"bud--" wrote in message
.. .
Existential Angst wrote:
"Jules" wrote in message
news
On Mon, 26 Oct 2009 23:04:48 -0700, terry wrote:

(http://en.wikipedia.org/wiki/Ring_circuit for the curious)

That was VERY inneresting!!!
Am I correct in observing that the diagram shows two "radial" connections
to the ring?

The text talks about "unfused spurs".

It took me a while to grok the "point" of the schematic, and when I did,
it left me with a very big Q:

How does a ring circuit SAVE copper? ?
Yeah, I can see how you can use thinner gauge wire, but now you have to
use twice as much of it!

If you went straight out to a load and straight back there would be twice
the wire. The circuit wanders around the building picking up loads as it
goes.

Excellent point! I see that!! That is really really neat! Iow, the
geometry of the installation is sort of part of the schematic!!


Current capacity (density) is directly proportional to cross-sectional
area, so it seems to me this system is 6 of one, half a dozen of the
other, mass-wise in copper.
The article pointed out some potent disadvantages, as well -- somewhat
dicey, eh?

Seems really weird from the perspective of the US. Must be quite reliable
because it is still being used. I was really surprised when I heard how
different UK wiring is.

Interestingly, NYC still has DC running to some older commercial
buildings!

Ended about 2 years ago.
http://cityroom.blogs.nytimes.com/2007/11/14/off-goes-the-power-current-started-by-thomas-edison/

And, NYC's 3 phase is 208, not 220 or 240 V, like most of the rest of the
country -- 208 is EXACTLY the rms voltage difference between two 120 V
sine waves 120 deg out of phase, making it, I think, the "purest" type of
3 phase.

The vast majority of 3 phase power in the US (that supplies 120V loads) is
208V (wye connection). New 240V (delta connection) systems are probably
quite uncommon.

Well, on the various ng concerned with machines all over the country, over
about 10 yrs I think I'm the ONLY one to reference 208 V, via NYC. Maybe
208 dominates in big industrial cities?
Even Long Island (NY) which perhaps has one of the highest concentration of
"small" machine shops ( 10,000 sq ft) in the country, uses 240 V.

But here's my Q:
For a given voltage, what difference would the end user see in terms of a
delta or wye connection?
And why is 208 wye, and 240 V delta?

And, is each leg of the 240 V delta 3 ph separated by equal 120 deg shifts,
like the 208?
I argue that it is not, that two of the phases *must* be 180 deg out of
phase, as that's the only way you could get 240 from two 120 legs. The 3rd
phase must be 90 deg to these two.
Visavis 208/120 V systems, which is exactly consistent with 120 phase angle.

I argue this, but others hotly disagree, but without really being able to
tell me wye.

If the above is correct, I surmise the reason is that the 208 3 ph is
supplied right from the generator, whilst 240 3 ph comes off of pole
transformers.

--
EA




--
bud--