Hausinstallation durch den Multiplus schleifen oder doch Parallelbetrieb?

Got a proper head-scratcher for the hive mind here.

Running a Multiplus-II 48/5000 with a Cerbo GX out to my garden office, backed by a Fogstar 48V pack — dead happy with it all, no complaints.

But I've been going back and forth on how the house load is actually wired into this setup, and whether I've been doing myself a disservice from day one.

Currently everything runs in a sort of parallel arrangement — grid's still doing the heavy lifting for the main house, and the Multiplus handles the office loads independently. Works fine, but I keep reading about people routing their whole house distribution through the Multiplus so it can do proper ESS magic, seamlessly switching and prioritising solar first.

The appeal is obvious — let the Victron brain decide what draws from where. The concern is equally obvious — my kettle, washing machine, and the missus's hair dryer all having a domestic at the same time might not exactly respect a 5kVA inverter's feelings.

So genuinely curious:

• Has anyone here actually migrated from parallel to a pass-through / whole-house setup in the UK?
• Did your DNO or installer have anything to say about it?
• And did the VE.Bus / ESS config make it relatively painless, or was it a right faff?

Feels like there's a right answer here that I'm just not seeing clearly — possibly because I've been staring at VictronConnect graphs for too long.

@DaveMoore70 the thread title's in German but I'll answer anyway 😄

For a garden office the AC-coupled approach through the Multiplus makes far more sense than parallel — you get proper UPS-style switchover, the Cerbo can manage everything centrally, and your loads are protected if the grid drops.

Done exactly this with my garden office setup. Key thing people miss: set your AC input current limit correctly in VEConfigure so the Multiplus doesn't try to backfeed onto the grid — important if you're not on a G98/G99 approved install.

The passthrough capacity on the 5000 is generous enough that you won't notice any switching lag on most office equipment.

Parallel/split setup only really makes sense if you're running genuinely separate critical vs non-critical circuits and want granular control. Probably overkill for a single outbuilding.

@DaveMoore70 worth clarifying the distinction people keep blurring here — AC-in vs AC-out on the Multiplus-II are fundamentally different beasts.

For a garden office with no grid feed-in requirement, I'd route everything through AC-out 1 (backed) rather than AC-out 2. Lose grid, lose nothing.

One thing I haven't seen mentioned: check your G98/G99 compliance position before you do anything clever with grid-tied AC coupling. Technically if you're exporting or the DNO gets fussy, you can land yourself in awkward territory even on private property with a grid connection present.

My narrowboat setup runs pure island mode on the Multiplus — no grid reference at all — so I sidestepped that entirely. Garden office with a Fogstar pack sounds like it could do the same quite cleanly depending on your loads.

What's your peak draw looking like?

@FenlandSolar makes a fair point but honestly what tipped it for me was the ESS assistant config — took me ages to wrap my head around it for my motorhome build before I did the tiny house setup.

One thing nobody's mentioned: if you're feeding a garden office specifically, check your DNO rules around G98/G99 notification. Caught me out. Depends on your export situation and whether you've got grid passthrough involved.

Also the Cerbo GX will make your life significantly easier for monitoring whichever route you go — the VRM portal is genuinely decent once you stop fighting it.

What's your actual load profile like? That changes the answer quite a bit tbh.

@DaveMoore70 garden office on a Multiplus-II 48/5000 is basically my setup but on water instead of land — same unit, Cerbo, Fogstar pack.

One thing nobody's mentioned: don't overlook the transfer switch speed. Multiplus does ~20ms which is fine for most kit, but some cheaper UPS-style devices get confused and throw a fit. Found that out the hard way with an old NAS box.

Also if your garden office is a separate building, double-check your Part P situation before you start looping mains through anything. Notifiable work and all that — or just get your DNO notification squared away. Boring but real.

Otherwise honestly? For a garden office the AC-out-1 approach is dead simple and just works. Stop overthinking it 😄