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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
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Getting 120v Single Phase from 3 Phase
Can you get 120v single phase by picking off one line of 240v 3 phase
as long as you have a neutral to carry the current back to the box? Thanks, Steve |
#3
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wrote in message oups.com... Can you get 120v single phase by picking off one line of 240v 3 phase as long as you have a neutral to carry the current back to the box? Thanks, Steve Yes, but be careful if you have 3 phase delta.. The high leg to ground (B phase if I'm not mistaken) yields 208 volts, not 120. Harold |
#4
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"DoN. Nichols" wrote in message ... In article .com, wrote: Can you get 120v single phase by picking off one line of 240v 3 phase as long as you have a neutral to carry the current back to the box? Not quite. The voltage won't be right for pure three phase. I think that with Wye connections, you will have something closer to 104V. I'm at a loss to understand that, DoN. Care to elaborate? I have wired three places with delta service, two of which used either the A and C phase and the neutral for 120V. All of it was done to code. The third place has a single phase panel along with the 3 phase, both of which are fed from the same taps from the transformers. And many are delta which *has* no neutral. All may be floating. In this case, he's already suggested that there would be a neutral, so it would be a 5 wire system. But a frequent variation has one of the three sides center tapped (the way the standard residential feed is supplied, 240V center tapped with the center tap grounded and neutral connected to that.) The breaker boxes for this have three buses, but only two of every three positions can be used for 120V single-phase breakers. The third phase is *way* too high. As stated above, I got around that problem in my current shop by having two panels, one strictly 3 phase, so none of the positions are lost. Harold |
#5
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"DoN. Nichols" wrote in message ... In article .com, wrote: Can you get 120v single phase by picking off one line of 240v 3 phase as long as you have a neutral to carry the current back to the box? Not quite. The voltage won't be right for pure three phase. I think that with Wye connections, you will have something closer to 104V. Typo? Should be about 140 volts from line to neutral with 240 wye (calculates to 138.6 or so) 208 wye gives 120 line to neutral... And many are delta which *has* no neutral. All may be floating. But a frequent variation has one of the three sides center tapped (the way the standard residential feed is supplied, 240V center tapped with the center tap grounded and neutral connected to that.) The breaker boxes for this have three buses, but only two of every three positions can be used for 120V single-phase breakers. The third phase is *way* too high. However -- from *any* reasonable 240V 3 phase, you can tie two of the three phases to the primary of a 240-120V step-down transformer, and power your equipment from that. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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#7
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wrote in message
oups.com... Can you get 120v single phase by picking off one line of 240v 3 phase as long as you have a neutral to carry the current back to the box? Thanks, Steve Yes, but depending on your load requirement, get an office building electrician to wire it. The entire USA gets 120 volt single phase from 3 phase sources. |
#8
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Harold and Susan Vordos wrote:
"DoN. Nichols" wrote in message ... In article .com, wrote: Can you get 120v single phase by picking off one line of 240v 3 phase as long as you have a neutral to carry the current back to the box? Not quite. The voltage won't be right for pure three phase. I think that with Wye connections, you will have something closer to 104V. I'm at a loss to understand that, DoN. Care to elaborate? I have wired three places with delta service, two of which used either the A and C phase and the neutral for 120V. All of it was done to code. The third place has a single phase panel along with the 3 phase, both of which are fed from the same taps from the transformers. If it had a neutral it wasn't a delta service. The 104V mentioned was a typo, it's really 138V and change. Square root of three thing for three phase power. 240V Wye service will give you 138V phase to neutral and 208V Wye service will give you 120V phase to neutral. And many are delta which *has* no neutral. All may be floating. In this case, he's already suggested that there would be a neutral, so it would be a 5 wire system. Known as Wye. But a frequent variation has one of the three sides center tapped (the way the standard residential feed is supplied, 240V center tapped with the center tap grounded and neutral connected to that.) The breaker boxes for this have three buses, but only two of every three positions can be used for 120V single-phase breakers. The third phase is *way* too high. I believe this is often referred to as the "wild" leg. As stated above, I got around that problem in my current shop by having two panels, one strictly 3 phase, so none of the positions are lost. There are / were a lot of strange variations on three phase power, but most anything new is going to be 208V Wye service. Larger industrial stuff will get 480V. Pete C. |
#9
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BW sez:
"...The entire USA gets 120 volt single phase from 3 phase sources." Cute - but not quite right. See John's answer above. Bob Swinney "bw" wrote in message ... wrote in message oups.com... Can you get 120v single phase by picking off one line of 240v 3 phase as long as you have a neutral to carry the current back to the box? Thanks, Steve Yes, but depending on your load requirement, get an office building electrician to wire it. |
#10
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"Pete C." wrote in message ... Harold and Susan Vordos wrote: "DoN. Nichols" wrote in message ... In article .com, wrote: Can you get 120v single phase by picking off one line of 240v 3 phase as long as you have a neutral to carry the current back to the box? Not quite. The voltage won't be right for pure three phase. I think that with Wye connections, you will have something closer to 104V. I'm at a loss to understand that, DoN. Care to elaborate? I have wired three places with delta service, two of which used either the A and C phase and the neutral for 120V. All of it was done to code. The third place has a single phase panel along with the 3 phase, both of which are fed from the same taps from the transformers. If it had a neutral it wasn't a delta service. Wrong!! One can have a three, four or five wire delta system. I have a 5 wire system, and it *is* a delta system. It is not a wye, which does not have the wild leg. Mine does have. Ground is established by tapping the center of one coil, which results in the longer path to ground from the other two coils. 208 volts from phase to ground. It's not conjecture, it's measured. The 104V mentioned was a typo, it's really 138V and change. Square root of three thing for three phase power. 240V Wye service will give you 138V phase to neutral and 208V Wye service will give you 120V phase to neutral. And many are delta which *has* no neutral. All may be floating. In this case, he's already suggested that there would be a neutral, so it would be a 5 wire system. Known as Wye. Again, wrong. It *is* a delta system. He's talking about 240 volts, not 208. As far as I know, single phase service to the typical house is just one leg of a three phase delta system. Isn't that how it comes from the power plants, the primary service? How it's delivered to the customer depends on the transformers that feed them. But a frequent variation has one of the three sides center tapped (the way the standard residential feed is supplied, 240V center tapped with the center tap grounded and neutral connected to that.) The breaker boxes for this have three buses, but only two of every three positions can be used for 120V single-phase breakers. The third phase is *way* too high. I believe this is often referred to as the "wild" leg. Agreed. As stated above, I got around that problem in my current shop by having two panels, one strictly 3 phase, so none of the positions are lost. There are / were a lot of strange variations on three phase power, but most anything new is going to be 208V Wye service. Larger industrial stuff will get 480V. My 3 phase delta 240/120 volt service was installed just 4 years ago, at my request. I did not want a wye service (for obvious reasons), and am transforming to 480V for one machine. Harold .. |
#11
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In article t,
Rick wrote: "DoN. Nichols" wrote in message ... In article .com, wrote: Can you get 120v single phase by picking off one line of 240v 3 phase as long as you have a neutral to carry the current back to the box? Not quite. The voltage won't be right for pure three phase. I think that with Wye connections, you will have something closer to 104V. Typo? Should be about 140 volts from line to neutral with 240 wye (calculates to 138.6 or so) Nope -- trying to remember which way the voltage was off, and getting it wrong. :-) 208 wye gives 120 line to neutral... Thanks, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
#12
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On Sat, 11 Jun 2005 01:23:02 -0500, Jon Elson wrote:
