trey824 Posted July 16, 2009 Report Share Posted July 16, 2009 correct me if im wrong,but are the two rail that the trains run on also carry a small amount of electric current? ive noticed it at interlockings as there are wires connected to the rails,also even in some stations. Quote Link to comment Share on other sites More sharing options...
trainman8119 Posted July 16, 2009 Report Share Posted July 16, 2009 correct me if im wrong,but are the two rail that the trains run on also carry a small amount of electric current? ive noticed it at interlockings as there are wires connected to the rails,also even in some stations. Yes there is a small amount of electricity. This is part of the signal system (or at least it should be). You will see this on Metra lines as well as freight. Quote Link to comment Share on other sites More sharing options...
Guest Posted August 11, 2010 Report Share Posted August 11, 2010 Yesterday I went for a visit on my day off to my firehouse. Our truck recieved a call of a "person on CTA tracks" so I took a ride with my truck company, we raced to the Pulaski/Congress Blue Line station, we hurried down to the platform and found a white male lying on the third rail of the inbound track, he was obviously electrocuted, It was a sad scene. Power was of course shut off to the rails while we removed the person off the third rail. Quote Link to comment Share on other sites More sharing options...
busfan2847 Posted August 11, 2010 Report Share Posted August 11, 2010 correct me if im wrong,but are the two rail that the trains run on also carry a small amount of electric current? ive noticed it at interlockings as there are wires connected to the rails,also even in some stations. Yes. The two running lines are the current return to complete the electrical circuit (however as with the neutral wire in your house circuit the voltage is ~0V). If the circuit is not completed the train will not move. This is the same for Metra Electric with the supply from the overhead and the return the running rails. The only time this is not the case is if there is a fourth rail (usually between the running rails) which is used for current return (London Underground is the main user of this with the third rail held at +420V and the fourth rail at -210V to give a total voltage of 630V dc). Note you will not get a shock from the running rails as you need a source of voltage high enough to cause sufficient current through the skin, muscles or hair. Quote Link to comment Share on other sites More sharing options...
busfan2847 Posted August 11, 2010 Report Share Posted August 11, 2010 Yes there is a small amount of electricity. This is part of the signal system (or at least it should be). You will see this on Metra lines as well as freight. Track circuits on non-electrified tracks can use basic dc voltages at low currents. For electrified tracks where the tracks are used for current return which would swamp dc track circuits. To get over this, AC track circuits use alternating current signals instead of DC currents. Typically, the AC frequency is in the range of audio frequencies, from 91 Hz up to 10 kHz. The relays are arranged to detect the selected frequency and to ignore DC and AC traction frequency signals. Again, failsafe principles dictate that the relay interprets the presence of the signal as unoccupied track, whereas a lack of a signal indicates the presence of a train. Quote Link to comment Share on other sites More sharing options...
Vinny Posted August 13, 2010 Report Share Posted August 13, 2010 There's a fourth rail on the O'Hare branch of the Blue Line (added when they redid the rails and ties). I haven't noticed it on other lines; is this becoming a new standard for CTA, or have something to do with the new 5000s? Quote Link to comment Share on other sites More sharing options...
Busjack Posted August 13, 2010 Report Share Posted August 13, 2010 There's a fourth rail on the O'Hare branch of the Blue Line (added when they redid the rails and ties). I haven't noticed it on other lines; is this becoming a new standard for CTA, or have something to do with the new 5000s? What's the location of the rail? For instance, there are rails on the inside of the rails on the L apparently to hold the trains' wheels if they derail. There is also the possibility it has to do with the new signal system, as some others have indicated up this thread, although that should have been substantially done. Quote Link to comment Share on other sites More sharing options...
Vinny Posted August 18, 2010 Report Share Posted August 18, 2010 What's the location of the rail? For instance, there are rails on the inside of the rails on the L apparently to hold the trains' wheels if they derail. There is also the possibility it has to do with the new signal system, as some others have indicated up this thread, although that should have been substantially done. It's more or less right down the middle (centered on the ties) and the lengths of rail are connected with a weld and heavy cable. I'll try to remember to snap some pics in the morning at Irving Park - IIRC the rail doesn't extend too far past the SB end of the platform. Quote Link to comment Share on other sites More sharing options...
Vinny Posted August 19, 2010 Report Share Posted August 19, 2010 What's the location of the rail? For instance, there are rails on the inside of the rails on the L apparently to hold the trains' wheels if they derail. There is also the possibility it has to do with the new signal system, as some others have indicated up this thread, although that should have been substantially done. OK, here's pictures of the fourth rail on the SB tracks at Irving Park. It's somewhat in the middle of the rails, with continuity established between each section. As I rode into town this morning I tried to take note of the presence of a 4th rail on the NB tracks. The middle rail at Irving Park continued to Addison, where it became two rails, still in the middle, both with continuity between sections of rail. Couldn't tell if it continued through the Kimball subway or not. After leaving the subway portal, on the Milwaukee L, there were still two rails in between the main rails, but these were close to the edges, probably to control derailments as you previously mentioned. No continuity between those rail sections, so probably no current travelling along those inner rails. I got off at Jackson in the Dearborn subway and there were no inner rails on the tracks there. So maybe the signaling is on the running rails in the Dearborn subway and the L but on the fourth (and fifth) rail on the O'Hare branch? Seems kind of random. Quote Link to comment Share on other sites More sharing options...
Wolfman Posted September 1, 2010 Report Share Posted September 1, 2010 Quote Link to comment Share on other sites More sharing options...
Wolfman Posted September 1, 2010 Report Share Posted September 1, 2010 It's an ATC sensor. Cab control. Nothing more. It was connected to the old tower at Jefferson Park. Very short-lived, but it's still there. They installed it sometime after the collision at Addison Street back in the early 1980s. Quote Link to comment Share on other sites More sharing options...
i8itall4u Posted September 1, 2010 Report Share Posted September 1, 2010 The 4th rail pictured is a balancing rail used to keep the track level at any given location. On the steel elevated structure there are usually always 2 of them. On gravel fill and in subways one, sometimes two are used to keep the track from pitching. Quote Link to comment Share on other sites More sharing options...
pudgym29 Posted September 8, 2010 Report Share Posted September 8, 2010 It is on portions of the northwest bound Blue Line. Here is a section of it at Belmont. Interestingly, there is no fourth rail on the southeast bound tracks here. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.