On 01/06/2017 3:40 PM, John McCoy wrote:
m wrote in
:

Not being an officially trained electrician, I've never looked into
the 220-230-240 volt or 120-115-110 volt issue. I'm pretty sure those
are all identical and interchangeable, but why are all the numbers
used interchangeably? Why don't we pick one number and use it? Why
does everyone talk about 120 volt outlets in their house, but the
outlet says 115 volts.

It's a variety of historical reasons. 110V is what Edison
originally used for his first DC systems (for reasons no
longer understood, that was considered "safe"). When Tesla
and General Electric developed AC systems, they picked 120V
as the "household" voltage, but because 110 was already in
the public conciousness, people continued to call it 110V.

115V comes about because the utility is allowed 5% tolerance
for line loss, and 115 just sounds better than 114 (which is
what 120 less 5% would be).

220V and 240V are the same story - Edison used 220V in his
first DC systems, and GE used 240 when they introduced AC.

230V is a different animal - that's a 3 phase voltage in the
US. It's the standard household voltage in the EU, so if
you see something marked 230/240 it's probably intended for
sale in the EU and US.

Believe it's more when and what voltages were standardized by what was
to eventually become NERC...the first standards meeting was held in
about 1896(!) and then there were updates to nominal voltages a couple
times thereafter -- but, the public consciousness can't be changed; we
all grow up with whatever it is we hear and then pass it along with only
a few modifying influences gradually adding to the diversity.