wrote: Can you get 120v single phase by picking off one line of 240v 3 phase as long as you have a neutral to carry the current back to the box? Thanks, Steve Only in a special circumstance, which is a 4-wire, center-tap grounded delta service. This has one 240 V L-L circuit with a center tap, just like everybody's home service. Then, it has another transformer that develops the 3rd phase. In this system, there are only TWO of the three hot wires that will give 120 V to neutral. (The third will give ~207 V, so you will definitely be able to tell which is which with a meter.) This service is pretty rare, at least around where I've lived. Corner-grounded delta is more common, but you can't get 120 V directly from that. You need a 240 - 120 step-down transformer. Corner-grounded delta is most obvious because 2-pole circuit breakers and disconnects are used. The 3-phase wires are hot, hot and neutral, and you can wire a 3-phase motor up to those 3 wires. (These are also labeled hot (A), neutral (B), and hot (C) phases, and therefore sometimes called grounded B phase.) If you have 208 V WYE service (sometimes called star) you have three 120 V circuits, from any line to neutral. But, in this system, you can't get 240 V, without a transformer. Like, the building I work in, has 208 V Wye for the office section, and we have little autotransformers to step 208 up to 240 for the window air conditioners. If you try this on a true 240 V Wye system, which has a neutral, you will get a rather high voltage of about 138 V. But, 240 V Wye is pretty rare. If you try this on a real delta system, you might kill all the lights in the building, as it may trip the ground fault protection. But, then, a true delta system doesn't have a NEUTRAL, although sometimes telling the difference between a neutral and a safety ground can be difficult. Delta transformers have a balancing transformer in them that makes it look like they are referenced to a neutral, but if you draw any current from line to neutral that unbalances it, the transformer should shut down. This normally wouldn't apply to open delta and corner or center-tap grounded deltas, as they are expected to feed unbalanced loads. Is that more than you wanted to know? No, but it might educate some of the self-proclaimed "engineers" who claim that the two opposite poles of the 240 center-tapped are "180 degrees out of phase." They are not "out of phase" - they are simply opposite polarity! It's a significant difference, in the realm of phasors and imaginary power and stuff. -- Thanks! Rich ------ " "Don't come back until you have him", the Tick-Tock Man said quietly, sincerely, extremely dangerously. They used dogs. They used probes. They used cardio plate crossoffs. They used teepers. They used bribery. They used stick tites. They used intimidation. They used torment. They used torture. They used finks. They used cops. They used search and seizure. They used fallaron. They used betterment incentives. They used finger prints. They used the bertillion system. They used cunning. They used guile. They used treachery. They used Raoul-Mitgong but he wasn't much help. They used applied physics. They used techniques of criminology. And what the hell, they caught him." " -- Harlan Ellison, "Repent, Harlequin, said the Tick-Tock Man" |
#13
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Rich The Newsgroup Wacko wrote:
On Sat, 11 Jun 2005 01:23:02 -0500, Jon Elson wrote: wrote: Can you get 120v single phase by picking off one line of 240v 3 phase as long as you have a neutral to carry the current back to the box? Thanks, Steve Only in a special circumstance, which is a 4-wire, center-tap grounded delta service. This has one 240 V L-L circuit with a center tap, just like everybody's home service. Then, it has another transformer that develops the 3rd phase. In this system, there are only TWO of the three hot wires that will give 120 V to neutral. (The third will give ~207 V, so you will definitely be able to tell which is which with a meter.) This service is pretty rare, at least around where I've lived. Corner-grounded delta is more common, but you can't get 120 V directly from that. You need a 240 - 120 step-down transformer. Corner-grounded delta is most obvious because 2-pole circuit breakers and disconnects are used. The 3-phase wires are hot, hot and neutral, and you can wire a 3-phase motor up to those 3 wires. (These are also labeled hot (A), neutral (B), and hot (C) phases, and therefore sometimes called grounded B phase.) If you have 208 V WYE service (sometimes called star) you have three 120 V circuits, from any line to neutral. But, in this system, you can't get 240 V, without a transformer. Like, the building I work in, has 208 V Wye for the office section, and we have little autotransformers to step 208 up to 240 for the window air conditioners. If you try this on a true 240 V Wye system, which has a neutral, you will get a rather high voltage of about 138 V. But, 240 V Wye is pretty rare. If you try this on a real delta system, you might kill all the lights in the building, as it may trip the ground fault protection. But, then, a true delta system doesn't have a NEUTRAL, although sometimes telling the difference between a neutral and a safety ground can be difficult. Delta transformers have a balancing transformer in them that makes it look like they are referenced to a neutral, but if you draw any current from line to neutral that unbalances it, the transformer should shut down. This normally wouldn't apply to open delta and corner or center-tap grounded deltas, as they are expected to feed unbalanced loads. Is that more than you wanted to know? No, but it might educate some of the self-proclaimed "engineers" who claim that the two opposite poles of the 240 center-tapped are "180 degrees out of phase." They are not "out of phase" - they are simply opposite polarity! It's a significant difference, in the realm of phasors and imaginary power and stuff. sorry Rich, but the two ends of a center-tapped winding *are* 180 degrees out of phase. sin(wt+pi) = -sin(wt). Cheers Terry |
#14
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On Sat, 11 Jun 2005 23:02:05 GMT, Rich The Newsgroup Wacko
wrote: No, but it might educate some of the self-proclaimed "engineers" who claim that the two opposite poles of the 240 center-tapped are "180 degrees out of phase." They are not "out of phase" - they are simply opposite polarity! It's a significant difference, in the realm of phasors and imaginary power and stuff. OK, what would a pair of sine waves look like if they *were* 180 degrees out of phase? How would they be different from a pair of sine waves that were "simply opposite polarity"? [1] John [2] [1] there's a relevant trig identity somewhere, I think [2] self-proclaimed "engineer" [3] [3] except for the BSEE, which makes me an other-proclaimed "engineer" |
#15
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On Sat, 11 Jun 2005 01:23:02 -0500, Jon Elson wrote: wrote: Can you get 120v single phase by picking off one line of 240v 3 phase as long as you have a neutral to carry the current back to the box? Thanks, Steve Only in a special circumstance, which is a 4-wire, center-tap grounded delta service. This has one 240 V L-L circuit with a center tap, just like everybody's home service. Then, it has another transformer that develops the 3rd phase. In this system, there are only TWO of the three hot wires that will give 120 V to neutral. (The third will give ~207 V, so you will definitely be able to tell which is which with a meter.) This service is pretty rare, at least around where I've lived. Corner-grounded delta is more common, but you can't get 120 V directly from that. You need a 240 - 120 step-down transformer. Corner-grounded delta is most obvious because 2-pole circuit breakers and disconnects are used. The 3-phase wires are hot, hot and neutral, and you can wire a 3-phase motor up to those 3 wires. (These are also labeled hot (A), neutral (B), and hot (C) phases, and therefore sometimes called grounded B phase.) If you have 208 V WYE service (sometimes called star) you have three 120 V circuits, from any line to neutral. But, in this system, you can't get 240 V, without a transformer. Like, the building I work in, has 208 V Wye for the office section, and we have little autotransformers to step 208 up to 240 for the window air conditioners. If you try this on a true 240 V Wye system, which has a neutral, you will get a rather high voltage of about 138 V. But, 240 V Wye is pretty rare. If you try this on a real delta system, you might kill all the lights in the building, as it may trip the ground fault protection. But, then, a true delta system doesn't have a NEUTRAL, although sometimes telling the difference between a neutral and a safety ground can be difficult. Delta transformers have a balancing transformer in them that makes it look like they are referenced to a neutral, but if you draw any current from line to neutral that unbalances it, the transformer should shut down. This normally wouldn't apply to open delta and corner or center-tap grounded deltas, as they are expected to feed unbalanced loads. Is that more than you wanted to know? Sounds like a lot of blithering crap from one of those 1940's vintage BS Audel books- absolutely no sense to made of it and zero credibility. And it's a very rare circumstance to find dedicated 230V or 208V compressors for A/C- vast majority are dual 208/230. |
#16
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Nuttin' personal, but I'm always amused by the perceptions (or just commonly
used expressions) that power or voltage comes out one terminal and goes back to the other one. I usually have nothing better to do than to ask.. then where does it go? In the context of power generation and distribution, does it go back to the generation source? What do they do with all the power they receive back? In a battery context, does the battery determine that the user has gotten their money's worth, and stop giving the user more voltage? Why did it go dead if there is power coming back into the other terminal? Does it become saturated wih negativity? Is the battery recycling program about using the unused power in dead batteries to make new batteries? Can folks visualize that the power is expended at the load? Transformed into light, mechanical energy, heat, and simply dissipated at the electrical load. Maybe it's been transferred into food to make it hot? My food is too hot, can I return some of this wasted energy to the power company (and get a credit?). Maybe visualization is too complex, but generally, there is always heat present and that can be felt or measured. Ground is always zero, right? Depends on where you're coming from, pal. So I guess you're saying ground is never zero? Definite maybe. What's neutral? Switzerland, I think. Again, depends on where you're coming from. Prototypes of the generator powered by free radon should be available in the first quarter of 2007. Be sure to check to see if you have radon. (which is the only useful info in this post). WB .................. wrote in message oups.com... Can you get 120v single phase by picking off one line of 240v 3 phase as long as you have a neutral to carry the current back to the box? Thanks, Steve ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
