I use a 5 amp resettable breaker in series with 10 amp Airpax on each TIU channel. In a derailment or other short, the Airpax trips first virtually instantly. An overload, such as in my PS 3 MUs when one engine starts in conventional and is a boat anchor, the 5 amp trips first. The Airpax will trip by shorting a 24 awg wire, where the the 5 amp thermal will just melt the wire. Works for me.