There is still a lot of so-called corner grounded Delta in St. Louis, Mo and
other older sections of some other towns.  This arrangement causes havoc
with all kinds of things, from computer equipment to remodeling and adding
juice, because it is obsolete.  You probably won't see corner grounded delta
in a new system ever.

Modern systems do run a specifically grounded wire with the phase wires, but
some of these WWII relic corner grounded delta systems didn't.  If the
connection of one phase to ground fails, the whole system can begin to float
up to high voltage, say from leakage from a high voltage transformer or even
static. Often this ground connection is just a slim chunk of thin wire to a
ground rod. You could literally have 440V in a plant, but each leg is
several thousand volts to ground.  Eventually a motor or two fails on
insulation, and the whole thing goes up in smoke without ever blowing a
breaker, or motor cases become live at 4000 volts without shorting to ground
because all the conduit is rusty and there is no ground cable.  Meanwhile,
the electrician trying to work on it thinks it is normal 440V, and fries his
brains out because he shoulda been using a hotstick.  Nobody likes corner
grounded delta, but they are still around causing trouble.  This nightmare
schenario is why these things were owtlawed before I was born.

--Lawrence


----- Original Message -----
From: "Anthony Bussan" <TBUSSA@WOODWARD.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, June 18, 2002 1:56 PM
Subject: Re: [EE]: Russia 380VAC three phase power Delta or Wye?


> Wye doesn't have to have a center tap to neutral if the phases are loaded
> correctly.  With Delta, I don't know what you mean by "center tap of one
> phase."  And I definitely wouldn't connect any phase to neutral on delta
> unless you like to see a lot of sparks.  A direct connection to ground
like
> that will probably blow apart your whole fuse box and take you with it.
>
> Anyway have fun,
> Tony
>
> -----Original Message-----
> From: Bob Blick [mailto:bblick@SONIC.NET]
> Sent: Tuesday, June 18, 2002 1:40 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]: Russia 380VAC three phase power Delta or Wye?
>
>
> > Just courious, what is 'wye' ?
>
> Hi Tal,
>
> Wye takes one leg of each phase and connects to neutral, so you have three
> "hot" legs and one neutral in the center. Sort of like the letter "Y".
>
> Delta connects the three phases in a loop. Neutral is usually the center
> tap of one phase, or one corner sometimes.
>
> Cheers,
>
> Bob
>
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