Closed Delta 120/240V 3-phase service

[[email protected]]

| [email protected] (Michael Moroney) writes:
|
|>[email protected] writes:
|
|
|>>| One weird setup I've seen, and I'm not totally sure exactly what it is:
|>>| 1 large 3 phase transformer (single can) with a small transformer can
|>>| below it on a pole. The small transformer has NO MV connection nor even a
|>>| MV bushing! It sits below the drops to the homes/businesses. The only
|>>| thing I can think it could be is the big can is 240V delta, and the high
|>>| leg powers the small can, with is a 208V/240VCT. The big can powers half
|>>| the residential services plus any 3 phase services, the small can powers
|>>| the other residential services. It's sort of Scott-T relative to the big
|>>| can. But this is a guess, I actually don't know how it's wired. I even
|>>| took a photo to try and figure it out. There are quite a few of these
|>>| setups in Philadelphia.
|
|>>If the big can is already 3 phase, why would anyone need to also have a
|>>Scott-T? That doesn't make sense. It must be something else. How many
|>>MV bushings on each can?
|
|>3 on the big can, 0 (yes, zero) on the small can.
|
|>I called it Scott-T like because I'm guessing the small can is fed from
|>the 240 delta high leg to neutral, which would be 90 degrees shifted from
|>the 240VCT winding. Assuming my guess at what it is is correct at all.
|
|>> How many secondary lugs?
|
|>4 on the big can, I believe 4 on the small can.
|
| I looked at my photo again, and it is understandable what is going on
| after all. See for yourself:
|
| http://www.accvio.com/temp/two_cans.jpg
| http://www.accvio.com/temp/two_cans_large.jpg (full size)
|
| It's not clear the large transformer has 3 MV bushings, but it does.
|
| One connection from the large transformer goes only to the small one, 3
| others (1 connected to a bare neutral) go below it and two additional
| leads from the small can go downward, for a total of 5 leads that run down
| the pole.
|
| There's another (probably) 120/240V service going left to right (with a
| drop to the upper right) that's appears not to be involved or connected,
| except for the neutral.
|
| It appears to me, if the large can is delta with the lead to the small can
| the high leg, that this is a 5 wire 2 phase circuit, or what many would
| call 4 phase, 4 poles spaced at 90 degrees and a neutral. Can anyone
| suggest an alternate possibility?

It looks to me like what is going on is that the first can provides common
208Y/120 like:

B
/
/
A-----N
\
\
C

And then the second can turns one of the phases into 120/240 like:

B
/
/
A-----N-----A'
\
\
C

Most of the loading is 3 phase where 208Y/120 serves the need, but some
load needs genuine 240 or split phase 120/240 and they didn't want to
hang a 2nd can up high to do it directly from MV (and can't bring the
MV down to where the 2nd can is now).

Just a guess.

 

[krw]

| In article <[email protected]>, phil-news-
| [email protected] says...
|> | In article <[email protected]>, [email protected]
|> | says...
|> |> | In article <[email protected]>, [email protected]
|> |> | says...
|> |> |>
|> |> |> >> B C
|> |> |> >> \ /
|> |> |> >> \ /
|> |> |> >>A----N----D
|> |> |> >> / \
|> |> |> >> / \
|> |> |> >> F E
|> |> |> >
|> |> |> >>A-N and N-D are both wound on the first core. B-N and N-E are both wound
|> |> |> >>on the second core. C-N and N-F are both wound on the third core. A third
|> |> |> >>of the 120/240 loads would be served from A-N-D. A third of the 120/240
|> |> |> >>loads would be served from B-N-E. A third of the 120/240 loads would be
|> |> |> >>served from C-N-F. Half of the 208Y/120 loads would be served from A,C,E
|> |> |> >>and N. Half of the 208Y/120 loads would be served from B,D,F and N.
|> |> |> >
|> |> |> >I always wondered if either any electric company offered such a service,
|> |> |> >or if there was any such thing as a breaker panel that would support it.
|> |> |>
|> |> |> Are we not forgetting about the primary windings for such a scheme?
|> |> |
|> |> | ...and how does this "six phase" differ from a center-tapped three-
|> |> | phase?
|> |>
|> |> When most or all of the loads are single phase, the "6 star" can keep the
|> |> loading balanced over the 3 incoming phases, while also providing genuine
|> |> 240 volts to those single phase loads. 240DCT or 240DVCT puts most of
|> |> the loading on one phase angle (which might be 2 incoming phase lines).
|> |> 208Y/120 balances the loads, but there's no 240. 240Y/139 is a bit rich
|> |> on the L-N circuits. 220Y/127 is sometimes a compromise.
|> |
|> | Maybe I'm dense, but I see *no* difference between the two schemes.
|> | ELectrically, I don't see how you could tell one from the other.
|>
|> A saw a bunch of different schemes in this thread. Maybe you can list
|> the specific schemes you think are alike but treated as different.
|
| Specifically, the six-phase "star" and three-phase center-tapped
| wye. With any two phases any number of others is a few transformers
| away.

I don't know which you mean by "three-phase center-tapped wye". Maybe you
can pick it out from this police lineup:

* * * * * *
\ \ / * * * | \ / \
\ \ / / \ / | | \ / \
N---* *---N---* / \ / | *---N---* N *
/ / \ / \ / | | /
/ / \ *---N---* *---N---* *---N---* | /
* * * * *

1 2 3 4 5 6 7

If you don't see the guilty party, maybe you can draw a picture

#2 be the culprit. Your "split-phase" three-phase from another
post.

Note that drawings are NOT to scale (relative to voltage).

Close enough for government work.

|> Can you describe an electrical system configuration which is capable of:
|>
|> 1. Supplying 120 and 240 volts (not 208 volts) in single phase to all
|> single phase loads.
|
| Look harder at a center-tapped wye. There is only 60degrees between
| the "negative" of phase-A and Phase-B.

I don't know which I need to look at.
#2

|> 2. Divides up the single phase load in three equal groups in order to
|> maintain a balance on each of the three phases of the utility supply.
|
| How does it divide anything? An imbalance can still be placed on
| any one (or two).

Of course an imbalance can always happen, and likely will. But it is a
statistical thing. If a building has 54 apartments, connecting 18 of them
to phase A, 18 to phase B, and 18 to phase C, would be "balanced" enough
for utility purposes. If the supply were coming in as 120/240DCT, then
all of the apartments would be on just one of the phases and the phase
loading would be as lopsided as if the entire building were supplied with
single phase power. If the utility insists on balancing the phases and
rejects single phase service for this reason, they will reject 120/240DCT.
If the supply is 208Y/120, that would satisfy the utility (18 apartments
supplied with phases A and B, 18 suppleid with B and C, and 18 supplied
with C and A). But it would not satisfied the need to have 240 volts.

