On Tue, 16 Sep 2003 02:27:15 +0100, David Baxter

wrote in :

On a recent trip to London, I happened to be looking out the windows of a
tube train on a deep level track, and noticed a pair of what appeared to be
unshielded, uninsulated copper wires, approximately 8 inches apart from each
other. They were mounted above the usual cables you see inside a tunnel, and
were considerably thinner - just think 30amp cooker cable. (At least, that's
how they looked.)

They'd appear to terminate a few meters before a station. Whereas the larger
cables would appear to either go down below platform level, or behind the
advertising boards, I was unable to see how these terminated - they simply
disappeared.

Can someone cast some light on what these two wires are and do?

From my readings on this group, they serve two purposes: when
shorted out, they cut traction current to the live rails; they also serve
as a telephone circuit so a driver can clip a handset to them to
communicate with a controller (I'm not sure if the electrical load of the
handset is enough to shut off traction current).

--
Ivan Reid, Electronic & Computer Engineering, ___ CMS Collaboration,
Brunel University. Room 40-1-B12, CERN