#17
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Fred Bloggs wrote:
On Sat, 11 Jun 2005 01:23:02 -0500, Jon Elson wrote: wrote: Can you get 120v single phase by picking off one line of 240v 3 phase as long as you have a neutral to carry the current back to the box? Thanks, Steve Only in a special circumstance, which is a 4-wire, center-tap grounded delta service. This has one 240 V L-L circuit with a center tap, just like everybody's home service. Then, it has another transformer that develops the 3rd phase. In this system, there are only TWO of the three hot wires that will give 120 V to neutral. (The third will give ~207 V, so you will definitely be able to tell which is which with a meter.) This service is pretty rare, at least around where I've lived. Corner-grounded delta is more common, but you can't get 120 V directly from that. You need a 240 - 120 step-down transformer. Corner-grounded delta is most obvious because 2-pole circuit breakers and disconnects are used. The 3-phase wires are hot, hot and neutral, and you can wire a 3-phase motor up to those 3 wires. (These are also labeled hot (A), neutral (B), and hot (C) phases, and therefore sometimes called grounded B phase.) If you have 208 V WYE service (sometimes called star) you have three 120 V circuits, from any line to neutral. But, in this system, you can't get 240 V, without a transformer. Like, the building I work in, has 208 V Wye for the office section, and we have little autotransformers to step 208 up to 240 for the window air conditioners. If you try this on a true 240 V Wye system, which has a neutral, you will get a rather high voltage of about 138 V. But, 240 V Wye is pretty rare. If you try this on a real delta system, you might kill all the lights in the building, as it may trip the ground fault protection. But, then, a true delta system doesn't have a NEUTRAL, although sometimes telling the difference between a neutral and a safety ground can be difficult. Delta transformers have a balancing transformer in them that makes it look like they are referenced to a neutral, but if you draw any current from line to neutral that unbalances it, the transformer should shut down. This normally wouldn't apply to open delta and corner or center-tap grounded deltas, as they are expected to feed unbalanced loads. Is that more than you wanted to know? Sounds like a lot of blithering crap from one of those 1940's vintage BS Audel books- absolutely no sense to made of it and zero credibility. And it's a very rare circumstance to find dedicated 230V or 208V compressors for A/C- vast majority are dual 208/230. What I wrote certainly seems to agree with this web site, which I'm pretty sure has got it all right : http://www.patchn.com/deltasys.htm I think this one could be considered pretty authoritative, too : http://ecatalog.squared.com/catalog/...3%2003-10.html As for the Air Conditioning, yes most 3-phase small AC are 208/230, but WINDOW air conditioners generally are NOT. Running a 230 V window unit on 208 will generally lead to short compressor life, hard starts, and thermal protector trips. Jon |
#18
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"Rich The Newsgroup Wacko" wrote in message news No, but it might educate some of the self-proclaimed "engineers" who claim that the two opposite poles of the 240 center-tapped are "180 degrees out of phase." They are not "out of phase" - they are simply opposite polarity! It's a significant difference, in the realm of phasors and imaginary power and stuff. -- Thanks! Rich "It's a significant difference, in the realm of phasors and imaginary power and stuff. Really, do tell? I think mostly "stuff." Bob |
#19
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"Wild Bill" wrote:
In a battery context, does the battery determine that the user has gotten their money's worth, and stop giving the user more voltage? Why did it go dead if there is power coming back into the other terminal? Does it become saturated wih negativity? Is the battery recycling program about using the unused power in dead batteries to make new batteries? It is quite simple! Since it is coming in to the OTHER terminal, it is coming back a "UNPOWER". As the battery fills up with unpower, pretty soon it balances out the power that is left. Then pffft nothing. But un power is a little more volatile, and so it evaporates just a little faster. This is why if you let the battery sit for a little while, you can get just a little more oomps out of it for a short time. jk |
#20
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Harold and Susan Vordos wrote:
"Pete C." wrote in message ... Harold and Susan Vordos wrote: "DoN. Nichols" wrote in message ... In article .com, wrote: Can you get 120v single phase by picking off one line of 240v 3 phase as long as you have a neutral to carry the current back to the box? Not quite. The voltage won't be right for pure three phase. I think that with Wye connections, you will have something closer to 104V. I'm at a loss to understand that, DoN. Care to elaborate? I have wired three places with delta service, two of which used either the A and C phase and the neutral for 120V. All of it was done to code. The third place has a single phase panel along with the 3 phase, both of which are fed from the same taps from the transformers. If it had a neutral it wasn't a delta service. Wrong!! One can have a three, four or five wire delta system. Huh? You always (unless you've got a 100yr old system) have a ground for your building system, so once you reach your building distribution you have a minimum of four wires for a strictly delta system, A, B & C phases and ground. A Wye system will have five, A, B & C phases, neutral and ground. The "Wild leg" delta system would also have five wires. Your "wild leg" delta system is not very popular these days since most three phase services are provided by three phase pad mount transformers so the potential cost savings from using two smaller and one larger single phase transformers to service the load doesn't exist. The "wild leg" is also a potential safety issue to people and equipment which is why the NEC requires the orange color coding and placement in the middle position of the panelboard. I have a 5 wire system, and it *is* a delta system. It is not a wye, which does not have the wild leg. Mine does have. Ground is established by tapping the center of one coil, which results in the longer path to ground from the other two coils. 208 volts from phase to ground. It's not conjecture, it's measured. Ground is not established by the center tap on one transformer, that is a neutral of sorts. Ground is always established by the ground rod(s) for your service. The ground and the neutral are always bonded together at the service entrance panel and never at any sub panels. The 104V mentioned was a typo, it's really 138V and change. Square root of three thing for three phase power. 240V Wye service will give you 138V phase to neutral and 208V Wye service will give you 120V phase to neutral. And many are delta which *has* no neutral. All may be floating. In this case, he's already suggested that there would be a neutral, so it would be a 5 wire system. Known as Wye. Again, wrong. It *is* a delta system. He's talking about 240 volts, not 208. As far as I know, single phase service to the typical house is just one leg of a three phase delta system. Isn't that how it comes from the power plants, the primary service? How it's delivered to the customer depends on the transformers that feed them. Ok, the "wild leg" configuration is technically a delta configuration. It is however more often referred to with various derogatory terms due to it's disadvantages. While older distribution was often fed in a delta configuration, that is being phased out for safety reasons. When the distribution transformers are fed in a delta configuration, in the event that there is a circuit loss on one of the phases feeding the transformer due to a cable break of a fuse blow, the line remains hot due to power feeding from the other phase through the delta wired transformer(s) and back down the "disconnected" phase. A Wye connected transformer does not present this risk since only one leg of the transformer winding is ties to a hot line with the other at neutral / ground potential. But a frequent variation has one of the three sides center tapped (the way the standard residential feed is supplied, 240V center tapped with the center tap grounded and neutral connected to that.) The breaker boxes for this have three buses, but only two of every three positions can be used for 120V single-phase breakers. The third phase is *way* too high. I believe this is often referred to as the "wild" leg. Agreed. As stated above, I got around that problem in my current shop by having two panels, one strictly 3 phase, so none of the positions are lost. There are / were a lot of strange variations on three phase power, but most anything new is going to be 208V Wye service. Larger industrial stuff will get 480V. My 3 phase delta 240/120 volt service was installed just 4 years ago, at my request. I did not want a wye service (for obvious reasons), and am transforming to 480V for one machine. Huh? What "obvious reasons"? 120/208 Wye service has no disadvantages that I know of. You can get 120v from any of the phases, allowing you to balance your single phase loads and single pole, two pole or three pole breakers breakers can occupy any panel position since all phases are equal to each other and to the neutral. I consider there to be considerable disadvantages to a system with a "wild" leg. You have no way to even come close to balancing your single phase loads on the three phase feed and you have the "wild" leg which can cause safety issues and/or equipment damage if people are not paying attention. From what I recall this configuration was primarily used to cut transformer costs when serviced from three single phase transformers and not for any technical advantage. Pete C. |
#21
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In article , Terry Given says...
sorry Rich, but the two ends of a center-tapped winding *are* 180 degrees out of phase. sin(wt+pi) = -sin(wt). Referenced from the centertap, of course. This is something that drives electricians just pure bonkers. They don't get it. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
#22
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In article , John Larkin says...
