trainrat: My layout was built in early 90's, before DCS. It used 6 "transformer handles/power districts", 70+ blocks each fed througha toggle switch, each block fed vis 14-gauge wire, and a 12 or 14-gauge (I forget which, bare wire which loops completely around the layout (both ends connected to transformer U terminals--2 pw ZWs & 1 KW). Every accessory and all track is grounded into the buss.
When DCS was released, a Z4000 was added, & 2 TIUs were slipped into the circuits from the transformers that fed the areas on the control panel. In fact, the ground is not fed through the TIUs, but all black outputs connect to a single wire that goes into the buss. No black input terminals have anything connected to them. Reason is that I didn't want to chance overloading a ground circuit in a TIU.
Light biulbs on some sidings.
I've been running happily ever since.