trolley wires

What type of overhed wires are used for modern light rail,traditional streetcar and trolley bus and how they differ?

The contact wire (which the trolley wheel or shoe or pantograph shoe touches) may be the same for all.

Usually the wire has a figure 8 cross section so the clamp (ear) used to support the wire does not produce a rough edge where the wheel or shoe passes.

Phosphor bronze (alloy of copper and tin with a little phosphorus added) is most common for good conductivity but not subject to significant stretching as pure copper is.

Trolley wire is figure-8 shaped conductor wire, usually an alloy such as phospher-bronze. The size depends on the load and current type. 600 volts DC requires the biggest wire, since high currents can be drawn. 25000 volts AC can get by with lighter wire since currents are lower for the same power, and there is less loss along the way with AC. Round trolley wire, common in the early years, is now seen only at museums, on yard trackage.

Actually, true 'figure eight' wire is fairly rare, being a kind of 'bar wire' used in specially high wear, high traffic situations. Most 'Light Railways' and railroad electrifications use 'Grooved Wire' for actual contact wire, which is essentially round in cross section but with a continuous grove on either side above the midpoint. screw bolt 'ears' hold the wire without interfering with the running surface, even with trolley poles. Grooved wire is almost an absolute necessity with pantograph or bow trolley. Round wire, seldom seen now was actually of round cross section and the ears were shaped around it
by hand, using special but rather crude tools. Only the bottom of round ware was unobstructed and, when worn, not even that. For us old timers, it was the source of the measured click made by trolley wheels, also now extinct.
Way back, 00 size wire which was if I recall a bit over 1/4 inch in diameter was popular with small, poor lines and 0000 (20% more diameter but geometrically bigger area) was the standard on the 'big' companies.
With todays "light" rail vehicles, 00 might pop like a fuse. There are bigger sizes, defined by circular mils, impossible for trolley shoes, but very nice for today's higher ampereage and, always favoured by railroad electrifications. Trolley wire was almost always Annealed Phospher Bronze. today, there are newer alloys with special conductivity and wear caracteristics.
LS

Today's new LRT lines have generally standarized on 350 MCM grooved hard-drawn copper. It is somewhat larger than 0000. As far as I know, only Denver uses a bronze trolley. Where catenary is used, a 500 MCM stranded copper messenger is used, and acts as a feeder in addition to messenger. Where single-suspension is used ( over streets usually) feeder is installed underground and tapped into the trolley wire every 500 feet or so. It is easly to spot the feeder taps if you look specifically for them

I have always been under the impression that most of the old streetcar companies used copper -- for example the BTC in Baltimore used 000 round wire until the end (1963). Trolley bus wire needed to be kept at a higher tension, so bronze wire, which has more tensile strength but less current-carrying capacity was used.

Pete Schmidt

Good additional information Peter. As you can tell, I'm from the era when
they took down 50 miles of copper wire and put up 5 miles of Bronze
every year. I also drew on local knowlege for general conclusions, aways dangerous. I didn't even know anyone used 000. here in New England,
History was about 00 and now was 0000. I do suspect that hardened bronze was more popular overall than you suspect as, Baltimore held a terminal philosophy
and probably just didn't bother (except for trolleybuses which were supposed to be around for a while). I also dont think we (Boston) generally had a different tension scheme for streetcars. This because I remember my youthful trips elsewhere and, my first views of trolley wire that looked like clothesline, draped over the trolley wheel, in a charming but mechanically
questionable way. Here we had plenty of feeders so immediate conductivity wasn't an issue (and the feeders were copper, they didn't have to flex or tolerate external damage, in theory anyway)
I seem to recall that annealed phospher bronze became widely available just about the time that the more marginal lines couldn't afford it anyway
so, you are correct, it was the standard only of the big wealthy companies with a future,
LS

My reference to figure-8 wire was actually grooved wire, it does have a figure-8 cross section. The other variety is figure-8 bar used in areas where minimal flex is desired, such as on curves in Boston's subway.

Hi All,

From observation, a vehicle, LRV, can successfully negotiate the trolley wires with its pantograph. A trolley, or streetcar, may or may not be able to negotiate a catenary with its wheel contact or its sliding contact. Depends upon the configuration of the catenary. The wheel might pop off the catenary, as it often does on trolley wire switches and pans, and the slide might just snag on some anomaly and tear the catenary down.