Sure, but your "six-phase" is no different than the normal three-
phase "wye". At least I don't see it.

|> ... that is not the "6 star" I described?
|
| I still don't see the difference between that and a center-tapped
| wye. Again, I'm not a power jock, so may be missing something
| subtile.

Maybe you saw something I didn't see. Check the above police lineup.

Nope. You saw it, just one of us isn't "getting it" (I could easily
be missing something - 65h work weeks do that after a while).

 

[[email protected]]

| In article <[email protected]>, phil-news-
| [email protected] says...
|> | In article <[email protected]>, phil-news-
|> | [email protected] says...
|> |> | In article <[email protected]>, [email protected]
|> |> | says...
|> |> |> | In article <[email protected]>, [email protected]
|> |> |> | says...
|> |> |> |>
|> |> |> |> >> B C
|> |> |> |> >> \ /
|> |> |> |> >> \ /
|> |> |> |> >>A----N----D
|> |> |> |> >> / \
|> |> |> |> >> / \
|> |> |> |> >> F E
|> |> |> |> >
|> |> |> |> >>A-N and N-D are both wound on the first core. B-N and N-E are both wound
|> |> |> |> >>on the second core. C-N and N-F are both wound on the third core. A third
|> |> |> |> >>of the 120/240 loads would be served from A-N-D. A third of the 120/240
|> |> |> |> >>loads would be served from B-N-E. A third of the 120/240 loads would be
|> |> |> |> >>served from C-N-F. Half of the 208Y/120 loads would be served from A,C,E
|> |> |> |> >>and N. Half of the 208Y/120 loads would be served from B,D,F and N.
|> |> |> |> >
|> |> |> |> >I always wondered if either any electric company offered such a service,
|> |> |> |> >or if there was any such thing as a breaker panel that would support it.
|> |> |> |>
|> |> |> |> Are we not forgetting about the primary windings for such a scheme?
|> |> |> |
|> |> |> | ...and how does this "six phase" differ from a center-tapped three-
|> |> |> | phase?
|> |> |>
|> |> |> When most or all of the loads are single phase, the "6 star" can keep the
|> |> |> loading balanced over the 3 incoming phases, while also providing genuine
|> |> |> 240 volts to those single phase loads. 240DCT or 240DVCT puts most of
|> |> |> the loading on one phase angle (which might be 2 incoming phase lines).
|> |> |> 208Y/120 balances the loads, but there's no 240. 240Y/139 is a bit rich
|> |> |> on the L-N circuits. 220Y/127 is sometimes a compromise.
|> |> |
|> |> | Maybe I'm dense, but I see *no* difference between the two schemes.
|> |> | ELectrically, I don't see how you could tell one from the other.
|> |>
|> |> A saw a bunch of different schemes in this thread. Maybe you can list
|> |> the specific schemes you think are alike but treated as different.
|> |
|> | Specifically, the six-phase "star" and three-phase center-tapped
|> | wye. With any two phases any number of others is a few transformers
|> | away.
|>
|> I don't know which you mean by "three-phase center-tapped wye". Maybe you
|> can pick it out from this police lineup:
|>
|> * * * * * *
|> \ \ / * * * | \ / \
|> \ \ / / \ / | | \ / \
|> N---* *---N---* / \ / | *---N---* N *
|> / / \ / \ / | | /
|> / / \ *---N---* *---N---* *---N---* | /
|> * * * * *
|>
|> 1 2 3 4 5 6 7
|>
|> If you don't see the guilty party, maybe you can draw a picture
|
| #2 be the culprit. Your "split-phase" three-phase from another
| post.

That is the same as the six-phase "star" or "6 star". So if you can't
see any difference, that's because there isn't any. I would not have
called this a "wye" of any sort since it doesn't look like a "Y". But
it could be TWO Y's interleaved.

To make this derived system, you need either:

1. 3 single phase transformer cores
2. 1 three phase tranformer E-core

Then you need to wrap these cores with 3 primary windings and 3 secondary
windings. Usually the secondaries go on the inside and the primaries go
on the outside, so the secondary at lower voltage and higher current has
less winding resistance.

Each of the 3 secondary windings needs to be either:

1. a pair of 120 volt windings which you can wire in series
2. a single 240 volt winding with a center tap right in the middle

All of the center points of these windings are wired/bonded together and
grounded. Then each of the three phases will have two poles 180 degrees
apart. Some people will call this six phases.


|> Note that drawings are NOT to scale (relative to voltage).
|
| Close enough for government work.
|
| <snip>
|
|> |> Can you describe an electrical system configuration which is capable of:
|> |>
|> |> 1. Supplying 120 and 240 volts (not 208 volts) in single phase to all
|> |> single phase loads.
|> |
|> | Look harder at a center-tapped wye. There is only 60degrees between
|> | the "negative" of phase-A and Phase-B.
|>
|> I don't know which I need to look at.
|
| #2

Let me relabel the terminals like so:

C' B
\ /
\ /
A----N----A'
/ \
/ \
B' C

Between A and A' you have 240 volts.
Between B and B' you have 240 volts.
Between C and C' you have 240 volts.
Between A and B you have 208 volts.
Between B and C you have 208 volts.
Between C and A you have 208 volts.
Between C' and A' you have 208 volts.
Between A' and B' you have 208 volts.
Between B' and C' you have 208 volts.
Between A and N you have 120 volts.
Between B and N you have 120 volts.
Between C and N you have 120 volts.
Between A' and N you have 120 volts.
Between B' and N you have 120 volts.
Between C' and N you have 120 volts.
Between A and C' you have 120 volts.
Between C' and B you have 120 volts.
Between B and A' you have 120 volts.
Between A' and C you have 120 volts.
Between C and B' you have 120 volts.
Between B' and A you have 120 volts.

Which connection pair do you need to ask about?


|> |> 2. Divides up the single phase load in three equal groups in order to
|> |> maintain a balance on each of the three phases of the utility supply.
|> |
|> | How does it divide anything? An imbalance can still be placed on
|> | any one (or two).
|>
|> Of course an imbalance can always happen, and likely will. But it is a
|> statistical thing. If a building has 54 apartments, connecting 18 of them
|> to phase A, 18 to phase B, and 18 to phase C, would be "balanced" enough
|> for utility purposes. If the supply were coming in as 120/240DCT, then
|> all of the apartments would be on just one of the phases and the phase
|> loading would be as lopsided as if the entire building were supplied with
|> single phase power. If the utility insists on balancing the phases and
|> rejects single phase service for this reason, they will reject 120/240DCT.
|> If the supply is 208Y/120, that would satisfy the utility (18 apartments
|> supplied with phases A and B, 18 suppleid with B and C, and 18 supplied
|> with C and A). But it would not satisfied the need to have 240 volts.
|
| Sure, but your "six-phase" is no different than the normal three-
| phase "wye". At least I don't see it.

