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Don, actually, installing a fuse in the common would provide better protection for the ancient PW Type Z/Zw transformer, as you can limit the current draw to 10 amps. Do note that all U terminals are connected internally, so you can use one as common for all circuits.  Having said that, the terminals are riveted to a common internal buss, and over the decades these connections may have deteriorated.

I also recommend using breakers rather than fuses.  The latter cost to much, as they'll blow on every derailment.  In a recent thread GRJ has piinted to a source for magnetic breakers.  I currentlyuse thermal breakers, which are slower and cheaper, but am considering whether to switch to the magnetics GRJ recommends..

RJR, this string is very confusing to me, but your comment seems to be at my level. Let me tell you where I’m coming from

in a previous chain I posted questions about my Christmas trains - two trains circling the tree on two circles of fastrack powered by my ZW.  One of the power lines and the carpet melted presumably because of my grand children’s derailments. I replaced the badly worn power lines with 16 gauge for the remainder of the season   I also decided to add some precautions to the permanent layout I’m building using tubular track, my ZW, and and a 1032.
So, I decided some kind of fuses or circuit breaker. Your answer to my question was unexpected and simple if I understand it. Put a circuit breaker on the common bus - U on the ZW. I had assumed it would be a 10 amp breaker on terminals A, B, & D for the three trains and a lower amp breaker for C. Tell me if there’s anything right about that.

with the 1032 I am using variable power  terminals U & B for the trolley. (U to the center rail).  Fixed power from B & C powers some accessories on the trolley lines and is converted to DC for a timer relay to control the stops & starts on the trolley line.

where do the circuit breakers go?

Don, I'll answer your last question first.  Breakers and fuses should always be on the transformer outputs, so they protect everything downstream.

A fuse or breaker in the U circuit has one purpose, to protect the transformer.  A postwar ZW shouldn't be subject to more than 10 amps.  FYI, the ZW internal breaker is in the U circuit, but is very slow acting. It provides no protection if there is a short between any of the ABCorD outputs, which is possible.

A current of less than 10 amps can cause considerable heating on the layout.  Breakers or fuses should also be put in each of the output circuits to protect the layout.    They should have the lowest amp rating that will operate your trains, which is usually less than 10 amps. On my layout, I run 6 TIU channels.  Some channels control areas where probably not more than 1 or occasionally 2 trains will be moving at once, such as yards.  These get 5 amp breakers.  Mainlines where I might have 3 locos running get 7.5 amps.  But I do not turn smoke on.

No fuse or thermal breaker opens immediately upon the current being exceeded.  There is a lag while the thermal elements heat up.  By using smaller amperage breakers, they open sooner on a short.  In another thread, Gunnrunner John mentioned certain magnetic breakers available from Digikey.  Magnetic breakers should open as soon as the rating is exceeded.  Electronic breakers, such as in the Lionel PH-180 Powerhouse,  also open upon exceeding the rating.  I am considering replacing my thermal breakers with magnetics, but have some higher priority matters to deal with.

FYI, I use Blue Sea marine push button breakers, available on-line from Defender Marine.  They are in the $5-$6 range and have worked well.

Hope this helps.

RJR

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