I used to run several P1 and P2 engines of an old postwar ZW with no extra anything added. The ZW did have an updated internal breaker in it though as it was professionaly rebuilt. Never had any issues, even when a car jumped the track and shorted. But I am also right there with hands on the throttle levers when running, so power was cut right away when the derailment happened. If I was leaving trains run without being right there at the throttle, then I would have to seriously think about fast acting seperate breakers on each of the track feed lines. Mike