KB185: Common Rail Wiring and Converting the Clinchfield

This article was last updated on Jan. 12, 2012, 3:18 a.m. | Print Article | Leave Feedback

I'm helping a friend rewire an existing layout from analog to digital.

You might be familiar with the layout, it is the original Clinchfield layout that Model Railroader built back in the late seventies, believe it or not.

The layout, of course, is blocked for analog through DPDT switches which have been eliminated.

I was able to repair the wiring back to original using the drawings that MR printed.

The layout uses common rail wiring, this is what I have to work with, and to rewire using home run wiring would be a MAJOR rework, not doable.

I was able to combine the blocks into 4 power districts, here's where I need help.

Using a Zepher comand station and PM42, because this is what we have, I need explanation and a complete wiring diagram, from command station thru PM42 to track.

I have looked in the DB150 manual, PM42 manual and the Zepher manual and can not find any wiring diagrams for common rail wiring.

We can understand your predicament.

In many cases, when we hear about problems with layout performance, it is because the railroad is a "legacy" layout, wired with common rail.

At the same time, we have to be realistic about the fact that there are a lot of railroads out there that are common rail and are operating Digitrax units.

So, we're sympathetic.

That said, it is not possible to use the PM42 with common rail wiring, this is the reason that there are no examples shown for common rail wiring.

The circuitry requires that each node of the PM42 be separate from the other.

But all is not lost.

In thinking about this, it seems that the best approach is to use a Dremel with a cutoff wheel and to cut new gaps on the common rail.

You could then solder a wire from the section that is created and connect it to the PM42.

Since you have divided the railroad into four power districts, this would seem to require only five such cuts and four solder connections.

You may want to increase the number of these solder connections for better power distribution.

Another source of grief is when gaps that were originally open close because of environmental changes.

The rail swells up because of heat and what once was an open gap is now a closed gap.

In creating your new electrical gaps, you may find it a good idea to glue a small piece of styrene in the open gap and then file it to shape.

In this way, the gap will always remain open.

The Zephyr is a very good choice for the Clinchfield since it probably will never use more than ten locomotives.

Also, using the PM42 is a good choice since a derailment on another portion of the railroad will not effect other portions of the railroad.

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