How do I connect Cab 2 to TIU for multiple contiguous loops

I would connect the Lionel wire to the common on the output side of your TIU. We have two wires and using a crimp connector they attach to the Lionel base like a huge "V" and the other ends go to the common for each loop.

Curious. Are the RMC commons all hooked together inside the transformer? If not you'll have to connect a wire to each common post if you add another loop on it. Depending upon how close the loops are TMCC/Legacy will work on a nearby non connected track like your test track next to the layout.

I have my Legacy system connected to all of the common outputs on my TIU. I have a Rev L TIU and the commons are not connected internally. I currently have only 2 loops of track, but plan to expand that to possibly 4 loops one of these days. I currently have 2 PH-180s for power, 1 per loop, and this all works quite well together. I am not familiar with the Z4k or the MRC transformers.

As the guys have mentioned the transformers must be in phase with each other, meaning both share the same common or outside rail.. There's a ton of info about  phasing in the archives (try a search)  .One thing nice about TMCC and legacy is... it's only a one wire connection from the "U" connection on the base to an outside rail. This will carry the tMCC signal over the whole layout providing the transformers are in phase. Yes some recommend putting the wire to the black on the tiu  but it's just as easy to attack it to an outside rail.  (same thing)

Good luck.

Thanks guys. Glad I asked, as I would have connected the cab 2 to the inputs on the TIU rather than the outputs. I'm at that age where I need to make notes before I take something apart!

BobbyD, sorry I can't answer your question about the MRC commons being wired together. Its been a while since I had it apart.

Rich