On Monday 03 May 2004 23:14, Don Maslin wrote:
> On Mon, 3 May 2004, Patrick Finnegan wrote:
> > On Monday 03 May 2004 22:14, Tony Duell wrote:
> > > > 208 is really a 240 volt 3 phase system measured in a star
> > >
> > > Is it? I'd assumed it was 120V neutral-phase, which is then 208V
> > > phase-phase.
> >
> > Tony is right here. At least in Indiana, Illinois, and the Code
> > Book, 208 three-phase is a "Y" setup with 120V from each phase to
> > neutral, and 208V from phase to phase. 240V three-phase is a delta
> > setup, with the neutral half-tapped between two phases, giving 240V
> > phase-to-phase,
>
> Wait a minute! By definition, a delta configuration can have no
> neutral. Else it is no longer delta.
>
> - don
When a neutral is put on a delta, it's wired like:
A
/ \
/ \
B--N--C
At least, that's what I've learned from reading NEC code books.
By contrast, a wye aka Y/star is wired like:
A B
\ /
\ /
N
|
|
C
I guess you could also call that a "flux capacitor" arrangement. :)
You can also put the ground one of the three delta phases, and end up
with this:
A
/ \
/ \
B/N----C
I've only heard of that arrangement before, I haven't actually seen it.
In general, though, it seems intuitive to me that you'd want to connect
some part of the secondary to ground, and avoid a floating secondary,
as you might run into "problems" if your 12kV(ish) primary becomes
coupled to the secondary, and there isn't a ground path to trip a
circuit breaker.
There's few things more dangerous than having your 208V line at
12kV+-208V (AC RMS) to ground when you're not expecting it.
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Received on Tue May 04 2004 - 00:22:56 BST