UK G99 Multiplus II 6k5 ENA reference

Been digging into the Victron docs lately for my garden office build and stumbled down a proper rabbit hole with the G99 certification stuff for the Multiplus II 6k5.

For anyone not familiar, G99 is the UK grid connection standard you need to comply with if you're exporting to the grid — and Victron have published their ENA reference certificate specifically for the Multiplus II range (3k through to 6k5, GX variants included). Worth bookmarking if you're planning any kind of grid-tied or hybrid ESS setup.

What I found interesting is how the 6k5 sits in that sweet spot for a lot of builds — big enough for a static caravan or a well-specced shepherd's hut, but not so large you're triggering the more complex G99 notification requirements straight away. That 3.68kW export limit still catches people out though if they haven't read the DNO paperwork carefully.

A few questions I'm still turning over:

• Has anyone actually been through the full G99 application with their DNO for a Multiplus II install? I've heard horror stories about waiting times.
• Are you running yours in ESS mode with grid feed-in enabled, or keeping it purely off-grid to sidestep the whole process?
• Any gotchas with the GX device settings when it comes to the UK grid profile?

My setup is currently off-grid so I've personally dodged the G99 process entirely — Fogstar Drift LiFePO4 batteries, Multiplus II 3k, Cerbo GX. But I'm seriously considering a hybrid approach for the office next year and I'd love to hear from people who've navigated the compliance side of things already.

Great topic @DefenderSolar! G99 is the Engineering Recommendation that governs how generators (including inverters/chargers) connect to the low voltage distribution network here in the UK. Essentially if you're exporting to the grid, your kit needs to comply with it.

For the Multiplus II 6k5 specifically, the ENA type-test certificate means Victron have done the legwork proving it meets the voltage, frequency and reconnection timing requirements - so you don't need individual site testing in most cases.

Worth noting the distinction between G99 and G98 - G99 applies to installations above 16A per phase, which the 6k5 hits on single phase. Means you'll need to notify your DNO before commissioning rather than just registering afterwards.

Has your DNO been straightforward to deal with so far? Some are quicker than others with the application process!

Good shout @DefenderSolar. Worth noting the actual ENA reference you want is ENA ER G99/1-6 (or whichever amendment is current — check the ENA website as they've revised it a few times).

The Multiplus II 6k5 holds a G99 type test certificate, so you shouldn't need to do the full individual installation application — but your DNO still needs notifying for anything above 3.68kW export. Most will want form G99/PV/1 or similar.

From my experience fitting a 5kVA unit, the DNO process is straightforward but slow — budget 45 days. Keep a copy of the Victron type test cert handy; some DNO engineers aren't familiar with it and it saves back-and-forth.

If you're genuinely exporting rather than just self-consuming, also check whether the certificate covers your specific firmware version.

@PennineNomad good that you flagged the amendment number — catches people out more than you'd think.

One thing worth adding: the 6k5 sits right at that threshold where you're looking at Type B connection requirements rather than Type A. Means more hoops with your DNO before you even switch it on. Had this exact headache with my cabin setup. Some DNOs are reasonable about it, others will drag it out for months.

If your garden office is genuinely off-grid with no grid export, you might sidestep some of the G99 faff entirely — worth being clear on your actual use case before going too deep into the certification rabbit hole.

Good thread this. One thing I'd add for anyone going through the G99 application process with a Multiplus II 6k5 — Victron publish a dedicated compliance document pack specifically for the DNO submission. Worth downloading the current version directly from the Victron Professional portal rather than relying on copies floating around forums, as the approved settings (particularly around ROCOF and vector shift thresholds) do get updated when new amendments drop.

Also worth having a conversation with your DNO early doors, before you get too far into the design. Some are more straightforward than others, and a few have additional local requirements on top of the base G99 spec. @DownsCruiser's point about amendment numbers applies here too — make sure your DNO is working from the same version as your documentation.

@DefenderSolar worth being aware that the 6k5 sits right on the boundary where your DNO may push back harder during the application process — anything above 3.68kW single-phase export tends to get extra scrutiny under the Type B classification thresholds.

In my cabin setup I went through Western Power Distribution (now National Grid ESP) and the back-and-forth on protection relay settings alone took several weeks. Make sure your installer has the Victron-specific G99 compliance documentation ready — Victron publishes a dedicated conformity declaration for the Multiplus II range that references the specific anti-islanding parameters and ROCOF settings. DNOs sometimes request this separately from the standard CE docs.

Also double-check your proposed export limitation figures early — if you're applying for zero-export rather than full export, that can considerably simplify the Type B application paperwork.