(N. American) line voltage: 120? 110? 117? - Page 1
Forum section: electronics / general

author: Analog Kid
author_rank: Super Contributor
timestamp: March 17, 2025, 07:50:57 pm
content: In the olden days (ca 1960) when I first got interested in the whole electricity/electronics thing, the most popular designation for line voltage here was, for some strange reason, 117 volts. (Why so specific an odd number?) Although you could find other sources that would put it at 110 or 120 volts.And nowadays I still hear/read lots of folks talking about "220" (the voltage across both phases of domestic power).But so far as I can tell, in all the places I've lived here in the US (not that many, but a few), the actual line voltage is 120 volts, almost exactly. So the correct value for the 2-phase reading is 240 volts, not 220.Discuss away. (And I'm curious to hear from those in 220/230/240 volt, 50 Hz lands.)

author: Siwastaja
author_rank: Super Contributor
timestamp: March 17, 2025, 07:59:25 pm
content: Terminology clarification: you don't have 2-phase power, you have split phase power. 2- and 3-phase electricity provides rotating vector by offering two degrees of freedom; in 2-phase system this is achieved by 90 deg, in 3-phase system by 120 deg phase shift.North America and some other countries prefersingle phasesupplies for households, with a twist of offering center tap off the transformer, providing two different single phase voltages, in this case 120V and 240V. The two 120V supplies are out of phase by 180 degrees and as such do not generate a rotating vector.This is no different from, say, audio amplifier having a 24V transformer with a center tap. No one calls it two-phase power supply.Having two voltages, one for smaller, other for bigger appliances, is quite sensible, but it's not two-phase. It has a specific name, which is "split phase".Two-phase is very rare in power distribution now, but normal in stuff like stepper or BLDC motors.

author: jpanhalt
author_rank: Super Contributor
timestamp: March 17, 2025, 08:04:47 pm
content: In my location in rural Ohio, it's 120/240. I inquired about that last Fall when I installed an electric water heater. I agree on the 2-pase comment.

author: TimFox
author_rank: Super Contributor
timestamp: March 17, 2025, 08:23:31 pm
content: Apparently, the NEC stipulated 120 V in 1984, although it existed before that in US.240 V for domestic higher voltage (stoves, air conditioners, etc.) derives from that.For 3-phase distribution, 208 V line-line gives 120 V line-neutral.

author: langwadt
author_rank: Super Contributor
timestamp: March 17, 2025, 08:34:00 pm
content: Quote from: Siwastaja on March 17, 2025, 07:59:25 pmbut I've seen that some places gets two out of three phases instead of split phase, so 120V/208V (and making it much simpler to generate the third missing phase if you need it)

author: Analog Kid
author_rank: Super Contributor
timestamp: March 17, 2025, 08:47:31 pm
content: Yeah, yeah, I know all about that "split-phase"/"2-phase" dichotomy. Have been involved in lotsa arguments over that.I still say that even though it's not the accepted term, "2-phase" does accurately describe domestic electric service here in N. America. There are 3 wires coming into our houses; one pair has 120 VAC of one phase, the other pair 120 VAC of the opposite phase. Therefore 2-phase in my book. (And yes, identical to a center-tapped transformer winding.)Similar to 3-phase but with the phases 180° out of phase instead of 120°.So sue me.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 17, 2025, 08:48:52 pm
content: Quote from: TimFox on March 17, 2025, 08:23:31 pmOK, so where did "117 VAC" come from?

author: tooki
author_rank: Super Contributor
timestamp: March 17, 2025, 08:52:49 pm
content: Quote from: Analog Kid on March 17, 2025, 07:50:57 pmIt was originally 110V nominal. Then raised to 120V. 115V is halfway between those, and it’s possible some places used a 115V nominal for a while, and 117V is halfway between 115V and 120V.But it’s been 120V nominal for a long time. But many people are stubborn and refuse to stop calling it “110V”.Europe switched from 220V to 230V nominal years ago. 230V being halfway between 220V of mainland Europe and 240V of the UK, such that 230 is actually within the tolerances of both.

author: themadhippy
author_rank: Super Contributor
timestamp: March 17, 2025, 08:57:36 pm
content: QuoteOfficially the uk is 230v single phase,we were 240v but to play nicely with europe we supposedly got turned down to 230V and they got turned up to 230V,what realty happened is they adjusted the lower and upper limits, so the uk can sit anywhere between 216V and 253V.In general domestic supply's are single phase but there are exceptions.Our 3 phase supply is 400v but many still refer to it as 415VQuoteBit like our archaic "400v single phase" supplies which were really 2 phases

author: TimFox
author_rank: Super Contributor
timestamp: March 17, 2025, 08:59:24 pm
content: Quote from: Analog Kid on March 17, 2025, 08:48:52 pmThe Mean Value Theorem?On older appliances and tube-era devices, the appliance’sinputvoltage rating was often 117 V, including tubes with line-voltage heaters such as the 117L7/M7GT. This may result in overvoltage issues on tube heaters if thesupplyvoltage is on the high side of the tolerance band.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 17, 2025, 08:59:38 pm
content: Quote from: tooki on March 17, 2025, 08:52:49 pmJust one question, and pardon my ignorance: do your households receive a single input of 230 V power, with just a hot and neutral (plus ground), no intermediate voltage?

author: themadhippy
author_rank: Super Contributor
timestamp: March 17, 2025, 09:03:09 pm
content: Quoteyes a single supply of240v230v phase to neutral,how we get thegroundearth depends on the incoming supply arrangement.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 17, 2025, 09:20:04 pm
content: Ground == earth, we all know that.You say po-TAY-to, I say po-TAH-to.

author: floobydust
author_rank: Super Contributor
timestamp: March 17, 2025, 09:24:33 pm
content: You have to understand why mains voltages keep rising. I've worked in the utility sectors- generation and transmission.What's happening is growth, in cities, in industry is placing more and more load on the grid.It's expensive to upgrade the grid, so instead let's push what is out there. We want maximum return to shareholders lol.What I have seen is old power lines are running at max. current and line losses go up due to their self-heating. It's simply too expensive and sometimes not possible (room) to increase the number of conductors or their size. Getting new power lines in place is a hassle with approvals and so for a given transmission line, just up the voltage.Existing infrastructure - if you up the voltage 10%, you get 10% less current and ~20% less I2R losses and stress in the power lines and transformers. They are current limited.Also some regions just have a terrible power factor which shows as high line voltage. Capacitor banks are kind of a last resort because they are super expensive. Tap-changing voltage regulators as well, and neither addresses the fundamental problem of more power needed.What I see is 123VAC when it's high and 118VAC low. 246V-236V.It makes it a real bitch to design with small power transformers which are commonly rated "115V" or "117V" primary.

author: Benta
author_rank: Super Contributor
timestamp: March 17, 2025, 10:20:34 pm
content: Quote from: Analog Kid on March 17, 2025, 08:59:38 pmThis may apply to the UK, but the standard in Central and Middle Europe is 3-phase 230 V to the home. Single-phase installations are a relic.Concerning the 220/230/240 discussion: it was an issue 25 years ago, but normal utility upgrading and tap-changing has resulted in 230 V pretty much everywhere (including the UK).It's a non-issue today.

author: Benta
author_rank: Super Contributor
timestamp: March 17, 2025, 10:37:36 pm
content: Quote from: Analog Kid on March 17, 2025, 08:47:31 pmI won't.But I encourage you to use correct terminology. The original terminology is "polyphase", which can refer to 2, 3, 5, 7 etc. phases.All other systems can be derived by swapping the wires on the existing phases.Split-phase is a 1-phase system with an inverted phase. Polyphase needs phase shifting (90, 120, etc.).