OK, what would a pair of sine waves look like if they *were* 180 degrees out of phase? Now stop. Yer gonna cause somebody's fuses to blow out... Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
#23
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jim rozen wrote: In article , John Larkin says... OK, what would a pair of sine waves look like if they *were* 180 degrees out of phase? Now stop. Yer gonna cause somebody's fuses to blow out... Jim HOw about really confusing them with the 30 degree shift going from wye to delta John |
#24
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"Pete C." wrote:
Harold and Susan Vordos wrote: "Pete C." wrote in message ... Harold and Susan Vordos wrote: "DoN. Nichols" wrote in message ... In article .com, wrote: Can you get 120v single phase by picking off one line of 240v 3 phase as long as you have a neutral to carry the current back to the box? Not quite. The voltage won't be right for pure three phase. I think that with Wye connections, you will have something closer to 104V. I'm at a loss to understand that, DoN. Care to elaborate? I have wired three places with delta service, two of which used either the A and C phase and the neutral for 120V. All of it was done to code. The third place has a single phase panel along with the 3 phase, both of which are fed from the same taps from the transformers. If it had a neutral it wasn't a delta service. Wrong!! One can have a three, four or five wire delta system. Huh? You always (unless you've got a 100yr old system) have a ground for your building system, so once you reach your building distribution you have a minimum of four wires for a strictly delta system, A, B & C phases and ground. A Wye system will have five, A, B & C phases, neutral and ground. The "Wild leg" delta system would also have five wires. Your "wild leg" delta system is not very popular these days since most three phase services are provided by three phase pad mount transformers so the potential cost savings from using two smaller and one larger single phase transformers to service the load doesn't exist. The "wild leg" is also a potential safety issue to people and equipment which is why the NEC requires the orange color coding and placement in the middle position of the panelboard. I have a 5 wire system, and it *is* a delta system. It is not a wye, which does not have the wild leg. Mine does have. Ground is established by tapping the center of one coil, which results in the longer path to ground from the other two coils. 208 volts from phase to ground. It's not conjecture, it's measured. Ground is not established by the center tap on one transformer, that is a neutral of sorts. Ground is always established by the ground rod(s) for your service. The ground and the neutral are always bonded together at the service entrance panel and never at any sub panels. The 104V mentioned was a typo, it's really 138V and change. Square root of three thing for three phase power. 240V Wye service will give you 138V phase to neutral and 208V Wye service will give you 120V phase to neutral. And many are delta which *has* no neutral. All may be floating. In this case, he's already suggested that there would be a neutral, so it would be a 5 wire system. Known as Wye. Again, wrong. It *is* a delta system. He's talking about 240 volts, not 208. As far as I know, single phase service to the typical house is just one leg of a three phase delta system. Isn't that how it comes from the power plants, the primary service? How it's delivered to the customer depends on the transformers that feed them. Ok, the "wild leg" configuration is technically a delta configuration. It is however more often referred to with various derogatory terms due to it's disadvantages. While older distribution was often fed in a delta configuration, that is being phased out for safety reasons. When the distribution transformers are fed in a delta configuration, in the event that there is a circuit loss on one of the phases feeding the transformer due to a cable break of a fuse blow, the line remains hot due to power feeding from the other phase through the delta wired transformer(s) and back down the "disconnected" phase. A Wye connected transformer does not present this risk since only one leg of the transformer winding is ties to a hot line with the other at neutral / ground potential. But a frequent variation has one of the three sides center tapped (the way the standard residential feed is supplied, 240V center tapped with the center tap grounded and neutral connected to that.) The breaker boxes for this have three buses, but only two of every three positions can be used for 120V single-phase breakers. The third phase is *way* too high. I believe this is often referred to as the "wild" leg. Agreed. As stated above, I got around that problem in my current shop by having two panels, one strictly 3 phase, so none of the positions are lost. There are / were a lot of strange variations on three phase power, but most anything new is going to be 208V Wye service. Larger industrial stuff will get 480V. My 3 phase delta 240/120 volt service was installed just 4 years ago, at my request. I did not want a wye service (for obvious reasons), and am transforming to 480V for one machine. Huh? What "obvious reasons"? 120/208 Wye service has no disadvantages that I know of. You can get 120v from any of the phases, allowing you to balance your single phase loads and single pole, two pole or three pole breakers breakers can occupy any panel position since all phases are equal to each other and to the neutral. I consider there to be considerable disadvantages to a system with a "wild" leg. You have no way to even come close to balancing your single phase loads on the three phase feed and you have the "wild" leg which can cause safety issues and/or equipment damage if people are not paying attention. From what I recall this configuration was primarily used to cut transformer costs when serviced from three single phase transformers and not for any technical advantage. I always assumed that it was done for convenience. I have 3 hot wires (A, B & C(wild)), I can run all my 120 stuff off A to neutral or B to neutral. I can run all of my 240 single phase stuff off A-B and I can run all of my 240 3-phase stuff off A-B-C. If I had Wye or corner grounded delta service then I would have to give up one of those conditions or purchase another transformer. By the way: center tapped delta service is very common here in the Chicago area. Wye service is strictly used in office buildings and warehouses. As a side note: I have a suspicion that Commonwealth Edison balances the overall service in an industrial park by locally grounding the center of alternate coils. IOW: that wire that comes into my building and that I call the wild leg, is not the same as my neighbor's wild leg. George. |
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Tom Quackenbush wrote:
jim rozen wrote: Terry Given says... sorry Rich, but the two ends of a center-tapped winding *are* 180 degrees out of phase. sin(wt+pi) = -sin(wt). Referenced from the centertap, of course. This is something that drives electricians just pure bonkers. They don't get it. Uh-huh. I'm not an electrician, but I play one on usenet (also, Gary seems to be MIA). What happens when you combine two out of phase signals? What happens when when you combine the two 120v circuits? You get 240 single phase service. Which is great because that's what I need for my air compressor. George. |
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I always assumed that it was done for convenience. I have 3 hot wires (A, B & C(wild)), I can run all my 120 stuff off A to neutral or B to neutral. I can run all of my 240 single phase stuff off A-B and I can run all of my 240 3-phase stuff off A-B-C. Anything that uses 220 only, ( 220 with two conductors and a ground) can be run off of any two legs. Only if the thing uses 120 and 240 volts and has a neutral wire going to it do you need to use the centertapped phases. If I had Wye or corner grounded delta service then I would have to give up one of those conditions or purchase another transformer. Nope By the way: center tapped delta service is very common here in the Chicago area. Wye service is strictly used in office buildings and warehouses. It is good for the electrical company when there is a mixed use of single and light three phase users. They save a transformer when three phase is required. As a side note: I have a suspicion that Commonwealth Edison balances the overall service in an industrial park by locally grounding the center of alternate coils. IOW: that wire that comes into my building and that I call the wild leg, is not the same as my neighbor's wild leg. All utility companies alternate on the hookup of the primary to the three phase high voltage lines, the ones on the extreme top of the pole with the big insulators. you neighbor may be on a different pole transformer. IF he is then his phasing is different than yours. John |
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john wrote:
I always assumed that it was done for convenience. I have 3 hot wires (A, B & C(wild)), I can run all my 120 stuff off A to neutral or B to neutral. I can run all of my 240 single phase stuff off A-B and I can run all of my 240 3-phase stuff off A-B-C. Anything that uses 220 only, ( 220 with two conductors and a ground) can be run off of any two legs. Only if the thing uses 120 and 240 volts and has a neutral wire going to it do you need to use the centertapped phases. If I had Wye or corner grounded delta service then I would have to give up one of those conditions or purchase another transformer. Nope One thing that is common in warehouses here is 208 Wye service. That gives 3, 120 Volt legs. Obviously, I can run a 240 3-phase motor on that service but it will only run at 208/240)^2 = 75% power. Worse yet, many electronic items just simply will not run. Alternatively, I can get 240 Wye service and run my 240 stuff at full power. As you mentioned, you can always run 240 single phase stuff across any two legs. (I can also use my 208V light bulbs from the previous example) But how do I get my 110V toaster oven to work in that arrangement? Same question for a corner grounded delta arrangement? By the way: center tapped delta service is very common here in the Chicago area. Wye service is strictly used in office buildings and warehouses. It is good for the electrical company when there is a mixed use of single and light three phase users. They save a transformer when three phase is required. As a side note: I have a suspicion that Commonwealth Edison balances the overall service in an industrial park by locally grounding the center of alternate coils. IOW: that wire that comes into my building and that I call the wild leg, is not the same as my neighbor's wild leg. All utility companies alternate on the hookup of the primary to the three phase high voltage lines, the ones on the extreme top of the pole with the big insulators. you neighbor may be on a different pole transformer. IF he is then his phasing is different than yours. Yea, I figured as much. We had an electrical storm here several years ago. Half the light bulbs in the building were getting dim while the other half were getting unusually bright. Then some of the bright bulbs began to blow. I figured that we must have lost the center ground and that the voltage was being split somewhere in the middle of the center tapped leg. No doubt based on the relative load on either side. I ran round the building frantically shutting everything off as light bulbs popped all around me. I then called the electric company and explained the situation. I must hand it to them, they arrived in truly record time! But I noticed that my neighbors lights were also bright in one window and dim in the next. I was just sort of pondering the fun that it would be to ground out one side of the transformer and then ground out the other side. Com Ed arrived before I worked up enough nerve to put theory to practice. |
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In article , George says...
