Trolley Pole question

I posted this on the SEPTA forum because of their use of both trolleys and trolley buses (err, sometimes).

I thought of this question (again) while riding the 102 home from work on Monday. I noticed at Drexel Hill Jct a box at operator height with buttons marked Media and Sharon Hill. Presumably the operator presses this button to indicate which route he is taking thus changing the signal/switch or some such combination. This made me think back (via a roundabout thought process!) to trolley poles and how they negotiate diverging routes.

Obviously pantographs contact the bottom of the wire and thus don't have to really negotiate divergances. But how do trolley poles such as on the city trolleys and the trolley buses know which route to take? Does the turning of the vehicle "pull" the pole onto the correct wire?

Simple question, perhaps, but I've always wondered how it worked.

Thanks,

Bob

If you ever notice, there is a little box on the overhead. That's what toggles the switch. When a trolley runs through it normally, the switch stays closed and the trolley goes straight. But when a trolley runs through the box with its turns signals on, then the switch opens and a the trolley goes in the desired direction. The tracklesses do the same thing.

And when the trolley switch doesn't work, the pole dewires with a "thunk" and the operator has to exit the car and re-wire it. This used to happen with some regularity with the PCC's operating on eastbound Route 13 at Chester and Woodland Aves.

Trolley poles tend not to survive bad wire switches. They often get wrecked and car has to go out of service to get the pole replaced.

There's not much of that nature that a trolley pole can survive. That's why the cars were equipped with pole retractors so that the pole could be pulled down by the retractor onto the roof of the car if it dewired for any reason.

I'm not familiar with SEPTA's particular wire hardware, but I've been to a number of museums and heritage trolley systems and I've never seen them use a trolley wire switch. I'm curious what advantage it has over a trolley wire frog. FYI, there is a description of a wire frog here: http://www.nmra.org/standards/rp-5_1.html.

I think there is some confusion on the difference between a Trolley Bus trolley switch, which is solely responsible for changing the direction of the poles to the proper wire, and a trolley frog, which merely directs the poles onto the proper wire based on what the vehicle is doing.

SEPTA's Subway Surface does not use trolley switches at any junction I am aware of. They do not need to, a trolley frog will work just fine and it has no moving parts to break or foul. The trolley's direction is determined well in advance of the pole clearing the frog by the trolley negotiating the switch, and since the trolley will never leave the area directly below the wires (except in instances like 9001 at 42nd and Spruce last spring), the pole can always be fixed along the longitudinal axis of the car. Thus when the car travels through the switch the pole is pulled to one side or the other of the trolley frog and directed onto the next section of wire, directly over the next section of track. I believe there are still a few power-on, power-off switches on SEPTA's trolley network, and these might occasion a box before the switch since the switch would be operated by either going full power or no power through a section of wire hooked to a relay that controlled power to the switch, but there'd most likely be a standard trolley frog down the wire from it.

The Trolley Switch which has been discussed prior to this is similar to the following picture: http://www.pages.drexel.edu/~wld25/P9160080.JPG. As you can see, there are boxes both before and at the switch point so as to move the trolleybuses' poles to the proper wire. These are required for SEPTA's Trackless Trolleys, and indeed of all Trolleybuses the world over because the frogs mounted on the pole swivels, allowing the trolleybus to negotiate it's way around stopped vehicles and other obstructions. However, that swiveling head on the trolleybus's pole means that when it travels through a simple trolley wire frog the poles could easily continue traveling on the straight direction, even though the trolleybus is traveling on the diverging route.

In Germany on Soligen's rather nice trolleybus system there are diverges which have both a trolley switch and a moving frog to cross the left diverging wire over the right straight wire. This is then followed by a section of straight, parallel wire so they operator can make sure the poles really did go on the right set of wires (according to the caption, the actual diverge is visible at the bottom of the hill, by the brown house with white trim in that last photo). Switches like these have higher numbers, and can thus be negotiated at far higher speeds than the simple switches found on SEPTA's and most North American trolley bus operator's systems.

That makes sense that the trolley wire switch is required for trolley coach operation. In places where both trolley car and trolley coach are running in the same street, from which wire (right or left with respect to normal running direction) does the single-pole trolley gather power? This would be the negative wire (-600V with respect to ground), correct?

Either wire of trolley bus overhead can be positive but in most systems in the U.S. the positive wire is on the left (driver's side). This makes it easier for both streetcars and trolley buses to share the positive wire since there are more instances where the bus can move to the curb and still be within reach of the negative wire. For wide streets shared by both vehicles there is a completely separate set of wires for trolley buses

Usually the positive wire is +600 and the negative wire is "0 volts to ground" to match the streetcar track. I have not heard of +300 for the positive and -300 for the negative on a trolley bus only system.

"moving frog to cross the left diverging wire over the right straight wire. "

For a shallow angle crossing, a crossing frog (yes, it's called that) with no moving parts would have a long gap between where the trolley shoe enters and where the shoe exits, increasing the chance of a wrong exit. So an array of linked moving runners (two shaped like equals signs end to end) is installed underneath so as a shoe enters from one end, it causes the runners to re-align to guide the shoe out the correct exit.

No trolley system accomplishes switching by having the trolley shoes tugged in one direction or another by the motion of the car or bus. For trolley buses there is always some guiding runner or mini-rail inside the frog. For streetcars the pole and the frog must have a proper geometric relationship (as the car makes a turn or not) so the shoe fits onto the proper ridges on the underside of the frog so as to go out the correct frog exit, or must use the same methods as used for trolley buses.