The normal three phase WYE is just:

B
/
/
A----N
\
\
C

Between A and B you have 208 volts.
Between B and C you have 208 volts.
Between C and A you have 208 volts.
Between A and N you have 120 volts.
Between B and N you have 120 volts.
Between C and N you have 120 volts.

There aren't any other ways to connect, and no way to get 240 volts.


|> |> ... that is not the "6 star" I described?
|> |
|> | I still don't see the difference between that and a center-tapped
|> | wye. Again, I'm not a power jock, so may be missing something
|> | subtile.
|>
|> Maybe you saw something I didn't see. Check the above police lineup.
|
| Nope. You saw it, just one of us isn't "getting it" (I could easily
| be missing something - 65h work weeks do that after a while).

OK, hope the above helps.

 

[[email protected]]

| Except, there is no connection to one lug of the big can except to
| the small can, so you get either:
|
| B
| /
| /
| N-----A'
| \
| \
| C
|
| or maybe
|
| B
| /
| /
| A-N
| \
| \
| C
|
| (trying to show a different voltage on A)
|
| or some combination. Not too useful IMO.
|
| There are quite a few of those things in inner city Philly, as well as
| some other odd practices.

Curious-er and curious-er. It might need an investigation.

I wonder if maybe there might be a Scott-T inside that big can and the
little can could be modifying it somehow.

 

[Tom Horne]

| In article <[email protected]>, phil-news-
| [email protected] says...
|> | In article <[email protected]>, [email protected]
|> | says...
|> |> | In article <[email protected]>, [email protected]
|> |> | says...
|> |> |>
|> |> |> >> B C
|> |> |> >> \ /
|> |> |> >> \ /
|> |> |> >>A----N----D
|> |> |> >> / \
|> |> |> >> / \
|> |> |> >> F E
|> |> |> >
|> |> |> >>A-N and N-D are both wound on the first core. B-N and N-E are both wound
|> |> |> >>on the second core. C-N and N-F are both wound on the third core. A third
|> |> |> >>of the 120/240 loads would be served from A-N-D. A third of the 120/240
|> |> |> >>loads would be served from B-N-E. A third of the 120/240 loads would be
|> |> |> >>served from C-N-F. Half of the 208Y/120 loads would be served from A,C,E
|> |> |> >>and N. Half of the 208Y/120 loads would be served from B,D,F and N.
|> |> |> >
|> |> |> >I always wondered if either any electric company offered such a service,
|> |> |> >or if there was any such thing as a breaker panel that would support it.
|> |> |>
|> |> |> Are we not forgetting about the primary windings for such a scheme?
|> |> |
|> |> | ...and how does this "six phase" differ from a center-tapped three-
|> |> | phase?
|> |>
|> |> When most or all of the loads are single phase, the "6 star" can keep the
|> |> loading balanced over the 3 incoming phases, while also providing genuine
|> |> 240 volts to those single phase loads. 240DCT or 240DVCT puts most of
|> |> the loading on one phase angle (which might be 2 incoming phase lines).
|> |> 208Y/120 balances the loads, but there's no 240. 240Y/139 is a bit rich
|> |> on the L-N circuits. 220Y/127 is sometimes a compromise.
|> |
|> | Maybe I'm dense, but I see *no* difference between the two schemes.
|> | ELectrically, I don't see how you could tell one from the other.
|>
|> A saw a bunch of different schemes in this thread. Maybe you can list
|> the specific schemes you think are alike but treated as different.
|
| Specifically, the six-phase "star" and three-phase center-tapped
| wye. With any two phases any number of others is a few transformers
| away.

I don't know which you mean by "three-phase center-tapped wye". Maybe you
can pick it out from this police lineup:

* * * * * *
\ \ / * * * | \ / \
\ \ / / \ / | | \ / \
N---* *---N---* / \ / | *---N---* N *
/ / \ / \ / | | /
/ / \ *---N---* *---N---* *---N---* | /
* * * * *

1 2 3 4 5 6 7

If you don't see the guilty party, maybe you can draw a picture

Note that drawings are NOT to scale (relative to voltage).


|> |> |> Also, doesn't six phase distribution mean six phase transmission? Six
|> |> |> phase transmission for any distance is going to be horrorendously
|> |> |> expensive just to keep a few apartment buildings at 120/240 V.
|> |> |
|> |> | No need for six-phase transmission to get six phases at the
|> |> | "apartment building". Like you, I don't see the point though.
|> |>
|> |> Which would you be willing to give up? Having 240 volts (and instead you
|> |> settle for a wimpy 208 volts) or having the phases balanced (this is more
|> |> of a utility concern)?
|> |
|> | Before I can tell you my preference in donuts, I need to see the
|> | difference between six and half a dozen. ;-)
|>
|> Can you describe an electrical system configuration which is capable of:
|>
|> 1. Supplying 120 and 240 volts (not 208 volts) in single phase to all
|> single phase loads.
|
| Look harder at a center-tapped wye. There is only 60degrees between
| the "negative" of phase-A and Phase-B.

I don't know which I need to look at.


|> 2. Divides up the single phase load in three equal groups in order to
|> maintain a balance on each of the three phases of the utility supply.
|
| How does it divide anything? An imbalance can still be placed on
| any one (or two).

Of course an imbalance can always happen, and likely will. But it is a
statistical thing. If a building has 54 apartments, connecting 18 of them
to phase A, 18 to phase B, and 18 to phase C, would be "balanced" enough
for utility purposes. If the supply were coming in as 120/240DCT, then
all of the apartments would be on just one of the phases and the phase
loading would be as lopsided as if the entire building were supplied with
single phase power. If the utility insists on balancing the phases and
rejects single phase service for this reason, they will reject 120/240DCT.
If the supply is 208Y/120, that would satisfy the utility (18 apartments
supplied with phases A and B, 18 suppleid with B and C, and 18 supplied
with C and A). But it would not satisfied the need to have 240 volts.


|> ... that is not the "6 star" I described?
|
| I still don't see the difference between that and a center-tapped
| wye. Again, I'm not a power jock, so may be missing something
| subtile.

Maybe you saw something I didn't see. Check the above police lineup.

In the situation under discussion were the only significant three phase
load is the elevator a three phase auto transformer wired in boost
configuration would solve the problem at a reasonable cost.

 

[Beachcomber]

In the situation under discussion were the only significant three phase
load is the elevator a three phase auto transformer wired in boost
configuration would solve the problem at a reasonable cost.

Tom:

Thanks for the suggestion. Could you elaborate a bit more on how this
would be connected please...

Are you saying that you would have standard split phase 120/240V from
one transformer... Then in addition to that, you would have 3
autotransformers (or one 3 phase autotransformer) for the 3 phase
load?

