That panel is not the main disconnect. Those four wires go
back to a main disconnect panel where the neutral and ground
finally come together.

Where is that main disconnect? That is the spot that
neutral and ground meet.

Ken Hall wrote:
Last time I got involved with it the neutral/ground/return bus in home
breaker boxes were all one bus. It was just brought to my attention
that today the neutral bus is separated from the ground, and 4 wires
are now used for 220v. In the old days 220v only used 3 wires.

When did this change and why?

Ken