I noted today that MTH recommends that accessories in a DCS layout be run from a separate transformer to avoid making the DCS signal pass through coil windings or a circuit board. However, using the ZW as an example, the accessories are typically run from a separate TAP on the transformer than the track voltage, AND the DCS signal is injected downstream to the transformer anyway (in the TIU). So does the DCS signal backfeed through the TIU into the ZW?
The accessory tap on your ZW technically is a separate transformer. You shouldn't have a problem.
I'm only about 99% sure of this but no, the DCS signal should not back-feed through the transformer windings. The DCS signal comes from the output side of the TIU. Your transformer is connected on the input side of the TIU.
Don't know about DCS feedback, but I use 2 ZWs with the A and D terminals to the TIU and the B and C terminals to accessories. Been doing it that way for years with no problems.
There is a DCS signal filter (aka choke) inside the TIU so that the DCS signal on the track does not "backfeed" into the transformer at the TIU power input connections. However, if you are using the so-called passive-mode where the transformer directly connects to the track, you should add this DCS signal filter (aka choke) between the transformer and the track.
The accessory taps on a PW ZW is not a separate transformer. The ZW has one primary winding and one secondary winding. All 4 "taps" are rollers running over the secondary. All output amperage flows through the same coil wire. Stan2004 is correct