Fast acting fuses or breakers rated near 8 amps should work very well for each lettered(A, B, C, D) output on the older 250 & 275 watt ZW's.
The way Lionel has the older ZW set-up is that only the return or common wire has circuit protection. As one or two others have mentioned before, you can almost weld with the older ZW's before the internal breaker trips.
J Daddy,
Thermal breakers are for use with stuff like air conditioning in a car. Personally I stay away from D.C. circuit protection in an A.C. envirement.
Lionel transformers put out A.C. voltage, your auto has D.C. voltage, so using auto circuit breakers is not the best thing to do.
For the average person to understand about electric work like A.C. and D.C. volts, D.C. is straight power like a battery, A.C. fluctuates between positive and negative many times a second-thus the name alternating current.
Lee F.
