Neutral connection topology with MultiPlus II GX – separated vs common neutral bus

Q&A and troubleshooting
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1

Dear community,

I would appreciate your advice regarding the correct way to connect a Victron MultiPlus II GX inverter to a residential installation.

As I understand, there are two possible wiring topologies for the neutral conductor.

Option 1 – Separated neutral buses (critical / non-critical loads)

  • The incoming grid neutral is connected to the neutral busbar for non-critical loads.
    This bus supplies loads such as the boiler, underfloor heating, air conditioners, etc.
  • The neutral for AC-IN of the inverter is taken from this same incoming neutral bus.
  • The neutral from AC-OUT is connected to a second, separate neutral busbar.
    All critical loads (heating boiler, circulation pump, etc.) are connected to this second neutral bus.
  • In the inverter settings, the ground relay is enabled to ensure correct operation of phase-dependent equipment (heating boiler and water pump).

Option 2 – Common neutral bus

  • There is one common neutral busbar for the entire installation.
  • All loads (critical and non-critical) are connected to this common neutral.
  • The inverter AC-IN neutral is taken from this bus.
  • The AC-OUT neutral is also returned to the same bus.
  • In this configuration, the ground relay in the inverter settings is disabled.

With the Victron inverter, both configurations appear to operate correctly. However, many electricians strongly advise:
“Never switch or separate the neutral conductor.”
According to them, Option 2 is the correct approach.

I would kindly ask the community to explain, with technical reasoning, which connection topology is safer — both for equipment and for people.

Thank you very much for your advice.

Additionally, I would like to clarify the switching devices used in both configurations:

Option 1 – Separated neutral buses

For switching between grid and inverter, a 2-pole changeover switch is used (for example, Hager SFT240).
In this case, both line (L) and neutral (N) conductors are switched.

Option 2 – Common neutral bus

For switching between grid and inverter, a 1-pole changeover switch is used (for example, Hager SFT140).
In this configuration, only the line (L) conductor is switched, while the neutral remains permanently connected (common neutral).

If helpful, I would also appreciate clarification on whether switching the neutral conductor (as in Option 1)
is recommended or discouraged when using a MultiPlus II GX in a residential TN system.

Thank you again for your support.

2

This only reflects to the switching of a neutral conductor to a load or sub-board.
Once you introduce an inverter and battery into the system, this no longer holds true. Neutral and N-E link switching is handled inside the Multiplus, and if the neutral from AC in to AC out is externally connected, the Multi will think that the internal Neutral switching relays are frozen and will report a fault.
And you are correct, if you need an external bypass for the inverter, then a 2 pole switch is required.

3

Thank you for your reply.

In my case, with the configuration shown in the screenshots (Option 2 – common neutral bus), no errors are reported and the inverter operates normally and without faults.

photo_2025-12-14_16-01-37
photo_2025-12-14_16-01-37696×346 43 KB

photo_2025-12-14_16-01-37 (2)
photo_2025-12-14_16-01-37 (2)403×161 11.9 KB

4

OK, so that is also an option. I had forgotten that that option existed.
However, there is no real technical objection for isolating or not isolating the neutrals: this choice would normally be made on a physical basis: whether or not the switchboard in use has a common neutral bar, or whether separate db’s or neutral bars are in use. PE should always be common.
Often when upgrading an old installation, it is impractical to separate the neutrals, so the external bypass option exists.