author: ejeffrey
author_rank: Super Contributor
timestamp: March 17, 2025, 10:55:15 pm
content: Quote from: tooki on March 17, 2025, 08:52:49 pmI would guess that people wrote "115 V" on appliances to emphasize that they were compatible with both 110 V and 120 V supplies, and continued doing so long after 110 V stopped being actually relevant. A lot more people look at labels on appliances than power company notices, so they interpret whatever sticker GE puts on something is the "standard."Another factor that leads to 115V labeling is multi-voltage worldwide devices. 115V is half of the European nominal 230V. If you have a power supply that has either a transformer with switchable serial/parallel primaries or a switching supply with a switchable bridge rectifier vs. voltage-doubler, it's naturally a 2:1 ratio. So someone designing for both markets might label the switch as "230/115". In fact I have a brand new meanwell power supply with such a switch labeled 230/115V.

author: langwadt
author_rank: Super Contributor
timestamp: March 17, 2025, 11:14:34 pm
content: Quote from: Benta on March 17, 2025, 10:37:36 pmand with two or more phases you can generated any other phase by linear combination, you can't do that with split phase

author: tom66
author_rank: Super Contributor
timestamp: March 18, 2025, 08:29:40 am
content: Quote from: Analog Kid on March 17, 2025, 08:59:38 pmStandard UK service is what is known as TN-C-S which is rare outside of the commonwealth. We get a single phase live, and a protective-earth-neutral conductor for return current. At the distribution board, the PEN conductor is split into actual neutral and earth. Earth will often be bonded to water pipework (but never gas). At the substation, the PEN is connected to a rather meaty set of earth rods and to the other end of the transformer secondary. Typical service is 80 or 100A, which gives up to 23kVA capacity, more than enough for most homes. For industrial units, and rarely residential properties, three phase is available. Every home has a distribution fuse, with most homes in the street swapping which phase they are on every so often (varies from street to street but it's common for your neighbour to be on a different phase).This system has one advantage, where you can get away with a cheaper cable to feed a premises, but has the major disadvantage that when the PEN conductor gets damaged, say, by clumsy workmen digging the road outside your house, it has the potential (heh) to raise anything earthed in your house to live voltage.In theory, this isn't dangerous, because whilst everything in the house raised up to live, there's nothing at earth potential to touch (you're standing in the house, on an insulated floor, and anything metal like the sink is also at this new potential). It becomes an issue though when you want to have a hot-tub or charge an EV outside the house, as these are in theory outside of the 'equipotential zone' and could risk the electrocution of someone who touches them during a fault.A bit of shortsightedness about 80 years ago creating headaches today, who would have thought that would be a thing, right?!

author: Zero999
author_rank: Super Contributor
timestamp: March 18, 2025, 08:55:56 am
content: Quote from: langwadt on March 17, 2025, 08:34:00 pmIn that case it's three phase, even if you only get two of them to power single phase loads.

author: EPAIII
author_rank: Super Contributor
timestamp: March 18, 2025, 11:15:13 am
content: And yet, in any other place, it IS TWO phases.You admit that a 90° system is a two phase system.What would you say a system with two signals, not three, but two that are 120° apart is? What answer could you possibly give other than it would be a two phase system.What about a system with two signals that are 60° apart? Would you call that "split phase"? I think you would call it a TWO phase system.What about 45° or 100° or 150°? Aren't they also TWO phase systems?OK, now be careful with your answers because I am going to sneak up on it.What about 160°?Then what about 170°?What about 175°?178°?179°?179.5°?179.9°?Just where do you put the dividing line between calling it two phase and split phase?There is no point that stands out as being logical.The truth of the matter is that a bunch of less knowledgeable workers in the LIMITED field of electric power saw the 90° system was called two phase so they just had to name another two phase system with another name.The US has TWO PHASE POWER. But we are ignorant enough to think that it just must be called something else. It is two phases that are derived by SPLITTING a single phase. FM (Freaking Magic)Period!Quote from: Siwastaja on March 17, 2025, 07:59:25 pm

author: langwadt
author_rank: Super Contributor
timestamp: March 18, 2025, 11:45:47 am
content: Quote from: EPAIII on July 10, 1975, 01:07:31 pmAt n*180 degree, where you can make one from the other.It is like 1D vs. 2D

author: Zero999
author_rank: Super Contributor
timestamp: March 18, 2025, 12:01:36 pm
content: Quote from: EPAIII on March 18, 2025, 11:15:13 amTwo phases 120° apart still is three phase, because the third can be generated with a plain old transformer.Quote60° is really three phase again, because a 120° phase can be split in two with a centre tapped transformer.Quote45° is two phase.The others you've listed don't exist because they're not 360° divided by an integer.The US has split phase power. It's a single phase split in two. Full stop.

author: themadhippy
author_rank: Super Contributor
timestamp: March 18, 2025, 12:05:17 pm
content: QuoteUp until the introduction of the 18th edition gas pipe work was bonded just like water,however the 18th changed it and now both only require bonding if the incoming pipework is conductive.

author: EPAIII
author_rank: Super Contributor
timestamp: March 18, 2025, 12:44:13 pm
content: One more magical thing about two phases of an AC signal is that the exact same two lines, with absolutely NO change in the signals on them can be VIEWED as any phase relationship that you wish.Please read that carefully and let it sink in. It took me some time to come to that, seemingly contradictory conclusion. But any two AC signals of the same frequency can be measured with ANY phase angle between them. I am not making this up. It is a FACT. It is even a principle that is used in power design circles. If you don't believe me, just look at those popular converters that accept TWO phase power or even single phase power input and provide TRUE three phase power to motors. The simplest of them simply pass two lines, PHASES through the unit while generating a third phase internally using one or more capacitors and perhaps other components. They ONLY generate ONE additional phase, not two.For the longest time I did not believe that those converters provided true three phase power (120°-120°-120°). But others always insisted that they do. I thought they must preserve the phase relationship of the two lines that have a simple wire path through the unit and thus would have a phase relationship of (90°-90°-180°). After all, those two lines that have a metallic path through the unit must maintain their original 180° relationship. So, at best, the third, generated line would be at 90° to each of them.But I was WRONG! I finally sat down and thought about it. What was happening was that just as DC measurements require a defined ground or reference point, so also do AC measurements. But AC measurements require not just a singular dimensional reference (Voltage) but a reference with two dimensions (Voltage and phase). While those converters passed the two AC supply lines straight through the unit to the motor, they DID NOT pass the earth ground or the neutral which should also be at the same potential as earth ground, through the converter. Oh, the motor's outer shell was connected to the safety ground, but neither that safety ground nor a neutral, which is also at ground potential, was used in the wiring of the working coils of that motor.The trick used in those converters is that the three phase output must be measured with respect to a different reference point on the AC vector plane. That reference point does not coincide with any of the three phases that are running the motor. Nor does it coincide with earth ground or neutral in the input power. It is a unique point in vector space which is both equally distant from the three phases and at the 120° phase relationship between any two. Thus, measured from one reference point (earth ground and neutral) you have the original 230V, two phase lines along with a third point at 90° phase angle to each of those. AND measured from the other reference point you have true, three phase power with the 120°-120°-120° phase angles.TWO phases In and THREE phases out, with DIFFERENT reference points.In most, dare I say all, of the motor circuits that additional reference point is not needed by the motor and it is not physically present.My point is that AC phase angles can not simply be measured between two lines carrying an AC signal. You MUST specify and USE a reference point for the system you are using.And with the 230 VAC power, commonly distributed to my house and virtually all other homes and other locations in the US, the reference point IS earth ground with TWO AC phases at 180° angles to each other about that reference point. Thus, once again, it is in every sense of the words, TWO PHASE POWER.What's more, the 90°-270° two phase power, incorrectly cited as the only two phase system, can be viewed as a 180°-180°, two phase power simply by changing the reference point for the measurement. Or, with the proper reference points, any other pair of angles that add up to 360°.Yea, FM!

