Postwar transformers' breakers are really slow and are there only to protect the transformer itself. If you're using a postwar Transformer, then using a fast acting breaker or fuse will help prevent welding the wheels to the rails or melted wire insulation (in the trains or layout) in the event of a prolonged derailment. As for the current rating you choose, that's another question that requires more detail from the user.
Most newer transformers have better (than postwar) breakers already in them from the factory. Instant breakers are what I prefer to add.
https://ogrforum.com/topic/air...al-mechanisms?page=1
If installed correctly, TVS diodes help protect sensitive electronics in command control equipped trains.
