Closed Delta 120/240V 3-phase service

snipped-for-privacy@ipal.net wrote:


You were ripped off. Find an honest business to buy from.
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On Mon, 18 Feb 2008 13:50:11 -0500 Michael A. Terrell
| snipped-for-privacy@ipal.net wrote: |> |> On Sun, 17 Feb 2008 13:10:44 -0500 Michael A. Terrell
|> |> | charles wrote: |> |> |> |> 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. |> | |> | |> | Gee thanks for that lesson. I've know and used it since the '50s. |> | If you need that extra bit of heat, you can buy the proper heating |> | element. Not at the over the counter type 'DIY' dumps, but at a real |> | plumbing supply house. |> |> Which means it is more expensive. And in many cases they have to special |> order it. I've already experienced the special order cost case with a |> 208 volts single phase motor (it was twice as much as a 240 volt motor of |> the same HP and mounting). | | You were ripped off. Find an honest business to buy from. |
It was like $120 instead of $60. That's no big deal considering the costs of dealing with A/C system failures, and having to shut down equipment to avoid over heating. The big hassle was it took 4 weeks to get that motor. Three 240 volt motors at $60 apiece burned up in the mean time.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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On Sun, 17 Feb 2008 12:20:31 +0000 (GMT) charles
|> > |> > 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.
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On Sun, 17 Feb 2008 03:57:14 -0500 Michael A. Terrell
| snipped-for-privacy@ipal.net 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.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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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.
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| |>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.
Yes, landlords go cheap on lots of things, not just the power.
The last apartment I lived in had 120/240. The complex consisted of 60 some buildings with 12 apartments each. Each building had a single phase pad mount. I don't know what its rating was as the nameplate was not visible (probably inside and I didn't care to get into it). Presumably it could have been as much as 167 KVA, the largest single phase pad mount I've seen in catalogs. That is probably fine for 12 apartment units.
| 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.
Yes, if they go buy one for the condo, they can choose between the $400 240 volt model and the $440 208 volt special order model. If they already have one from the house they now live in and want to take it with them, it's probably a 240 volt model.
| 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.
Exactly. The costs for 208 volt models can be from both the smaller market as well as the special order handling.
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snipped-for-privacy@ipal.net wrote:

I haven't seen people agreeing with you, or supporting your theories.

Sure you do. We've all seen brownouts. My line voltage was about 105 volts for a month while the area was rebuilt after some hurricanes. It was 27 volts for half a day. Fluorescent lights didn't work right at 105 volts, but it didn't bother the refrigerators.

Apparently he needed the proper appliances. He made the decision to convert to three phase, so don't blame the equipment that he was to cheap to convert, or replace.
One TV transmitter site I worked at was supplied with 480 Wye service only. That was fine for most of the transmitter and cooling system, but the crystal ovens and oscillators ran on 120 single phase so we had to install three 2 KVA 480 to 120 volt transformers to power everything else.

I've lost three air conditioner compressors in the last nine years at my home, and all were running at the rated voltages. Microdyne lost at least a half dozen a year, all were three phase, and running the right voltage. How can you prove it was under voltage, not that the air conditioner couldn't handle the load? Tty air conditioning a TV station's control room and studios. We had a five ton unit just for the VTRs and effects racks.

Gee, Phil. If the owner has to buy and maintain the appliances, why would they buy the cheapest shit made? They aren't that stupid. Well, at least around here. Their cost for the appliances are in bulk, and at wholesale. A lot of damage to their buildings is avoided by supplying the appliances, and they can charge higher rent. The longer an appliance lasts, the more money they make off it.

Where is this? Defects in a building can get the landlord and or management company fined. for failing to make repairs in an acceptable time. In severe cases, the building can be condemned. After that, the owner has a little time to do the repairs, and get a new certificate of occupancy. You're just trying to blow smoke up my ass, as usual.

Name ONE thing a renter needs to run on 240 volts that isn't supplied by a decent landlord.

