Wire and component protection, may be better served at a lower amperage.  I use a parallel PH 135 power supply, thermal cut-outs 7.5 amps X 2 (15 amps).   Dead short derails created a lot of arc and spark/damage to rails and wheels before the power supplies would shut down.  Early IC Controls BPC, Block Power Controllers also failed with internal wire traces fried. 

Repaired all, and installed 7.5 amp fuses to 8 different track blocks, Replacing fuses relatively easy compared to some of the repair.  I've done a (5) engine consist/Atlas SW's still within the 7.5 amp track block limit.  

Best wishes, Mike CT. 

Track block fuses upper center picture.  Fuse holders are a Grainger product.   Glass fuses (7.5 amps) available at most auto parts stores. 

Although a bit spendy, you can't beat the PSX-AC for trip speed. Well worth the investment.

I have not had a z 4000 for several years but it does have breakers on it.  I am sure someone will chime in with the details.  Breakers after breakers seems to be redundant and I am with Mike on adding fuses.  I now run Z 1000s (3 of them) and I have10 amp quick blow fuses added to provide that quick protection.  Like you, my buss wiring is 16 ga - the thought of a 50% overload for an hour causes chills down my back- I would want something to blow a lot faster if I had that level of overload or a high resistance ground (arc welder?) happening.  I vote for adding fast blow fuses!

PS- this thread will promote some interesting discussion. 

Thermal breakers are very slow acting.  Truthfully, if I were using them with a 10A transformer, I'd probably size the breakers at 7 amps.  I have a 2A thermal breaker on my bench transformer for testing stuff on my rollers.  I can run a locomotive that's drawing around 3 amps for several minutes without the breaker tripping, it does trip pretty quickly when the current goes up approaching 4 amps.

I use the Lionel PowerHouse 180 transformers, they have an excellent electronically triggered breaker that is MUCH better than thermal breakers.  I simply add a TVS for spike protection and leave it at that.

An automotive quick blow fuse (glass or blade type) is going to trip far, far faster than a thermal breaker. I'd recommend the automotive fuse over a thermal breaker, as the automotive fuse will trip almost instantly. 

Awhile back I acquired a lot of circuit breakers that were being thrown out because the shelf life had expired ( I did not know that unused breakers expired ) anyway I got some 3,5, 7 1/2, and 10 amp circuit breakers. I have been using the 71/2 amp breakers with my ZW. 4 blocks and 4 breakers with a dead short they take about 30 seconds to pop. Should I drop that down to 5 amp breakers and would they pop sooner?

What are the expert thoughts on these breakers for an inline fuse coming out of a ZW:

They are "instant."  The spec sheet includes a delay curve.  I believe this says it will trip with 135% of rated current at .1 second.  Am I reading this correctly?  Is this quick enough for modern trains (of course complemented with TVS)?

I bought and received these breakers last month, but haven't installed them yet.  Side question, should these be installed inline to a dedicated accessory circuit or is to track power only necessary?

Magnetic breakers are great, that's what to use if you find a reasonable price.  That's one of the best choices.

@oldtoymaker,

That is a long time for a dead short to trip. I would drop the breaker or go to fuses.

@HOKIE71

I believe you are right about the length of time that is really slow. I did find the ones JD2035RR posted and I have the same question would these be suitable protection and will it still work on 18v because they are listed as 125vAC?

I have 5A breakers on my postwar ZW transformers, and use the internal breaker(s) on my ZW-L.  The 5A ones kick instantly, and the ZW-L onse within 2 seconds or so.  My trains draw a (measured) 2A running which reads about 1.5 on the ZW-L meters, and I run one or two at a time, pulling 12-15 cars each, flat track plan.  Seems to all work.