I've never heard of anything like this. Aren't auto transformers not
permitted (from the utility primary to customer secondary) because of
safety concerns? Or if it is a customer provided transformer
(perhaps a buck-boost XFR), wouldn't you need a utilility transfomer
on the primary 3-phase line anyway?

It doesn't seem that you would be saving anything here.

Beachcomber

 

[[email protected]]

| In the situation under discussion were the only significant three phase
| load is the elevator a three phase auto transformer wired in boost
| configuration would solve the problem at a reasonable cost.

What if you don't have any need for three phase power at all? Suppose your
building has elevators that work fine on single phase power. The building
is so big, however, the power company doesn't want to drop only one phase
into it; they want to have all three phases coming in, in some approximation
of a balanced load. And you need to supply 240 volts, not 208, to each
tenant. What would you set up?

 

[[email protected]]

|
|>In the situation under discussion were the only significant three phase
|>load is the elevator a three phase auto transformer wired in boost
|>configuration would solve the problem at a reasonable cost.
|>--
|>Tom Horne
|>
|
| Tom:
|
| Thanks for the suggestion. Could you elaborate a bit more on how this
| would be connected please...
|
| Are you saying that you would have standard split phase 120/240V from
| one transformer... Then in addition to that, you would have 3
| autotransformers (or one 3 phase autotransformer) for the 3 phase
| load?

With just 2 extra small transformers, you can add a couple extra phases
to a normal 120/240 split phase and end up with 4 lines, 3 of which are
the same as 208 wye, if you use the original incoming three phase
distribution to derive it.

Or you can do it with just 1 weird transformer. Using a single phase
transformer with a 139/277 volt split phase, you wire it's primary B-C
if the original single phase is A-N (or wire it C-N if the original
single phase is A-B). Connect the 139/277 center tap to one line end
of the 120/240. Voila, you now have a Scott-T emulating 277 delta.

*
|
|
N <-- this is the original 120/240
|
|
*-----*-----* <-- this is the added 139/277


| I've never heard of anything like this. Aren't auto transformers not
| permitted (from the utility primary to customer secondary) because of
| safety concerns? Or if it is a customer provided transformer
| (perhaps a buck-boost XFR), wouldn't you need a utilility transfomer
| on the primary 3-phase line anyway?

Autotransformers are safe as long as they are "up there" on the pole out
of reach and properly grounded, or well sealed in a pad mount enclosure.


| It doesn't seem that you would be saving anything here.

Probably not.

 

[krw]

| In article <[email protected]>, phil-news-

|> | Specifically, the six-phase "star" and three-phase center-tapped
|> | wye. With any two phases any number of others is a few transformers
|> | away.
|>
|> I don't know which you mean by "three-phase center-tapped wye". Maybe you
|> can pick it out from this police lineup:
|>
|> * * * * * *
|> \ \ / * * * | \ / \
|> \ \ / / \ / | | \ / \
|> N---* *---N---* / \ / | *---N---* N *
|> / / \ / \ / | | /
|> / / \ *---N---* *---N---* *---N---* | /
|> * * * * *
|>
|> 1 2 3 4 5 6 7
|>
|> If you don't see the guilty party, maybe you can draw a picture
|
| #2 be the culprit. Your "split-phase" three-phase from another
| post.

That is the same as the six-phase "star" or "6 star". So if you can't
see any difference, that's because there isn't any. I would not have
called this a "wye" of any sort since it doesn't look like a "Y". But
it could be TWO Y's interleaved.

No, not "interleaved" but split. Invert each phase, as in a center-
tapped transformer (I.e. split) and you're there.

To make this derived system, you need either:

1. 3 single phase transformer cores

Kinda like they do now on the pole.

2. 1 three phase tranformer E-core
Kinda...

Then you need to wrap these cores with 3 primary windings and 3 secondary
windings. Usually the secondaries go on the inside and the primaries go
on the outside, so the secondary at lower voltage and higher current has
less winding resistance.

Ok, I'm confused. This is different how?

Each of the 3 secondary windings needs to be either:

1. a pair of 120 volt windings which you can wire in series
2. a single 240 volt winding with a center tap right in the middle

Exactly (is there a difference?).

All of the center points of these windings are wired/bonded together and
grounded. Then each of the three phases will have two poles 180 degrees
apart. Some people will call this six phases.

Right; split-phase "wye".

|> Note that drawings are NOT to scale (relative to voltage).
|
| Close enough for government work.
|
| <snip>
|
|> |> Can you describe an electrical system configuration which is capable of:
|> |>
|> |> 1. Supplying 120 and 240 volts (not 208 volts) in single phase to all
|> |> single phase loads.
|> |
|> | Look harder at a center-tapped wye. There is only 60degrees between
|> | the "negative" of phase-A and Phase-B.
|>
|> I don't know which I need to look at.
|
| #2

Let me relabel the terminals like so:

C' B
\ /
\ /
A----N----A'
/ \
/ \
B' C

Between A and A' you have 240 volts.
Between B and B' you have 240 volts.
Between C and C' you have 240 volts.
Between A and B you have 208 volts.
Between B and C you have 208 volts.
Between C and A you have 208 volts.
Between C' and A' you have 208 volts.
Between A' and B' you have 208 volts.
Between B' and C' you have 208 volts.
Between A and N you have 120 volts.
Between B and N you have 120 volts.
Between C and N you have 120 volts.
Between A' and N you have 120 volts.
Between B' and N you have 120 volts.
Between C' and N you have 120 volts.
Between A and C' you have 120 volts.
Between C' and B you have 120 volts.
Between B and A' you have 120 volts.
Between A' and C you have 120 volts.
Between C and B' you have 120 volts.
Between B' and A you have 120 volts.

Which connection pair do you need to ask about?

I don't. You seem to see a difference between this "star" and an
ordinary 3-phase "wye" that delivers residential 240V split-phase.
I don't see anything new or particularly interesting here, but am
trying.

|> |> 2. Divides up the single phase load in three equal groups in order to
|> |> maintain a balance on each of the three phases of the utility supply.
|> |
|> | How does it divide anything? An imbalance can still be placed on
|> | any one (or two).
|>
|> Of course an imbalance can always happen, and likely will. But it is a
|> statistical thing. If a building has 54 apartments, connecting 18 of them
|> to phase A, 18 to phase B, and 18 to phase C, would be "balanced" enough
|> for utility purposes. If the supply were coming in as 120/240DCT, then
|> all of the apartments would be on just one of the phases and the phase
|> loading would be as lopsided as if the entire building were supplied with
|> single phase power. If the utility insists on balancing the phases and
|> rejects single phase service for this reason, they will reject 120/240DCT.
|> If the supply is 208Y/120, that would satisfy the utility (18 apartments
|> supplied with phases A and B, 18 suppleid with B and C, and 18 supplied
|> with C and A). But it would not satisfied the need to have 240 volts.
|
| Sure, but your "six-phase" is no different than the normal three-
| phase "wye". At least I don't see it.

