Main A/C switch trips

[tombstone220]

Could anyone point me in the right direction?
This morning I awoke with no AC (window air unit not on). The main AC breaker had tripped. I found that with nothing on or plugged in (while on shore power), it would trip after about 6 seconds. The gauge at the panel shows 120V. I reset my Magnum inverter/charger a couple of times (it still inverts with no problems). I turned off shore power and started the generator but it seems like there is no output (inverter didn't see it). Everything worked fine yesterday but today I have no way to charge my batteries. Everything on the panel is original (1982 Morgan). The Inverter is new 2017. Could the rotary shore power/Gen switch be it?

[Oceanride007]

Earth leakage devise somewhere?. Did generator run your AC can you connect it directly.

[Cheechako]

Those breakers do go bad sometimes.