author: madires
author_rank: Super Contributor
timestamp: March 18, 2025, 12:54:24 pm
content: BTW, there's another setup called high-leg delta (https://en.wikipedia.org/wiki/High-leg_delta). Could be US specific, as I haven't seen that over here.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 18, 2025, 12:58:15 pm
content: Quote from: EPAIII on March 18, 2025, 11:15:13 amSome people call split-phase two-phase, I know that. There is a real reason though why it has aseparatename (split-phase), and that is to distinguish it from theearliertwo-phase power distribution, which did have a 90 deg phase shift.Fair enough: we can agree that calling it a "two-phase system" is common enough to be considered correct, due to the sheer volume of usage. In that case, "split phase" would be anadditionalattribute given to a two-phase system, to distinguish it from a more "true" two-phase system. I can accept that as a valid opinion. This isn't something worth fighting over. Instead, why not try to understand the difference?The fundamental important factor is that two-phase system, just like its successor three-phase system, can directly make motors rotate. You understand that immediately if you draw the phase shifts on a unit circle. 2-phase power system defines sine and cosine. Important note: from 2-phase power, one can derive 2 more "phases". This is commonly done in motors: a 2-phase, "2-pole" aka 1-polepair per phase motor has 4 poles. Think about the pole as a nail around which you wind some wire, so that it pulls or pushes e.g. a permanent magnet rotor, depending on the direction of current. You get the two extra poles by just choosing in which direction you wind the wire. But no one calls it 4-phase motor as such, that would be wrong. There's a separate name: pole.Similarly, 3-phase motors have 6 poles in the minimum configuration: 180 degree phase shift done by winding direction. Therefore, 3-phase electric transmission inherently provides phase shifts of 0, 60, 120, 180, 240 and 300 degrees. It is still wrong to call it 6-phase transmission.Just like it is wrong to derive another phase 180 degrees from a single-phase supply and call that 2-phase transmission!We don't have to stop here. You can generate infinitely more "phases" by just connecting more wires to your supply. You could call every branch after the fuse box "a phase", and I have heard some people say that. These phases just have 0 degree shift. It is nevertheless wrong. This example already proves that the value of phase shiftdoes matterfor the definition of somethingbeing a phase.OK, me saying that, next you probably define a phase such that it needs anon-zerophase shift between another phase. So let's give some extra cable length for another parallel branch to delay the signal and cause 0.000001 deg phase shift. Now single-phase became two-phase power?You can also generate opposite "phases" by swapping the line and neutral wires of any non-earthed class II appliance. Does this make every single-phase power system two-phase? Of course not.And motors were historically very important for the industrialization. Basically all we had first was generators, motors and incandescent bulbs. 2-phase power supply did rotate AC motors. 1-phase power supply was very lousy for this, and still is; it requires something like a capacitor-based delay to generate another internal phase. Which makes a "1-phase capacitor run motor" really a 2-phase motor. You can run it from 2-phase system without the capacitor. But you can't run it from split phase system.QuoteThis arrangement deserves its own name. Like: "a three phase supply with one phase missing". Technically, it's a very non-optimal two-phase system. Using that kind of terminology, split phase system isinfinitely non-optimal two-phase system.You are of course free to ignore this split-phase terminology and continue calling it two-phase system. It is however worth understandingwhythe "split phase" name was coined. Language is your ally, not your enemy; use it to reduce confusion and add information, instead of hiding and misleading.Serious misunderstandings in a way of "connecting something wrong accidentally" are very unlikely though, as there are no practical "real two-phase" power distribution systems left anymore. Therefore mis-use of "two-phase" term isn't very serious. But remember this is a forum full of EEs, not just random sparkies, and pedants like me.Arrogancy does not help at all.

author: EPAIII
author_rank: Super Contributor
timestamp: March 18, 2025, 12:59:54 pm
content: A third phase can be generated with a transformer? Any different phase angle could be generated with one form of circuitry or another. SO WHAT??60° is really three phase again? But what about 55° or 87°? Must I choose examples that are not commensurate with 90°, 120° or 180° just to make a point.45° is two phase.Well, thanks for that admission.The others you've listed don't exist because they're not 360° divided by an integer.What? Obviously you have not seen the plethora of circuits that I have. Fact is, two signals can have ANY phase angle with respect to each other. There is NO mathematical restriction to it. You are looking at this with blinders on. I have seen circuits where one signal could be adjusted to ANY phase angle you care to name, relative to a reference signal.Quote from: Zero999 on March 18, 2025, 12:01:36 pm

author: madires
author_rank: Super Contributor
timestamp: March 18, 2025, 01:09:59 pm
content: Quote from: EPAIII on March 18, 2025, 12:44:13 pmThat should be classic Y wiring without neutral. Another example is the cross section of the neutral wire in a 3-phase cable. All wires have the same cross section, with the neutral wire being able to handle the max current in the worst case scenario, i.e. only one phase loaded.

author: jpanhalt
author_rank: Super Contributor
timestamp: March 18, 2025, 01:16:34 pm
content: I remembered reading years ago that true 2-phase was still available in older parts of Philadelphia, PA. Google AI has this to say today:QuoteI did not confirm whether that was still accurate.

author: Zero999
author_rank: Super Contributor
timestamp: March 18, 2025, 01:23:15 pm
content: Quote from: EPAIII on March 18, 2025, 12:59:54 pmWell of course any phase relationship is possible between two signals, but you appear to no be able to understand the concept of a rotating vector, i.e. that AC power is typically generated with an alternator consisting of a magnet spinning inside a number of coils.Two signals 180° apart is not two phase, because one signal is simply the other inverted.60° is not six phase, because it can be generated from three phase, with just a transformer flipping them by 180°. A 12 pulse rectifier is still a three phase system.How many phase is 1°? The answer is 360, because they can all be generated with centre tapped transformers, from the the 1° phases and neutral.

author: schmitt trigger
author_rank: Super Contributor
timestamp: March 18, 2025, 01:31:07 pm
content: And there is of course the case of Japan. With 100V and 200V split phase for homes.And half of the country is 50 Hz, the other is 60 Hz.And up to a few years ago, some older NYC buildings were still served with DC power.

author: tom66
author_rank: Super Contributor
timestamp: March 18, 2025, 01:41:52 pm
content: Quote from: schmitt trigger on March 18, 2025, 01:31:07 pmI recall reading that there are -still- some parts of San Francisco served by DC power provided by the utility. This is used for old elevators based on DC motors for instance. The distribution is at 250 volts DC, and nowadays provided by PG&E converters located throughout the city that operate off the conventional mains AC.

author: joeqsmith
author_rank: Super Contributor
timestamp: March 18, 2025, 02:27:43 pm
content: Quote from: Analog Kid on March 17, 2025, 07:50:57 pmI don't think it matters. If I use 220 or 240 to describe a mains circuit, everyone will know what I am referencing. I have never had anyone correct me. Maybe they figure I am a hopeless cause, or like me, they don't care. I have also never heard be so anal that they use 237.69 mains in a statement....Likewise, I always refer to it as single phase, unless it is at work where we deal with 3-P. If someone says 208, I think most will assume derived from 3-P transformer. In the context of the outlet, the tapped 3-P may be powering our 1-P equipment. I've never heard anyone get confused about it. Maybe that's an electrical thing.I repaired my dad's old tube hi-fi a couple years back. Forums were filled with people using variacs or buck transformers to power their old hi-fi in fear of damaging the transformers from modern AC power.