The normal three phase WYE is just:

B
/
/
A----N
\
\
C

Between A and B you have 208 volts.
Between B and C you have 208 volts.
Between C and A you have 208 volts.
Between A and N you have 120 volts.
Between B and N you have 120 volts.
Between C and N you have 120 volts.

There aren't any other ways to connect, and no way to get 240 volts.

That's funny, because that's exactly how I get the 240V for my house
off the 3-phases on the pole.

|> |> ... that is not the "6 star" I described?
|> |
|> | I still don't see the difference between that and a center-tapped
|> | wye. Again, I'm not a power jock, so may be missing something
|> | subtile.
|>
|> Maybe you saw something I didn't see. Check the above police lineup.
|
| Nope. You saw it, just one of us isn't "getting it" (I could easily
| be missing something - 65h work weeks do that after a while).

OK, hope the above helps.

Nope. I'm still wondering why you see your "star" as any different
than what we see on 90% of the poles in the country.

 

[krw]

What makes you think that its up to you to chose? The utility
company is going to tell you what is available. The elevator company is
going to tell you what they need, as well. As usual, you're playing
another of your long winded, and useless games of 'What if'...

What if Phil bought his own bigass transformer?

 

[krw]

Of course, the answer is D). That is why tower light monitors are
required.


What is real fun is when you move to a different tower, and still
have to monitor the lights at the old transmitter site. I had to do
that at WACX. I used a 1.024 MHz crystal and divided it by 1024, then
filtered it to get a fairly clean sine wave. A current transformer
monitored the circuit. The sine wave was on, when there was at least one
light out. That way, when the beacons flashed, the signal dropped for a
second.

I "worked" at WPGU-FM (at the time the only network affiliated
student station) for a while. Their transmitter was on a 12-story
dorm building about a mile from the studios (in the basement of
another dorm building). THe logs were taken remotely over a phone
line with a contraption that consisted of a rotary phone dial and
meter. One of dial "positions" ('9', IIRC) returned the antenna
light current, which was logged every half hour along with all the
rest of the stuff.

At the other end, I used a 567 tone decoder to detect the 1 KHz
signal. There was a small, but bright LED in the mater operator's field
of view. They logged when it started flashing, and when it stopped. If
the light went out it meant there was no AC at the old site, and that
was logged in and out, as well.


BTW: My choice would have been F). Find the idiot who wrote the test
and make them re-write it so that all questions were closer to the
proper answer. There should be no throw away questions on a test like
that.

As far as I was concerned, the whole test was throw away questions
like that. It was a waste of a day and a trip to Chicago.

 

[[email protected]]

| [email protected] wrote:
|>
|>
|> | In the situation under discussion were the only significant three phase
|> | load is the elevator a three phase auto transformer wired in boost
|> | configuration would solve the problem at a reasonable cost.
|>
|> What if you don't have any need for three phase power at all? Suppose your
|> building has elevators that work fine on single phase power. The building
|> is so big, however, the power company doesn't want to drop only one phase
|> into it; they want to have all three phases coming in, in some approximation
|> of a balanced load. And you need to supply 240 volts, not 208, to each
|> tenant. What would you set
|
|
| What makes you think that its up to you to chose? The utility
| company is going to tell you what is available. The elevator company is
| going to tell you what they need, as well. As usual, you're playing
| another of your long winded, and useless games of 'What if'...

Maybe you should read some of the tariffs. Most jurisdictions do have
some requirements that certain services must be made available of so
requested. The only "what if" here is "what if someone knew what they
were allowed to really ask for".

 

[Beachcomber]

| What makes you think that its up to you to chose? The utility
| company is going to tell you what is available. The elevator company is
| going to tell you what they need, as well. As usual, you're playing
| another of your long winded, and useless games of 'What if'...

I think that logically, the process goes something like this.

1. The architect or building contractor responsible for the
electrical system needs to research the utility tariffs and policies
and determine what services are available.

2. Further research may be necessary to see what services are
available at the specific location of the building under construction.


This may be different then #1.

3. Given the available choices, it is up to the person designing the
electrical system within the building the most economical and useful
service, given the specific needs of the building (elevators, HVAC,
pumps, machine shop tools, etc.) That is, should it be 120/208,
120/240, volt single phase or three phase, open wye, or closed-delta,
etc.

#3 is the most interesting and the most difficult, apparently, from
the comments offered on this thread. It doesn't seem that there are
any carved-in-stone rules for what is best, only tradeoffs and
different opinions.

Have I got this right?

Beachcomber

 

[charles]

Obviously, you don't and you've been flogging another dead horse.
You can take any simple subject and turn it into mind numbing drivel.
You've flogged this one for a week and made zero progress. Even if you
got answers, they would only be valid for one location, not the entire
planet earth.

You bitch about no availability of 208 volt appliances. How many do
you see that are marked 240 VAC only? I see a lot that are marked
208-240 VAC. So your water heater is a few volts low. It won't make
much difference in the output.

Power is a function of the voltage squared. So a 3kW heater at 240v
becomes 2.25kW at 208v. It may not be significant if it's used for storage
heating but as an instantaneous heater it would matter.

 

[[email protected]]

| In article <[email protected]>, phil-news-
| [email protected] says...
|> | In article <[email protected]>, phil-news-
|
| <attempt to snip to size>
|
|> |> | Specifically, the six-phase "star" and three-phase center-tapped
|> |> | wye. With any two phases any number of others is a few transformers
|> |> | away.
|> |>
|> |> I don't know which you mean by "three-phase center-tapped wye". Maybe you
|> |> can pick it out from this police lineup:
|> |>
|> |> * * * * * *
|> |> \ \ / * * * | \ / \
|> |> \ \ / / \ / | | \ / \
|> |> N---* *---N---* / \ / | *---N---* N *
|> |> / / \ / \ / | | /
|> |> / / \ *---N---* *---N---* *---N---* | /
|> |> * * * * *
|> |>
|> |> 1 2 3 4 5 6 7
|> |>
|> |> If you don't see the guilty party, maybe you can draw a picture
|> |
|> | #2 be the culprit. Your "split-phase" three-phase from another
|> | post.
|>
|> That is the same as the six-phase "star" or "6 star". So if you can't
|> see any difference, that's because there isn't any. I would not have
|> called this a "wye" of any sort since it doesn't look like a "Y". But
|> it could be TWO Y's interleaved.
|
| No, not "interleaved" but split. Invert each phase, as in a center-
| tapped transformer (I.e. split) and you're there.

