Circuit Breaker Circuit Placement

No, do not put it in the common!  You need to put it on the hot side.  A breaker on the common does NOT protect against the any of the A, B, C, D outputs being connected to each other.  There is no breaker protection with the ZW design for that scenario, and if that happens, it allows unlimited current to flow and certainly destroy the transformer and likely get hot enough to cause a fire.  The factory breaker was incorrectly put in the ground circuit, that's a bad design from the start!

Note that none of the red lines have any circuit breaker protection.  If any one of the posts are connected together and the rollers are not PERFECTLY aligned on the same winding, massive current can flow and bad things happen.

As you can see, the circuit breaker only protects for current flow between the U posts and one of the A,B,C,D posts.  Not good enough!

@gunrunnerjohn posted:

If any one of the posts are connected together and the rollers are not PERFECTLY aligned on the same winding, massive current can flow and bad things happen.

If I am recalling the test I did several years ago correctly, a difference of 6-7 volts resulted in a 30+ amp short that pegged the ammeter I was using.

Rob, I remember you mentioning a test.  Truthfully, even a couple of turns difference will cause immense currents to flow and probably destroy the transformer windings.  Once you burn the enamel off, it's lights out!   I've seen a ZW with a few turns on the secondary cooked, I suspect that's what happened to it.

Not an expert on this topic, but I do have questions.

How do most folks get away with this when running a train from one block to the next? I have read that you should simply make the (ZW) handle positions match as closely as you can. I'm sure not every person creates a perfect match every time, so what's the secret? I'm guessing the answer is short duration as the train contact rollers quickly traverse from one block to the other?

Also, if you run your engine slowly and encounter such a voltage mismatch between blocks, wouldn't it most certainly burn up any wires that connect both sets of contacts together, assuming your engine has more than one set? I would guess a PTC of the appropriate rating would be a good idea to connect in one of the wires coming from one set of contacts in this case? That is what I do to all of my passenger cars where two sets of contact rollers exist, as a precautionary measure against awkward derailments, or in this case, awkward throttle mismatches.

George

@GeoPeg posted:

How do most folks get away with this when running a train from one block to the next?

Short duration and resistance of the wiring & connections.

@GeoPeg posted:

Also, if you run your engine slowly and encounter such a voltage mismatch between blocks, wouldn't it most certainly burn up any wires that connect both sets of contacts together...

This has been burning up the wiring in Polar Express cars by the hundreds.

Thank you, everyone!  So, a new question.  Should I be putting breakers on the B and C channels also?

It depends if you are using B and C for track power or as power for accessories. Best practice would be to use a breaker on all  channels you actually use. That said, if B and C are track power, then it is a must. If they are used for auxiliary power for accessories and the like what I would recommend is a fast blow auto fuse if the cost of a quick blow breaker is too expensive.  IME auxiliary power unless you miswired something is unlikely to have routine shorts the way track power will (derailments or other fun stuff), so  fast blow fuse is rarely going to blow and takes like 5 seconds to swap out and is cheap.

`I would size any protection to the smallest wire in the circuit.

@John H posted:

`I would size any protection to the smallest wire in the circuit.

I actually recommend sizing the protection to the largest load you anticipate, that may be far smaller than the #12 wire you used to wire the layout.

Can someone recommend a line of circuit breakers to use and where to buy them?  I assume these are also needed for the KW transformers.

Thanks.

@TrainCzar posted:

Can someone recommend a line of circuit breakers to use and where to buy them?  I assume these are also needed for the KW transformers.

Thanks.

Here's a thread that should be helpful.

airpax-snapac-hydraulic-magnetic-circuit-breaker

@gunrunnerjohn posted:

I actually recommend sizing the protection to the largest load you anticipate, that may be far smaller than the #12 wire you used to wire the layout.

You're right. I should have been more specific. I was leaning more to the accessory side of things. 5 amps would melt a lot of accessory wires in a short.

better idea..........toss out your ZWs  and use Bricks.