ECN Forum Forums General Topics of the Trade General Discussion Area Railways

Harold,
When I've been in America I kind of like having to stop at a grade crossing for a train. I'd seen all the old movies and TV shows with the big "X" signs, red lights and the bell, but just pulling up and hearing that bell going the first time I got "lucky" was great, as it just has such a completely different feel to the system over here.

I haven't ridden that many trains in the U.S., but when I went out to Nebraska I decided to go Amtrak to see some more scenery, so I rode New York to Chicago to Omaha. Wonderful experience! (I just had to try the NYC Subway while I was there as well!)

Scott,
Yes, it's 25kV 1-ph 50Hz with return path via the running rails. This is the standard electric system for the longer-distance (by U.K. standards) services across the country. The network takes power from our "National Grid" distribution network.

The other main system used is 3rd rail DC at about 750V (I think there are still some sections at 660V). 3rd rail is used throughout what used to be the Southern Region of British Railways, which covers London down to the South Coast (only about 50 miles). The northern section of that region is very much commuter country with frequent stops.

There used to be some other standard systems in urban areas, such as 1500V DC overhead, but they've all been phased out now. The only other systems are for city transit networks, such as the London Underground (subway). That uses 630V DC with 3rd and 4th rails.

Paul,

I think the Tyne and Wear Metro and Dublin use 1500V DC and Manchester Metro 750V DC overhead – I’m not too sure about Sheffield. Traditional tramway (trolley) systems such as Blackpool, Manx Electric and Snaefell Mountain Railways plus Llandudno, Crich, and Seaton use 550V DC.

Interesting that London Underground (4 rail) and old British Rail (3 rail) use different voltages of 660V and 750V respectively, especially as they share the same tracks in numerous place, i.e at Richmond and Wimbledon on the District and on the Bakerloo and Metropolitan sections. Any idea how they do that – can the Underground stock take the extra voltage or is the fourth rail energized to 90V above ground where the two systems mix?

I have to confess that I haven't really followed the modern metro developments of recent years. It's been a while since I read the details on this, but I think the 1500V DC overhead systems were phased out on British Railways lines by the 1970s or thereabouts, but they may well have been re-introduced on some of the newer mass-transit systems.

I guess I should've mentioned the old "tram" (U.S.=trolley) systems, but it slipped my mind. I've been on the Blackpool trams and the line down in Seaton, Devon.

They were gone before I was born, but it's also worth mentioning the "trolley buses." They had electric traction but ran on normal rubber tires on the road to give greater manueuverability. Pick-up was by two overhead arms.

I've not been able to find a definitive answer on the 660 vs. 750V issue. I've seen older books which quote 660V for the whole of the old Southern Railways area. I'm wondering whether increased traffic meant that at some point they decided to raise the supply to a nominal 750V to allow for greater voltage drop and just regulate it down on-board. I've tried a few web searches, but not found any answer to this.

On the Underground, again I'd like to get a definitive explanation of the development, but from what I've been able to piece together, it seems that most of the network now runs with +420V on the 3rd (outer) rail and -210V on the 4th (central) rail to make up 630V nominal.

Where tracks are shared with 3rd-rail only trains, they apparently revert to full positive supply on the 3rd rail and bond the 4th rail to the running rails and ground.

Some parts of the Underground used other methods years ago. The Central line originally had just a central 3rd conductor rail with return via the running rails. I think it was converted to 3rd/4th rails during the 1950s, if I recall correctly.

One of the other Yerkes tube lines (Bakerloo I think) originally reversed the polarity on the rails due to leakage to the tunnel walls, but was later changed to the normal arrangement.

I'm not even sure if the split 420/210 supply has a solid ground on it or whether it might be resistance grounded. It seems to be remarkably difficult to get the full technical details anywhere.