One thing that is common in warehouses here is 208 Wye service. That gives 3, 120 Volt legs. Obviously, I can run a 240 3-phase motor on that service but it will only run at 208/240)^2 = 75% power. No, it runs at full power. Motors however draw more current and run hotter. The typical approach (inexpensive) is to simply put a buck/boost transformer at each item that really requires 240 volts. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
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George wrote: john wrote: I always assumed that it was done for convenience. I have 3 hot wires (A, B & C(wild)), I can run all my 120 stuff off A to neutral or B to neutral. I can run all of my 240 single phase stuff off A-B and I can run all of my 240 3-phase stuff off A-B-C. Anything that uses 220 only, ( 220 with two conductors and a ground) can be run off of any two legs. Only if the thing uses 120 and 240 volts and has a neutral wire going to it do you need to use the centertapped phases. If I had Wye or corner grounded delta service then I would have to give up one of those conditions or purchase another transformer. Nope One thing that is common in warehouses here is 208 Wye service. That gives 3, 120 Volt legs. Obviously, I can run a 240 3-phase motor on that service but it will only run at 208/240)^2 = 75% power. Worse yet, many electronic items just simply will not run. Thats one of the nice things about using 240 volts. Overvoltage is usually less harmful than undervoltage Alternatively, I can get 240 Wye service and run my 240 stuff at full power. As you mentioned, you can always run 240 single phase stuff across any two legs. (I can also use my 208V light bulbs from the previous example) But how do I get my 110V toaster oven to work in that arrangement? I've never run across a 240 volt Wye supplied from an electric company. IF you had a neutral supplied with the Wye connection you would have 120volts for your toaster. a delta connection would require a transformer if there were no center tapped transformer. Same question for a corner grounded delta arrangement? the only place I've ever seen a corner grounde system was in a DC-6 aircraft, and that was 115 volts leg to leg. By the way: center tapped delta service is very common here in the Chicago area. Wye service is strictly used in office buildings and warehouses. Everywhere I've been it was the same. 208 Wye was used where most of the loads were 110/220 single phase in apartment buildings and stores, otherwise it was 240 volts red leg delta service. you neighbor may be on a different pole transformer. IF he is then his phasing is different than yours. Yea, I figured as much. We had an electrical storm here several years ago. Half the light bulbs in the building were getting dim while the other half were getting unusually bright. Then some of the bright bulbs began to blow. I figured that we must have lost the center ground and that the voltage was being split somewhere in the middle of the center tapped leg. No doubt based on the relative load on either side. I ran round the building frantically shutting everything off as light bulbs popped all around me. I then called the electric company and explained the situation. I must hand it to them, they arrived in truly record time! But I noticed that my neighbors lights were also bright in one window and dim in the next. I was just sort of pondering the fun that it would be to ground out one side of the transformer and then ground out the other side. Com Ed arrived before I worked up enough nerve to put theory to practice. I had the same thing happen in florida caused by a lightning strike. It was like in the sci fi movies.. the fans were going up and down in speed and the lights were flashing, It happened a day after the storm. The day before they changed the fuse on the pole and i told them there were other problems. I could smell the burned transformer oil. John |
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"Pete C." wrote in message ... Harold and Susan Vordos wrote: snip----- Huh? You always (unless you've got a 100yr old system) have a ground for your building system, so once you reach your building distribution you have a minimum of four wires for a strictly delta system, A, B & C phases and ground. A Wye system will have five, A, B & C phases, neutral and ground. The "Wild leg" delta system would also have five wires. That's what I've been talking about, a wild leg system. That's what I have. The wild leg measures 208 volts to ground, or neutral. Your "wild leg" delta system is not very popular these days since most three phase services are provided by three phase pad mount transformers so the potential cost savings from using two smaller and one larger single phase transformers to service the load doesn't exist. The "wild leg" is also a potential safety issue to people and equipment which is why the NEC requires the orange color coding and placement in the middle position of the panelboard. Yep! That's what I have, the wild leg as the B phase, and it's orange. One difference-----I have three transformers on the pole in my yard, all the same size. They are not pad mounted. Ground is not established by the center tap on one transformer, that is a neutral of sorts. Ground is always established by the ground rod(s) for your service. The ground and the neutral are always bonded together at the service entrance panel and never at any sub panels. Yeah, and thanks for correcting me. I fully meant neutral, but my fingers got away from me. i hae a basic understanding of the difference between a ground, and a neutral. My panel (Square D) provides for a neutral, and I have it. I have a true 5 wire system, run to each individual box in the shop. Again, wrong. It *is* a delta system. He's talking about 240 volts, not 208. As far as I know, single phase service to the typical house is just one leg of a three phase delta system. Isn't that how it comes from the power plants, the primary service? How it's delivered to the customer depends on the transformers that feed them. Ok, the "wild leg" configuration is technically a delta configuration. It is however more often referred to with various derogatory terms due to it's disadvantages. While older distribution was often fed in a delta configuration, that is being phased out for safety reasons. That's an interesting comment. When I discussed three phase service with PUD, our provider, I was advised that our area, which is relatively remote, was in bad need of an update, that they were going to provide the second leg of the three phase service to lighten the load on the single leg, which is, as I recall, something like 14,000 volts. I was told if I would pay for the third leg, it would be installed simultaneously, saving me considerable money, which it did. It dropped the cost from my original inquiry many years ago from $30,000 to just over $18,000. The point being that, while it's not necessarily a popular service, they had no problems providing it to my specs. I was required to provide a large CT can, naturally. When the distribution transformers are fed in a delta configuration, in the event that there is a circuit loss on one of the phases feeding the transformer due to a cable break of a fuse blow, the line remains hot due to power feeding from the other phase through the delta wired transformer(s) and back down the "disconnected" phase. Which likely explains the crazy voltages I found when returning from vacation many years ago when we resided in Utah. Our entire house was wired with 3 phase, and one of the lines connected to a transformer worked loose, enough to lose a proper connection. We lost a few things from crazy voltages. Our refrigerator had been out of service for a long time, spoiling everything inside. A Wye connected transformer does not present this risk since only one leg of the transformer winding is ties to a hot line with the other at neutral / ground potential. But yields only 208 volts. A good friend moved from one shop to another, the second serviced by a Y service. His CNC machines didn't like that one bit. Regardless of the fact that machine tools should have motors that can run on either voltage, I very much prefer to have the higher voltage, regardless of the inconvenience of losing the B phase for 120V service. I've managed to work around that very nicely in all situations. Huh? What "obvious reasons"? 120/208 Wye service has no disadvantages that I know of. You can get 120v from any of the phases, allowing you to balance your single phase loads and single pole, two pole or three pole breakers breakers can occupy any panel position since all phases are equal to each other and to the neutral. Read above. Unless one has 208 volt motors, they tend to run hotter than necessary if 240 volt motors are run on 208. I don't consider that an advantage. I consider there to be considerable disadvantages to a system with a "wild" leg. You have no way to even come close to balancing your single phase loads on the three phase feed and you have the "wild" leg which can cause safety issues and/or equipment damage if people are not paying attention. From what I recall this configuration was primarily used to cut transformer costs when serviced from three single phase transformers and not for any technical advantage. Pete C. I can't argue with your thoughts, but I'm very comfortable with delta service, the only three phase I've used for more than 36 years, although my first service was an open delta. You know what they say about an old dog. PUD wasn't nearly as concerned about my load balance as you appear to be, given the fact that they are the ones that wired my two panels, from the pole to the CT can and meter base (one for three phase, the other for single phase, which serves both the shop and house, a 375 amp unit). They were more than aware that I was using the delta service in both capacities. Harold |
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Harold and Susan Vordos wrote:
