What's wrong with this subpanel?

[humpndunk]

Bought this 35 year-old house 5 years ago. On numerous occasions have found the 50A breaker in the main panel that supplies a subpanel in the detached garage, tripped for no apparent reason. Little if anything running in that garage at the time. I have a suspect as to what it might be, so I'm posting a pic of the subpanel to ask if others see the same thing I do. Thanks.

 

[Megawatt]

Bought this 35 year-old house 5 years ago. On numerous occasions have found the 50A breaker in the main panel that supplies a subpanel in the detached garage, tripped for no apparent reason. Little if anything running in that garage at the time. I have a suspect as to what it might be, so I'm posting a pic of the subpanel to ask if others see the same thing I do. Thanks.View attachment 96395

Since that’s the sub panel you need to install a separate ground bar. Sub panels have to be isolated from the neutrals. The white wires on the 2 double pole breakers needs to be taped black since it is being used as a live conductor. Take out that green screw and throw it away. Where is the big #6 bare wire coming from.

 

[humpndunk]

Since that’s the sub panel you need to install a separate ground bar. Sub panels have to be isolated from the neutrals. The white wires on the 2 double pole breakers needs to be taped black since it is being used as a live conductor. Take out that green screw and throw it away. Where is the big #6 bare wire coming from.

Agreed the white hot wires on the double pole breakers should be taped black.
And agreed that the neutral and ground should not be connected in the subpanel.
What does the green screw actually do? It looks to me like the two bars are connected (bonded?) via the strap at the top with brass-colored screws?
I hate to re-engineer the box that's been in service for decades, but if I think if I did I would separate the neutral and ground bars (remove the strap at the top?) then move the two white wires currently connected to the ground bar over to the neutral, and the four bare wires currently on the neutral bar over to the ground.
How do I know if that ground is actually working? The #6 bare copper wire goes through the wall and into the ground outside the structure. I can't follow it any further.

 

[Megawatt]

Agreed the white hot wires on the double pole breakers should be taped black.
And agreed that the neutral and ground should not be connected in the subpanel.
What does the green screw actually do? It looks to me like the two bars are connected (bonded?) via the strap at the top with brass-colored screws?
I hate to re-engineer the box that's been in service for decades, but if I think if I did I would separate the neutral and ground bars (remove the strap at the top?) then move the two white wires currently connected to the ground bar over to the neutral, and the four bare wires currently on the neutral bar over to the ground.
How do I know if that ground is actually working? The #6 bare copper wire goes through the wall and into the ground outside the structure. I can't follow it any further.

A sub panel should have 4 wires from the main panel. It looks like the ground wire is going to a ground rod which should be taken out. Yes you could remove the brackets attaching the 2 existing neutral bars in the panel. If you don’t have 4 wires coming from your main panel then don’t remove the ground rod. When you post a question then I am going to tell you what you can do by the 2020 NEC code book. I know some of it doesn’t make sense but I have told you what the code book states about sub panels.

 

[Megawatt]

Agreed the white hot wires on the double pole breakers should be taped black.
And agreed that the neutral and ground should not be connected in the subpanel.
What does the green screw actually do? It looks to me like the two bars are connected (bonded?) via the strap at the top with brass-colored screws?
I hate to re-engineer the box that's been in service for decades, but if I think if I did I would separate the neutral and ground bars (remove the strap at the top?) then move the two white wires currently connected to the ground bar over to the neutral, and the four bare wires currently on the neutral bar over to the ground.
How do I know if that ground is actually working? The #6 bare copper wire goes through the wall and into the ground outside the structure. I can't follow it any further.

The green screw bonds the neutral bar to the panel and that is done at the first panel after the meter. All sub panels are not required or allowed to be bonded to the sub panel