They do it because it works reliably, and at a reasonable cost. It really isn't up to you, and there is no valid need for any 240 VAC for anything the owner doesn't supply.
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On Sun, 17 Feb 2008 19:59:03 -0500 Michael A. Terrell
| snipped-for-privacy@ipal.net wrote: |> |> On Sun, 17 Feb 2008 03:57:14 -0500 Michael A. Terrell
|> |> |> |> 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. | | | I haven't seen people agreeing with you, or supporting your theories.
Maybe if you look beyond just who is posting, you'd see more. There are already some that are posting, too. The rest are quiet and you cannot tell if they agree or not.
|> | 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. | | | Sure you do. We've all seen brownouts. My line voltage was about 105 | volts for a month while the area was rebuilt after some hurricanes. It | was 27 volts for half a day. Fluorescent lights didn't work right at 105 | volts, but it didn't bother the refrigerators.
Yes, I have seen brownouts before. Some things work OK at reduced voltage and some things done. You get both in each class of appliance.
|> 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. | | | Apparently he needed the proper appliances. He made the decision to | convert to three phase, so don't blame the equipment that he was to | cheap to convert, or replace.
More likely he didn't know. I didn't discuss lots of details with him at the time, since I was only 12 years old. I knew WHAT three phase was for, but I had no idea how the systems were configured, or that it really mattered. What I knew then was that he did say the voltage was too low and he was trying to get the power company to fix it.
I suspect when he asked for three phase, he didn't know the choices and might have been expecting to get 240DCT/120. I don't know if his shop equipment needed 240 or 208. I just know he was trying to get it redone up to the day he died. I don't know why it was not redone. I can only guess and many possible explanations seem plausible.
| One TV transmitter site I worked at was supplied with 480 Wye service | only. That was fine for most of the transmitter and cooling system, but | the crystal ovens and oscillators ran on 120 single phase so we had to | install three 2 KVA 480 to 120 volt transformers to power everything | else.
And the transmitter manufacturer didn't integrate things so that it could be connected to a single power source?
|> 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. | | | I've lost three air conditioner compressors in the last nine years at | my home, and all were running at the rated voltages. Microdyne lost at | least a half dozen a year, all were three phase, and running the right | voltage. How can you prove it was under voltage, not that the air | conditioner couldn't handle the load? Tty air conditioning a TV | station's control room and studios. We had a five ton unit just for the | VTRs and effects racks.
The motors burned out very frequently, generally lasting no more than two weeks as summer come on along with the new computers in place. Once the 208 volt motor was put in, the problem completely went away. Clearly the A/C servicing people believed it was a voltage issue. Based on what changes took place, I'd agree it was.
That doesn't mean there can't be failures for other reasons. But in the above case, it was clearly voltage with 99% confidence. Go ahead and pick on the 1% if you want.
|> 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. | | | Gee, Phil. If the owner has to buy and maintain the appliances, why | would they buy the cheapest shit made? They aren't that stupid. Well, | at least around here. Their cost for the appliances are in bulk, and at | wholesale. A lot of damage to their buildings is avoided by supplying | the appliances, and they can charge higher rent. The longer an | appliance lasts, the more money they make off it.
Actually, in a great many cases, they _are_ that stupid. While motor based appliances might well burn up, heating element appliances may have no issued. BTW, dryers tend to have the motor on L-N, not L-L. So the motor would be getting what it expects even on 208Y/120. Ranges and water heaters are NOT going to have a shortened life due to running on a reduced voltage. So they _can_ get away with using 240 volt stuff on 208 volts.
|> 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. | | | Where is this? Defects in a building can get the landlord and or | management company fined. for failing to make repairs in an acceptable | time. In severe cases, the building can be condemned. After that, the | owner has a little time to do the repairs, and get a new certificate of | occupancy. You're just trying to blow smoke up my ass, as usual.
I'd like to see them get fined for such things. Generally, they don't.
|> 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. | | | Name ONE thing a renter needs to run on 240 volts that isn't supplied | by a decent landlord.
In renting situations, probably nothing. But in at least a lot of cases, and maybe most, where 208 volts is supplied, the appliances are 240 volt models.
When the building is converted to condo, the picture changes. And this is where most of the reports of this issue come from.
|> 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. | | | They do it because it works reliably, and at a reasonable cost. It | really isn't up to you, and there is no valid need for any 240 VAC for | anything the owner doesn't supply.
As long as the landlord supplies correct voltage appliances for whatever is supplied, all is well. Sadly, that is not the case quite often.
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snipped-for-privacy@ipal.net wrote:

Why should they? Early TV stations had the studio at the transmitter site, and 120 VAC was readily available. In this case, a transmitter built in 1952 was moved to a new site to build a low power TV station in the mid '80s. The "Studio" was in a house 50 feet away. The "Studio" had 120/240 single phase service. the transmitter building didn't.
<http://maps.google.com/maps?q=lisbon+Florida&ie=UTF8&oe=UTF-8&t=h&ll (.859862,-81.773995&spn=0.001644,0.002494&z&iwlocdr>

What kind of company continues to use the wrong compressor?

