Phoenix Inverter 120V VE.Direct NEMA GFCI on manual transfer switch

Been looking into something similar for my garden office setup and it's got me thinking about the UK equivalent situation.

Has anyone here used a Victron Phoenix Inverter (230V obviously, given we're in the UK) with a manual transfer switch, and how did you handle the neutral-earth bonding question?

From what I understand, pure sine wave inverters like the Phoenix have a floating neutral by default — which makes sense for most standalone off-grid use. But the moment you start thinking about switching between inverter and mains supply, things get complicated quickly.

My specific concern:

• Garden office currently runs off a Fronius/Victron hybrid setup
• Occasionally I want to switch to grid when battery is low
• My manual changeover switch is a fairly basic double-pole unit

The question is whether bonding neutral to earth on the inverter output causes any issues when you also have a path back to the DNO supply's earth. In a proper Victron Multiplus setup this is handled automatically, but with a standalone Phoenix and a manual switch, you're doing it yourself.

A few things I'm unsure about:

1. Does bonding neutral-to-earth at the inverter cause a fault condition with your RCD/RCBO when you switch to grid?
2. Should the bond only exist at one point in the system at any given time?
3. Anyone used a Victron Energy Cerbo GX or similar to automate the switching cleanly?

Would be interested to hear from anyone who's gone down the manual transfer switch route rather than splashing out on a Multiplus. Feels like there's a gap in the documentation for this specific use case.

@TransitConvert Yes, done exactly this in my van build. Phoenix 12/1200 feeding a rotary transfer switch (Contactum unit, nothing fancy).

Couple of things to flag for UK installs:

• Phoenix VE.Direct models are fine but don't bother with the manual transfer switch if you're also running a Victron MPPT — just use the BMS/DVCC integration and let it handle source switching intelligently
• UK regs technically put this in BS 7671 territory if it's a garden office with a fixed installation — worth a conversation with a Part P sparky before you commit
• GFCI is American terminology; you want RCD protection here, ideally Type A or Type F depending on your loads

The Phoenix is rock solid in my experience. Three years, zero issues. The transfer switch contacts are more likely to fail than the inverter itself.

What's your battery chemistry?

@TransitConvert The Phoenix VE.Direct range talks beautifully to a Cerbo GX for automation, but for a garden office you'll want to check your DNO obligations under G98/G99 before getting clever with any grid-tie arrangement — the Phoenix is inverter-only so you're fine, but the transfer switch itself needs to prevent parallel operation, which a proper break-before-make Contactum or Hager rotary does correctly.

Worth noting: the Phoenix 230V/50Hz models are natively correct for UK sockets, so no adapter nonsense unlike the poor OP's NEMA headache. My own setup uses a Fogstar Drift LiFePO4 pack feeding a Phoenix 24/1600 and the VE.Direct comms make the whole thing genuinely smart rather than just "big torch battery."

Get the neutral switching right on that transfer switch — floating neutral from the inverter vs. earth-referenced grid supply will cause nuisance RCD trips otherwise.

Nothing screams "professional installation" quite like your garden office switching between grid and inverter while you're on a Teams call pretending the connection is fine.

Relevant to my situation — I've got a static caravan and I'm working through a very similar decision.

One thing worth flagging that nobody's mentioned yet: if you're using a Phoenix VE.Direct specifically, the VE.Direct port can only connect to one device at a time. So if you want a Cerbo GX for automation (as @OldSailor suggests) and a MPPT solar controller talking on the same bus, you'll need to plan your communications topology carefully — potentially using a VE.Bus model instead, which gives you more flexibility.

Also for the transfer switch itself, worth confirming the unit is rated for the inverter's surge current at startup, not just continuous load. What's the peak draw you're expecting? That'll determine whether a 16A or 32A changeover is appropriate.

@TransitConvert the key thing to nail down before anything else is your garden office's earthing arrangement. When you disconnect from the grid on a transfer switch, you need to decide whether your inverter is operating in a floating or earthed-neutral configuration — Victron's UK documentation covers this but it trips people up constantly.

For the Phoenix specifically, the EarthRelay function (available on some models) automatically connects neutral to earth when grid is absent. This matters enormously for your RCD/GFCI-equivalent protection downstream.

Running a similar setup in my motorhome, I've learned that getting this wrong means your RCDs either nuisance-trip constantly or — worse — fail to trip when they should.

@BlownFuse static caravan regs under BS 7671 add another layer here, worth checking Part 7 specifically.

A competent electrician familiar with both off-grid systems and the 18th Edition wiring regs is genuinely worth the money before switching anything over.