If you run the same number and size locos all the time you might find a value that gives you some protection but what if you have 10 locos on your command layout knowing that each one can pull 5A starting a train and 1.5A running a steady speed what value fuse are you going to use 50A ? 15A ? Where in between ? The fuse between the power supply and the track is for protecting the power supply not the command boards in the loco. Perhaps on occasion they might save a board that is just happenstance. So that fuse would be sized to protect the power supply. The place for a device to protect the locos boards is between the motors and the motor driver board and perhaps between pickup rollers so that a derailment can't burn up the wires between rollers and boards. This is a problem on multi-unit locomotives where there are pickups on each unit and if one should derail and one of the pickups find outside rail "common" it creates a short through all the wires running between pickup rollers. If these wires run through the wiring harness in a multi unit loco or a talgo type train such as a GM AeroTrain, a Zepher, or a UP M-10,000 you can loose the entire wiring harness from the loco to the rear car. This kind of short would likely blow your fast blow fuse protecting your power supply also. Something I discovered is the super flex wire with silicone insulation can stand up in short conditions much better than vinyl covered wire. I originally started buying this wire just for the extra flex it gives on pickups mounted on trucks that swivel, but noticed the added benefit So I now add protection from overload and shorts in three places between track and power supply, between pickup rollers and between motor and driver board. That includes spike protection for which I use TVS diodes in addition to overcurrent protection. j
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