In the USofA, You can always get three-wire service, with 2 feeds
that are nominally 120V to ground, and 240V from each other, at 60
The voltage tolerances vary by jurisdiction from 2-8% of the nominal
voltages. In many places, you can also get 4-wire residential service,
still with 120V on each hot to ground, but with each of the three lines
at 208V from each other.
Most of Eurasia appears to use 2-wire service with 220V to ground,
or variations thereof.
A lot of residential outlets will measure 125 V. The trend over the
years has been to higher voltages as it is more efficient.
110 Volts originated with the original Edison systems where the
voltage supplied was 110 VDC. The reason he picked this voltage was
a compromise between safety and efficiency and the ability to match a
suitable incandescent lamp filament with a useful life expentancy and
a suitable output level in lumens. Minimizing excessive voltage drop
and the cost of expensive copper conductors was also a consideration.
When AC replaced DC, the 110 voltage stayed the same. In the 1950's
this increased to 120 volts. Many devices were still rating stamped
110v. 115v. or 120v.
FWIW, here's a pointer to an "INTERIM OPINION ON EMERGENCY VOLTAGE
REDUCTION MEASURE" that
was up before the California state PUC with regards to lowering the
nominal line voltage to
117VAC during times of electrical energy shortage.
Makes sense that with a lower voltage the demand for power decreases.
However, this only
follows for resistive devices. Constant power loads (like motor-driven
equipment) would demand
greater current and cause increased conductor loss as well as increasing
risk of failure to
Dunno if they ever implemented this; at my house the voltage gyrates
quite a bit throughout the
day anyway so it's hard to tell what the "nominal" is.
One solution if there is not enough power to go around is to lower the
line voltage. This is called a brownout.
Another solution is to have rotating blackouts as California did a few
Remember that this is only for California where most electrical
consumers are at the far end of the (transmission) line. They pretty
much don't like large conventional power plants in California (be they
nukes, coal-fire, hydro-electric dams, or gas fired units) and are not
building a whole lot more.
Because of this, a lot of California power comes from outside the
state (Oregon, Washington, British Columbia) in the north and Hoover
Dam and other sources (Nevada - Arizona) in the south. There is
only one Nuke in the state and quite a few medium and smaller sized
hydro-electric dams in the mountains. Geothermal also makes a small
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