I have a friend who, on one of his older postwar-style layouts, had a double-track arrangement that looped across itself at one end with a double-track 90-degree crossing. One leg of this crossing led into a wide uphill 072 curve that led up to an upper level. Because trains ascending the grade needed additional voltage, this segment was isolated and fed from another set of terminals on the ZW feeding it higher voltage.
He tells me during one run session, a train pulled by a MTH Proto-1 locomotive experienced a derailment in the loop that caused the loco to stop across the two power districts. Full grade-climbing voltage was now running into one end of the locomotive through its wiring and out into a short circuit. As he was moving to his control panel to shut off the power (duckunders had to be navigated to do this) , the stopped loco, which did not have a smoke unit, suddenly started doing an impromptu imitation of a smoker 
.
By the time he was able to lift the errant loco off the rails, most of the internal wiring's insulation was quite thoroughly roasted. The ZW took its sweet time tripping, presumably because the one axle that derailed didn't present enough of an amperage draw to trip the breaker. He was able to replace the ruined wires one by one and at the end, the unit came back to life (also subsequently passed inspection by an MTH tech)
In a similar vein, I had one of those first-gen K-Line F3's (the six-motored KCC C&O) derail on another friend's ZW-powered layout. This incident managed to roast the coil spring inside the T-bar coupler on the leading A unit. I only noticed this after I ran the set at home and noticed the front coupler would no longer open. When I took it out to check the mechanism the spring literally crumbled. Must've gotten pretty hot to do that. That wire certainly wasn't large enough for the ZW pumping current through it to sense a short. While I never saw the thing glowing, I imagine it would have to have gotten pretty hot to damage the spring to that extent. I later replaced it with a spring cut from a retractable ballpoint pen.
---PCJ
