Two units in parallel - grid power shown on GX web page is 'wrong'

Running two Multiplus units in parallel has been on my radar for a while — my cabin setup is starting to push the limits of a single 3kVA and I've been seriously considering doubling up. So this thread caught my attention.

What I find interesting is how the GX device handles metering when you've got two units talking to each other. From what I've read, the VE.Bus system should aggregate everything cleanly, but there seem to be edge cases — particularly around grid input readings — where the numbers just don't add up. One unit might report a figure that looks like it belongs to the whole system, while the other throws in its own interpretation.

Has anyone here actually gone through the parallel commissioning process themselves? Specifically:

• Did you notice discrepancies in the grid power figures shown on the Remote Console vs what your actual meter was showing?
• Was it a configuration issue (ESS settings, grid meter setup) or something deeper in how the two units were synced?

My gut says a lot of these "wrong" readings trace back to not having a proper grid meter installed — relying solely on the inverter's internal measurements when you've got two units seems like it's asking for trouble. A Victron Energy Meter (or even a good third-party CT clamp setup) feels like a non-negotiable at that point.

Curious whether anyone running a parallel Multiplus setup in the UK has had a smooth experience or whether it's been a proper headache to dial in. The Victron community forums have some threads on this but they tend to go deep into the weeds — would love to hear from people who've actually lived it.

Been down this road with my shepherd's hut setup — the grid power display discrepancy when running parallel units is a known quirk rather than a fault.

What's happening is the GX device is typically summing the AC input readings from both Multiplus units, but there can be a timing/calibration offset between the two units' internal measurements. The displayed figure ends up slightly skewed.

Worth checking:

• Both units are on identical firmware
• The VE.Bus cable between them is seated properly
• Run an assistant reset via VEConfigure on both simultaneously

The actual power flow is usually fine — it's a reporting artefact. You can verify with a proper clamp meter on the incoming feed to see what's genuinely being drawn.

@DontPanic25 what firmware are yours currently on? That narrows it down considerably.

@DontPanic25 Worth knowing that the "wrong" grid reading in the GX portal is almost always down to the second unit's AC sense not being properly configured — it's a classic parallel setup gotcha. When VEConfigure sees two units, it needs to know which one is the "master" for grid metering; if that's not sorted, you'll get doubled or halved figures depending on firmware version.

Check your VEConfigure parallel settings — specifically the AC input current sense on the slave unit. On my cabin setup I had identical symptoms before I realised the slave was still set to report independently.

Also make sure both units are running identical firmware. Mixing versions in parallel causes all manner of oddities that look like display bugs but are actually sync issues underneath.

@DontPanic25 Which GX device are you using — Cerbo or Venus GX? I'm planning a similar parallel setup for my shepherd's hut and I've been wondering whether the grid metering issue is resolved through a firmware update or whether you actually need an external energy meter (like the Victron ET112) wired in separately to get accurate readings across both units. Have seen conflicting info on this. Also, are both your Multiplus units identical firmware versions? I've read that mismatched firmware between parallel units can cause all sorts of weird reporting behaviour on the GX dashboard, quite separate from the AC wiring side that @SaltyHiker mentioned.

@DontPanic25 The grid reading issue in parallel setups comes down to how the GX aggregates AC data from both units — it's a known quirk and Victron have documented it in their ESS assistant notes, though not exactly prominently.

Worth checking your VE.Bus firmware is identical across both Multiplus units before you go further. Mismatched firmware versions cause all manner of bizarre reporting behaviour in the GX portal, not just the grid figures. Had this exact headache when I paralleled my two units in the shepherd's hut — spent three evenings debugging what turned out to be a firmware delta between the two.

Also make sure you've run the parallel wizard properly via VEConfigure and that both units share the same phase assignment. The GX will produce garbage readings if the assistant config isn't mirrored exactly.

@DontPanic25 Had the same head-scratch moment on my narrowboat when I paralleled two units — turns out the GX was just displaying one phase's reading and smugly ignoring the other, like it couldn't be bothered to do basic maths.

Check your VE.Bus system is properly configured as a parallel system rather than two separate inverters — the Cerbo needs to see them as one logical unit or the AC summation goes completely sideways.

Also worth double-checking your VE.Configure settings are identical across both units, because even a minor mismatch in AC input current limits had mine showing phantom grid figures that would've alarmed any reasonable person (and me).