You mean like having 2 three phase 208Y/120 transformers, one fed 180 degrees
out of phase from the other, and combining their outputs with neutrals tied
together? That's what I meant by interleaved. If that's not what you are
saying, then I don't understand what it is you are saying.


|> To make this derived system, you need either:
|>
|> 1. 3 single phase transformer cores
|
| Kinda like they do now on the pole.

Yes. Except instead of using 120-volt-only transformers (there are such
things ... just 2 lugs on the secondary), they need to use the 120/240 volt
transformers (plenty of those around) and understand the concept to know
how to wire it up.

Metering that could be an issue. In the case of the apartment building,
individual tenants would be metered at 120/240 so it's not an issue. But
if this needs to be metered in its "6 star" configuration, it can be done
with 3 CTs, each carrying the 180-degree-opposite conductor pairs running
in opposing directions just as a single CT would be used for single phase
power.


|> 2. 1 three phase tranformer E-core
|
| Kinda...

It could be done. The manufacturing just has to provide a pair of 120
volt windings, or a series 120/240 tapped winding, and sufficient terminal
board space to deal with it.


|> Then you need to wrap these cores with 3 primary windings and 3 secondary
|> windings. Usually the secondaries go on the inside and the primaries go
|> on the outside, so the secondary at lower voltage and higher current has
|> less winding resistance.
|
| Ok, I'm confused. This is different how?

The difference is that a traditional E-core 208Y/120 transformer would have
only ONE 120 volt winding per core bar (times the 3 core bars). Two such
windings at 120 volt each, or a 120/240 volt series winding (connected in
series inside the winding instead of at the terminal board) would be needed
for the "6 star" configuration.


|> Each of the 3 secondary windings needs to be either:
|>
|> 1. a pair of 120 volt windings which you can wire in series
|> 2. a single 240 volt winding with a center tap right in the middle
|
| Exactly (is there a difference?).

Yes, there is a difference. In #1 you have 4 wires coming from the secondary
winding to the terminal board. In #2 you have 3 such wires because the
winding is series connected, possibly a continuous single wire, inside the
winding itself, and just tapped at a mid-point.

It's a difference in construction. Some people might be more familiar with
one over the other.


|> All of the center points of these windings are wired/bonded together and
|> grounded. Then each of the three phases will have two poles 180 degrees
|> apart. Some people will call this six phases.
|
| Right; split-phase "wye".

Keep the "wye" in quotes, then; it's not really wye. I would never call it
a wye at all. It's a 6 pointed radial star.


|> |> Note that drawings are NOT to scale (relative to voltage).
|> |
|> | Close enough for government work.
|> |
|> | <snip>
|> |
|> |> |> Can you describe an electrical system configuration which is capable of:
|> |> |>
|> |> |> 1. Supplying 120 and 240 volts (not 208 volts) in single phase to all
|> |> |> single phase loads.
|> |> |
|> |> | Look harder at a center-tapped wye. There is only 60degrees between
|> |> | the "negative" of phase-A and Phase-B.
|> |>
|> |> I don't know which I need to look at.
|> |
|> | #2
|>
|> Let me relabel the terminals like so:
|>
|> C' B
|> \ /
|> \ /
|> A----N----A'
|> / \
|> / \
|> B' C
|>
|> Between A and A' you have 240 volts.
|> Between B and B' you have 240 volts.
|> Between C and C' you have 240 volts.
|> Between A and B you have 208 volts.
|> Between B and C you have 208 volts.
|> Between C and A you have 208 volts.
|> Between C' and A' you have 208 volts.
|> Between A' and B' you have 208 volts.
|> Between B' and C' you have 208 volts.
|> Between A and N you have 120 volts.
|> Between B and N you have 120 volts.
|> Between C and N you have 120 volts.
|> Between A' and N you have 120 volts.
|> Between B' and N you have 120 volts.
|> Between C' and N you have 120 volts.
|> Between A and C' you have 120 volts.
|> Between C' and B you have 120 volts.
|> Between B and A' you have 120 volts.
|> Between A' and C you have 120 volts.
|> Between C and B' you have 120 volts.
|> Between B' and A you have 120 volts.
|>
|> Which connection pair do you need to ask about?
|
| I don't. You seem to see a difference between this "star" and an
| ordinary 3-phase "wye" that delivers residential 240V split-phase.
| I don't see anything new or particularly interesting here, but am
| trying.

A true WYE is not split phase. That makes a contradiction of terms.
But if you know of a manufacturer that makes such a transformer AND
calls it "split phase wye" or some such thing, please do point to
their catalog reference. I've looked at a lot of transformer catalog
info online and have never seen such a thing in a single transformer.



|> |> |> 2. Divides up the single phase load in three equal groups in order to
|> |> |> maintain a balance on each of the three phases of the utility supply.
|> |> |
|> |> | How does it divide anything? An imbalance can still be placed on
|> |> | any one (or two).
|> |>
|> |> Of course an imbalance can always happen, and likely will. But it is a
|> |> statistical thing. If a building has 54 apartments, connecting 18 of them
|> |> to phase A, 18 to phase B, and 18 to phase C, would be "balanced" enough
|> |> for utility purposes. If the supply were coming in as 120/240DCT, then
|> |> all of the apartments would be on just one of the phases and the phase
|> |> loading would be as lopsided as if the entire building were supplied with
|> |> single phase power. If the utility insists on balancing the phases and
|> |> rejects single phase service for this reason, they will reject 120/240DCT.
|> |> If the supply is 208Y/120, that would satisfy the utility (18 apartments
|> |> supplied with phases A and B, 18 suppleid with B and C, and 18 supplied
|> |> with C and A). But it would not satisfied the need to have 240 volts.
|> |
|> | Sure, but your "six-phase" is no different than the normal three-
|> | phase "wye". At least I don't see it.
|>
|> The normal three phase WYE is just:
|>
|> B
|> /
|> /
|> A----N
|> \
|> \
|> C
|>
|> Between A and B you have 208 volts.
|> Between B and C you have 208 volts.
|> Between C and A you have 208 volts.
|> Between A and N you have 120 volts.
|> Between B and N you have 120 volts.
|> Between C and N you have 120 volts.
|>
|> There aren't any other ways to connect, and no way to get 240 volts.
|
| That's funny, because that's exactly how I get the 240V for my house
| off the 3-phases on the pole.

Which connections give you 240 volts? If you are getting 240 volts from
A-B or from B-C or from C-A, and if the phase angles really are 120 degrees
as a true three phase WYE would be, then you are going to get 139 volts
at A-N, B-N, and C-N. I don't think that is what you want.

FYI, I did find one utility offering 240Y/139 service for some portions
of their service area, as a replacement for 240D.

