I'm totally new to modelling and getting older (retired train driver) so may be brain not as sharp as it was. LOL   So far have only installed 4 motors (Cobalt digital iP) Catch point, single point and double slip.  I'm wiring all point motors from their own power supply a Digitrax Zephyr Track power will be from a Digitrax booster. To it things simple (so I thought) I am wiring all in the same manor. Red wire from Rail A on the Digitrax to the first (on the end) DCC in of the point motor and Black wire Rail B to the second DCC in on the point motor. I know not pos/neg but keeps it simple for me.
All work fine accept the single turnout point motor. When I tested it there was a short as soon as the test loco hit the frog. However when I reversed the the DCC in wires all was well.  

If someone could explain why that happened I would be very grateful. I must have a fundamental lack of understanding of how these circuits work.   As I have another 20 motors to instal I would like to know what I'm doing wrong.  For the test track power was supplied from the Zephyr.  

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Nothing too complicated..

The Digital IP frog terminal (3)  is simply the DCC feed in, switched back out again.
It is a SPDT switch - single pole, double throw with the DCC IN as the left/right of the switch and the frog terminal as the common of the switch.
So if there is a frog short, the fix is to swap over the DCC IN terminals to swap the polarity of the frog terminal.

Swapping the DCC IN does not alter the operation of the Digital IP motor.


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Thanks Mick
Seems I have lots to learn re this DCC stuff but thats the enjoying part and keeps the grey matter moving.

Thanks again
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I think that, while it is generally regarded that there is no 'polarity' in the normally accepted sense in DCC, I find it does help to understand such arrangements as this if you consider your red and black wires as a polarity.  
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