by rail10
is the third rail system used on the lirr similar to the one used in the nyc subway?
Railroad Forums
LIRR third rail power supply
- Discussion of the past and present operations of the Long Island Rail Road.
Moderator: Liquidcamphor
by Clem
The geometry of the LIRR's third rail and the Subways' rail are different. The subway spaces its rail closer to the running rail and has lower insulators.
If you go back to 1910, when the BRT and the LIRR had a joint service, there was a compromise shoe that would move to work on both systems. See Seyfried's Volume 7. There's a picture of it in there.
The LIRR is presently 750 Volts, raised after the arrival of the M-1's from the NYCTA's 600 Volts. When the M-1's first arrived, the voltage was so low in some places, that the overhead lights wouldn't work. They had to change the light ballasts to get the lights to start on West Hempstead's 200-Volts.
Clem
If you go back to 1910, when the BRT and the LIRR had a joint service, there was a compromise shoe that would move to work on both systems. See Seyfried's Volume 7. There's a picture of it in there.
The LIRR is presently 750 Volts, raised after the arrival of the M-1's from the NYCTA's 600 Volts. When the M-1's first arrived, the voltage was so low in some places, that the overhead lights wouldn't work. They had to change the light ballasts to get the lights to start on West Hempstead's 200-Volts.
Clem
by MACTRAXX
Clem: Interesting! Do you know the difference off hand? I also know the shoes are different also. NYCTA shoes are much more rounded than the more squared LIRR shoe. Another thing I remember from the past was the very small rod third rail in places like West Hempstead and visible on older yard tracks. Has it all been replaced? With the low voltage at WH and the light problems you describe how did trains even start up from there? MACTRAXX
EXPRESS TRAIN TO NEW YORK PENN STATION-NO JAMAICA ON THIS TRAIN-PLEASE STAND CLEAR OF THE CLOSING TRAIN DOORS
by Clem
MAC,
I'm not sure of the subway's configuration. If I can find it, I'll post it here.
The low voltage was enough to get the trains rolling. DC motors are very good at handling lower voltages. The problem was in the overhead lights. The reduced speed and resultant output of the motor alternators (which generate AC for lighting, etc.) wouldn't generate enough power to relight the tubes after passing over crossing gaps.
What you recall is the old "T" rail that was used as third rail on some yard tracks. It was a very light rail without any base. Special brackets were used to stand it up on the insulators. It still survives on some yard trackage. Since the new Fibreglas insulators can't be used with it, you'll find it with the old brown porcelain ones.
Around 1981 or so, the Railroad began using a composite third rail which is steel with aluminium strips applied to the sides. This reduced the resistance in the rail and the voltage drop between feeders and substations. The newer rail is also bonded between joints with aluminium bars instead of steel ones.
What some folks fail to realize is that the running rails comprise the return path for the 750 volt propulsion current. So when a train is operating nearby, the running rails are carrying current just as the third rail does. The reason it's not insullated and you don't get shocked with it is that this return path is shared with the ground. As the ground is nowhere nearly as good a conductor as the running rails, care has to be taken not to interrupt the return path when running rails are removed. More than a few vandals discovered this the hard way when stealing copper return wires or impedance bonds. They got zapped.
The return current in the ground also tends to seek out more attractive paths toward the substation which can be buried water or sewer pipes. This too has caused injury to utility workers. It also distroys the piping long before its time. This is the reason for the heavy bonds between lengths of running rail.
Clem
I'm not sure of the subway's configuration. If I can find it, I'll post it here.
The low voltage was enough to get the trains rolling. DC motors are very good at handling lower voltages. The problem was in the overhead lights. The reduced speed and resultant output of the motor alternators (which generate AC for lighting, etc.) wouldn't generate enough power to relight the tubes after passing over crossing gaps.
What you recall is the old "T" rail that was used as third rail on some yard tracks. It was a very light rail without any base. Special brackets were used to stand it up on the insulators. It still survives on some yard trackage. Since the new Fibreglas insulators can't be used with it, you'll find it with the old brown porcelain ones.
Around 1981 or so, the Railroad began using a composite third rail which is steel with aluminium strips applied to the sides. This reduced the resistance in the rail and the voltage drop between feeders and substations. The newer rail is also bonded between joints with aluminium bars instead of steel ones.
What some folks fail to realize is that the running rails comprise the return path for the 750 volt propulsion current. So when a train is operating nearby, the running rails are carrying current just as the third rail does. The reason it's not insullated and you don't get shocked with it is that this return path is shared with the ground. As the ground is nowhere nearly as good a conductor as the running rails, care has to be taken not to interrupt the return path when running rails are removed. More than a few vandals discovered this the hard way when stealing copper return wires or impedance bonds. They got zapped.
The return current in the ground also tends to seek out more attractive paths toward the substation which can be buried water or sewer pipes. This too has caused injury to utility workers. It also distroys the piping long before its time. This is the reason for the heavy bonds between lengths of running rail.
Clem
by MACTRAXX
Clem: Good reply as always! You answered many of my questions including giving some insight on third rail DC power.I often wondered why tracks in third rail territory had double thick copper bonds at joints. Why when the LIRR replaced third rail did they cut it in sections instead of loosening the bolts on the joiner plates? As for the composite third rail I remember back in the mid 80s when the LIRR began to place third rail along the Ronkonkoma branch for installation. I noticed a silver sticker on the rail itself. I peeled it off and kept it - it was called TRANSDUCTOR from the H.K. Porter Company. I still have this sticker today. Thanks again - MACTRAXX
EXPRESS TRAIN TO NEW YORK PENN STATION-NO JAMAICA ON THIS TRAIN-PLEASE STAND CLEAR OF THE CLOSING TRAIN DOORS
by pennsy
Hi All,
Excellent discussion fellas. I knew about the 600 VDC, and had heard about the switch to 750 VDC. By the way, this matches the trend towards 750 VDC in the West coast. All the Light Rail Vehicles, subways etc. use 750 VDC. And yes, you do NOT want to get zapped by it since the current available is up in the KiloAmp range. It will literally fry you.
