In article ,
John Ammeter wrote:
Why does everyone think the voltage is 110/220??

Because that *is* what it 'used to be'.

If that actually was the voltage you had in your house you'd be very
unhappy. The nominal voltage is 118/236 with a +/- 5% range so you can
see that 110/220 is actually outside the acceptable range.

Over the years, the 'standard' has changed. *Several* times.

110V

115V

117V

120V

were _all_ the 'standard' over the years -- I have pieces of equipment
with all those voltages on the manufacturer's 'plate'.

In 'common'/casual usage, even when the 'standard' was 115V or 117V,
it was frequently referred to as "110V". In part because of 'mental
inertia' -- the standard had been 110V for a lot of years before the
'nominal' network voltage was raised to 115V. And it wasn't all that
many years before the 'standard' went to 117V, and then on to 120V.

Essentially, it is a 'class label', not an exact value.

There's even _more_ 'inertia' with regard to naming of the "2 hots, 180
degree out-of-phase" voltage level. It is *still* not infrequently
referred to as "220" even though the actual line voltage has been much
closer to 240 for 30+ years. A lot of people don't even recognize the
inconsistency of referring to '1 hot' as 120V, and '2 hot' as 220V.

The 'silliness' continues at the next higher voltage step. 'plates' on
gear will likely state (correctly) 480V, but calling it '440V' is still
_very_ common.

"commonly accepted wisdom" is that 110V, 115V, 117V, and 120V all
refer to the same thing, and similarly for 220V, 230V, and 240V.

It's similar to the "fact" that a "12 V battery" typically puts out 13.6V.