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The switches are so high it's not possible to see how they function on the ground. I really tried to look up information about this on the internet, but there's very little info available, and the info that is there is incomplete. I saw this diagram but still don't understand how the switch works.

enter image description here

It seem simple to have a trolley pole follow the wire, it is simply U shaped and a spring pulls it up, so that force is applied against the wire. However I cannot possibly imagine how does the switches function, mechanically speaking. Also, how do they prevent a short-circuit at the switches' frog where both poles touches each other.

Also, back when tramways (UK: tram, US: streetcar or trolley) also had a trolley pole, did they have switches using the same mechanics as in a trolleybus switch?

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  • $\begingroup$ The secret is that there isn't any switch in the catenary. The crossover ( X ) is isolated. There is a short dead zone between the isolators if the trolly takes the upper leg ( B ). The part ( 4 ) is just a bus bar and termination - nothing moves. $\endgroup$ – Phil Sweet Aug 14 at 19:44
  • $\begingroup$ I can understand the isolation part (although this means the bus runs on innertia and should NOT stop when the pole is in the isolated part or the bus can't restart). But if there's no switch in the catenary, how does the trolley pole pass the switch and to go the correct direction ? $\endgroup$ – Bregalad Aug 15 at 6:43
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We don't have trolleybuses in Ireland where I live so I've never had a good look at the systems used. I'm sure that many ingenious solutions have been invented to manage the switching but here's one:

The switches of the trolleybus network are controlled by the driver of the trolleybus. A switching contact rail is added to the trolleybus network before each switch. If the driver of the trolleybus wants to switch the trolleybus network switch, he operates a switch, which briefly switches on the trolleybus's heating system (a large power consumer). Current must be drawn when driving on the switching contact rail. If the driver of the trolleybus does not want to switch the trolleybus network switch, he operates another switch that switches off the high voltage system of the trolleybus. Thus no current is drawn when driving on the switching contact rail, and the trolleybus network switch does not switch. Source: obus-ew.de.

This seems to be similar to many tram systems in that the driver makes the route selection rather than an automatic switcher. The article goes on to explain some of the problems encountered (some almost comical) with the system in Eberswalde, Germany, and you may find some of the other pages of interest.

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In your diagram the switch boxes marked as (1) are critically important. As the bus begins a turn it pulls one trolley ahead of the other. If turning to the left, the right trolley is pulled slightly ahead of the left. If turning to the right, the left trolley is pulled slightly ahead of the right one. The sequence that the trolleys contact switch (1) tells the it how to switch the tracks in switches (2) and (4).

The above came from a conversation I had with a San Francisco Muni tech many years ago when I worked as a tech at AT&T. He was down the street from a pole I was working on.

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  • $\begingroup$ That's an interesting approach, but sometimes the bus turns only after the switch so if it does that there's a half chance the trolley pole goes the wrong direction+ derails. Also you don't explain how the mechanical switch (2 and 4) works. Also this fails explain how it'd work for retro tramways using only a single trolley pole. $\endgroup$ – Bregalad Aug 15 at 6:41
  • $\begingroup$ @Bregalad, at least in San Fran, anyway, the trolleys are located sufficiently rearward that the bus is well into it's turn before the trolleys slide across the activating switches. As for single trolleys, I never did find out how those worked, though I always figured it was just mechanical pressure on the switch. Also, I'm sure Transistor's answer is applicable to many trolley systems. $\endgroup$ – BillDOe Aug 15 at 20:53

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