On Jan 3, 6:21*am, "Jerry" wrote:
"Geoffrey S. Mendelson" wrote in ...

snip
: The UK used several systems, and a friend of mine who traveled
to London
: in the 1970's found that there were four different electrical
systems in use
: in various parts of the city. By that time they had been
standardized to
: 240 volts 50Hz, but the older plugs and lightbulbs (different
ones for
: different systems) remained.

Hmm, surely the 1970s were a tad late for different voltages
(certainly for London), the national grid had been started long
before WW2 and was complete not long after, are you are not
thinking of the different designs of electrical circuits and
sockets in use or perhaps a different time period?

I suppose that some building with their own (derived/generated)
power supplies might have had (still have) 'odd' systems to suit
their own needs, an exception rather than the rule.
--
Regards, Jerry.

A national grid has no need to standardize end user voltages, only
frequency.

Many different HV line voltages are used: houses and small businesses
get their power off a "pole pig" or a ground mounted transformer. They
always have trim windings and somewhere in the system must be a tap
changer setup because I2R losses change over the day as the power
demands vary widely.

It would be possible to have 220 in Northern England, 240 in Scotland
and 230-or 117, or 277, or any number at all-in Southampton. because
off a stepdown transformer you are rarely going more than 500 meters
to 1 km, usually less.

Switchmode equipment doesn't care. Solid state analog equipment is
regulated and has a design input range, power amps are often
unregulated and just make less power at lower line voltage. Tube
(valve) equipment wants its heaters at bogey voltage. In the case of
tungsten filaments on transmitting tubes it needs to be close to spot
on.