On 13 Apr, 10:21, David Hansen
wrote:
On Tue, 13 Apr 2010 08:59:03 +0100 someone who may be "Mortimer"
wrote this:-

Would signalling or GSM use such high voltages? I'd expect low voltages for
anything that didn't require large amounts of power and would therefore
incur I-squared-R losses. I thought that the proposed GW electrification
would be OHLE, so why would it need 650V supplies?

650V, which is low voltage, is the standard signalling supply and
has been used since at least the 1960s as part of power signalling
schemes. It is used for the same reason that higher voltages are
used in electricity distribution systems, to minimise losses and
conductor cost.

The voltage is reduced and rectified as necessary for use with
signalling equipment.

Why choose an odd Voltage like 650V? What frequency? Single or three
phase?