"Pete C." wrote in message ... Harold and Susan Vordos wrote: snip----- Huh? You always (unless you've got a 100yr old system) have a ground for your building system, so once you reach your building distribution you have a minimum of four wires for a strictly delta system, A, B & C phases and ground. A Wye system will have five, A, B & C phases, neutral and ground. The "Wild leg" delta system would also have five wires. That's what I've been talking about, a wild leg system. That's what I have. The wild leg measures 208 volts to ground, or neutral. Your "wild leg" delta system is not very popular these days since most three phase services are provided by three phase pad mount transformers so the potential cost savings from using two smaller and one larger single phase transformers to service the load doesn't exist. The "wild leg" is also a potential safety issue to people and equipment which is why the NEC requires the orange color coding and placement in the middle position of the panelboard. Yep! That's what I have, the wild leg as the B phase, and it's orange. One difference-----I have three transformers on the pole in my yard, all the same size. They are not pad mounted. That's how everything used to be and I believe both the wild leg and open delta configurations were primarily used as a way to save transformer costs. Ground is not established by the center tap on one transformer, that is a neutral of sorts. Ground is always established by the ground rod(s) for your service. The ground and the neutral are always bonded together at the service entrance panel and never at any sub panels. Yeah, and thanks for correcting me. I fully meant neutral, but my fingers got away from me. i hae a basic understanding of the difference between a ground, and a neutral. My panel (Square D) provides for a neutral, and I have it. I have a true 5 wire system, run to each individual box in the shop. Most panels these days are fairly modular and provide bolt in options of neutral and ground bars. Again, wrong. It *is* a delta system. He's talking about 240 volts, not 208. As far as I know, single phase service to the typical house is just one leg of a three phase delta system. Isn't that how it comes from the power plants, the primary service? How it's delivered to the customer depends on the transformers that feed them. Ok, the "wild leg" configuration is technically a delta configuration. It is however more often referred to with various derogatory terms due to it's disadvantages. While older distribution was often fed in a delta configuration, that is being phased out for safety reasons. That's an interesting comment. When I discussed three phase service with PUD, our provider, I was advised that our area, which is relatively remote, was in bad need of an update, that they were going to provide the second leg of the three phase service to lighten the load on the single leg, which is, as I recall, something like 14,000 volts. I was told if I would pay for the third leg, it would be installed simultaneously, saving me considerable money, which it did. It dropped the cost from my original inquiry many years ago from $30,000 to just over $18,000. The point being that, while it's not necessarily a popular service, they had no problems providing it to my specs. I was required to provide a large CT can, naturally. Much of the grid in this country is badly in need of an update unfortunately. Between cheap utilities not wanting to invest in plant upgrades and wing nut eco freaks the grid has been festering and decaying while the load just keeps getting larger. Oddly enough the grid and service here in fairly rural North Texas is pretty good. They seem to prefer using individual transformers for each house or two instead of a secondary bus on the poles with a dozen homes off of one transformer. My neighbor and I share a 50kva unit on the pole between us. When the distribution transformers are fed in a delta configuration, in the event that there is a circuit loss on one of the phases feeding the transformer due to a cable break of a fuse blow, the line remains hot due to power feeding from the other phase through the delta wired transformer(s) and back down the "disconnected" phase. Which likely explains the crazy voltages I found when returning from vacation many years ago when we resided in Utah. Our entire house was wired with 3 phase, and one of the lines connected to a transformer worked loose, enough to lose a proper connection. We lost a few things from crazy voltages. Our refrigerator had been out of service for a long time, spoiling everything inside. Similarly bad things happen if you loose the neutral on a typical 120/240 residential service. A Wye connected transformer does not present this risk since only one leg of the transformer winding is ties to a hot line with the other at neutral / ground potential. But yields only 208 volts. A good friend moved from one shop to another, the second serviced by a Y service. His CNC machines didn't like that one bit. Regardless of the fact that machine tools should have motors that can run on either voltage, I very much prefer to have the higher voltage, regardless of the inconvenience of losing the B phase for 120V service. I've managed to work around that very nicely in all situations. Nope, a Wye connected transformer yields whatever you spec it to yield, 208/120 is just the most popular for light commercial use, if you need more power you get 480/277 Wye. Of course if you get the 480/277 then you also need a transformer to give you 208/120 as well. As for the CNC machines, back when I worked on them I seem to recall every one I worked on could be wired for a pretty wide range of input voltages. They also have the small buck/boost autotransformers you can use on the few machines that truly can't be restrapped for 208. It would certainly be my preference to use a few autotransformers on one or two problem machines rather than go with a wild leg system. Huh? What "obvious reasons"? 120/208 Wye service has no disadvantages that I know of. You can get 120v from any of the phases, allowing you to balance your single phase loads and single pole, two pole or three pole breakers breakers can occupy any panel position since all phases are equal to each other and to the neutral. Read above. Unless one has 208 volt motors, they tend to run hotter than necessary if 240 volt motors are run on 208. I don't consider that an advantage. Most machines I've seen can accommodate a wide input voltage range, for the few machines that can't you use the small inexpensive buck/boost autotransformers. I consider there to be considerable disadvantages to a system with a "wild" leg. You have no way to even come close to balancing your single phase loads on the three phase feed and you have the "wild" leg which can cause safety issues and/or equipment damage if people are not paying attention. From what I recall this configuration was primarily used to cut transformer costs when serviced from three single phase transformers and not for any technical advantage. Pete C. I can't argue with your thoughts, but I'm very comfortable with delta service, the only three phase I've used for more than 36 years, although my first service was an open delta. You know what they say about an old dog. PUD wasn't nearly as concerned about my load balance as you appear to be, given the fact that they are the ones that wired my two panels, from the pole to the CT can and meter base (one for three phase, the other for single phase, which serves both the shop and house, a 375 amp unit). They were more than aware that I was using the delta service in both capacities. The utilities aren't that concerned with balance since they can just switch a few residential streets between phases to balance things. I just like my power system to be balanced, since that seems to be the only place in my life where I have any hope of achieving balance. Of course, not running any large business, I'm still stuck with my rotary phase converter. Pete C. |
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John You mention in thi reply below that you have seen a corner grounde system in a DC^ aircraft. That surprizes me. Most other aircraft use 120/208 3 phase Y configurations. Maybe I dont understand whata corner grounde is. I thought it would be a delta with one corner grounded. Jerry "john" wrote in message ... George wrote: john wrote: I always assumed that it was done for convenience. I have 3 hot wires (A, B & C(wild)), I can run all my 120 stuff off A to neutral or B to neutral. I can run all of my 240 single phase stuff off A-B and I can run all of my 240 3-phase stuff off A-B-C. Anything that uses 220 only, ( 220 with two conductors and a ground) can be run off of any two legs. Only if the thing uses 120 and 240 volts and has a neutral wire going to it do you need to use the centertapped phases. If I had Wye or corner grounded delta service then I would have to give up one of those conditions or purchase another transformer. Nope One thing that is common in warehouses here is 208 Wye service. That gives 3, 120 Volt legs. Obviously, I can run a 240 3-phase motor on that service but it will only run at 208/240)^2 = 75% power. Worse yet, many electronic items just simply will not run. Thats one of the nice things about using 240 volts. Overvoltage is usually less harmful than undervoltage Alternatively, I can get 240 Wye service and run my 240 stuff at full power. As you mentioned, you can always run 240 single phase stuff across any two legs. (I can also use my 208V light bulbs from the previous example) But how do I get my 110V toaster oven to work in that arrangement? I've never run across a 240 volt Wye supplied from an electric company. IF you had a neutral supplied with the Wye connection you would have 120volts for your toaster. a delta connection would require a transformer if there were no center tapped transformer. Same question for a corner grounded delta arrangement? the only place I've ever seen a corner grounde system was in a DC-6 aircraft, and that was 115 volts leg to leg. By the way: center tapped delta service is very common here in the Chicago area. Wye service is strictly used in office buildings and warehouses. Everywhere I've been it was the same. 208 Wye was used where most of the loads were 110/220 single phase in apartment buildings and stores, otherwise it was 240 volts red leg delta service. you neighbor may be on a different pole transformer. IF he is then his phasing is different than yours. Yea, I figured as much. We had an electrical storm here several years ago. Half the light bulbs in the building were getting dim while the other half were getting unusually bright. Then some of the bright bulbs began to blow. I figured that we must have lost the center ground and that the voltage was being split somewhere in the middle of the center tapped leg. No doubt based on the relative load on either side. I ran round the building frantically shutting everything off as light bulbs popped all around me. I then called the electric company and explained the situation. I must hand it to them, they arrived in truly record time! But I noticed that my neighbors lights were also bright in one window and dim in the next. I was just sort of pondering the fun that it would be to ground out one side of the transformer and then ground out the other side. Com Ed arrived before I worked up enough nerve to put theory to practice. I had the same thing happen in florida caused by a lightning strike. It was like in the sci fi movies.. the fans were going up and down in speed and the lights were flashing, It happened a day after the storm. The day before they changed the fuse on the pole and i told them there were other problems. I could smell the burned transformer oil. John |
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"Pete C." wrote in message ... My 3 phase delta 240/120 volt service was installed just 4 years ago, at my request. I did not want a wye service (for obvious reasons), and am transforming to 480V for one machine. Huh? What "obvious reasons"? 120/208 Wye service has no disadvantages that I know of. You can get 120v from any of the phases, allowing you to balance your single phase loads and single pole, two pole or three pole breakers breakers can occupy any panel position since all phases are equal to each other and to the neutral. Well there are disadvantages from the 208 voltage, a lot of motors will not run at 208 with out overheating them. And my band was blade welder didn't really like it either, had problems welding the larger blades. The oven elements also don't seem to get as hot, cloths dryer, etc..... William... |
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In article fQire.47092$_o.36229@attbi_s71, William says...
