In my opinion, 10 amps is too high for a KW. 10 amps is right for a 275-watt ZW. I would go to a 7-amp. FYI, LIonel literature from that era said to apply a 75% factor in determining maximum continuous power demand.
Breakers, like fuses, do not pop immediately upon a slight overamperage. If you muck around on the internet, you'll find charts by fuse mfrs showing how soon they open
An alternative is an electronic circuit breaker as used in the Lionel PH-180, schematics for which are available on the forum, but as of now, finished units are not available.