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Monday, October 21, 2013

Grand Union Overhead

I've seen some Grand Union track-plans published.  But never for the overhead wires!

So the engineering dept of the Dan D. Sparks Plywood Development and Transportation Co. has its work cut out for it designing a reliable working overhead cantanary wires for this intersection.

This detail from a Shorpy photo is the only photo I've ever seen of a (non-modern light rail) Grand Union Intersection. Its a bit asymmetrical with one of the streets cutting off at an angle like that.  But lets see what can be learned from this photo anyway.

This is my interpretation of the wiring configuration gleaned from the Shorpy photo. And I believe this arrangement can be improved upon. I know one factor for reliable overhead construction is that the pulloff wires should be perpendicular to the contact wire. Something that the traction company in the photo hadn't yet discovered in those early years. Having a pulloff wire pulling the contact wire at an angle will increase the tension on one side of the contact wire, and cause slack on the other end. Nice balanced overhead tension is desirable. 

Another interpretation. Here I'm trying to counteract pulloff wires pulling off at an angle by having a second pulloff pull from the other direction. But I have found that the tension of having too many pulloff wires tends to cause the contact wires to loose their tension and sag. A model overhead needs to be a simplified version of the prototype.

Getting a little too complicated here. The nice thing about the rotationally symmetrical design of the Grand Union is that each contact wire has a mirror image counterpart that it can pull off from. All that the line poles have do is simply hold the whole thing up!

Here we go! To get a pulloff wire that  pulls off the contact wire at a right angle when there isn't a place for the other end of the pulloff wire to anchor to requires a backbone wire. Support wires can attach to the backbone wire at an angle, but the backbone wire provides a place for the wires pulling off the contact wire to attach at a right angle.

I think I have done enough figurings. I think now its time to dive in and start laying in some of these wires and see where it gets me. Doing these drawings has given me a good idea of what I need to do and the confidence needed to cut into the mainline wire and add in the turnout pans and diverging route wires. Yes sir! It has given me the confidence to cut in and lay in those diverging routes!


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