Clive D.W. Feather wrote:
In article , Marland
writes
Readers may remember that the Met Loco Sarah Siddons at one time was also
modified to run on third rail and did some tours to the South Coast, at the
time though the traction motors and circuits could cope with the higher
voltage IIRC the braking compressors could not so they were isolated and
braking air came from the older Southern Multiple unit that was coupled to
it.

I remember one such tour to Portsmouth Harbour. At both photo stops I
went forward to look at the loco. On one of them I spoke to the BR pilot
or inspector, who was complaining that the driver had a very light hand
on the controller. At the other I was talking to the LU driver who said
every time he put the controller too far round all the breakers went
because of the higher voltage.

So the impression I got was that the wiring could handle 750V (that's
just insulation) but the motors couldn't and so you had to keep some
resistance in the circuit.

IIRC, at the time South Western and South Central divisions were 650 V
near London, rising to 750 V once past the M25-to-be and 850V after
Southampton. While South Eastern division was 750 V throughout.


Surely the breakers went because the current was too high, not the voltage?
Of course, the current could become excessive because of the higher
voltage.