author: Monkeh
author_rank: Super Contributor
timestamp: March 18, 2025, 02:48:07 pm
content: Quote from: tom66 on March 18, 2025, 08:29:40 amApart from that being the standard across North America..

author: IanB
author_rank: Super Contributor
timestamp: March 18, 2025, 04:44:29 pm
content: As far as voltage is concerned, there is a difference between the nominal or standard value, and the actual value you receive.The split phase supply to American homes is nominally 120/240 V, according to the standard.What you actually receive may not be this. It depends whether you are in a city, or at the end of a long supply line in a rural area. It depends on the current position of tap changers on your local supply. It depends on the current demand from yourself and all your neighbors. It depends on the current situation with local solar installations back feeding the grid. It can really be quite variable.

author: TimFox
author_rank: Super Contributor
timestamp: March 18, 2025, 05:32:21 pm
content: I have posted this page previously: it is the standard order form for new installations (domestic and commercial) from the Chicago utility Commonwealth Edison.Note the section "Equipment and voltage

author: bdunham7
author_rank: Super Contributor
timestamp: March 18, 2025, 05:53:39 pm
content: Quote from: Monkeh on March 18, 2025, 02:48:07 pmNot really, although some urban installations are functionally similar to that because individual customers may not have access to an appropriate ground.Here it is mostly what you might call "IT-MGN", meaning completely isolated secondary feeds to customers with the neutral grounded at each customer's service entrance point.

author: ferdieCX
author_rank: Regular Contributor
timestamp: March 18, 2025, 06:52:26 pm
content: Uruguay is enough small to be irrelevant, but you asked about 220V/50 Hz countriesHere the distribution is 3-phase, but the connections are usually Delta (we call it triangle), 3 wires without neutral conductor.Most homes get 2 wires, the industries and some homes get the 3 wires.Very big industries with their own transformation station, usually get 6000V and transform down to Star (3-phase + neutral conductor) 240V/400vIn the 90s, the state owned utility (called UTE) started very slowly to migrate to Star configurationThe protective ground is always local to each installation.In the 60s, the nominal voltage was 220V, in the 70s it changed to 230V

author: Analog Kid
author_rank: Super Contributor
timestamp: March 18, 2025, 07:00:45 pm
content: Quote from: EPAIII on March 18, 2025, 11:15:13 amThank you. You're the first person I've encountered who has expressed this.Now all we have to do is convince the bone-headed electrical industry to adopt the right terminology here ...

author: Analog Kid
author_rank: Super Contributor
timestamp: March 18, 2025, 07:06:09 pm
content: Quote from: Zero999 on March 18, 2025, 12:01:36 pmYes, but that's just a consequence of the stubborn refusal of the electrical industry to recognize the two phases.You do agree that if you have two signals coming into a circuit that are 180° out of phase with each other that you now have two phases, right? (Like in a push-pull amplifier, say.)Or is it only when the signals are 179.99999° out of phase that you would recognize them as two distinct phases? (as the boneheaded electrical industry does)It's just a matter of terminology, having nothing at all to do with the way the system actually works.

author: Monkeh
author_rank: Super Contributor
timestamp: March 18, 2025, 07:07:31 pm
content: Quote from: bdunham7 on March 18, 2025, 05:53:39 pmIt's not a neutral if it's not grounded at source.For a quickly sourced example, here's a view inside a padmount where the neutral grounding is plainly visible:https://youtu.be/nCdJrkvRSSw?t=347I'll have to have a proper skim for some views of pole mounts which make it clear - it's hard to see the detail from the ground sometimes.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 18, 2025, 07:08:04 pm
content: Quote from: Analog Kid on March 18, 2025, 07:06:09 pmNo, 179.99999° would not count as two phases, just like 0.0000001°, 0.0000002°, 0.0000003°, 0.0000004° and 0.0000005° do not count as five phases, like in your world view. Could you please consider reading my post above, even though it's a bit lengthy.Allof this is covered in that reply already. It makes little point to discuss it further if you are unwilling to read the replies, but the TLDR is: what can be derived by swapping two wires do not usually count as "phases", and for very good reasons. If you really want to go that way, the implication is that 3-phase power does not exist, and my house has 6-phase power.The fundamental problem you are having is you are conflating the word "phase" with something it did not originally even mean. You are thinking about "circuits" or something.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 18, 2025, 07:11:10 pm
content: Quote from: Zero999 on March 18, 2025, 01:23:15 pmYes it is.Who cares how the two phases are derived? That's not relevant.Neither is the whole deal of rotating vectors for electrical motors.If that is the criterion for how we identify phases of electrical supplies, then we need some new terms, instead of just handwavingly sweeping "phases" away because they don't comport with, say, delta-configured motors.This is all just a bunch of sophistry, and the domain of a hidebound industry that clings to its terminology.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 18, 2025, 07:18:19 pm
content: Quote from: Siwastaja on March 18, 2025, 07:08:04 pmWell sure, I've read it. At the top you wrote:QuoteSo I take that as an affirmation that calling a 120-0-120 system "two phase" is at leastnot incorrect(you said so yourself), which is all I could expect from this discussion. Even if it's not the commonly-accepted term for this arrangement.And I agree that understanding the difference (in terminology and in actual system configuration) is important; I'm certainly not against that.So are we OK here?

author: Siwastaja
author_rank: Super Contributor
timestamp: March 18, 2025, 07:19:59 pm
content: Quote from: Analog Kid on March 18, 2025, 07:11:10 pmYou realize that if this is all irrelevant, then you indeed can just call the same signal (or the same signal delayed by 0.00000000001deg for a few times) as many "phases" as you wish?It's not a useless definition as such, but it has other names, like "circuits". "Phases" by very definition haveeverythingto do with the rotational machine; somespecifictime delays, not just "something".

author: Siwastaja
author_rank: Super Contributor
timestamp: March 18, 2025, 07:22:15 pm
content: Quote from: Analog Kid on March 18, 2025, 07:18:19 pmLet's be more clear: it is "not incorrect" in the sense that ultimately, language is what people make it to be. Split phase system is so widely called two-phase - also within some industries - that it would be foolish to fight against that. We need to accept some confusion in our language.That does not remove the need of explanations ofwhatandwhy- quite the opposite, accepting the ambiguity as reality only reinforces the need of such explanations!

author: Siwastaja
author_rank: Super Contributor
timestamp: March 18, 2025, 07:26:02 pm
content: You can also think about it this way: consider, say, a motherboard CPU buck power supply, which have been polyphase for a long time.Say you have ten half bridges driving ten inductors into the output capacitance.If those half bridges are driven with the same signal, it is not called a 10-phase buck converter, but 10 parallel buck converters.If those half bridges are driven with signals 0.5deg apart, it is called a "failed attempt to build a 10-phase buck converter".Finally, if itiscalled a 10-phase buck converter, then every engineer knows exactly what the target phase shift between the units is. Ergo, the deciding factor of what counts as phase and what does not is theusefulnessfor the engineering purposes, such as minimizing ripple current, or making a motor run.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 18, 2025, 07:27:20 pm
content: Quote from: Siwastaja on March 18, 2025, 07:22:15 pmI never said it did (remove the need for such explanations), and I never would.Knowledge is a Good Thing.

author: Gyro
author_rank: Super Contributor
timestamp: March 18, 2025, 07:31:02 pm
content: Quote from: Analog Kid on March 18, 2025, 07:18:19 pmWhy not just call it a center tapped transformer, which is what it is. Ooh, does that mean we have 2 phase circuitry in the secondary side of our simple bench PSUs?

author: Analog Kid
author_rank: Super Contributor
timestamp: March 18, 2025, 07:35:19 pm
content: How many phases would you say are separately at work in this circuit?If you said "2", I would agree with you.You couldcallit "split phase" if you like, and you would not be wrong, but it would still be 2 phases.

