If the 200a is the service disconnect and the 100a is a feeder off of that (SER 4 wire) the cable only needs to be protected against physical damage and the drywall should do it.
If the 200a is double lugged and the 100a is a service entrance conductor, there are more issues than a sch80 PVC pipe can cure. (excessive service conductor inside the building for starters)
If these are both service conductors you would be better off tapping the service outside and running the cable down the outside wall, coming into the back of the 100a panel.


Greg Fretwell