so I’m troubleshooting an off grid system with a Genset .
The installer has the ground relay active and when victron is the power source there’s near Zero neutral to ground voltage .
He did NOT bond the neutral to ground at the 3 phase diesel generator ,which resulted in a floating neutral .15 volts neutral to ground difference.
I corrected it and bonded the neutral at the to the ground at the generator , but when the Genset is running the ground to neutral voltage is reduced ,but it’s still 3 volts at the main panel in the home and the sub panels .
at the generator and generator transfer switch panel it’s near Zero .
As mentioned by Ludo the neutral may be too thin. Note that if the load has switching power supplies the third order harmonics will add in the neutral ( 3 phase system)
and not cancel so that is why sometimes neutrals are doubled up. For loads with odd order harmonics in three phase systems, neutral current is additive and can cause higher current in the neutral than would be normally expected.