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: March 18, 2025, 07:39:26 pm
content: Quote from: Analog Kid on March 18, 2025, 07:11:10 pmReading your posts, I know you will NEVER change your mind, but here it goes anyways:Following your statement, tell me if it is possible to build a two phase motor, powered by a (0,180 degree) supply that will beself-starting, without ancillary devices?No, of course you can't.

author: Monkeh
author_rank: Super Contributor
timestamp: March 18, 2025, 07:43:02 pm
content: Quote from: Monkeh on March 18, 2025, 07:07:31 pmAnother Canadian example:https://commons.wikimedia.org/wiki/File:Single_Phase_Pole_Mount_Transformer.jpgYou can clearly see the centre tap is bonded to the transformer case - it then runs down to the uppermost of the three LV lines heading off to the left. At that point, it also connects to the primary side ground, the cable coming in from the right (I can't see where that runs off to, but it should be going to the next pole with the primary), and an unseen cable going around the back of the pole - which almost certainly connects to a ground wire running down the side of the pole (we'll see one of those shortly).https://pv-magazine-usa.com/wp-content/uploads/sites/2/2024/01/2023-08-17_14_11_50_Transformer_near_the_top_of_utility_pole_65401EW_along_Aquetong_Lane_in_the_Mountainview_section_of_Ewing_Township_Mercer_County_New_Jersey.jpgIn this one, from NJ, you can quite clearly see the same case bonding - less of the rest of the structure, unfortunately. You can also see the primary ground coming off the back.https://metglas.com/wp-content/uploads/2016/12/Outdoor-Transformer-Power-Pole.jpgThen we have this shot from a NJ company, no idea where the pole is. Once again, visible case bond on the centre tap, which is then jointed to a curly wire which connects to the ground wire up the side of the pole and to the tensioned ground wire which runs along with the primary. The ground wire on the side of the pole then further connects to the back side of the transformer - this is the ground connection for the primary winding.These all equate to TN-C-S.I am, of course, open to examples of a completely ungrounded 'neutral' at an LV transformer like these.Some padmounts:https://etac.ca/wp-content/uploads/2024/02/Components-of-a-Padmount-Transformer-Compartments-Diagram.jpghttps://cdn.prod.website-files.com/66b236099e39348f6967371b/66b236099e39348f69673bb9_Padmount%20Capabilities-min.webphttps://metapowersolutions.com/wp-content/uploads/2023/03/sheme.jpghttps://www.hwe.coop/sites/default/files/images/image2.jpghttps://www.reinhausen.com/fileadmin/images/impulses/optimizing-the-service-life-of-equipment/the_vrdt_is_the_ideal_solution_to_solve_voltage_problems_in_our_distribution_grids/reinhausen-vrdt-with-ecotap-vpd-for-single-phase-transformers.jpg

author: Siwastaja
author_rank: Super Contributor
timestamp: March 18, 2025, 07:44:39 pm
content: Finally, I can see a clear reason why all of this phase stuff doesn't feel intuitive to many. It is because not many work with actual multi-phase systems anymore (if they ever did), so it's not obvious what they are and why they are needed. So, in our minds, the word "phase" just becomes synonymous with a "circuit" or "part of the full supply" or something like that. We lose the intuition about the time domain.I mean, in Continental Europe most houses get a 3-phase supply, me included, but really that's just different design for whatever reason, them being actualphasesis irrelevant. Since we don't have old-school large rotational machines at our homes, them being actual "phases" do not matter the slightest. For example, I don't have any appliance in delta configuration (in some countries, they would have everything in delta; same end result), so the whole house could be rewired with US/UK style beefier 1-phase input (230V in this case), paralleled to those 3 phase wires. I would not notice.With that change, two things would happen:* 3-phase motors would stop working, but like 99%, I don't have them,* the name "phase" would have to be changed into "circuit"You now see the connection? It's called a phase because it can turn motors! Otherwise it's just a circuit.Now with that modification, my home would definitely be single phase. Exactly like in the UK. Without any center taps. Now, let's swap the polarity of one of these "circuits", swapping line and neutral. It's of course a dangerous modification, but technically possible nevertheless. Is my house now 2-phase? I don't think so.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 18, 2025, 07:44:45 pm
content: Quote from: UnijunctionTransistor on March 18, 2025, 07:39:26 pmI totally agree with you, at least on the motor part.But I still do not see how that determines how we identify the number of phases in a system.If you added the qualifier "two phases that are not suitable for driving a motor with", then I could live with that.Driving motors is one usage of electricity, but not the only usage.How can you not see that there are two phases present here, even if they won't drive a self-starting motor?

author: Siwastaja
author_rank: Super Contributor
timestamp: March 18, 2025, 07:50:43 pm
content: Quote from: Analog Kid on March 18, 2025, 07:44:45 pmBecause really, thatisbuilt-in to the word "phase". You don't realize it because you have notneededthe concept. Your needs have been satisfied with single-phase power. Really, you are thinking about havingmultiple circuits, withdifferent voltages, provided by a transformer. All useful concepts. But they are not really phases.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 18, 2025, 07:53:22 pm
content: Quote from: Siwastaja on March 18, 2025, 07:50:43 pmThey are too phases!They're just not the kinds of phases that are capable of driving motors.Since when did the capability of driving motors govern the terminology here?As I wrote above, driving motors is not the only use of electricity. Maybe if it was there'd be some justification for this restrictive terminology. But it ain't, so there isn't.

author: langwadt
author_rank: Super Contributor
timestamp: March 18, 2025, 07:56:07 pm
content: Quote from: Analog Kid on March 18, 2025, 07:53:22 pm

author: Siwastaja
author_rank: Super Contributor
timestamp: March 18, 2025, 08:03:31 pm
content: Quote from: Analog Kid on March 18, 2025, 07:53:22 pmOf course it isn't. But also, "phase" is not the only word related to electricity. You have plenty of suitable terminology available, yet you stubbornly choose to stick to the word "phase". You are just fixated of it being the correct term.Motors are relevant to the history of the term, but of course there are other consequences of the specific time delays: for example here with more than one actual phase, resistive heaters can be ran at 400Vrms between two phases, or at 230Vrms between any phase and neutral. This is straight from the generator and distribution system, without transformers (or taps) for the other voltage! This also isn't possible in your system. For you, 120VAC is made with an actual transformer. You could just have two - or one larger - and nothing would change.Rethink once more carefully. Consider my questions with 0.000001deg and so on phase-shifts defining 5 phases, or langwadt's example of a resistor divider generating a lot of "phases". These are all phases with your very broad definition. Is that definition useful?Besides, even if you don't feel that motors are relevant, remember that motors are pretty much the same as generators, and most of your grid's energy is still produced with those rotating machines, turned by steam from nuclear, coal, or whatever powerplants, hydropower or even wind. Terminology inherits from there, to the grid, to the final leg of distribution. You are clearly only interested in that final leg, and have a disconnect there. In reality, only one of the three grid phases enter your house. You think it becomes two there. I don't agree. Once it's single-phase, it cannot be made multi-phase without a specific thing called phase converter (electronic inverter or rotational machine again).

author: Analog Kid
author_rank: Super Contributor
timestamp: March 18, 2025, 08:14:52 pm
content: Quote from: langwadt on March 18, 2025, 07:56:07 pm[fixed quoting]Fair question:I would say yes. If you look at the voltage across the two resistors at any point in time, measuring from the outside in towards the ground point, then they're clearly in antiphase (180° out of phase), so therefore 2 phases.

