Re: Wiring Up a Manual Turntable?



When you discuss reversing phase/polarity segments and use of auto-reverse devices in an article, I suggest you discuss WHY a reversing segment must be longer than one’s longest train. Not too long ago I was a total newbie, and often saw that rule recited (including in universally respected websites). But I didn’t see a cogent (and non-technical) explanation for that rule, or similarly, a clear and concise explanation why two reversing segments cannot be connected to one another.

I figured out the reasons underlying both those rules after giving the issue considerable thought (because frankly I did not intuitively understand “why”). In retrospect my failure to understand was influenced by my (mistaken) “forward-looking” focus on how an AR device switched phase/polarity of the reversing segment as the front wheels of the engine passed from the reversing segment to the non-reversing “mainline.” Coming from the world of DC, I was amazed at the prospect of auto-reversing and simply failed to consider what was going on at the rear of the train as the phase/polarity of the reversing segment switched based on what was happening at the front of the train.

Once I began to look “both ways,” and to consider both front and rear consequences of a change in phase/polarity, the underlying rationale for both rules came into sharp focus. That in turn led to an understanding of the relationship of the AR segment to the segments to which it is directly connected and an appreciation of why two reversing segments cannot be directly connected to one another.

Bill D
N&W Steam Only

On Feb 22, 2021, at 9:10 AM, wirefordcc <> wrote:

Hi Dave,

I should have said, keep those ideas coming! The one scary thing I worry about is running out of ideas for my column. I scan my Q&A forum, as well as some of the other forums for ideas. So far, so good.


Allan Gartner

-----Original Message-----
From: <> On Behalf Of Dave Emery via
Sent: Sunday, February 21, 2021 2:57 PM
Subject: Re: [w4dccqa] Wiring Up a Manual Turntable?

Alan, I think ‘wiring a turntable for DCC’ would make a great MR column.


Join to automatically receive all group messages.