Is the control that keeps popping the breaker on the ZW too? Can you temporarily wire the problem loop to the ZW controls running a train without a problem? And the train that's running fine to the transformer that keeps popping the breaker?
I'm curious as to the result, but I'm stumped.
Just a side bar, the breaker on the ZW is designed to protect the transformer, not your train. I understand if you're running other than standard postwar stuff, you want to put an inline 10A fuse on the positive feed to the track, the electronics in the newer trains (Lion Chief, TMCC, Legacy, etc..) could be toasted before the ZW breaker pops. I have two post war ZW's and any feeds for track power for my Lion Chief engines have a 10A fuse and fuse holder (from Advance Auto Parts). Cheap insurance.
