The PTC with an ERR install is totally different than using the PSX-AC for circuit protection of the track power, and they serve two different purposes.
When I install the ERR Cruise Commander Lite, I use a 1.1A hold PTC in series with the motor to protect the board in case of a motor stall. It doesn't affect the normal operation, but if you stall, it will keep the excessive current from toasting the output FET motor drivers.
I also use a PTC when I run track power between an engine and the tender to protect the wiring in case of a derailment. I put it in series with the connection between the two. If the engine or tender derail and a roller lands on an outside rail, sometimes it'll cook the wire before the breaker trips. This also works well for passenger cars between the pickups.
