| Assuming this is a residential service, the 320 amp will be minimum #400 MCM Copper with either THHN/THWN or XHHW insulation, the 200 amp will be #2/0 with either of the same insulations.
Assuming the 320 amp is the feeder to the meter, no equipment ground is needed. The grounding electrode conductor will be # 2 copper. The 200 amp is probably for the panelboards, and each feeder will need an equipment ground conductor of #6 copper. Be sure to separate, insulate and isolate the neutral from the equipment ground at each panel. | 
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