The information on the label found on the back of a PH-1 transformer includes it's nominal output values. It can deliver more than 7.3Amps for brief periods before it's internal circuit breaker trips, like in the event of a direct short of it's outputs. When properly functioning, its internal breaker is adequate to protect the transformer.
I believe your question is founded with concern for protecting the TIU and Train electroinics from damage in the event of a derailment. In which case, if you were to use a PP11-0-7.50A-OC-V, the PH-1 would trip this 7.5A external breaker instantaneously if a derailment causes a direct short circuit between hot (+AC) and common(-AC).