Well there are disadvantages from the 208 voltage, a lot of motors will not run at 208 with out overheating them. Buck/boost transformer. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
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"William" wrote in message news:fQire.47092$_o.36229@attbi_s71... "Pete C." wrote in message ... My 3 phase delta 240/120 volt service was installed just 4 years ago, at my request. I did not want a wye service (for obvious reasons), and am transforming to 480V for one machine. Huh? What "obvious reasons"? 120/208 Wye service has no disadvantages that I know of. You can get 120v from any of the phases, allowing you to balance your single phase loads and single pole, two pole or three pole breakers breakers can occupy any panel position since all phases are equal to each other and to the neutral. Well there are disadvantages from the 208 voltage, a lot of motors will not run at 208 with out overheating them. And my band was blade welder didn't really like it either, had problems welding the larger blades. The oven elements also don't seem to get as hot, cloths dryer, etc..... William... Exactly! I'm still at a loss to understand why the delta system is such a problem. Seems to me the Wye system, *for a machine shop*, would be far more disadvantageous. You'd have to be completely out of your mind to request it if delta was available. Harold |
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"Pete C." wrote in message ... Harold and Susan Vordos wrote: snip---- That's how everything used to be and I believe both the wild leg and open delta configurations were primarily used as a way to save transformer costs. Regardless of reason, machine shops are typically provided with this service. The higher voltage is very desirable, and in some cases mandatory. I question your logic about saving transformer costs if individual machines would require buck/boost transformers. Between the area required to store them, and the increased cost of labor for installing them, seems to me it's a terrible waste of money when it can be dealt with by installing the delta system instead of the wye. A Wye connected transformer does not present this risk since only one leg of the transformer winding is ties to a hot line with the other at neutral / ground potential. But yields only 208 volts. A good friend moved from one shop to another, the second serviced by a Y service. His CNC machines didn't like that one bit. Regardless of the fact that machine tools should have motors that can run on either voltage, I very much prefer to have the higher voltage, regardless of the inconvenience of losing the B phase for 120V service. I've managed to work around that very nicely in all situations. Nope, a Wye connected transformer yields whatever you spec it to yield, 208/120 is just the most popular for light commercial use, if you need more power you get 480/277 Wye. Of course if you get the 480/277 then you also need a transformer to give you 208/120 as well. But you've overlooked the fact that it does *not* yield 240 volts, the optimum voltage for machine tools. I'm having more than a little trouble understanding why you feel delta is such a bad deal when it solves all problems aside from the wild leg issue. I can't think of one small machine shop that is wired wye------not one. Many of my friends are still in business in Utah, all of which have the delta service. Could be it's a regional thing. Dunno. As for the CNC machines, back when I worked on them I seem to recall every one I worked on could be wired for a pretty wide range of input voltages. They also have the small buck/boost autotransformers you can use on the few machines that truly can't be restrapped for 208. Or you could use 3 phase delta and ignore buying buck/boost transformers and their inherent problems. I thought that was an excellent idea. It would certainly be my preference to use a few autotransformers on one or two problem machines rather than go with a wild leg system. You keep speaking of these problems, but I've had 3 phase delta systems since 1967, and aside from the one failure, which would have occurred be it delta or wye, I've never had any problems. From that I conclude that the problems, while possibly serious, are highly unlikely to plague the average person. I'm more than willing to gamble on these ethereal problems than request wye service and know for damned sure I'm going to face other problems, which I would. I get the idea you're geared to light commercial, where wye service is the norm. Machine shops do not use it----for obvious reasons. Places that have a lighting load that tends to be the largest power demand is where you find lots of wye service, at least in my experience. Most machines I've seen can accommodate a wide input voltage range, for the few machines that can't you use the small inexpensive buck/boost autotransformers. We've already kicked that around. Why buy more transformers when you can get the proper voltage? The utilities aren't that concerned with balance since they can just switch a few residential streets between phases to balance things. I just like my power system to be balanced, since that seems to be the only place in my life where I have any hope of achieving balance. Of course, not running any large business, I'm still stuck with my rotary phase converter. Pete C. Yeah, the one that puts out 240 volts---------do you get my drift? Funny, I get the distinct idea you think I made a mistake by installing the delta system. You couldn't be more wrong if you tried. It serves my purpose perfectly, very unlike a wye system. Harold |
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Harold and Susan Vordos wrote:
"Pete C." wrote in message ... Harold and Susan Vordos wrote: snip---- That's how everything used to be and I believe both the wild leg and open delta configurations were primarily used as a way to save transformer costs. Regardless of reason, machine shops are typically provided with this service. The higher voltage is very desirable, and in some cases mandatory. I question your logic about saving transformer costs if individual machines would require buck/boost transformers. Between the area required to store them, and the increased cost of labor for installing them, seems to me it's a terrible waste of money when it can be dealt with by installing the delta system instead of the wye. The transformer cost savings was for the large oil filled cans on the pole, by using only two for open delta, or two smaller and one larger for the unbalanced wild leg. The buck/boost autotransformers are quite small and inexpensive. They are dry type autotransformers, not full isolating transformers with multiple windings so they are much smaller than you would expect for their capacity. The KVA size required for the autotransformer is not the full KVA of the load. The sizes you would need for an average machine are about shoe box size and around $150 new. http://www1.mscdirect.com/CGI/NNPDFF...PARTPG=NNLMK32 The other point is that many machines have appropriate taps and connections on their motors and/or internal transformers and would not require the buck/boost. A Wye connected transformer does not present this risk since only one leg of the transformer winding is ties to a hot line with the other at neutral / ground potential. But yields only 208 volts. A good friend moved from one shop to another, the second serviced by a Y service. His CNC machines didn't like that one bit. Regardless of the fact that machine tools should have motors that can run on either voltage, I very much prefer to have the higher voltage, regardless of the inconvenience of losing the B phase for 120V service. I've managed to work around that very nicely in all situations. Nope, a Wye connected transformer yields whatever you spec it to yield, 208/120 is just the most popular for light commercial use, if you need more power you get 480/277 Wye. Of course if you get the 480/277 then you also need a transformer to give you 208/120 as well. But you've overlooked the fact that it does *not* yield 240 volts, the optimum voltage for machine tools. I'm having more than a little trouble understanding why you feel delta is such a bad deal when it solves all problems aside from the wild leg issue. I can't think of one small machine shop that is wired wye------not one. Many of my friends are still in business in Utah, all of which have the delta service. Could be it's a regional thing. Dunno. How is 240v "optimum" for machine tools? A lot of machines larger than bench top size can be strapped for operation on 480v input as well. When I did CNC service, I don't recall seeing a single machine that didn't have a 480v input option. I would consider "optimum" voltage for a machine to be any voltage that it can be strapped for. If it was designed with those taps then it should operate just as well on any of them. The "optimum" voltage that you would want to use based on external factors would be one of the higher voltage options based on smaller required wire gauge, reduced voltage drop, etc. From that standpoint 208v and 240v are essentially equal. If a machine has taps for both 208v and 240v then there is no advantage or disadvantage to either, only the convenience of what you have available. If there are a sufficient number of machines that can take 480v to fill a decent portion of a 480v panel then that is an even better choice. I didn't say that delta was bad, I said that delta with a wild leg was bad, they are two different things. Take a (pure) delta service for the three phase and use a proper transformer to provide 208/120 Wye and I'd be happy. No wild leg anywhere, and you've still got your 240v delta that you like, as well as the familiar and flexible 208/120. Of course it would still be preferable to go with the 208/120 Wye to begin with and save the complexity. I also didn't say that there were not plenty of shops with the wild leg service. If it's already in place in a shop and in good condition there is little reason to change it. I would not use it for a new installation. As for the CNC machines, back when I worked on them I seem to recall every one I worked on could be wired for a pretty wide range of input voltages. They also have the small buck/boost autotransformers you can use on the few machines that truly can't be restrapped for 208. Or you could use 3 phase delta and ignore buying buck/boost transformers and their inherent problems. I thought that was an excellent idea. What inherent problems? For the few machines that might require them in a decent sized shop cost should not be an issue. They are quite small so space should not be an issue. They are not difficult to wire so installation should not be an issue. Many years ago I worked for a mid sized printing company. The building had 208/120 service, and there was only one machine in the entire company that required the buck/boost transformers, a press made in Sweden. It would certainly