Trolley Pole v. Pantograph

What's the advantage of pantographs v. trolley poles? Why did the T switch when the LRV's were introduced?

I assume that a pantograph, being bi-directional, does not require operator intervention when changing ends. Are there other advantages? Since the T and many other systems use(d) trolley poles, there must be some advantage there.

One advantage of the pantograph is that it can't ever slip off the wire, meaning the driver never has get out, walk back, and reset it when it comes undone like they sometimes had to with trolley poles. But I'm not sure if that happened often or was just a rare thing.

What about wear characteristics of pantograph vs pole on the wire?

Both use carbon shoes so that the wire is not worn down, the carbon also serves as a lubricant. Overhead for pantograph has to be zig zag in order to prevent the carbon from forming a groove. Pantographs can operate at higher speeds and can transfer more power. Poles are fussier about curved sections.

Pantographs work better at turnouts ( switches). Trolley frogs, required with poles, can be touchy and often in need of adjustment. It is not possible to go through trolley frogs with any speed. I would think 30mph is about it.

- Pantographs are bi-directional. Trolley poles are not.
-The wear surface on a pantograph is huge compared to that of a trolley pole, so the pantograph should need maintenance much less often. (Plus, one pantograph can do the work of 2 trolley poles.)

-Pantograph overhead is different to maintain from trolley overhead. Trolley overhead needs to be pretty much right above the center of the rail to keep the pole on the wire. Pantograph wire is good as long as its over the tracks where the pantograph can reach - I think pantographs have at least two feet of contact surface. Pantograph wire might be a little harder to hang since it needs to be at a higher tension then trolley wire, but its placement around curves, and at turnouts and switches is much easier to hang.

-Pantograph wire is hung in a zig-zag pattern to use the whole surface of the pantograph - if it stayed dead-center over the tracks, it would wear a groove in the pantograph.


The challenges of pantograph vs pole overhead are different. Basically :

-Pantograph overhead requires some higher tensions, but doesn't have a problem with overhead frogs/switches. Pantographs are bi-directional.

-Overhead wire needs much* lower tension, but you have to keep it over the center of the tracks - on curves, and frogs. If its crooked, the trolley poles will de-wire. Trolley poles also go only one-way (Trailing behind the base, usually at the back of the car).

*Trolley overhead can be strung up very quickly, and fairly simply on a straight section from a repair standpoint - its fairly easy to fix. From my understanding (and experience with trolley poles), a little bit of sag in the overhead will be pushed up by the trolley pole, but won't necisarily do any damage because of the geometry between the trolley pole and the wire. If a pantograph hits some wire with low tension, its more likely to catch on the wire hanger, hence the higher tension.

It's funny, I would have thought that trolley wire would enable more flexibility than a pantograph in terms of staying directly above the train/rails. The image that comes to mind is those "trackless trolley" buses that pull way over to the side of the road to make a stop, while the wire remains in the travel lane. This seems to suggest more side-to-side leeway than the couple feet of zig-zag allowed with a pantograph. But maybe the trackless trolley analogy is not quite appropriate?

Trackless trolley poles are made differently. They're a longer pole with a swiveling harp. They've come a long way from the earlier versions, but they still de-wire occasionally, especially at turnouts. There really isn't a way for a pantograph to de-wire unless it snags something that shouldn't be there to begin with. I believe that pantographs started out in popularity in the west on interurbans, but for some reason the rest of the country seems to have gone primarily with poles. Both have their selling points, and one of the pole's is that replacement of a damaged pole can be done in 1/2 hour whereas a pantograph is a project.

wear and tear on wayside system itself a hanger wire might be hanging from the contact wire pantograph dewires a hundred feet of contact wire.

Type7trolley wrote:One advantage of the pantograph is that it can't ever slip off the wire, meaning the driver never has get out, walk back, and reset it when it comes undone like they sometimes had to with trolley poles. But I'm not sure if that happened often or was just a rare thing.

Actually de-wiring of trolley poles occured rather frequently on some lines. It usually would happen at a turnout, or on a sharp turn if a car took the turn too fast. I remember, on Philadelphia's Subway-Surface Route 13 at Chester & Woodland Avenues eastbound ( where the 13 joined with Route 11) there is a slight ( less than 90 degrees) turn where Chester Ave ends and the car turns into Woodland Ave. More than one time the pole on the PCC cars then in use would dewire halfway through the turn, requiring the operator to exit the car and re-wire the pole.

The use of trolley poles was not restricted to lines which operated at slow speeds. Both the Cincinnati & Lake Erie Railroad and the Chicago, North Shore and Milwaukee Railroads operated at speeds approaching 80 MPH with trolley pole equipped equipment. ( The C&LE often ran its trolley pole equipped Red Devil lightweight interurbans at 90 MPH in revenue service and in a filmed "race" with an airplane achieved a top speed of 110 MPH).

typesix wrote:Both use carbon shoes so that the wire is not worn down, the carbon also serves as a lubricant.

Except those lines that used trolley wheels.

Trolley poles are definitely cheaper and more lightweight, and standard overhead is much cheaper than catenary (especially constant-tension catenary.) Still, pantographs with CT catenary are much less likely to dewire or tear down the wire, especially when reversing, and there's not even a remote electrocution hazard for trainmen since they never have to futz with a pantograph.

Surprised more American heritage lines don't use bow collectors on their streetcars. Not as versatile as the pantograph, but cheaper, probably lighter, and looks more authentic. Also, it obviates the need for wire frogs that trolley shoes and wheels need.

mtuandrew wrote:

typesix wrote:Both use carbon shoes so that the wire is not worn down, the carbon also serves as a lubricant.

Except those lines that used trolley wheels.

Trolley poles are definitely cheaper and more lightweight, and standard overhead is much cheaper than catenary (especially constant-tension catenary.) Still, pantographs with CT catenary are much less likely to dewire or tear down the wire, especially when reversing, and there's not even a remote electrocution hazard for trainmen since they never have to futz with a pantograph.

Surprised more American heritage lines don't use bow collectors on their streetcars. Not as versatile as the pantograph, but cheaper, probably lighter, and looks more authentic. Also, it obviates the need for wire frogs that trolley shoes and wheels need.

The Skokie Swift had very good results with what amounted to a bow collector, for those very reasons. It didn't exactly look authentic, since it was unique (at least in the U. S.), but it did the job.

Although I don't know about the forces and mechanical advantages of pantographs over bow collectors, the Skokie Swift bow collectors needed an airfoil (mounted halfway up) to provide additional pressure for the shoe on the trolley wire above.

Swiveling trolley shoes would allow good trolley pole operation on staggered pantograph overhead, although,
1. Frogs would be needed at junctions with frogs having movable points needed at facing turnouts,
2. The wire would have to not zig and zag as sharply from side to side, for example left, straight, right, straight, left, instead of left, right, left, right, etc.

Frequent dewirements at low speed usually mean poorly maintained overhead. A spark other than at a section break or frog means that firm contact between wheel/shoe and wire has been unexpectedly lost for a moment and maintenance might be needed at that spot.

Is the wire itself coated with something? If so, what is it?

GEL wrote:Is the wire itself coated with something? If so, what is it?

Not usually - the conductor on all systems is usually just a solid copper wire with no coatings.