Assuming the layout is a loop, you will want to insulate the center rails in at least one point between two modules. You don't want the DCS signal propagating from 2 directions. If the layout is more than a dozen or so modules, you may need to insulate in more locations to break the layout into blocks. If you have signal problems, add a magic filter or bulb to each block (especially needed if TIU is earlier than rev L).
Bob