author: bdunham7
author_rank: Super Contributor
timestamp: March 18, 2025, 08:41:53 pm
content: Quote from: Monkeh on March 18, 2025, 07:43:02 pmThey would if those grounds at the pole were a necessary part of the setup and the neutral-to-ground connection at the customer service entrance were not. But it is the other way around here--the neutral-ground bond at each service drop is mandatory and the utility-side grounds are added under certain circumstances. You'll see grounds at the pole for some installations but not all, all according to local requirements. I think you'll more likely see them where there is a significant distance between the pole and the customer. The whole point of me calling it IT-MGN (probably not a good term, I just made it up) is not that the secondary is actually ever isolated, but rather that the neutral is grounded in many places on the utility side. Unless I misunderstand it,TN-C-S provides the customer with a separate ground (earth) wire from the utility. Our system never does. Well, not usually. There is actually quite a bit of variety in the actual utility installations, but the residential/light commercial service drops are almost all the same 3-wire L-N-L 240/120VAC split phase.High density urban locations as well as very dry, permanently frozen or very wet areas may have additional features to cope with the ground conditions. But I've lived quite a few places and they've all been as I describe.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 18, 2025, 08:42:24 pm
content: Regarding multiphase power driving motors:Isn't 3-phase power (120° apart) really the only form of multiphase power in common use? (There could be other schemes, like 4 phases 90° apart, but so far as I know they're either nonexistent or uncommon.)That being the case, shouldn't we view 3-phase power as a special use case because of this? We can recognize what I'm calling "2-phase" power as something that does actually exist, but is quite different from the common industrial usage of 3-phase.Or something like that ...

author: TimFox
author_rank: Super Contributor
timestamp: March 18, 2025, 08:43:59 pm
content: One can define these questions more exactly using linear algebra."Basis vectors" can "span a space" if they are "linearly independent".No two sinusoids 180ofrom each other can be added with constant co-efficients to make another sinusoid 90oor 120ofrom one of the two sinusoids.However, a second sinusoid at 90oor 120ofrom the first sinusoid can be added, with appropriate constant co-efficients, to make a sinusoid with any desired phase angle from the first sinusoid.(If the angle between the two is really small, then the co-efficients are not particularly useful, but since the basis vectors are linearly independent, it is still possible.)

author: Monkeh
author_rank: Super Contributor
timestamp: March 18, 2025, 08:47:32 pm
content: Quote from: bdunham7 on March 18, 2025, 08:41:53 pmI think you perhaps do. The utility provides a single neutral conductor - at the installation, both the current carrying neutral conductors and the grounds connect to it. In the UK, at least, the two are split at the service head (the termination of the utility supply cable, akin to the meter box in your installations) - in your case, the two are split in the first panel. There's no electrical difference.Again, I'm open to any examples of LV supplies where the 'neutral' is not bonded to earth at the origin of supply, and therefore not a neutral. I've not seen one single example, rural or urban, where there's sufficient resolution in the image to tell one way or another where this is the case.

author: TimFox
author_rank: Super Contributor
timestamp: March 18, 2025, 08:48:57 pm
content: Quote from: Analog Kid on March 18, 2025, 08:42:24 pmFor power distribution, 3-phase is the most common multiphase power.For other purposes, such as following shaft rotation, a "synchro" sensor uses 3 phases, while a "resolver" uses 2 phases in otherwise similar rotation sensors.

author: Xena E
author_rank: Frequent Contributor
timestamp: March 18, 2025, 08:58:49 pm
content: Question:In the United States of America where the common domestic supply is ≈ 120/240Vac and the single domestic dwelling unit is supplied from the ubiquitous single "Pole pig" transformer, the output is obviously a single centre tapped winding of 240Vhow is/are the primary/primaries energised?

author: Analog Kid
author_rank: Super Contributor
timestamp: March 18, 2025, 08:59:47 pm
content: Quote from: TimFox on March 18, 2025, 08:43:59 pmWell, so what?What you've posted is a distinction without a difference.Congratulations: you win today's pontification/pedantry prize.

author: bdunham7
author_rank: Super Contributor
timestamp: March 18, 2025, 09:01:47 pm
content: Quote from: Monkeh on March 18, 2025, 08:47:32 pmActually, looking more closely at your first example from Alberta, CA, I think that actually is one. I see nothing to indicate that there is actually a connection between the ground and any of those secondary wires. The reason that transformer needs to be grounded is that it is a single-wire earth-return primary which is used in more remote areas. You'll see that there is only one HV line. I don't think that ground line even connects where you think it does, and if it did it should be connected to the center line.Here's a picture of the transformer in my back yard that feeds my house (and 4 others). There's no ground connection anywhere and in case you're looking at that guy wire to see if it is connected, don't bother--it has an interrupting insulator in it further down.

author: TimFox
author_rank: Super Contributor
timestamp: March 18, 2025, 09:04:39 pm
content: Quote from: Analog Kid on March 18, 2025, 08:59:47 pmUtter nonsense.I was clarifying the issue between center-tap single phase and polyphase using real mathematics.You win today's fear of math prize.

author: langwadt
author_rank: Super Contributor
timestamp: March 18, 2025, 09:07:03 pm
content: Quote from: Analog Kid on March 18, 2025, 08:14:52 pmso with a string of four resistors you have four phases? is a +/- lab supply two phase DC?

author: Analog Kid
author_rank: Super Contributor
timestamp: March 18, 2025, 09:13:18 pm
content: Here's the transformer feeding my dwelling:Looks mysterious to me. There's a single HV conductor coming in at the top to the primary, from one of the two wires coming from the left. (The wire at the right is a guy wire.)So how does this work? This is standard 120-0-120 service (let's call it "split phase"), branching off to the left and right.So is the other leg of the (incoming HV) power transmitted through the earth?

author: bdunham7
author_rank: Super Contributor
timestamp: March 18, 2025, 09:14:27 pm
content: Quote from: Monkeh on March 18, 2025, 08:47:32 pmOK, so if I have a mansion with a 500 foot driveway and the utility transformer is roadside and the meter box is on the side of my house with the service panel in the basement then what wires do I have coming to my house and then into the house? And where are the grounding points? Assuming UK, TN-C-S, etc.

author: Monkeh
author_rank: Super Contributor
timestamp: March 18, 2025, 09:21:29 pm
content: Quote from: bdunham7 on March 18, 2025, 09:01:47 pmYou might want to take a much closer look. You can quite clearly see the case bond on the centre tap, follow the wire down and it runs to the top of the three LV wires (yes, it can be the top one if they want it to be..), where it fits into the crimp connection with four other wires - one running to whatever load is connected, one up to what I'm fairly sure is the HV ground, one which runs around to the right hand wire (of unknown destination.. but appears to be the pole the HV phase is coming from) with a tap off for the transformer bracket, and one which disappears around the back.QuoteAnd here is what appears to be the ground connection, circled in green. Hot legs circled in black and red, and the matching neutrals to customers circled in yellow:You'll note the two hot legs do not have that additional connection. Guy wires are not used electrically.

author: IanB
author_rank: Super Contributor
timestamp: March 18, 2025, 09:24:26 pm
content: Quote from: Xena E on March 18, 2025, 08:58:49 pmQuote from: Analog Kid on March 18, 2025, 09:13:18 pmThis video illustrates a typical situation:

author: jpanhalt
author_rank: Super Contributor
timestamp: March 18, 2025, 09:25:02 pm
content: Quote from: Analog Kid on March 18, 2025, 09:13:18 pmOMG, have you considered that line voltage may be well above your household (e.g., 1440 or more) and there's a ground? It amazes me how many posts have been wasted on arguing about a matter of convention/semantics with absolutely zero chance of having any effect.

