This is just the strangest thing that I have seen.
I am using Ross Track and Switches, and I have the following locomotives:
MTH SD70 - PS3
MTH Amtrak Genesis - PS3
MTH Amtrak Genesis - PS2
Lionel Polar Express Berkshire (2-8-4) - Lion Chief
Lionel Pennsylvania Flier (0-8-0) - Lion Chief
Lionel Thomas The Tank Engine (0-6-0) - Lion Chief
Lionel GP38 - Conventional
Lionel FT with Rail Sounds (2 each) - Conventional
Lionel General with Smoke only - Conventional
All of these locomotives run perfectly on the entire approx 34 ft long L shaped loop, with one exception:
The MTH Amtrak Genesis - PS3 sparks when going over one specific piece of 0-42 curve track.
If going fast enough it just sparks, and keeps going.
If going slower, it sparks and throughs the breaker.
I have attached my layout with an arrow pointing to the piece of track in question.
I have looked at the track and at the bottom of the Locomotive, but see nothing out of the ordinary.
Again, it is only this one piece of track where this happens
For what it's worth: My two Steamers struggle to get thru this curve without the rear drive wheels slipping over the rail, and to the inside of the turn.