Re: Right. Own up.

On Sat, 8 Mar 2008 07:14:15 +0000 (UTC), wollman@xxxxxxxxxxxxxx (Garrett
Wollman) wrote:
In article <1cm3t39ib02tgae675646gf1bt8lcsq1nb@xxxxxxx>,
Jasper Janssen <jasper@xxxxxxxxxxxx> wrote:

So you mean you had a plug with a grounded neutral, and two 120VAC 'live'
phases 180 degrees out of phase? You'd think VOZ engineers would be
familiar with that, that's (modulo plug type) a textbook
big-appliances-feed from the US (well, 220/110 there. But who's
counting.).

Actually, the connector you describe is obsolete in the U.S.; for big
appliances you'd have a NEMA 14 configuration (two poles plus neutral
and safety ground) rather than a NEMA 10 (two poles plus neutral, no
ground). That said, the 10 configuration is still quite common in
older homes; my clothes dryer has such a connector. You wouldn't
expect to see such a thing in a in a commercial or industrial setting,
where the 6 configuration (two poles plus ground, no neutral) is more
common for high-power gear.

Well, it depends on what he was freaking out about. I'd assumed it wasn't
the lack of safety ground, but I could be wrong. Systems where
neutral=safety ground do exist, btw, especially in commercial settings
(TN-C http://en.wikipedia.org/wiki/Earthing_system).

As for voltages, 240/120 is probably more common in residences than
220/110 these days, since 120 is the nominal standard.

It is? I'd missed that.

230/115 and
235/117 are also observed[1],

Can you tell the difference? When the UK switched from 240 +-5% to nominal
230 to harmonise with the rest of europe (which moved from 220 to 230),
they made it 230 -5% +10%, ie they went from 228-252 to 208.5-253. This
neatly made it so that they didn't have to do anything.

Voltages vary an awful lot more than frequencies do.

and in big cities (particularly New York) 208/120.

That'd be the moral equivalent of our 220/127 systems, I suppose, where
standard is 380/220 (or, today, 400/230). A way to get the same nominal
standard mains voltage except with a vastly different phase configuration.

Commercial buildings, of course, will have three-phase: smaller ones
get 208/120, but larger ones get 480/277 and step it down internally
to 208/120. (Elevators and large HVAC systems tend to like 480, and
277 is good for all kinds of gas-discharge lighting.) The cogen plant
at work tends to run slightly over-voltage; our UPSes measure 485-490
on the incoming feed.

You'd think the larger threephase systems would do 416/240, but maybe the
standardisation on 480 happened before the development of the 120/240
two-phase system and wide availability of domestic 240 appliances. That or
someone (ie, Westinghouse or some similarly rather important Someone)
really liked factors of two that aren't really all that useful in power
generation.

We typically have, as I said, 127/220 in very old houses (AFAIK those are
never upgraded to 130-odd/230, BICBW), 230/400 almost everywhere
domestically (most houses just use one leg plus neutral, but three phase
cable is laid to every house just in case -- and to be able to move a
house between phases to balance loads), 400/680 in bigger threephase rigs,
680/1200 in yet bigger ones, and I believe that's where the system breaks
down. It's a lot simpler that way, and there's a limited amount of hopping
systems you can do with motors, as well.

[1] In particular, 117 is what a voltmeter shows in my place of abode.

It may be 120 when it leaves the transformer, though.

Jasper
.

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