Re: Short Protection in Yards

Earl T. Hackett <hackete1@...>
 

I've heard of so many schemes to minimize the effect of shorts that I can't remember them all - but none, including automatic reversing boosters, appeared to really solve the problem. My approach to the whole short circuit problem is to simply eliminate the possibility of a short ever occurring - or at least reduce the probability of such an occurrence to an acceptable level. You can take a look at the file I recently uploaded on reverse loop wiring in the files section to see a detailed description of the approach I usually take.

There are two basic causes for a short to occur during normal operation, a derailed metal wheel bridges the gap between two rails of opposite phase or a wheel or conductive truck bridges an insulating gap separating rail segments of opposite phase.

In facing point movements, the threat is from derailed wheels bridging gaps between adjacent rails. That is easily eliminated by insuring that rails of opposite phase have spacing between them much wider that the wheel thickness. To eliminate this problem, I extend the electrical continuity of the frog at least 1.25" in both directions from the point of the frog. With commercial turnouts this could be difficult to achieve, but it results in rails of opposite phase being well separated from each other (at least 1/4" or 6 mm) so a metal wheel can not bridge the gap.

In trailing point movement, there is the potential that an operator will mistakenly run through a turnout with the points thrown against him. All my turnouts have a DPDT switch operated with the movement of the points. One pole controls track power to the frog of the switch. The other pole is used to set signal aspects. As on the prototype, operators are expected to obey signal aspects. If you don't have signals, the second pole could be to control power to a length of rail on the approach to the frog that is at least 1 1/2 times the length of your longest locomotive. If an operator tried to run against the switch while pushing cars, the cars would derail at the points but no short would occur. If he tried to run against the switch with the loco in the lead, the dead rail would cause the loco to stop until the points were aligned properly.

The above relates to conventional turnouts. Double slips and crossings are special problems and elimination of shorts is a bit more complicated, but not particularly difficult.

----- Original Message -----
From: minaret5
To: WiringForDCC@...
Sent: Monday, January 16, 2006 7:16 PM
Subject: [WiringForDCC] Re: Short Protection in Yards


Earl,

As I stated in my original post, I'm just setting up short circuit
protection in the yards, so there is no specific problem now to
relate. All I want to know is if the entire yard is protected
together, where in the event of a short caused by derailment or
anything else,

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