When they buy in quantity, they pay the same price for either version.

Then the judges are crooked.

One of the county's largest group of condos is a few miles from here. It is so big that some contractors do nothing but work to build new units, and maintain existing units. It is called, "The Villages"

Then the property isn't up to minumum housing codes, and can not legally be leaased or rented.
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On Wed, 13 Feb 2008 16:13:15 +0000 (UTC) Michael Moroney
| snipped-for-privacy@ipal.net writes: | |>Maybe an ASCII art picture will help: | |> 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. | I strongly suspect the answer to both is an absolute No Way, esp. if | you think about how the heck you'd design the panel. You'd have to invent | nonstandard breakers that would do lots of skipping to be useful. Of | course such a service would really be useful only in an apartment building | where there would be multiple standard panels, mostly residential split | phase (1/3 A-D 1/3 B-E 1/3 C-F) and a 3 phase panel for elevator service, | so no need for an actual panel for this 7 wire service.
I have seen 6-pole disconnects, presumably intended for large motor control. But I have seen them up to 600 volt 400 amp. That's a huge motor.
A 6 phase panel is just too bizarre.
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snipped-for-privacy@ipal.net wrote:

Got it. Thanks. It was the "center tap" that threw me. It is really 6 windings in a star configuration.
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| snipped-for-privacy@ipal.net wrote: |> Maybe an ASCII art picture will help: |> |> 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. |> |> You could also get 120 volts from A-B or B-C or C-D or D-E or E-F or |> F-A, but you would not want to. |> |> You could also ignore the center tap and rewire it for 416Y/240. |> |> If the windings can be split and wired in parallel, you could rewire |> it for 208Y/120 with double the amperage. |> |> A transformer with dual secondary 120 volt windings on each of the |> three cores would be quite flexible, being able to be configured for |> any of these three systems (but you would have 12 wires coming off |> the cores on the secondary side). |> |>> ---------------------------------------/----------------------------------| |>> Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address |>> below | first name lower case at ipal.net /
|>> ------------------------------------/-------------------------------------| | | | Got it. Thanks. It was the "center tap" that threw me. It is really 6 | windings in a star configuration.
If you have a common single phase 480 volt transformer with a pair of 120 volt windings that can be wired in parallel or series, I suppose you would call that a 2 winding secondary. But what if the windings are just tapped in the center and cannot be separated for parallel wiring? Would you still call that a 2 windings secondary? Either kind of winding could be used on each bar of the E-core to make the 240/208/120 6 point star configuration.
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snipped-for-privacy@ipal.net wrote:

Phil I agree. I had something else in my mind. Maybe just reading posts too late at night!
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snipped-for-privacy@notreal.none (Beachcomber) writes:

Do the elevator companies even offer a single phase elevator system in the size you need? (how many HP is such an elevator motor). Since the system has to control the motor, possibly reversing it, you may not be able to simply replace the motor with a single phase motor.
Do you have a need for 240V (not 208V) residential devices? If not, there's no real advantage of 240V delta or open delta over standard 208Y/120 service. The only real place I see where 240V delta has a place is residential service with a small 3 phase load, such as a workshop or large A/C unit. That's simply because homes have 240V and 120/240V single phase appliances.
I have seen open delta 3 phase in residential areas of Baton Rouge LA for whole house A/C. 1 large and one tiny transformer.
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On Wed, 13 Feb 2008 16:33:34 +0000 (UTC) Michael Moroney
| snipped-for-privacy@notreal.none (Beachcomber) writes: | |>I'm wondering if the simplicity of a single phase 240/120 V service |>for a small elevator building is in some way superior to the slightly |>more complex 3 phase- 208/120 V. wye service. | |>Can a small hydraulic passenger elevator serving a maximum of 3 flloor |>run OK on a 240 V. single phase circuit? If wired the other way, this |>would probably be the only 3 phase load. | | Do the elevator companies even offer a single phase elevator system in | the size you need? (how many HP is such an elevator motor). Since | the system has to control the motor, possibly reversing it, you may | not be able to simply replace the motor with a single phase motor. | | Do you have a need for 240V (not 208V) residential devices? If not,
Yes.
| there's no real advantage of 240V delta or open delta over standard | 208Y/120 service. The only real place I see where 240V delta has a place | is residential service with a small 3 phase load, such as a workshop or | large A/C unit. That's simply because homes have 240V and 120/240V single | phase appliances.
As do condos in very large buildings where not all big appliances are provided as part of the condo arrangement.
Suppose you buy a condo with 208Y/120 service, of which you get 2 lines of that. It has appliances included in the sale because the developer bought special 208 volt versions. You live there a few years and one of them fails and you need to buy a replacement. Go to Sears or some place like that and ask for 208 volt versions as if you were in this situation and see how easy it is.
Some modern ranges could easily handle 200 to 240 volts by means using a thermostat that manges the heat even so that at 208 volts there are some times the element goes off to maintain the correct temperature. It would be on for 208 volts more than for 240 volts.
| I have seen open delta 3 phase in residential areas of Baton Rouge LA for | whole house A/C. 1 large and one tiny transformer.
I'm sure when A/C systems started showing up, with many using 3-phase, they were among the first to get them down in the very hot south.
I wonder how many of those big+little transformer setups were Scott-T instead.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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snipped-for-privacy@ipal.net writes:
I was asking the original poster who was wondering about getting 240V delta or open delta service for a small building with an elevator.