author: Monkeh
author_rank: Super Contributor
timestamp: March 18, 2025, 09:26:22 pm
content: Quote from: bdunham7 on March 18, 2025, 09:14:27 pmMaking the assumption we're dealing with an underground, single phase supply, you'd have a straight concentric supply cable with a total of two conductors running to the meter box. Inside the meter box this cable would terminate into a head with a fuse on the line, a sealed terminal block on the neutral, and a sometimes-customer-accessible earth block on the side linked internally to the neutral. From that point, you have a 'ground' which is merely a separate path to the same neutral as your load currents. Depending on other factors, that may or may not be further connected to local ground rod(s), mats, foundation earthing elements, electrically conductive structural components, or conductive pipework which is buried.E: This is a TN-C-S cutout ('PME', although PME is not required to be TN-C-S):This is a TN-S one:Don't mind the second cable, it's a looped supply. Customer comes off the top.

author: Xena E
author_rank: Frequent Contributor
timestamp: March 18, 2025, 09:28:53 pm
content: Quote from: Xena E on March 18, 2025, 08:58:49 pmSo.Studying the photo posted by bdunham7I see that the primary is a single phase HV.Soooo. That determines it to be single phase driven primary, centre tapped single phase secondary. QED.Argument over.Quote from: Analog Kid on March 18, 2025, 09:13:18 pmIf you live in a remote rural area then yes that is a thing that is sometimes done...X

author: TimFox
author_rank: Super Contributor
timestamp: March 18, 2025, 09:29:03 pm
content: It's reasonable for a single wire from the utility to the junction of [transformer case], [primary low terminal], and [secondary center-tap] to be grouped with the other low-voltage wires (120 - 0 - 120 V) to the domestic load, while the single wire [primary high terminal] connects through that switch to a single wire physically spaced far from the low-voltage wires.My feed in Chicago (single pole transformer feeding me and several neighbors) in the alley behind my house looks the same.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 18, 2025, 09:31:03 pm
content: Quote from: jpanhalt on March 18, 2025, 09:25:02 pmI don't get it; what are you getting at?So the incoming HV is 1,440 volts? Didn't know that, although I thought it was in that ballpark.Yes, there must be a ground, though I really don't know how that's all connected.Let me ask again: is that other leg of the power (from the HV line) transmitted through the ground (through the earth itself)?

author: Monkeh
author_rank: Super Contributor
timestamp: March 18, 2025, 09:37:24 pm
content: Quote from: Analog Kid on March 18, 2025, 09:13:18 pmThe second wire running off to the left on the crossarm is the ground from the next pole back. Note the lack of an HV bushing. It's a bit of a tangle and not the clearest shot, but if you look closely there's a thin, bare wire hanging above the LV connections under the transformer, this will be the ground connection to the neutral. It will be connected to both the ground wire coming across from the prior pole, and a grounding element (rod, typically) at the bottom of the pole. You'll note that same ground wire connecting to the bottom of the surge arrestor connected just under the crossarm, and hanging off on a bracket next to that is the cutout, which is a fuse carrier and switch (note the ring, that's for grabbing with a hook on the end of a very long, very non-conductive pole)

author: TimFox
author_rank: Super Contributor
timestamp: March 18, 2025, 09:37:58 pm
content: Quote from: Analog Kid on March 18, 2025, 09:31:03 pmFrom the Commonwealth Edison document I posted above, the nominal HV feed to pole transformers is 4000 V rms in Chicago.A recent submission from ComEd to the feds about transformer policy:"ComEd buys a limited number of dual primary ratio (4kV and 12kV) transformers.These transformers are installed in areas with a 4kV supply. ComEd periodically changes 4kVsupplies over to 12kV. The dual ratio transformer allows for easy and quick changeover from4kV to 12kV with minimal interruption to the customer. While some dual ratio transformers maystay in service at 4kV for many years, the goal is to eventually have all operating at 12kV.ComEd recommends that dual winding transformers be tested only in the configuration it isexpected to be in during its ultimate (final) use."From inspection of my alley, there is a ground wire as well, to the primary low side, but it doesn't require anywhere near as much insulation as the single HV feed wire.I doubt that a literal "earthen" ground feed is legal by Chicago code, which also requires two grounded connections at a domestic house (in my case, a ground rod near the meter and a wire from the breaker box to a copper cold-water pipe).

author: bdunham7
author_rank: Super Contributor
timestamp: March 18, 2025, 09:43:39 pm
content: Quote from: Monkeh on March 18, 2025, 09:21:29 pmYes, upon closer examination this does appear to have the neutral bonded to the ground there. But see what I wrote previously about this being a remote, single-HV wire earth return example.QuoteSharp eye there! You're right, there's a 6AWG wire hidden on the back side of the pole. But I'm not sure how it affects the discussion. My system has many grounds, one more doesn't change anything other than making my assertion of full-floatedness incorrect. Again, if I had TN-C-S, would my neutral be bonded to ground at the house?

author: bdunham7
author_rank: Super Contributor
timestamp: March 18, 2025, 09:50:39 pm
content: Quote from: Monkeh on March 18, 2025, 09:26:22 pmOK, make that last part mandatory and you've described the US system pretty well.

author: themadhippy
author_rank: Super Contributor
timestamp: March 18, 2025, 09:51:12 pm
content: Quoteis it? could be 2 phases

author: Monkeh
author_rank: Super Contributor
timestamp: March 18, 2025, 09:53:19 pm
content: Quote from: bdunham7 on March 18, 2025, 09:43:39 pmWhich conveniently has that wire connected to one which runs off in the same direction as the incoming HV phase.QuoteBecause, fundamentally, it is the connection to ground at the source which defines the 'TN' part of the nomenclature (Terra Neutral). The C part (Combined) is defined by the neutral running alone to the customer property, and the S (Separate) signifies it is then split into two conductors for utilization. You can, of course, have a TN-C system with no separate protective earth.. and nobody does that, for extremely good reasons related to undesired death.Yes, if you have TN-C-S the neutral is 'bonded' (split) into the ground conductor. Whether any further connection to the literal physical ground is made at that point depends upon the circumstances. Your code, so far as I know, requires a local rod to achieve this. Here, this may or may not be necessary, along with bonding to services such as water and gas. If they're not electrically connected to the physical soil, they need not be.Again, although some of the specifics on both ends of the installation differ, electrically this is the same setup we have. One conductor (your centre tap, our other side of the winding.. well, if it's a single phase transformer. Mine's 3ph, but I only get the one.) is connected to earth at the transformer, becoming a neutral conductor, that conductor runs to the property and has both the current carrying neutrals and the protective earths connected to it.

author: bdunham7
author_rank: Super Contributor
timestamp: March 18, 2025, 09:56:18 pm
content: Quote from: themadhippy on March 18, 2025, 09:51:12 pmYes, the overhead HV lines are actualy two legs of a three phase distribution system. But the primary of the sole transformer has but a single winding, so all you get is a single phase output.

author: Monkeh
author_rank: Super Contributor
timestamp: March 18, 2025, 09:59:15 pm
content: Quote from: bdunham7 on March 18, 2025, 09:56:18 pmActually, in that case I'm 100% positive it's a single phase and an earth return. There's only one HV bushing on the transformer, one HV cutout, one lightning arrestor.Also, I think he was being a bit tongue in cheek considering the, uh.. technical difficulties we've been experiencing with the difference between single phase and polyphase in this thread.

