1920's wiring.... - Page 8

>> 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?

> 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!

> 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?

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

<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.

> Existential Angst wrote:

>>> 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.

>> 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.
>

>> 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.

>> 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?

>208V has 3 - 120V transformers. One endpoint of each transformer is
>connected together to form a "neutral". You have 120V from each of the
>phase conductors to the neutral. That is a major advantage when you are
>supplying 120V loads (compare to 240V delta). The voltage between phase
>conductors is 208V. A 3-phase motor would be 208V. A diagram of the
>transformer connections looks like a Y-wye (or star).

>A 240V delta system starts out with a 120/240 transformer like is used
>for a residential service. The center tap is the neutral, just like with
>a residential service. For the 3-phase, 2 transformers are added, one
>end of each connected to the ends of the original transformer and the
>other end connected together to be the 3 phase "high leg". A diagram of
>the transformer connections looks like a triangle or delta. The voltage
>from the high leg to neutral is 208V. There may only be 2 transformers
>(open delta). I suspect this system came from original 120/240V single
>phase systems where some 3-phase load had to be added. You can add a
>transformer, which can be much smaller than the original one (depending
>on the 3 phase load).

> wrote:
>
>

>>> 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?

>>
>> 208V has 3 - 120V transformers. One endpoint of each transformer is
>> connected together to form a "neutral". You have 120V from each of the
>> phase conductors to the neutral. That is a major advantage when you are
>> supplying 120V loads (compare to 240V delta). The voltage between phase
>> conductors is 208V. A 3-phase motor would be 208V. A diagram of the
>> transformer connections looks like a Y-wye (or star).

>
> This is a picture of one of those transformer arrays. The incoming
> phases to the customer is black,red.blue
>
> http://gfretwell.com/electrical/3_p_wye-wye.jpg

>

>> A 240V delta system starts out with a 120/240 transformer like is used
>> for a residential service. The center tap is the neutral, just like with
>> a residential service. For the 3-phase, 2 transformers are added, one
>> end of each connected to the ends of the original transformer and the
>> other end connected together to be the 3 phase "high leg". A diagram of
>> the transformer connections looks like a triangle or delta. The voltage
>>from the high leg to neutral is 208V. There may only be 2 transformers
>> (open delta). I suspect this system came from original 120/240V single
>> phase systems where some 3-phase load had to be added. You can add a
>> transformer, which can be much smaller than the original one (depending
>> on the 3 phase load).

>
> This is a picture of that transformer array, the 120/240 phases are
> typically black & red and the high leg is required to be orange by
> code.
>
>
> http://gfretwell.com/electrical/High%20Leg%20Delta%20transormers.jpg

>
> There is another way you can see delta in a place that doesn't need
> any 120v load. They make a standard delta with either 2 or 3
> transformers and ground one phase leg AKA "corner grounded delta".
> That will look a lot like single phase to someone who is not aware
> since there will just be 2 ungrounded conductors and the 3d phase will
> be white. The equipment will look like single phase with 2 pole
> breakers.
>
> That is one place where you will need those 2 pole "delta" rated
> breakers.

>
> You can also have ungrounded delta but that will be in a special place
> like a glass factory where the first fault to ground won't bring down
> the power. There are special monitoring requirements for that.