No you need to bring both lines back to the secound panel and you need to keep them seperate on two different busses. The neutral (white) and the Ground wire (green) can be on the same bus in the main panel but on any sub-panel (also known as your secound panel), they must be kept seperate and the neutral bar must not be in direct contact with the panel. It usually has what looks like plastic brackets that mount to the back of the panel box keeping both the panel and the neutral bar seperate.

So it doesnt mater what kind of panel your talking about, whether you have a sub panel or main panel they must have both wires. The difference is if what you are talking about is a sub-panel you must bring both green and white lines back to the sub panel and install them on two seperate buses. *for your knowledge the main panel is the panel directly fed by your meter. Sub-panels are panels fed from another panel by a breaker or fed from a fused Main disconnect. Also if your secound panel is not fed from a breaker at the main panel and its fed directly off of the main bus from the first then it is considered a secound section of the same panel. or in your case the secound section of the main panel. But in order to be taped off from the bus on the first panel legally, both panels must be within sight of each other or else this against code.

If you need more info read more about grounding and bonding in any electrical book you can get from a barnes and noble. you might as well if your going to do that kind of work yourself. But just in case you should probably have a licenced electrician inspect the work. it should not cost much one hour at a service charge rate. Between $125.00-$150.00 (this is a NYC. rate your area might be less) not a bad idea concidering that you will at least have piece of mind its safe.

I hope this helps

-Anthony

Anthony,
Thanks for the information. The second panel in my case is just another main panel. Both panels are fed by the meter not one fed by the other. They sit within 3 inches of each other and both have the thick aluminum wiring coming from the meter into the top. My meter is a 320/400 amp meter. My two main panels are 200 amp each. The neutral/ground is bonded in both main panels with a ground wire going between the two panels.

I think you're right that I should just get an electrician in to take a look. Once I have him out I'll post what he says.

Thanks,
Scott