I have a new (6 mos.) Lionel ZW-L transformer, complete w/ the circuit breakers that are designed to protect the electronics of modern locomotives. Before, using postwar ZW's, I had added 3A high-quality Eaton circuit breakers inline from my ZWs to the tracks that operate locos.
This was per the You Tube video by Mike Adams at:
https://www.youtube.com/watch?v=aVeCPeeeRNk
The breakers Mike recommended in the video have been replaced by:
Eaton FAZ-C3-1-SP
Adams recommends the 3A over the 5A; my locomotives operate at about 2A, BUT the Adams solution is NOT for overload- it is for a direct short. 3A seems right, and he makes the case that 5A is too much. I have used them for (now) 2+ years, and they work instantly, in the case of a direct short such as (what happens most often to me) I place an engine or car on the track improperly. They will not protect against a spike or over-voltage in the system; some other devices are for that. The Eatons are for shorts only.
When I went to the ZW-L, I just left the Eaton breakers in the circuit. Between the ZW-L and the track.
Yesterday, I caused a direct short removing a light from a O Gauge switch- and "BANG" immediately the Eatons did their job. The ZW-L breakers did NOT trip. Until I hear better- the Eatons will stay in my system.