Hooking up a 10 amp fuse To protect dcs and the TIU.

Since I'm no Electrical Engineer, I have my 10 amp "fast blow" automotive fuses hooked up on the out-puts of each TIU channel (which may not be correct). I have had many shorts and occasions when the fuse has blown with a noticeable "pop", and have never had any issues with the TIU channels.

Fuses in a DCS environment should always be in the Hot wire between the transformer and each TIU channel input (red post).

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I agree with Barry as to location.  I also recommend a manual reset circuit breaker rather than a fuse.  It's cheaper in the long run.

I assume, David, that you are only using terminal 1 on the ZW. 

If it doesn't blow in normal operation, I would recommend dropping to a 7 or even a 5-amp fuse or breaker, for quicker popping upon a derailment.

I power all 4 terminals of the TIU, and use auto fuses between the transformers and TIU.  Though I seldom blow a fuse, this set-up has worked well for me.  I know some people recommend more exotic fuses but these work OK.  I like to change out the fuses depending on how many amps the particular locomotive/car combination draw on the track at the time.  So sometimes a 7.5 amp, while other times 3 amps is plenty.  With auto fuses this is simple to do.

I also run a TVS between the transformers and TIU on each of the 4 channels.