question

Hello, The system essentially doesn't need a isolated GND connection, but some gridcodes do.

Hardware wise the system can work when floating from ground.

So depending if you choose to feedback PV power (and therefore must select a gridcode to be allowed to do so), or not this can be done.

Thank you for your answer Johannes, my goal is to use Multipluses with ESS assistant, so I need to select a gridcode. However, this still doesnt completely explain, why Multiplus should be able to do this (according to the statement of that company that installs them in the Czech Republic) and Multiplus 2 shouldnt. But I asked more companies who install Victron equipment for grid connected solar powerplants in Czech Republic and all of them claim the same, ie. Multiplus can be used with TN-C grid, Multiplus 2 cant. If it was only about the grid code selection as you mentioned, then it should be same for both, Multi 1 and also Multi 2, but it seems it isnt. I dont really need to know the details (although I would be interested in that), I just want to be sure, that if I actually chose to use Multiplus 1 instead of Multiplus 2, although it is older and more expensive, I would be able to use it for grid connected ESS system on TN-C grid in my house in Czech Republic. Thank you in advance for your answer.

Here in Slovakia is the same problem, most of houses are having TN-C. I already purchased multiplus II gx 48V 5000W, but I do not plan to feed the grid, so my case is simpler, but I am not an electrician, so I am asking is there any problem in using the grid via multiplus if the battery power is not enough? How should be the grounding done if N and PE are not handled separately? Any other thing I should make attention? If it can be solved, then I guess 3 phase installation can be done in TN-C too , right?

Hello, I'm also interested in this topic, but I have some electricity related education and therefore I can explain the stuff here better, regarding the grid code in CZ+SK region.

Modern power distribution grid in houses is done as TN-C-S eg. protective earth is common and separated, which means that from the power distribution grid on the pole/at street there is TN-C wire scheme done. This scheme consists of four copper conductors marked as L1,L2,L3 and PEN (PEN mean Protective Earth + Neutral combined as the letter C in TN-C).

The N in PEN is connected to the centre of transformer at nearby power grid substation and the PE conductor is connected as often as possible, to provide secure+safe protective earthing even when there could be some faulty earthing point during live span of this local power grid.

The L conductors are live, each carries one of the three phases (each one is 120deg shifted (phase angle of sinus curve of each one) from the others to provide rotating electromagnetic field to easily power motors for instance).

The TN-C grid is common to be router to main house electrical cabinet where main power-off switch, circuit breakers, RCB and others are located. Then in this cabinet the PEN is connected to common ground of the whole house, to provide protective earthing as close to circuit breakers, RCB and users to ensure that protective equipment will work as good as possible.

From this point where PEN is connected to common ground, there is no PEN anymore - it is now TN-C-S grid - where PEN conductor is Separated to two conductors - the Neutral and the ProtectiveEarth. And those N plus PE should never be connected directly again.

That is the "theory".

Older code used to wire house with two conductors only. One is the live conductor and the second one is PEN - this PEN wire is connected to both Neutral and Earth contacts in socket.

Modern code use to wire house with one conductor more and therefore there is Live, Neutral and PE separeted.

Sorry for really long start, but I felt that this matter need to be described clearly, to prevent misunderstanding and electrical hazards.

Regarding power inverters like Multiplus II as @Johannes Boonstra (Victron Energy Staff) stated, these inverters can operate with floating earth, which means that they are double insulated and the protective earth is not essential to ensure safe state of the outer shell of the Multiplus II.

And IF I'm correct - where there is only Live conductor and PEN (combined conductor) the correct way to connect them to the invertor is to connect Live to Live terminal and PEN to Neutral terminal, plus use a short wire to connect Neutral terminal and GND terminal - am I correct? That should act like wall socket in TN-C system described above. And this wiring scheme would be the same on the input side and the output side of Multiplus II.

Please let us know :-) Thanks a million!