A section of four-rail 630v DC electrified track on London Underground's District Line at Earl's Court station.<br>
From top to bottom the four rails are:<br>
<ul>
<li>Positive rail: +420v DC</li>
<li>Left-hand running rail</li>
<li>Negative rail: -210v DC</li>
<li>Right-hand running rail</li>
</ul>
The diamond between the negative and left-hand running rail is the train stopping mark - where the front of the train should be to ensure the entire train is in the platform and aligned with the monitors, etc.<P>

A good explanation of the reasons behind the four-rail electrification system can be found on the <A HREF="http://www.trainweb.org/tubeprune/tractioncurr.htm">Tubeprune</a> website.
<p>
Photo by <a href="mailto:cmckenna@sucs.org?subject=rail-photo-at-railfaneurope">Chris McKenna</a> 20/08/2005.
Larger, higher quality copies of most of my pictures are available, please email if you want a copy.
#cmckenna@sucs.org