A: The circuit breakers in postwar transformers were designed to protect the transformer, not the trains. Modern transformers are far more friendly when it comes to protecting the circuit boards within all new trains.
I have heard of some operators with postwar transformers who have put low-amperage fuses in their track circuits for just this reason, but the darned things tend to blow under what might be considered “normal use” with older postwar trains, particularly the dual-motored ones. You may have to experiment until you find a fuse amperage rating you can live with as a happy medium given that you operate a mix of new and old trains.
Scott’s Odds-n-Ends, specializing in toy train electrical products, sells circuit breakers designed for layouts. Four breakers are packaged in one casing, and you can choose from 10-amp, 15-amp, or 20-amp ratings.
It really shouldn’t matter on which side of the two-wire track circuit you install your circuit protection, so the ground would be fine. Perhaps it may be wise to break down and buy a couple of the new power sources that are more compatible with today’s circuit-board technology.
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I am using a classic ZW as my main power source, and wired a 10-amp automotive fuse into the third-rail feed as a circuit breaker. The problem became one of cost: the fuses, which blew instantly at the slightest derailment, cost nearly $1 each to replace. Even when I was standing right by the transformer I could not cut the power quickly enough to save the fuse. After a while, I removed the protection and take my chances. My home layout is 10 x 15', single track main line, with a 4 track yard.
If you're running multi train loops it might be better to put the fuse or circuit breaker on the center rail feed. On most transformers, the ground is common or all grounds tied together.
This can be checked with an ohm meter. Check the resistance between the outer rail of one track (circuit) and the outer rail of another. If it shows a dead short, the gropunds are all common in your transformer, and a fuse in the ground won't protect the circuit or the train.
J. Vobbe
retired radio engineer
I have 3 cw-80's & 2 type r 110 watt transformers ,so far i havent had any problems with the older one's & i run conventional & command control, i will take my chances & not add any circuit breakers.