Inverter generator on Multiplus AC IN

Right, so this has been rattling around in my head since I wired up the shepherd's hut last autumn, and I genuinely lost sleep over it.

I'm running a Victron Multiplus-II 48/5000 with an earth rod out in the field, and I occasionally plug in a little Honda EU22i inverter generator on AC-IN as a backup charger when the panels sulk for a week (which, this being Britain, is roughly every fortnight).

Now — and here's where I go full pedant — the Honda's output is a floating/symmetrical arrangement. No N-PE bond at the generator end. The Multiplus, when it detects generator input, transfers that floating neutral situation onto your system, and suddenly you're in interesting territory with your earth rod setup.

The question I kept circling was: should the generator itself provide the N-PE bond, or does the Multiplus handle it internally?

Short answer from my reading: the Multiplus-II does not create an internal N-PE bond on AC-IN. It expects the source to behave like a proper supply. With a floating generator output and a local earth rod, you arguably need that bond at the generator, otherwise your earth fault protection becomes a bit theoretical.

I ended up fitting a switched neutral-earth link at my AC-IN panel, only active when the genny's running. Crude but functional. My RCDs now actually trip when I want them to.

Has anyone else navigated this with a different approach? Particularly curious whether anyone's used the Victron AC-IN current limit settings to manage smaller gennies without all this palaver.

@JubileeClipHero the earth rod situation trips people up constantly with inverter gens on Multiplus AC-IN.

Key thing: the Multiplus has a built-in transfer switch and an internal neutral-earth relay. When shore/gen power is present, it breaks the inverter's neutral-earth bond and passes through whatever earthing the source provides.

Problem with most inverter generators (Honda EU series, Yamaha EF, etc.) — they're floating neutral from factory. So with no earth reference at AC-IN, your RCDs can behave erratically or not trip at all.

Solutions:

• Bond neutral-to-earth at the generator frame using a shorting plug
• Or enable Victron's internal ground relay via VEConfigure (ground relay setting) — this forces the bond regardless of source
• Your earth rod then provides the actual earth path

For narrowboats specifically, BSS requires RCD protection, so getting this right matters. I'd verify with a socket tester after any changes.

What got me was the PowerControl setting — spent an embarrassing afternoon convinced my Honda EU22i was being strangled by the Multiplus until I realised I'd left the input current limit at 16A in VEConfigure when the little Honda tops out around 8A in practice.

Knocked it down to 7A, set PowerAssist to kick in when the generator starts groaning, and suddenly everything played nicely together. The Multiplus just breathes when it's not fighting an overloaded generator.

Worth remembering inverter generators like the EU22i produce genuinely clean sine wave, so the Multiplus accepts them beautifully — it's the cheap open-frame types that cause grief on AC-IN.

@ExSquaddie49 is absolutely right about the earthing side, just wanted to add that input current limit is often the overlooked culprit before people start chasing phantom wiring gremlins.

@MarineVicky my Yamaha EF2200iS had me convinced it was haunted before I realised the input current limit was set lower than my kettle's ambitions.

@JubileeClipHero the earth rod issue is the one that catches nearly everyone — but the bit that took me longest to resolve on my cabin setup was transfer switch timing.

The Multiplus has a configurable AC input transfer delay, and inverter generators with soft-start throttle-up sequences can take 2–3 seconds to stabilise frequency and voltage. If your transfer delay is too short, the Multiplus sees a wobbly incoming supply and rejects it repeatedly — you'll hear it clunking in and out trying to accept the generator.

In VictronConnect (or VEConfigure if you're on desktop), look at the AC Input Voltage Range and Transfer Switch Settings. Widening the acceptable frequency tolerance slightly — inverter gens can drift 49.5–50.5Hz during warm-up — made my Honda EU30is connect cleanly first time, every time.

Don't widen voltage tolerance too far obviously, but frequency tolerance is generally safe to relax marginally.