#### Re: Where to isolate on large loops and wye

D B

Another take on the terrific discussion of the question of the minimum length between AR-switched segments.  Hopefully thought-provoking if not illuminative.

Alan, another thought for you (and Wouter):

What if (for some reason) you need to have two AR-segments connected;  say, for example that you need an AR segment to enter a turntable (for reasons unknown — this is a hypothetical).  Of course the turntable would be normally AR-wired to accommodate the multiple tracks to which it may be connected.  Now, the train will be short, just the loco (and possibly a tender).

Would it be possible to avoid the death spiral of the AR segments fighting with each other by varying the timing of the AR switches so one, e.g., the one connected to the turntable, is “faster” (quicker response time) than the other, e.g., the one connected to the lead-in track.  That way, the turntable AR would match the polarity of the lead-in track before the AR for the lead-in track was triggered.

We have something like that in the timing between our AR switches and any in-line circuit-breaker, the reaction time for which is typically longer than that of the in-line AR switch.

Could that work?  Don’t know why one would want/need to do this, but the potential variability of AR timing suggests some interesting possibilities for other applications as well.

If it is indeed theoretically possible, would this work only in situations (such as this hypothetical) where the AR segment is very short — the length of a loco.  Not sure I understand why that would be the case, however.

Bill D
N&W Steam Only

On Feb 26, 2021, at 10:57 AM, whmvd <vandoornw@...> wrote:

Don,

One multi-axle pick-up truck isn't always enough. Not if a loco with two trucks is involved, because then the two trucks are electrically connected. A one-truck length will then leave both gaps bridged by one unit leading to the problematic outcome.

Wouter

On Fri, 26 Feb 2021 at 14:52, Don Vollrath <donevol43@...> wrote:
Gents, any good AR control unit will detect a short circuit that occurs on either (or both) rail as metal wheels connected together on multiple axles roll across and span the isolating gaps while exiting an AR section and enter into a fixed polarity section of track. So that causes the exiting AR section to align its polarity to be the same as the fixed polarity track. That part is done.

As that same multi-axle pickup rolls onto and spans the next isolating gaps (either rail or both) to enter a different AR controlled section of track there will be another connection to cause the next AR unit to align itself to the fixed polarity track.

So the minimum length of fixed polarity track separating two separately controlled  AR sections of track needs to be only as long as a milt-axle pickup truck. Think loco, or passenger car, or tender. It doesn’t even need to be used for that purpose as long as there is an electrical connection between axles and wheels on at least one side of the truck to be connected together. This is what will cause the entering AR controller to also align itself to the fixed polarity track.

A convenient choice may be a turnout located between the AR sections  with insulating joiners on all 6 rails and wired for fixed polarity. (Or As someone else has pointed out... am entire double crossover with all 8 rails isolated )

DonV

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