A particularly interesting device, and one which gave a terrific display of arcing, dropping rivulets of sparks, was the "trolley guard", a galvanized iron device much like an upside-down v-shaped screen trough which was positioned over trolley wire as well as covering an area alongside and slightly below. These guards were primarily used where a trolley or trackless trolley crossed a railroad grade crossing, and as the guard was live, a collector dewirement did not necessarily result in the trolley's losing current. In the case of trackless, a "negative" guard paralleled the positive one. As the guard was shaped like a trough, it contained the collector within it's live cage-like enclosure. A pole's shoe or wheel could conceivably deflect eight inches side to side underneath the wire on the guard.

pennsy wrote:Hi All,

From observation, a vehicle, LRV, can successfully negotiate the trolley wires with its pantograph. A trolley, or streetcar, may or may not be able to negotiate a catenary with its wheel contact or its sliding contact. Depends upon the configuration of the catenary. The wheel might pop off the catenary, as it often does on trolley wire switches and pans, and the slide might just snag on some anomaly and tear the catenary down.

Wire, when suspended between two fixed points forms a curve called a catenary. By using a long, heavy catenary, called a messenger wire, trolley wire can be suspended over longer distances between fixed supports with less vertical deflection. Hangers spaced short distances apart suspend the trolley wire from the messenger.

There are two major differences between wire designed for poles and wire designed for pantographs. One is in the design of pull-offs, devices used to keep wires in line on curves. Both types use a series of span wires tensioned from a backbone wire to shape the curve. Pull-offs designed for use with pantographs are longer and tensioned from slightly above horizontal. They are compatible with pole operation. Shorter horizontal pull-offs designed for use with poles are tensioned at horizontal, and are not compatible with pantographs. Junctions between wires are handled in three ways. Wire designed for use with poles use castings called frogs which guide the shoe or wheel. They are located at points where the angle of a diverging pole is sufficient to make the pick-up device follow the proper wire. Wire designed for pantographs only has no junctions. Diverging wires are deadended above the through wire and drop to the same level so the pan can follow them. Compromise wire uses short gliders to carry pans over frogs, section insulators and other devices which may cause snags. All can use either somple or compound catenary suspension.

Trolley wire cross sections are show here: http://books.google.com/books?id=ikgJAA ... N95rlHcFdo

3rdrail wrote:A particularly interesting device, and one which gave a terrific display of arcing, dropping rivulets of sparks, was the "trolley guard",.

Significant arcing should not occur at a trolley guard unless the trolley wheel or shoe has actually dewired or unless there is no trolley wire (contact wire) within the guard and the wheel or shoe always bounces around up there. In the latter case hopefully a series of ridges at the exiting end guides the wheel or shoe back onto the contact wire that resumes.

Some catenary uses pull offs rather than horizontal span wires even on the straightaways (tangent track) to keep the contact wire aligned over the track. It is not unusual for, from line pole to line pole, to find: pull-off on left side, no pull off, pull off on right side, no pull off, pull of on left side, no pulloff, etc. This produces the needed zig-zag or stagger to even out the wear on a pantograph shoe. Supposedly compromise pole and pan wire construction works OK with a lesser amount of stagger.

(The messenger is always supported by horizontal span wires if not by bracket arms or the horizontal members of line pole towers.)

Disney Guy wrote:

3rdrail wrote:A particularly interesting device, and one which gave a terrific display of arcing, dropping rivulets of sparks, was the "trolley guard",.

Significant arcing should not occur at a trolley guard unless the trolley wheel or shoe has actually dewired or unless there is no trolley wire (contact wire) within the guard and the wheel or shoe always bounces around up there. In the latter case hopefully a series of ridges at the exiting end guides the wheel or shoe back onto the contact wire that resumes.

Pardon me. I thought that it would be readily understood by knowledgeable traction enthusiasts that I was speaking of instances whereby the collector came into contact directly with the guard, since a wheel/shoe which stays in contact with the wire does not make physical contact with the guard except electrically. In such a case, the guard does not fulfill it's function. It's sort of like a monk wearing a condom. (In theory.)

New trolley wire question:

Does anyone have historical information on how a railroad installed catenary for pantographs if it decided to electrify a line that crossed a street with trackless trolley operation and mesh wire guards in place over the trolley wires?

Or for that matter vice versa, the transit company wished to construct or extend one of its electric lines on a street that crossed an electric railroad's right of way. (I do know of some instances where an interurban trolley company was required to build an overpass if it wished to cross a "main line" railroad's track, even without overhead wire issues.)

Hi DG - I don't think that that would be too big a problem theoretically as a pantograph tends to be fairly flexible vertically, having the ability to ride over any irregularities in a crossover device. It also doesn't need the guidance that poles need, and unless it snags and as long as electrical current is maintained (even with a short lapse), there should be no problem. The trolley coach wires would have to be enclosed by a "guard", as we discussed above.

This illustration is from a favorite book of mine, given to me by a good friend in the industry years ago. It's from a 1948 Ohio Brass Co. catalog which lists their trolley and trolley coach line materials at the time. I don't see why this, or some similiar crossover would not work in pairs for the application which you have described. I really think that it would come down to who was "superior". ie. who was there first, as most likely, most railroads would say "no", but in theory it would work at reduced speed, I believe.