Maybe you are getting ONE phase of 120/240 via ONE split phase transformer
tapped to ONE phase (connected L-N) or TWO phases (connected L-L) of the
primary distribution lines. But just because there is three phase on the
distribution does NOT mean you are getting it. You are most likely getting
one of: 208Y/120 three phase (my grandfather actually did get this at his
home), or 120/240 single phase, or that old 240DCT/120 setup.


|>
|> |> |> ... that is not the "6 star" I described?
|> |> |
|> |> | I still don't see the difference between that and a center-tapped
|> |> | wye. Again, I'm not a power jock, so may be missing something
|> |> | subtile.
|> |>
|> |> Maybe you saw something I didn't see. Check the above police lineup.
|> |
|> | Nope. You saw it, just one of us isn't "getting it" (I could easily
|> | be missing something - 65h work weeks do that after a while).
|>
|> OK, hope the above helps.
|
| Nope. I'm still wondering why you see your "star" as any different
| than what we see on 90% of the poles in the country.

208Y/120 is _very_ different. 208Y/120 has THREE line wires coming out at
120 degree phase angle equal intervals. The "6 star" (maybe we can call
it 240*/208/120) has SIX line wires coming out at 60 degree phase angle
equal intervals.

If I provide you with exactly 3 transformers which are wired up with one
winding for the primary voltage and one winding for the secondary at 120
volts, it can be wired up by connecting the primaries in whatever they
need for the type of service (delta or wye) and connecting the secondaries
in a wye configuration. There, you have 208Y/120 just like 90% of the
three phase poles in the country (I'll just accept your stats of 90% as I
do not know the actual figures).

I have never seen, and never heard of, any "6 star" or 240*/208/120 setup
anywhere. I have never seen any utility tariff (I've looked through a few
dozen over the past few years) that offers such a service.

I HAVE seen a couple three phase setups where a 120/240 volt pole pig was
used, and only HALF of it was wired up to get 120 volts. I HAVE seen one
manufacturer detail that they do make cans with the 120 volt windings in
parallel internally, and still have 3 lugs with one of them not connected.
So these are not necessarily a case of wasting half the capacity. The 3rd
lug may simply be there are part of the process of manufacturing only one
set of empty cans instead of two different sets.

 

[[email protected]]

| krw wrote:
|>
|> In article <[email protected]>,
|> [email protected] says...
|> >
|> > What makes you think that its up to you to chose? The utility
|> > company is going to tell you what is available. The elevator company is
|> > going to tell you what they need, as well. As usual, you're playing
|> > another of your long winded, and useless games of 'What if'...
|>
|> What if Phil bought his own bigass transformer?
|
|
| Progress Energy, who bought Florida Power, wouldn't let you provide
| any transformers. They did the calculations, and set their own
| transformers. Three phase availability was determined by your location,
| but generally any building above a certain level was three phase. Even
| small convenience stores and gas stations are three phase around here.
| The only home I've seen with an elevator had three phase power, along
| with an Onan diesel three phase generator with an automatic transfer
| switch.

Maybe Florida has no provision to require the utility to provide standard
voltages (like 240 volts). Some other states do. And such a requirement
is NOT a problem to meet (although if you want to change an existing setup
I can expect you have to pay the full costs).

Do you know if that home has 208Y/120 or 240DCT/120 ?

This system is overkill for a single home:

* *
\ /
*--*--*
/ \
* *

But this system could do the job adequately:

*
/
*--*--*
\
*

Which to choose depends on whether the distribution supply needs to be kept
in balance or not. Utilities require (and this is a reasonable requirement)
that larger services be three phase so they can keep the lines in the area
in balance.

I've not seen generators that readily do either of these diagrammed examples,
so I suspect that house is either 208Y/120 or 240DCT/120. And the 240DCT/120
can be done at least three different ways.

 

[[email protected]]

|
|>| What makes you think that its up to you to chose? The utility
|>| company is going to tell you what is available. The elevator company is
|>| going to tell you what they need, as well. As usual, you're playing
|>| another of your long winded, and useless games of 'What if'...
|>
|>
| I think that logically, the process goes something like this.
|
| 1. The architect or building contractor responsible for the
| electrical system needs to research the utility tariffs and policies
| and determine what services are available.
|
| 2. Further research may be necessary to see what services are
| available at the specific location of the building under construction.
|
|
| This may be different then #1.
|
| 3. Given the available choices, it is up to the person designing the
| electrical system within the building the most economical and useful
| service, given the specific needs of the building (elevators, HVAC,
| pumps, machine shop tools, etc.) That is, should it be 120/208,
| 120/240, volt single phase or three phase, open wye, or closed-delta,
| etc.
|
| #3 is the most interesting and the most difficult, apparently, from
| the comments offered on this thread. It doesn't seem that there are
| any carved-in-stone rules for what is best, only tradeoffs and
| different opinions.
|
| Have I got this right?

Basically, yes. One point is that to choose 120/240 when the building size
(in terms of load) is above the point where three phase is required means a
greater cost. Unlike single homes, such developments, even if residential
in nature, are treated like commercial, at least up to the point where the
tenant metering takes place. So the developer has to pay most or all of the
electrical service installation costs. Since traditional 208Y/120 is lower
in cost (one stock transformer, one entrance disconnect), it may well be
the one chosen. It can cost more to then get special appliances for each
unit to operate at 208 volts. Or, as appears to be the case quite often,
the developer just passes the cost on to the owner(s) or tenants in the
form of poorly chosen appliances, or leaving it up to condo buyers to find
the 208 volt appliances, or suffer with 240 volt appliances. The fact that
so many cases are decided in bad ways does not mean better choices are not
available; they just cost a little more.

I do know some apartment buildings are large enough to have transformers
on each floor. I was in one building many years ago that had 8 units on
each of 12 floors. There was a transformer on each floor, and metering
for each tenant was in a small room on the same floor. The meter room did
not have the transformer. That would certainly be essential of the feed
was at distribution voltage (I don't know what it was in that building as
I did not actually inspect the rooms). I do know it had 208 volts to each
unit, and specially bought 208 volt appliances. But they could have just
done this with a single phase transformer on each floor and saved on the
cost of appliances but getting normal 240 volt ones. In this case, it
would not have been any more expensive, and it would have been at least
as well balanced across the distribution phases as the existing setup.
Any needs for three phase power could have been satisfied with a separate
three phase transformer at the top or bottom of the building. It would
have to be separately metered, anyway.

 

[[email protected]]

| [email protected] wrote:
|>
|> Maybe you should read some of the tariffs. Most jurisdictions do have
|> some requirements that certain services must be made available of so
|> requested. The only "what if" here is "what if someone knew what they
|> were allowed to really ask for".
|
|
| Obviously, you don't and you've been flogging another dead horse.
| You can take any simple subject and turn it into mind numbing drivel.
| You've flogged this one for a week and made zero progress. Even if you
| got answers, they would only be valid for one location, not the entire
| planet earth.

