I know the post war ZW has a 15 amp circuit breaker installed inside on the common side. Sounds like your ZW's breaker might be getting worn out but I doubt it, plus all the trains and lighted cars you are using put a large load on it.
Another option is to buy another ZW and use it for one of your three passenger trains. 3 or 4 engines powered plus at least 11 lighted passenger cars is a very large load for any post war ZW. Like gunrunnerjohn mentions a post war ZW may put out close to 220 usable watts to the track even though the power rating is 275 watts(used from the wall outlet).
What I have done is to install 7 amp 120 volt AC fast acting circuit breakers on each output terminal(A, B, C & D) between the transformer and the track. I bought these breakers at www.mouserelectronics.com Personally I don't recommend using circuit breakers from automotive use as they are for use with DC(direct current) and you are using AC(alternating current). I studied electrical work for 3 years at a vo. tech. school near Reading PA, plus I studied automotive work at a vo. tech school in south Miami FL.
Lee Fritz
