" decision is giving me analysis paralysis.

Great thread @VanKev! One practical thing worth thinking about is how you connect the van to the house — you really want a proper transfer switch or interlock setup rather than anything dodgy at the consumer unit. Even temporarily backfeeding through an extension lead feels fine until it isn't. Also worth checking your DNO agreement, as technically feeding the house grid-side during an outage can cause issues if a linesman is working nearby. Assuming you're just running critical loads on a sub-circuit, that's much cleaner anyway. What sort of loads are you thinking of covering?

@VanKev I actually went the other direction — built my boat system specifically to double as house backup, which shaped every decision from day one.

Biggest lesson: don't underestimate your load audit. First power cut I tried running the fridge, a lamp, and phone chargers simultaneously and discovered my inverter was sweating far more than expected.

Worth mapping out your actual critical circuits before committing to any connection method. My boat runs Fogstar Drift lithium now and the peace of mind during last winter's outages was genuinely worth every penny of the build cost.

@VanKev worth knowing that the Victron MultiPlus 12/3000 will struggle to sustain meaningful house loads for long — you're limited by the 12V battery bank capacity more than the inverter rating. Even a modest 200Ah LiFePO4 pack (Fogstar Drift cells are popular for van builds) only gives you ~2.4kWh usable. That covers lighting and phone charging comfortably, but run a kettle or electric shower and you'll drain it within the hour.

If you're seriously considering house backup, I'd evaluate whether upgrading to a 24V or 48V architecture makes more sense long-term — the cable sizing alone becomes far more manageable.

@VanKev I've been doing exactly this since last winter and it's been brilliant during the few cuts we've had. One thing nobody's mentioned yet — think carefully about which circuits you want to back up. I ran a short extension lead to a small consumer unit feeding just the fridge, a few lights, and phone charging rather than attempting the whole house. Keeps the draw sensible and your battery lasts far longer. Much simpler than any permanent wiring solution too, and the van stays fully mobile. Works a treat for us anyway!

@VanKev I do something similar — my van lives on the drive most of the time so it made sense to have a proper transfer switch sorted. The bit nobody mentions is the cable run from van to house; worth thinking about voltage drop over that distance, especially if you're trying to push any decent loads through it. I've got a decent length of 16mm² run to my consumer unit and it makes a real difference. Also handy to keep the van plugged into shore power via an extension when it's on backup duty, so you're not just draining your batteries.