[snip explanation why you'd want 120/240V service in a condo)
I agree that 120/240V service should always be supplied for residential service.
I'll amend my earlier answer to say if the configuration is a small apartment building small enough to power all the residences off a single transformer providing 120V/240V service, an open delta to provide for an elevator or other small 3 phase load would be appropiate.

I was real curious what was going on in the Baton Rouge case so I did study the wiring enough to figure out it was open delta. I don't think I've ever seen a Scott-T type setup using two pole pigs.
I take that back, sort of.
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.
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Michael Moroney wrote:

You are not likely to see too many Scott T transformers with three-phase supplies feeding three-phase loads, as you simply don't need them. It is far more likely that the Large+small transformers are open delta.
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I've heard that many single unit 3 phase transformers are internally wired as Scott-T, since this requires only two cores and two sets of windings instead 3 cores/3 sets of windings. Both the primary and secondary are wired in the configuration of the 3 phase side of a true Scott-T configuration.
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wrote:
|>As do condos in very large buildings where not all big appliances are |>provided as part of the condo arrangement. | | [snip explanation why you'd want 120/240V service in a condo) | | I agree that 120/240V service should always be supplied for residential | service. | | I'll amend my earlier answer to say if the configuration is a small | apartment building small enough to power all the residences off a single | transformer providing 120V/240V service, an open delta to provide for an | elevator or other small 3 phase load would be appropiate.
Or a Scott-T if the original 120/240 volt pole pig is a two-bushing type. Then a small one bushing transformer connected to the 3rd phase would give you the 90 degrees difference that Scott-T needs.
|>| I have seen open delta 3 phase in residential areas of Baton Rouge LA for |>| whole house A/C. 1 large and one tiny transformer. | |>I'm sure when A/C systems started showing up, with many using 3-phase, they |>were among the first to get them down in the very hot south. | |>I wonder how many of those big+little transformer setups were Scott-T instead. | | I was real curious what was going on in the Baton Rouge case so I did | study the wiring enough to figure out it was open delta. I don't think | I've ever seen a Scott-T type setup using two pole pigs.
What you would see in a Scott-T is that one transformer, preferrably the big one, would have 2 bushings, and the other would have 1 bushing. Each of the bushings would be connected to separate MV phases to get the 90 degree phase relationship.
| I take that back, sort of. | | 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? How many secondary lugs? While I have seen a few single-can three phase transformers in pole pig in pictures from other countries, I've never seen them in the USA. Pad mounts are different and do come in big three phase tanks.
See if you can get multiple photos each at the same distance taken in a partial circle around the transformer setup so it can be seen in 3-D by pairing selected photos. Take them on a dismal cloudy gray overcast day. If you have exposure setting, take a second set overexposed by 2 stops (to get more detail in the wiring itself). If using film, Tech Pan is the best choice unless something in color provides clues.
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| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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snipped-for-privacy@ipal.net writes:

If I remember correctly, both transformers had 1 MV bushing, connected to different phases, and the secondary was wired as open delta.
There are maybe two places near here where there are 2 transformers of equal (physical) size that I think are wired as open delta. I'll take a closer look, just in case.

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.

4 on the big can, I believe 4 on the small can.

There are a fair number around here (central Mass.), maybe 5-10% of all pole installations. Want photos? :-)

Any photography will have to wait several months before I go to the Philly area again. I have a single photo of one setup which doesn't help figuring out what's going on since the LV wiring is all bundled up.
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