Adhering to safety regulations and fireman's switch

Been scratching my head over this one for a while now and figured someone here would know the answer.

I've got a static caravan on a rural plot — fully off-grid with a Victron Multiplus II at the heart of it. Planning to tidy up the AC wiring properly and I want to make sure I'm doing things by the book, particularly around the fireman's switch requirements.

My setup is essentially an ESS-style arrangement (even though it's off-grid, I've got the inverter/charger feeding a small consumer unit). My question is around where the fireman's switch needs to sit and whether the regs treat an inverter output the same way as a grid supply for these purposes.

Specifically:

• Does the inverter output side count as a "source of supply" that needs its own isolation point accessible to the fire service?
• If I've got both a solar input and the Multiplus output feeding into my CU, do I need separate isolation for each, or does one main switch cover it?
• Is there a specific part of BS 7671 I should be referencing here?

I'm in a caravan so it's not a domestic dwelling in the traditional sense, but I'm trying to treat it as seriously as one from a safety standpoint. Doesn't seem right to cut corners just because it's a static.

Anyone dealt with this during an EICR or had a sparky flag it up? Would love to know what approach people have actually taken in practice rather than just what looks good on paper.

Hey @BigAl, great question and one that catches a lot of people out with off-grid setups!

For a static caravan with a Multiplus II, you'll want a proper AC isolator (fireman's switch) on the output side, ideally mounted externally and clearly labelled. Even though you're off-grid, Building Regs Part P and BS 7671 still apply to fixed electrical installations, and emergency services need a safe way to isolate power quickly.

Victron actually recommends fitting an AC disconnect on both input and output sides anyway. Worth checking whether your DNO has any specific requirements too, even without a grid connection some councils get funny about static caravans.

Have you had a conversation with a Part P registered electrician yet? Given it's a static caravan rather than a permanent dwelling the rules can sit in a slightly grey area, so getting it properly signed off is definitely worthwhile. 👍

Good point from @JackieEdwards75 but worth digging into the specifics for your Multiplus II setup.

The fireman's switch requirement under BS 7671 applies to high-voltage discharge lighting circuits primarily, but building control inspectors increasingly flag any prominent off-grid inverter installation — static caravans included — and want a clear means of isolation visible from outside.

Practically speaking: a clearly labelled, red-handle rotary isolator mounted externally, rated for your DC bus voltage (so not just an AC-side switch), is what most people end up fitting after a site inspection catches them out.

I've got something similar on my narrowboat — Victron MPPT feeding a Fogstar lithium bank — and I mounted a 200A Victron Battery Protect alongside a dedicated emergency DC isolator near the companionway. Saved a headache later.

Check your local building control interpretation specifically; it varies considerably between councils.

What @PanelEwan said about specifics is spot on — I'd add one thing from bitter experience fitting out my shepherd's hut build.

The fireman's switch (or emergency switching device as BS 7671 prefers) for off-grid inverter systems is a grey area because the regs were written assuming grid-tied. Your DNO isn't involved, but Part P compliance and building regs still apply to habitable static structures.

Key practical point: your Multiplus II's remote on/off terminals are not a substitute. You need a physical, labelled, clearly accessible switch that isolates the AC output and trips the inverter simultaneously — ideally on a dedicated consumer unit.

Check Amendment 2 of BS 7671:2018 specifically. Some building control officers are applying it, others aren't — complete lottery depending on your local authority.

Got a similar headache with my garden office setup last year. Quick question for the thread — does the fireman's switch requirement actually apply differently depending on whether the inverter output is treated as a separate circuit or classed as the main supply point?

My Fogstar-fed Victron setup had an electrician tell me one thing, then a building control officer say something completely different. Nobody could agree on whether the BS 7671 regs for emergency switching applied to my inverter the same way they would a DNO connection.

@ExFirefighter11 — given your background, what's the actual practical concern driving the requirement? Is it isolating incoming supply, or specifically stopping backfeed? Because in a fully off-grid static caravan there's no grid to backfeed to, which makes me wonder if the whole thing is being applied incorrectly.