be my preference to use a few autotransformers on one or two problem machines rather than go with a wild leg system. You keep speaking of these problems, but I've had 3 phase delta systems since 1967, and aside from the one failure, which would have occurred be it delta or wye, I've never had any problems. From that I conclude that the problems, while possibly serious, are highly unlikely to plague the average person. I'm more than willing to gamble on these ethereal problems than request wye service and know for damned sure I'm going to face other problems, which I would. I get the idea you're geared to light commercial, where wye service is the norm. Machine shops do not use it----for obvious reasons. Places that have a lighting load that tends to be the largest power demand is where you find lots of wye service, at least in my experience. Failures due to poor maintenance can and will occur with any power system. Annual IR camera inspections really are cheap insurance since they can usually spot these problems developing before they can do any damage. These days when you can get a handheld IR thermometer for $50 at Sears you can do the inspections yourself and save even more money. Granted it's a little slower than with an IR camera, but not that much slower. Do a monthly scan, input the data to a spreadsheet and pickup problem trends even faster. Wye service is indeed good for buildings with a lot of lighting load, 480/277 is particularly good for that. The main thing is that you are indicating that there is a big disadvantage to 208v vs. 240v which I just don't see. I think your making more of the difference between 208v and 240v than there is justification for. The allowable voltage range for your 240/120 3ph delta wild leg service is from 220v-254v at the service entrance (from a chart referencing ANSI C84.1-1989). If the service is considered acceptable over a range of 34v I just don't see a 32V difference between services as significant. Large motors are built to handle widely varying power and load conditions, and power supplies for controls either have plenty of tap adjustment range for older machines, or switching supplies for newer machines that are happy on anywhere from 98v - 250v. Your motors might run a few degrees warmer but still well within their specified operating range and your controls should be perfectly happy as well. Most machines I've seen can accommodate a wide input voltage range, for the few machines that can't you use the small inexpensive buck/boost autotransformers. We've already kicked that around. Why buy more transformers when you can get the proper voltage? Again, because not many machines would actually require it, and the fact that your "proper" 240V service is allowed to vary over a 34v range anyway. Basically I think the 14% or so difference is of little to no significance for 95% of the possible machines you might run, and for those few the fix is easy and inexpensive. The utilities aren't that concerned with balance since they can just switch a few residential streets between phases to balance things. I just like my power system to be balanced, since that seems to be the only place in my life where I have any hope of achieving balance. Of course, not running any large business, I'm still stuck with my rotary phase converter. Pete C. Yeah, the one that puts out 240 volts---------do you get my drift? Er, no, a couple weeks ago I had 269V! A call to TXU had that fixed in less than one hour fortunately (good response). And actually the 240V is some 9% high for the machine, as it's motor is rated for 220/440. Funny, I get the distinct idea you think I made a mistake by installing the delta system. You couldn't be more wrong if you tried. It serves my purpose perfectly, very unlike a wye system. I think my main point is that I feel the Wye system would have served your needs equally well and would have simplified the installation by avoiding your use of separate panels for your single and three phase loads to avoid the wild leg issue. Pete C. |
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Pete C. wrote: The allowable voltage range for your 240/120 3ph delta wild leg service is from 220v-254v at the service entrance (from a chart referencing ANSI C84.1-1989). If the service is considered acceptable over a range of 34v I just don't see a 32V difference between services as significant. Large motors are built to handle widely varying power and load conditions, and power supplies for controls either have plenty of tap adjustment range for older machines, or switching supplies for newer machines that are happy on anywhere from 98v - 250v. Your motors might run a few degrees warmer but still well within their specified operating range and your controls should be perfectly happy as well. Most machines I've seen can accommodate a wide input voltage range, for the few machines that can't you use the small inexpensive buck/boost autotransformers. We've already kicked that around. Why buy more transformers when you can get the proper voltage? Again, because not many machines would actually require it, and the fact that your "proper" 240V service is allowed to vary over a 34v range anyway. Peter, Do you think it would be OK to run the 240 motor on 197.6V ? Because that's what could happen when you hook it up to a 208 service. Most all power companies have a 5% tolerance on their service voltage. So a 240 service can go from 238 to 252. And a 208 service can go from 197.6 to 218.4. The purpose of a 208 service is to serve buildings with large lighting loads and small 3-phase loads. There is a lot of commercial 240 3-phase and a lot of houses that have their own 3-phase wells will also have a grounded center tap delta. I happen to have a 10HP 3-phase pump with a straight 3-phase service, 3hot wires and no neutral to the pump. The bank across the street from my house has a 25KVA and 2 10KVA transformers, in a center tap grounded delta. My house 120/240 single phase also comes off of this same bank. Don |
#39
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Harold and Susan Vordos wrote: "William" wrote in message news:fQire.47092$_o.36229@attbi_s71... "Pete C." wrote in message ... My 3 phase delta 240/120 volt service was installed just 4 years ago, at my request. I did not want a wye service (for obvious reasons), and am transforming to 480V for one machine. Huh? What "obvious reasons"? 120/208 Wye service has no disadvantages that I know of. You can get 120v from any of the phases, allowing you to balance your single phase loads and single pole, two pole or three pole breakers breakers can occupy any panel position since all phases are equal to each other and to the neutral. Well there are disadvantages from the 208 voltage, a lot of motors will not run at 208 with out overheating them. And my band was blade welder didn't really like it either, had problems welding the larger blades. The oven elements also don't seem to get as hot, cloths dryer, etc..... William... Exactly! I'm still at a loss to understand why the delta system is such a problem. Seems to me the Wye system, *for a machine shop*, would be far more disadvantageous. You'd have to be completely out of your mind to request it if delta was available. Harold You're right, Harold. I think the 3 transformer delta service is the better of the two. One advantage is that when one transformer goes out a trouble shooter from the power company (me) can go out and rebuss it into an open delta and have you back up and running in 30 minutes. The two transformer open delta is only good for 86.6% of the KVA rating of the two transformers. So you might have to shed some load. Don |
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Don Murray wrote:
Pete C. wrote: The allowable voltage range for your 240/120 3ph delta wild leg service is from 220v-254v at the service entrance (from a chart referencing ANSI C84.1-1989). If the service is considered acceptable over a range of 34v I just don't see a 32V difference between services as significant. Large motors are built to handle widely varying power and load conditions, and power supplies for controls either have plenty of tap adjustment range for older machines, or switching supplies for newer machines that are happy on anywhere from 98v - 250v. Your motors might run a few degrees warmer but still well within their specified operating range and your controls should be perfectly happy as well. Most machines I've seen can accommodate a wide input voltage range, for the few machines that can't you use the small inexpensive buck/boost autotransformers. We've already kicked that around. Why buy more transformers when you can get the proper voltage? Again, because not many machines would actually require it, and the fact that your "proper" 240V service is allowed to vary over a 34v range anyway. Peter, Do you think it would be OK to run the 240 motor on 197.6V ? Because that's what could happen when you hook it up to a 208 service. Most all power companies have a 5% tolerance on their service voltage. So a 240 service can go from 238 to 252. I think something is wrong with your math there or you have a typo. At a +/- 5% tolerance the nominal 240V service would range from 228V to 252V. According to that ANSI spec 220V to 254V is acceptable. And a 208 service can go from 197.6 to 218.4. The purpose of a 208 service is to serve buildings with large lighting loads and small 3-phase loads. There is a lot of commercial 240 3-phase and a lot of houses that have their own 3-phase wells will also have a grounded center tap delta. I happen to have a 10HP 3-phase pump with a straight 3-phase service, 3hot wires and no neutral to the pump. The bank across the street from my house has a 25KVA and 2 10KVA transformers, in a center tap grounded delta. My house 120/240 single phase also comes off of this same bank. The different sized transformers is what I referenced about cost savings for the wild leg configuration, with the 10KVA transformers costing less than the 25KVA transformer. A quick look on the Grainger site doesn't even find any 240V 3ph motors at all. They all seem to be spec'ed for 208-220/440 or 208-230/460. The Baldor site is also devoid of any 240V rated three phase motors, they list motors with 208-230 range and some at 220V or 230V. The Baldor spec's indicate for a 2HP motor the FLA difference between 208V and 230V is .5A (12 vs. 11.5). If the entire current difference was dissipated as heat, which it is not, that's a whopping 104W extra to dissipate from the surface of a beefy 60# motor - hardly a big deal in just about any application. So once again I think that there are very few machines that would actually have any adverse effects from running on a 208V service. An existing building with wild leg delta service that was in good condition would be fine with me. For a new installation I would not spec. a wild leg delta service. Pete C. |
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