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I am using an inverter that internally bonds neutral and ground. It feeds a main panel via transfer switch (as required by code). Of course my main panel also bonds neutral and ground by code. The inverter manual gives the following justification:

NEUTRAL and GROUND are bonded inside the inverter to comply with the National Electric Code (NEC) requirement that any AC source must have a neutral to ground connection.

Is the manual correct on this point? I thought the main panel was supposed to be the sole point of G-N bonding? However, assuming I connect each inverter terminal to the correspondingly named one on the main panel -- as recommended by the manufacturer -- this creates ground currents. As shown in the following drawing, there are now two G-N bonding points, effectively making both conductors into a single conductor and therefore sharing the return path current).

enter image description here

I'm pretty sure that ground currents are not allowed except by utility companies. The idea being that grounds within a building need to be at the same voltage for safety reasons. What is the best way to avoid ground currents if the inverter and main panel both bond G-N?

Update It was suggested to just add another switch pole for N. This may work in some situations, but I'd prefer a more general solution. For example, we may not have multiple neutral wires everywhere, as in the following situation.

enter image description here

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  • \$\begingroup\$ Maybe ask the manufacturer or an electrician? How is the transfer switch wired, how does it switch live and neutral? Maybe the unit is not meat for permanent residential installations that connect to existing systems, but RVs and boats where the inverter itself is the mains source. \$\endgroup\$
    – Justme
    Commented Jan 17, 2023 at 7:05
  • \$\begingroup\$ @Justme Good point that boats and RVs don't have a main panel with G-N bonding, explaining why the inverter would bond them. The manual doesn't say you can't feed a building. But it does say "NEVER connect the AC output of the unit directly to an Electrical Breaker Panel/ Load Centre which is also fed from the utility power / generator". Implying that the connection must be "indirect". Presumably because a direct connection to corresponding main panel terminals has the problem noted in the question. And yes the question is indeed how would an electrician solve the problem. \$\endgroup\$ Commented Jan 17, 2023 at 7:19
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    \$\begingroup\$ Maybe ask in DIY stack exchange. diy.stackexchange.com/help/on-topic \$\endgroup\$
    – user57037
    Commented Jan 17, 2023 at 8:12
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    \$\begingroup\$ @mkeith Let the inverter supply the ground/neutral bond for the whole installation. NEC 250.142 specifies that G-N bonding should occur either in the utility, or "within the enclosure of the AC service disconnecting means." Given this, letting the inverter G-N bond everything doesn't sound code compliant to me. (Also it doesn't scale to multiple inverters, and unbonding the main panel sounds like a lot more work than unbonding the inverter. And how would somebody keep track of this in case the inverter is removed later?) \$\endgroup\$ Commented Jan 17, 2023 at 16:54
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    \$\begingroup\$ I’m voting to close this question because it is more of a building code question than it is an electronics design question. \$\endgroup\$
    – user57037
    Commented Jan 27, 2023 at 7:32

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