Excellent discussion fellas. I knew about the 600 VDC, and had heard about the switch to 750 VDC. By the way, this matches the trend towards 750 VDC in the West coast. All the Light Rail Vehicles, subways etc. use 750 VDC. And yes, you do NOT want to get zapped by it since the current available is up in the KiloAmp range. It will literally fry you.
by Nasadowsk
AFAIK, London used a forth rail because at the time, it was not known if you could use the running rails. Remember that it was one of the earlier large scale high current electrifications. I recall reading that there was also considerable concern about corrosion, etc.
I've heard a few more recent LRT systems have looked at 1.5kv due to expected higher running speeds and longer distances.
Hey, history repeats itself! Interurbans went up to 1.2kv, and even ran dual system (600/1.2k) equipment.
I think the record still stands at 2400 for third rail. It was not a success. Bart runs 1kv, but is mostly (all?) direct fixation track, which means the ballast/dirt won't creep as close. Oh yeah, and it doesn't snow in the bay area much.
ISTR that Switzerland, of all places, had 1.5kv third rail on a few narrow gauge lines, at one time.
I've heard a few more recent LRT systems have looked at 1.5kv due to expected higher running speeds and longer distances.
Hey, history repeats itself! Interurbans went up to 1.2kv, and even ran dual system (600/1.2k) equipment.
I think the record still stands at 2400 for third rail. It was not a success. Bart runs 1kv, but is mostly (all?) direct fixation track, which means the ballast/dirt won't creep as close. Oh yeah, and it doesn't snow in the bay area much.
ISTR that Switzerland, of all places, had 1.5kv third rail on a few narrow gauge lines, at one time.
by MACTRAXX
Clem: Some further thoughts I have on this third rail issue: I would like to know about,for example tracks around PSNY which have both third rail and overhead wire-how does the return circuit handle these voltage differences? We all know how electricity and water do not mix-how dangerous was it to be around the third rail when it was very wet or for example an emergency in a rainstorm? Was the stray current a problem even when it was bone-dry for example? You mentioned insulated boots elsewhere-are these commercially available? What you said about them saving you at least a few times from injury or worse they are well worth having if necessary! The London 4-rail observations were interesting also. Thanks-MACTRAXX
EXPRESS TRAIN TO NEW YORK PENN STATION-NO JAMAICA ON THIS TRAIN-PLEASE STAND CLEAR OF THE CLOSING TRAIN DOORS
by dukeoq
Back around forty years ago, when the railroad still carried mail, it was the job of one of the yard jobs in the Jamaica Storage yard to go to the mail dock at the east end of the Advance yard to pick up a loaded mail car for one of the eastbound diezel trains.
One very rainy evening we went to make such a move and I had been out switching the yard for several hours and was much wetter than I thought.
I climbed down off the platform at the mail dock and got between the cars to pull the cutting lever when I was hit with what felt like a Chinese gong slamming across the top of my head.
I knew immediately what had happened. I was on third rail and could not move or cry out. People walking around on the platform did not know what was happening below as I stood there motionless, my lamp held high over my head to give a sign to the engineer and no one knew my trouble.
Eventually the sensation wore off and I was able once again to move.
My wet pants must have brushed for a very brief moment onto the third rail and made my head feel like it was hit by a sledge hammer.
That was 600 volts and I was very careful not to mix third rail and wet clothing after that.
One very rainy evening we went to make such a move and I had been out switching the yard for several hours and was much wetter than I thought.
I climbed down off the platform at the mail dock and got between the cars to pull the cutting lever when I was hit with what felt like a Chinese gong slamming across the top of my head.
I knew immediately what had happened. I was on third rail and could not move or cry out. People walking around on the platform did not know what was happening below as I stood there motionless, my lamp held high over my head to give a sign to the engineer and no one knew my trouble.
Eventually the sensation wore off and I was able once again to move.
My wet pants must have brushed for a very brief moment onto the third rail and made my head feel like it was hit by a sledge hammer.
That was 600 volts and I was very careful not to mix third rail and wet clothing after that.
by Dave Keller
That was too close!
We're very glad (as I'm sure you are, too) that you're able to talk about it with us now!
Dave
We're very glad (as I'm sure you are, too) that you're able to talk about it with us now!
Dave
by pennsy
Hi All,
That sounds like something I have heard before. You were quite fortunate in that case. I have heard of similar occurences but with snow. That one wasn't so lucky. I have a cousin working the NYC subways as an electrician on the signals etc. Every now and then he tells me of someone that didn't make it. And that is 600 VDC. I understand that some of the third rails on the east coast are just like the ones on the west coast, 750 VDC.
That sounds like something I have heard before. You were quite fortunate in that case. I have heard of similar occurences but with snow. That one wasn't so lucky. I have a cousin working the NYC subways as an electrician on the signals etc. Every now and then he tells me of someone that didn't make it. And that is 600 VDC. I understand that some of the third rails on the east coast are just like the ones on the west coast, 750 VDC.