One pan, one pole on cars, locos, and freight motors ...

[westernrrtx]

This is just a guess . If the motor or car was off the wire the air compressor does not operate. Eventually it would loose air pressure in the main reservoir. Some pans are released to lift pneumatically. The single pole allows for easy charging of the air in a dead motor and is handy as a back up if the pantograph gets torn up.

[Warren Thompson]

This is just a guess . If the motor or car was off the wire the air compressor does not operate. Eventually it would loose air pressure in the main reservoir. Some pans are released to lift pneumatically. The single pole allows for easy charging of the air in a dead motor and is handy as a back up if the pantograph gets torn up.

That's a good point. I once saw a photo of a Great Northern heavy electric, pan-equipped locomotive that had a strange trolley pole at one end (instead of a shoe or wheel, it had a bizarre V-shaped gizmo). A railfan familiar with the GN told me the pole was used to activate the air-compressor so the pan could be raised.

[3rdrail]

A major reason for the single pole to be equipped on motors on some roads was that a pole was necessary to activate certain things such as crossing signals. Pacific Electric often used poles for this reason alone.

[JimBoylan]

A major reason for the single pole to be equipped on motors on some roads was that a pole was necessary to activate certain things such as crossing signals. Pacific Electric often used poles for this reason alone.

P.E., one of the Salt Lake City lines, and Lackawanna & Wyoming Valley "Laurel Line" put poles on Diesel locos for this reason.
PRR MP-54 MU cars have a hand pump for releasing the air latch so the springs can raise the pan.

[Stmtrolleyguy]

One of the other reasons for both a pan and a pole is that the two can't really run well together.

A pantograph requires (usually) a continuous flat wire to run under. At a switch, a new wire simply extends sideways, following the side track, and the pantograph, mounted on the locomotive, goes sideways with the locomotive, and runs along the wire that follows the track off to the side. A trolley pole can't do that. A trolley wheel/pole has a u-shaped grove that guides the shoe along the wire. When the overhead wire comes to an intersection, it needs a frog where the wire is allowed to break (just like a railroad track frog provides a place for the flange to cross over the straight rails when a car takes a siding). This frog would catch on the edge of a pantograph, and could damage the wire. Most of the time, wire is strung for either pantographs or trolley shoes, but not both.

(Think a little bit about sliding a shoebox and a hockey stick across a hardwood floor - an uneven board will catch the shoebox, but the hockey stick might slide right over the small bump.)

Also, trolley wire is supposed to be hung directly over the center of the rail, so that the trolley shoe follows the car at switches. The trolley shoe has a replacable carbon insert that contacts the wire and takes the wear and tear. Run a pantograph with the wire directly over the center of the track, and you wear a hole through the middle of your pantograph. (There's a reason they're a few feet wide. Pantograph wire is actually supposed to zigzag a little bit from side to side to wear down a wider area on the pantograph)

As mentioned earlier, trolley wire takes much lower tension (and less maintenance) then overhead wire for pantographs because the upwards force of the pole is lower then that of a pantograph.

Anyone still confused?

[Warren Thompson]

One of the other reasons for both a pan and a pole is that the two can't really run well together.

Run a pantograph with the wire directly over the center of the track, and you wear a hole through the middle of your pantograph. (There's a reason they're a few feet wide. Pantograph wire is actually supposed to zigzag a little bit from side to side to wear down a wider area on the pantograph)

That's why the CTA had to re-configure (i.e. "zig-zag") the North Shore catenary for use by the Skokie "Swift" cars equipped with those innovative trolley-pans.