First off, the postwar transformers are rated on input power, and you have to take that into consideration when you add circuit protection and calculate the load they'll support. Let's say the efficiency of the PW-ZW is 80%, that's a reasonable assumption. The ZW rated at 275 watts is really a 220W output transformer, so we're talking 11-12 amps at full throttle. My recommendation would be to provide suitable circuit protection based on the real capacity of any transformer, the PW-ZW included.
For the ZW, if you are feeding multiple tracks, I'd provide each output with circuit protection suitable to support the load on that output. I'd also provide unified circuit protection in the common ground lead to avoid multiple outputs totaling more than the transformer should be loaded to. That way you can provide proper protection for each output and also not be constrained to a fraction of the usable capacity of the transformer. Each output could have an 8-10 amp fuse or fast circuit breaker, and the common ground connection could have a 12 amp fuse or fast circuit breaker.
