Earth leakage trip on switching over inverter to main supply

[Gene]

I had a case where the we installed an inverter and inverter db that we split the circuits for load shedding purposes, all wiring was previously on the E/L of main DB (Lights also). So upon connecting the new inverter DB we split the light circuit from the E/L and put all the lights on the inverter DB, skipping the E/L, some plugs we did put on E/L, so when running on the inverter everything is fine, when switching over the changeover sw to eskom the main db E/L trips, but inverter E/L stays on, funny thing is the lights is not on the E/L and is connected upstream on a double pole breaker isolator supplying from the main isolator bypassing both the earth leakages in the 2 DB's
Now i traced the light circuit and found some connections that was connected to a 12V power supply supplying 4x 12Volt downlighters, i isolated these wires and everything now works fine, E/L now working 100%
How come is this, could it be the 4 x 12 v lights on the power supply, where i normally connect 1 power supply per downlight as per spec.?
And why did it trip the E/L when it was connected before the E/L?
I tried looking at older posts but could not find anything similar, anybody to steer me in the right direction...?

[Dave A]

You have to be really careful about getting your neutral onto the correct neutral busbar relative to the live, even though the circuit wasn't on any of the E/L units. Was the live on the load side of the inverter and the neutral connected to a neutral bar on the supply side of the inverter perhaps?

[Gene]

Thanks for the reply, yes wiring on db is correct as well the Inverter db, only theory i have is that the lighting circuit neutral could be mixed - thus the trip, so just disconnected it in the roof.