On the RW, A,B,D,U are not common at the same time - you select one ROW from the outlined in my post above to meet your needs.
I think, if I get all your nuances just right, I would want A as the common post, and so wee will use that ROW for our information:
A is your common for BOTH the track and accessory circuits. This goes to the outside rail of your track.
A-C will give you 9VAC constant voltage, again using A as the common, for your accessories.
A-U gives you 6-19VAC vairable voltage, again using A as the common, for your track. U gets wired to the center rail.
You would place your TVS diodes between A-U and A-C. Your external breaker can be installed on the line wire that goes between U and the center rail of the track. You will want another on the C wire that goes to your accessory bus to as well.
CCA is not a nice to work with as just copper is.
