FWIW, you can normally use a considerably lower value thermal breaker than the maximum rating of the transformer. For my test bench, I have a 2 amp breaker, and I've yet to have a normally operating locomotive on the rollers trip the breaker.
For tracks, I like something in the 6-7 amp range. A 10 amp thermal breaker requires considerably more than 10 amps for a significant period of time to trip.
Here's a chart for the TE Connectivity Potter & Brumfield Relays W28 series, a very popular type that is used on a number of transformers. If you look at the 3-20 amp models, for a 135% overload, it'll trip only after one hour! That being the case, you have 10amp capability using the 7 amp breaker unless you have continuous power draw at the 10 amp range. The 10 amp breaker won't trip for a loooooooong time with over 13 amps of current.
