I have an old ZW, 50's era, and a new Legacy Mikado I want to run. I've searched through quite a few threads and they all say to get a circuit breaker to protect the insides of the modern trains.
Could someone please post a pic or two of what a breaker installed looks like? And then maybe a part # and where to get them?
As they say a picture is worth a thousand words! Thanks.
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Circuit breaker / TVS "school" HERE.
Why dont you use a in line fuse holder. Put it on the hot or plus terminal then hook to track or whatever. Use a 5 or 6 amp fuse . This is cheap and easy way to do this...
I am using fuses as well. I went to Radio Shack, bought glass automotive fuse holders, and fast-acting fuses (or something like that). I believe I am using 10amp fast-acting fuses for each handle of my ZW. As soon as something happens, the fuse blows. Actually, the power is usually off before I notice it!
Circuit Breakers protect transformers from over current. TVS protects the insides of engines from voltage spikes. You need both components. The voltage spikes that can damage engine innards will not trip breakers as over current does.
The Breaker connects inline on the Hot[A,B,C or D,] wire which is referred to as "in series" by Sparktricians. The TVS connects between the Hot and Common["U"] wires or terminals ["across the line" or parallel in electricspeak].
See fuzzy photos below for the most basic,simple TVS placement between U and A posts of pw ZW:
Dewey - For some reason only the last picture is showing.
Would the purchase of a new transformer; modern ZW or Z-4000 eliminate the need for the TVS or fuse?
Yes, Jeff, it would. The newer transformers are full of electronics and they all contain fast acting circuit breakers that not only protect the transformer, but also anything connected to the outputs, be it trains or accessories.
Resetable CBs are also available from after-market train folk, like Scotts-Odds-n-Ends.
It usually is helpful for those who are learning to state what an acronym means.
In this case, TVS stands for Transient Voltage Supressor.
Alex
I edited the post above Jeff--hopefully you can see through the "fuzz".
Johnsgg1:
Breakers protect against over current surges but will not trip upon a Voltage Spike which requires a TVS to "clamp" it.
If you have tech data to the contrary share it with us. Thanks.
Dewey - Pics came through.
So not to oversimplify, but I might. A newer ZW or Z4000 will eliminate the need for the circuit breakers but the TVS, Transient Voltage Supressor, will still be needed for protection.
Having the trains up only at Christmas it gets a little harder to remember all the nuances involved.
Thanks for all the comments!! 
As regards transformers with relatively "quick-acting" thermal breakers, no need for external breakers. That is my opinion based on a Z4k I once owned as well as use of 180 watt Power Houses.
At one point I used homemade four channel Breaker Boxes [4 Potter-Brumfield breakers] linked to my pw ZWs. These breakers tended to be slower to trip upon over loading [too many lighted cars] but a "dragging derailment" tended to trip almost immediately. Nothing scientific just my random experience over time.
I apply TVS for all type transformer wire runs except when playing with the postwar electro-mechanical engines that my Grand kids run[Thomas,etc].
As regards the need for and use of the Transient Voltage Suppressors[TVS]on all existing O-gauge transformers; I have relied on written coverage plus information from EEs such as Bob Nelson of Austin from the CTT Forum and in the very early years of this Forum by Cam[Penn Station]. In a more recent time EE Dale Manquen has been a great resource for the Forum regarding not only TVS but a broad range of O-gauge electronic applications.
Personally, I am long since obsolete regarding electronics. 
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