pw zw circuit breaker keeps tripping

How do you know? John, we need more than that to work on.

List everything you are running off all outputs too, including every illuminated car, every switch, and every accessory.

To really get straight to the solution, an ac ammeter is indispensable.

That is typical of how ZW circuit breakers fail.  Replacement circuit breakers are available from the part venders like the Train Tender.  It is also recommended that you put six to ten amp circuit breakers on the out put of each of the lettered terminals, as the 25 amp circuit breaker protecting the ZW transformer is too large to protect your trains.