Good day. I live in South Africa where you get something like loadshedding. For those who don't know what loadshedding is, its basically when the power manufacturers (Eskom) switches off the grid power in certain areas, because there is not a lot of electricity available. So if you want to have electricity in that time when the grid power is off you have to have a generator. I've installed a change over switch in my property where you can select whether you want grid power or generator power. 

 

Now, here is the issue...When I select the generator side of the switch it works perfectly. It feeds power to my home and the E/L doesn't trip at all. When the grid power comes back on and I switch it back to grid power, the E/L trips. It doesn't stay off or trips further when I switch it back on. So I was wondering why does it trip when the grid power comes back on but doesn't trip when the generator is on.

I bet you have a neutral bonding issue. Do you have a plug tester - can you check that your earth leakage works correctly when running on the generator?

 

PS. This is a South African site. (and we are all painfully aware of loadshedding.)