Its a tmcc environment that will use 4 BPCs each with itsown TPCs powered by a mixture of pw ZW and modern PoHo [180 watts] transformers. The layout is moderate size, has a powerbus that connects into each of the BPCs and one Common for all lines. {There isseparate power for accessories/switches}. I have wired the layout into power districts by removing the center pin in various locations. Each district will be powered by a separate lead from one of the BPCs and therefore possibly a different tpc/transformer combination.
As a train clears one district and goes to the second, will the TPC manage the voltage to prevent shorts or do i need make each district fully isolated by removing a pin from the outside rail and installing some relays?
I have a single TPC and no BPCs, but I will give your question a shot.
The TPCs are set by the Cab1 controller, so I do not believe they will be able to do any management of the voltage. As long as you 1.) have all your sources phased which it sounds like you do with a single common and 2.) have the voltages set the same (or as close as you can get) I think you should be OK with shorts / sparking. The BPCs should lend some assistance to the management of power to your blocks.
Even if you completely isolate each district by isolating the outside rail the locomotive will still be bridging two blocks momentarily thereby not achieving what I believe is you intended result. Also, if using tubular track I believe that you will need to isolate both outside rails as the outer rails are electrically coupled through the ties. Other brands such as Atlas do have the outside rails isolated due to plastic ties.
If the track voltage between the two blocks is the same there is no issue. If the rack voltage between the blocks is different you will get some momentary reverse current flow from the block at the higher potential into the block at the lower potential. This is not a short, it’s how elecricity works. If the reverse flow is minimal and for a short period of time there isn’t a reason for concern.
Prior to installing TMCC I used a BPC to temporarily control both blocks or districts at the same voltage while the pickup rollers were crossing the center rail gap separating one district from another. As someone noted already, when I installed TMCC all of my districts had the same voltage, usually 16v set by the Cab 1/Command Base, and crossing over had no impact.