On Tue, 22 Aug 2017 16:55:39 +0100, Jim Lesurf
wrote:

In article , Johan Helsingius
wrote:
On 22-08-17 12:37, Dave Plowman (News) wrote:

So what are the nominal voltages - given everyone seems to say
different?

Maybe Wikipedia is clear enough:

"...
the nominal voltage at the source should be 120 V and allow a range of
114 V to 126 V (RMS) (-5% to +5%). Historically 110 V, 115 V and 117 V
have been used at different times and places in North America. Mains
power is sometimes spoken of as 110 V; however, 120 V is the nominal
voltage."

Maybe it is. However, clear or not, I've more than once found errors in
Wikipedia, so I'd regard it as a guide to what is probably correct rather
than a reference.

Maybe a bit more authoritative is the table published by the Pacific
Gas and Electric Company. Naturally it is more complicated than a
simple blanket tolerance.

Standard 120V
Service +/- 5% 114 to 126
Utilization -13% +6% 104.4 to 127.2
Nameplate Motor 115
NEMA +/- 10% 103.5 to 126.5


So the NEMA tolerance is taken from the Nameplate nominal of 115V.
Lots of new terms to look up, then.

d

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