Just to clarify a few details, pictures 3, 4, 5 and 6 actually show the old substation controls and equipment. Notice that 75% or more of the control equipment consisted of "vapor" relays, and and other standard EMD components, like the thru-cable relay on the bus-bar in picture 3.

The only portions reused were the EMD rectifier bank, and the GE "JR" line breaker.

Jeff

Did any property ever do this? I would think that it has no advantage over an overrunning trolley rail, while having all the same disadvantages of the under running system, PLUS being more prone to ice accumulation.

There were guarded over running systems that didn't guard the top; I recall the Michigan Electric design that had brackets that held a 2 x 6 along the track side of the rail, and a wider board on the field side. The intention of the outer board being higher than the rail head was to keep anything that fell across the rail from actually touching it. Michigan electric / Michigan Railways used this system with 1200VDC, and briefly with 2400 VDC. Not for long though, before lowering the voltage to 1200.

Doesn't the Washington DC slot system count as a third rail? I have no idea if it is over running, sideways running or otherwise.

Third and Fourth rails as the hot and return connections were both made by the plow.

Jeff

Why not? If current is seen in a section that is above some threshold for leakage, yet below some threshold for equipment - raise an alarm. If there is a small load on the section, like a string of bulbs, for example, it is relatively easy to monitor that as well, and figure that value into the system.

I am not sure what currents are realistically involved with 600 V shocks from a third rail, but I imagine they are quite a bit less that what a string of bulbs would take.

Of course, if a locomotive is in a section and someone touches the rail while it is there, then the system will not work, so call the ambulance.

I also wonder if one could make a similar safety system that works off the body capacitance, much like "touchless" touch switches that came around in the 1970s.

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Will

Don't know the electrical characteristics of an electric locomotive, but:

It could also be possible to work off of a low-voltage resistance measurement. Pass a low voltage down the lines, measure the resistance, and if it's within the normal ranges for a locomotive, energize the rail to the full voltage. Then, when it senses the resistance rise above a certain level (meaning that the train has passed), lower the voltage and continue on in "sense" mode.

In theory, it should be possible. Probably not perfect, but possible.

There is a system used in a French city with a centered third rail to which power only flows when the light rail vehicle is directly over the segment. Cannot find the web reference quickly, so not sure whether the third rail is energized by electronics or magnetism. Werner Siemens' first electric railway actually used the two rails.

The biggest problem with these "sense currents greater than leakage but less than normal operation" schemes is, what do you do about nuisance trips? Standard breakers are designed to prevent burning up equipment due to major faults, and that normally takes a certain amount of time, so it's no problem to have the breaker automatically reset after a fault. The worst that can happen is that the fault still exists and it will trip out again immediately. Even twenties era breakers can be set to only re-close a certain number of times before they lock out and require human intervention.

But if the avowed purpose is to keep Mrs. Smith's poodle from being electrocuted when it gets on the ROW, what procedure do you follow before you restore power? Since the system is supposed to protect unoccupied track, there may be no train, and therefore no operator, present to make a visual inspection. What do you do, leave the power off while a supervisor tries to drive through rush hour traffic to make an on-site inspection?

There was a time when no trespassing meant just that. What covers some properties provide on their trolley rails is for the protection of workers who have business along the tracks. Some properties have historically chosen not to provide any, and injuries from electrocution are extremely rare. I worked in the Plant Maintenance Dept. of the CTA for thirteen years. In that time, the department had four fatalities from men being struck by trains; all on expressway median trackage, due to the excessive background noise making it impossible to hear approaching trains. In that same length of time, I can't recall any electrocutions amongst the maintenance forces, although there were a couple of old timers who had zapped themselves years before, and survived. There were a couple trespassers that got killed, but they weren't where they belonged now, were they?

I think you guys are worrying over a problem that doesn't exist.

:) wouldn't that be nice :)

Dennis, your statements on this thread are nostalgic for a paradigm of liability that is straight from the 1920s. I won't get political and say whether it should or shouldn't be. However I can safely say that it isn't...

CTA got grandfathered. But I don't believe it has been possible, for lo these past 50 years, to build a new third rail system without coverboards. Even if it was an in-mine or in-plant railroad that was wholly insular, I think OSHA would expect them there.
What's more, if the "contact wire has shocked a human" detection technology were reasonably possible, there would be an expectation of its being installed, under peril of lawsuit if it wasn't.

Unfortunately in this type of lawsuit, the railroads usually send a lawyer which have that same deprecated view of personal liability. They come off as territorial, vain, "blaming the victim", and callously indifferent to horrible personal tragedy. The court is horrified and offended by this, and rules against them more out of spite than anything else.

Maybe if the magic black box detects an anomaly that could be Mrs. Smith's dog - kill the DC, and put a burst of maybe 70 V AC on the line, current limited - that will give the pooch something to think about.

Seriously, we all know it is a problem that does not exist. Getting yourself killed with 600 V DC takes a bit of effort - overwhelmingly most people with these types of shocks go away with just a painful burn and scar. Just about every old time ham radio guy has been bitten at some point, and they are able to brag about it. But the insurance people, and the public, do not know this, and pretty much do not want to believe it. This is what is keeping third rail out of our museums. I would love to see third rail somewhere, anywhere, like for IRM's S-motor, but it is really just a pipe dream. Coming up with a safe system that is "legally" realistic may be folly, but it is the only choice we have.

If anything, it is a fun brain exercise.

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Will