Nigel says:

I have to confess that I’m not a DCC expert but have a reasonable understanding of it. But I would invite anyone who reads what follows to correct it if the logic is in any way wrong.

Let’s look at the reverse loop first of all and assume it’s connected to only one power district. As part of your wiring, you will include a reverse loop module to flip over the polarity when it detects a short circuit caused by the train entering/existing the loop. It’s a tried and tested method so as long as you’ve included insulated joiners in the correct places and wired everything up correctly, it should work fine.

Now we add in the second power district. In the absence of a track diagram, it’s a little difficult to imagine exactly what you mean when you say that the reverse loop will join to 2 different power districts but no matter, we can still analyse your problem logically.

Although you have two power districts connecting to the loop, a train entering the loop will only be on one of them, not both (and even if it was on both, it probably wouldn’t matter), so all the reverse loop module is doing is comparing the polarity of the track that the train is on and the loop and flipping it in the loop if necessary. The module is not doing anything to the polarity in the main power district which is unaffected.

Also, the polarity in your three power districts will be consistent because, if it wasn’t, a train moving from one district to another would cause a short circuit so to all intents and purposes, the module won’t care (not that it has a mind to care but you get my drift!).

So to summarise, I don’t think it would be a problem but, as I said at the outset, I’m no expert and also have never put this into a practical trial to confirm one way or the other.