I am a bit confused at what you mean as pass through from input to output.
What I am calling 'pass through' is If the neutral line of the input is connected directly to the neutral line of the output. So, as an example, the manual transfer switch in the picture you provided has a neutral that is 'pass through'
Edit: After looking at the Solark Manual more closely, I concluded there should be no neutral from the Sol-Arc to the Transfer switch. I have corrected the diagram in my previous post.
BTW: you have a typo on the switch picture. The Solark Output Phase X in the lower right should probably be Phase Y.
Grounding is a bit hard to advise without knowing more about what is already set up for your system.
My *
guess* is that the earth ground ties into your system at the 400A service entrance on the outside of your house. I am also guessing there is a neutral-Ground Bond at the service entrance as well. From the main service entrance, it looks like you have a separate 200A feed to each of the breaker panels inside. These feeds probably each have a ground wire to a ground bus in the breaker panel. I am also guessing that there is
*no* connection between Neutral and Ground in either of the breaker boxes. (These guesses are based on what the most likely thing the electrician did to meet code)
Assuming the above is correct, you will notice that from any point along the ground wire, there is one and only one path back to the earth ground point at the service entrance. That means there is no ground loops.... and you want to keep it that way. One way to do that would be to leave the existing ground connection on both panels but not have ground from panel one or the Solark go to panel 2. This would be a bit weird because ground is not being routed with the power. (This may not even be to code)
The other way to rout ground is to completely disconnect the ground from the 400A Feed to Panel 2 and feed ground from panel 1 to panel 2 (This is what I tried to show in my diagram above)
The reason I show the ground coming from Panel 1 to the transfer switch and not from the solark is
1) doing both would create a ground loop and
2) this allows the solark to be totally removed without disturbing the ground path to Panel 2).
Your transfer switch does not appear to have connections for ground wires.... but it is a metal box so the box should be grounded. Your ground wire should be 6AWG between the two boxes, so traditional wire nuts for connecting the ground inside the transfer switch are probably not viable. You may want to purchase a
grounding busbar to mount inside the switch box. (Just make sure the mount grounds the box as well)