How do you know there is "zero progress"? Just because I have failed to
educate YOU on the issue does not mean I have failed to open the eyes of
others to the issues AND solutions.


| You bitch about no availability of 208 volt appliances. How many do
| you see that are marked 240 VAC only? I see a lot that are marked
| 208-240 VAC. So your water heater is a few volts low. It won't make
| much difference in the output. If you buy at the right places, 208 volt
| stuff isn't hard to find, even in the deep south. If you are in an
| apartment, it is up to the landlord to provide the major appliances, and
| repair or replace them when they quit. So, if the building is big
| enough, they are supplied three phase. no matter how much you want to
| yak about what ifs, no one really gives a damn, except the local power
| company, and the owner of the building.

I have real experiences with such low voltage issues.

My grandfather had this issue with his home when he obtained three phase
service for his home to power three phase motors in his shop. He had
problems with a stove that was slow to heat up, an electric dryer motor
that burned out a couple times, and occiaisional issues with the air
conditioning. Apparently he needed 240DCT/120 and they gave him 208Y/120.

I worked in a commercial building at an ISP at the beginning of the
popularity of the internet. As the heat output in the computer room
went up, and it was expanded into a 2nd room, it taxed the A/C system
more. The A/C system was rated for that level of heat, but kept failing
anyway. The building was originally single phase, but was converted
over to three phase many years prior to our occupancy (apparently due
to one tenant installing some equipment that needed some major amount
of power. The A/C systems were single phase, and now running on 208
volts. The A/C servicing company had to special order a 208 volt single
phase motor to replace the 240 volt single phase motors that kept burning
out. Once the 208 volt motor was in, it worked fine.

The fact is, there are problems with 208 volt services. Yes, there are
appliances that can work on 208 volts. Some work less well. Some work
just fine. Some will fail.

If it is a building where the owner buys the appliances, the owner needs
to consider the costs of those appliances as part of the overall cost
savings strategy. In cases where the residents have to buy their own,
such as many condominium arrangemnts, this is a cost passed on to the
residents (so the developer might not give a damn).

To be cheap, landlords might well buy the very cheapest appliances that
are available, which might be 240 volt just because there is a larger
market for these. Then when residents complain that it takes longer to
cook food and recover heat in the water tank, the landlord just says to
accept it or move out at the end of the lease. Do not under any case
think that landlords will be sure there are no problems.

I have pointed out the alternative to get true 240 volts. Not all cases
would be able to utilize that without extra costs. Certainly a retrofit
won't be free. But in many cases it can be a no greater cost to supply
genuine split-phase single phase 120/240 volt service to residential units.

Part of the problem is that too many developers and engineers continue to
think inside the 208 volt box. They think it is an accepted norm (and it
is so relative to the people they deal with: landlords and developers who
can shield them from the real problems of residents). So they don't even
think about it. They just whack out a variation of the same old same old
and people are then stuck with no improvement and have to accept it.

 

[[email protected]]

| In article <[email protected]>,
|> [email protected] wrote:
|> >
|> > Maybe you should read some of the tariffs. Most jurisdictions do have
|> > some requirements that certain services must be made available of so
|> > requested. The only "what if" here is "what if someone knew what they
|> > were allowed to really ask for".
|
|
|> Obviously, you don't and you've been flogging another dead horse.
|> You can take any simple subject and turn it into mind numbing drivel.
|> You've flogged this one for a week and made zero progress. Even if you
|> got answers, they would only be valid for one location, not the entire
|> planet earth.
|
|> You bitch about no availability of 208 volt appliances. How many do
|> you see that are marked 240 VAC only? I see a lot that are marked
|> 208-240 VAC. So your water heater is a few volts low. It won't make
|> much difference in the output.
|
| Power is a function of the voltage squared. So a 3kW heater at 240v
| becomes 2.25kW at 208v. It may not be significant if it's used for storage
| heating but as an instantaneous heater it would matter.

It depends on how many people want to use hot water and how _soon_ after
a previous person has used it up.

It does appear that modern ranges with electronic controls on cooktops
and ovens do a fine job with 208 volts or 240 volts. They just have
more "on time" at 208 volts than at 240 volts for whatever setting is
involved. My father's range at 240 volts is on about 75% of the time
at the top setting. I suspect it will work fine at 208 volts.

Other things might not do so well at 208 volts. It can, for example,
affect the sustained temperature a house can be kept at when electric heat
is used and the outside temperature is in a deep cold spell.

I think the USA might well have been better off with "everything 240 volts"
as is the case in the UK (though I would not want those ring circuits).

I described a while back an electrical system design that I would put in
place if it were my say to do so, if I could have done it way back in time
when changing over would be little or no cost, based on knowledge I have
today (they did not have it back then, over 100 years ago). That system
would be 288 volts always connected line to line. It would have 144 volts
line to neutral in single phase systems (e.g. split phase as the USA has
now). It would have 166 volts line to neutral in three phase systems in
a star/wye arrangement. Everything except incandescent lights would be on
288 volts. Nothing would use the 144 or 166 volt connections. There would
be a small transformer serving a light or group of lights to step the 288
volts down to 12 or 12/24 volts. This would mean the use of filaments that
would be thicker, and could run hotter. That should at least make up for
the loss in the transformer (as is now the case to justify the use of low
voltage lighting). Fluorescent lighting could be run directly on the 288
volt connection. My system would have avoided the voltage discrepancy
issues the USA currently has between 208 volts and 240 volts, while having
a lower "relative to ground" voltage in the wiring than the UK has.

 

[Beachcomber]

Part of the problem is that too many developers and engineers continue to
think inside the 208 volt box. They think it is an accepted norm (and it
is so relative to the people they deal with: landlords and developers who
can shield them from the real problems of residents). So they don't even
think about it. They just whack out a variation of the same old same old
and people are then stuck with no improvement and have to accept it.

Generally, if you are a renter, you experience a lack of choice in
many aspects of your housing. You may have lack of choice in being
subjected to noise from the Bickersons in the apartment above you or
the sax player next door. You may not have the choice of doing your
laundry in your unit, or painting your walls lime green, or having
your own parking space. If your landlord provides a 240V dryer on a
208V circuit, then yes... your clothes will take longer to dry. You
have no choice. The lower voltage might have the dryer heater cycle
on for a longer period of time, but the maximum wattage delivered will
definately be less.

In the US, at least, condo unit owners may have it better, in that
they might have a few more things under their control. Most
multi-unit condos have an in-unit washer and dryer, so at least you
might have a choice about getting the dryer at the correct voltage.

I would argue that its still more of a hassle though (for most
people), and it may be hard to find or order the one you want that
runs properly on 208V. You will probably be faced with increased
expense, as well. Perhaps the one currently on sale has only the 240V
element.

Beachcomber