Wiring Revisited

Last post I’d connected all the feeders to the bus wires, and thought I was done. Remember this image?

Completed wiring under table


Remember this line from the previous post?

“You and I both know this is going to bite me in the ass. Next time, I’ll make the feeders longer, run them to a terminal strip, and attach the bus wires there.”

Well, about that.

As soon as I connected power, the power supply immediately shut down. So I went back and did what I should have done in the first place.

tresting wiring


The above image shows the reworked wiring for the ‘urban’ side of the layout. I had to cut the terminal blocks down the center with a hacksaw to isolate the two sides. The bus wires go to one set of terminals, and jumpers connect the remaining terminals where the feeder wires attach. I wired the layout ‘hot’, with the power pack connected, so any shorts would show up immediately. I also checked continuity on every connection.

Close-up of the terminal blocks:

Closeup wiring blocks

The completed re-wiring:



Completed wiring


The lower row of terminal strips feed the ‘sawmill’ side of the layout, and the circuit board is the auto-reverser for the diamond. But there was a bit of a problem with that.

Diamonds are where two tracks cross at grade, and on a model railroad, the polarity of the frogs has to be aligned with the active route or a short circuit will occur. This can be done with a DPDT toggle switch wired to the frogs, or with an auto-reverse module. I elected to go with the auto-reverse.

Auto-reverse works by ‘tripping’ or shorting and then resetting the frogs to match the polarity of the active track. For it to work, the auto-reverse has to have a lower ‘trip’ threshold than the power pack. After examining drawings and drawing on the collective experience of the internet, I wired the crossing with the auto-reverse. I found that the crossing would work on one track, but not the other. When the locomotive would traverse the crossing on the other track, the power pack would trip. It was apparent the auto-reverse wasn’t.

I used a Digitrax AR1 module, and the detection threshold is adjustable from 0.5A to 3.5A. Even on the lowest setting, the module still wouldn’t trip before the power pack. It would sort of work, in that the loco would enter the diamond, the power pack would trip, then the module, and the locomotive would continue. Apparently a small N-scale loco at low speed draws less than 0.5A. After a minute’s thought on whether I could live with this, the answer was ‘no’.

A little carving and fitting to the benchwork, and some research, and I’d wired and installed a DPDT switch below the diamond. I oriented the switch so that the throw would correspond to the siding desired. It works great, but I’m not happy about spending the money for an auto-reverse that didn’t do the job. Well, I’ll have it for the next layout.

I’ve run trains on every track of the layout, and there are no wiring or track issues. Trains will run equally well forward and backward, and there aren’t any electrical dead spots. The layout is now operational, in that I can run trains and do the switching the layout was designed for. I’ll spend some time doing that to make sure the infrastructure is solid. The construction part of building the Northern Pacific project is complete, and I’m really looking forward to the modeling part.



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