author: TimFox
author_rank: Super Contributor
timestamp: March 18, 2025, 10:02:35 pm
content: Quote from: bdunham7 on March 18, 2025, 09:56:18 pmAgain, US usage: There are substations distributed around Chicago, with very high voltage 3-phase input, and medium-high-voltage (4 or 12 kV line-ground) three-phase outputs.In residential neighborhoods, single-phase 120-0-120 is sent to each house, from a single-phase transformer on a pole as discussed above, where the high-voltage primary connects from one HV phase to a grounded (neutral) wire.For commercial or industrial customers, high-voltage 3-phase goes through a local transformer for three-phase supply (e.g., 208 V line-line, with others as discussed in that ComEd document I posted above).

author: bdunham7
author_rank: Super Contributor
timestamp: March 18, 2025, 10:03:11 pm
content: Quote from: Monkeh on March 18, 2025, 09:59:15 pmI believe that conversation was in reference to my system with 2 HV wires, not the SWER (maybe) orAnalogKid'sskyline neutral.Yes, I got that part. My two HV lines would be 120 degrees apart if you measured each to ground as I believe our HV distribution system is a ground-referenced WYE arrangement. It has 4 HV wires coming from the substation anyway.

author: Xena E
author_rank: Frequent Contributor
timestamp: March 18, 2025, 10:05:05 pm
content: Quote from: themadhippy on March 18, 2025, 09:51:12 pmEDIT: refering to Analog kids transformer.Not that type of transformer, one HV connection, the other is (normally) fed from a grounded star point on a three phase distribution transformer.Phase to phase would have two HV insulated inputs, (EDIT: as per bdunham7 Transformer). And anyway across two phases is still a single phase input, (to be pedantic).X

author: Monkeh
author_rank: Super Contributor
timestamp: March 18, 2025, 10:05:28 pm
content: Quote from: bdunham7 on March 18, 2025, 10:03:11 pmMy bad, mixed up posts. It's getting messy in here.I can see an HV bushing on both sides on the crossarm on yours, but with the pole and transformer in the way I can't see if there's a second HV bush on the transformer or a second cutout. I take it you can see them yourself.

author: bdunham7
author_rank: Super Contributor
timestamp: March 18, 2025, 10:07:03 pm
content: Quote from: Monkeh on March 18, 2025, 09:53:19 pmThat wire doesn't look very taut, so I presumed it doesn't go far. But I suppose it could be a return all the way to a substation. Some utilities do mix HV and LV like that and even bond the two together at the transformer.

author: bdunham7
author_rank: Super Contributor
timestamp: March 18, 2025, 10:19:49 pm
content: Quote from: Monkeh on March 18, 2025, 10:05:28 pmYes, apparently the idea that a given word can have two different but perfectly reasonable meanings and that you might occasionally have to be more specific hasn't caught on.Yes, there are two separate HV bushings on the transformers and two separate fuse holders as well. Here's my neighbors transformer, perhaps you can spot the ground on this one too? It's a long shot, so not as sharp--sorry!

author: Monkeh
author_rank: Super Contributor
timestamp: March 18, 2025, 10:26:37 pm
content: Quote from: bdunham7 on March 18, 2025, 10:19:49 pmNot quite as clear, so no, I can't really see it for certain. I'm not even sure where each lead is going from the transformer (or to it, for that matter). I'm quite confident it will be there, though - the transformer case will be connected to it. The utility is not going to be happy relying on customer connections to control potentials on their equipment, even on the LV side.

author: TimFox
author_rank: Super Contributor
timestamp: March 18, 2025, 10:32:05 pm
content: Quote from: Monkeh on March 18, 2025, 10:26:37 pmUS: The pole transformer in my alley (Chicago) has a single high-voltage bushing with a single-pole disconnect switch on the primary side.The case, primary, and secondary center-tap are connected to a grounded wire far from the high-voltage primary wire, as in the photo posted by Analog Kid from his location.

author: themadhippy
author_rank: Super Contributor
timestamp: March 18, 2025, 10:35:13 pm
content: Quoteto avoid confusion i meant 2 live conductors 120oapart

author: TimFox
author_rank: Super Contributor
timestamp: March 18, 2025, 10:40:23 pm
content: Quote from: themadhippy on March 18, 2025, 10:35:13 pmTwo live conductors, 120oapart when measuring voltages to ground, can be connected to a single-phase load (transformer primary) to get a single-phase waveform across the load and across its secondary winding.

author: tom66
author_rank: Super Contributor
timestamp: March 18, 2025, 10:40:31 pm
content: Quote from: Xena E on March 18, 2025, 09:28:53 pmSeehttps://en.wikipedia.org/wiki/Single-wire_earth_returnOnly viable at lower power levels, up to around 500kVA or so.Another example is HVDC earth electrodes, if you look around the start of many HVDC lines you will see an earthing electrode that shoots off and enters an electrode site about 5-10km away from the converter. The purpose is to provide a return for parasitic currents, but it can also allow a bipolar link to work in monopolar mode during maintenance or a fault condition. It is placed far away from the station to avoid galvanic corrosion.

author: tooki
author_rank: Super Contributor
timestamp: March 19, 2025, 07:46:33 pm
content: Quote from: ejeffrey on March 17, 2025, 10:55:15 pmYep, I agree on all of that!

author: tooki
author_rank: Super Contributor
timestamp: March 19, 2025, 07:55:11 pm
content: Quote from: Analog Kid on March 17, 2025, 08:59:38 pmJust to expand on what Benta said: Yep, in Central Europe at least, three-phase service is completely normal. I live in a 1 bedroom apartment, but it has three-phase service, so the oven and cooktop both run on 3-phase power. The other circuits in the apartment are also divvied up among the phases.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 20, 2025, 06:44:41 am
content: Quote from: tooki on March 19, 2025, 07:55:11 pmYes. These cooktops basically have different burners wired in three groups, and the wiring brought to the junction box. It means, one can parallel them all up, and wire it to, say, 35A fuse on a single phase. Or, they can be wired to three separate 16A fuses and connected to different phases. The heaters still connect between phase and neutral, and there are no interactions between the heaters, so it being an actual 3-phase supply (with 120-deg phase shifts) is irrelevant: you could as well wire them to three separate 16A circuits branched off a bigger single-phase supply.So our European 3-phase home wiring really reduces to being just 3 different circuits, with fairly small main fuses (25A being typical here, 35A for those who want to pay premium). A single-phase 75A fused supply would have no downsides in 99% of homes (which do not utilize either the 3-phaseness of turning motors or running old-school rectifiers, or the inherent dual-voltage-ism of such system (230V & 400V depending on connection)). A single-phase supply, like in the UK, has then the benefit of not having to balance the loads over the phases. 25A is surprisingly little, and accidentally blowing a main fuse is not unheard at all. Oven, dishwasher and older-generation vacuum cleaner at the same time is enough to do that.But there are always people who feel like 3-phase power at home is somehowcooloradvancedthing to have, and the Americans and the British are somehow uncivilized due to their 1-phase house supplies. This I don't agree with. Their system is superior in most cases. Then again, I can buy a big old-school lathe with a large 3-phase motor and just plug it in without a VFD if I so wish. Maybe this "industry-at-home" is a BIG plus to a small minority.

author: Xena E
author_rank: Frequent Contributor
timestamp: March 20, 2025, 07:04:05 am
content: Three phase suplies in UK domestic dwellings are not completely unknown, though they are very rare, possibly because of the generally smaller size of British housing stock.Only larger houses and HMO usually have them although some are being installed for Fast/multiple EV charging reasons.X

author: Siwastaja
author_rank: Super Contributor
timestamp: March 20, 2025, 07:23:00 am
content: EVs are often designed so that maximum charging power can be had in either 1- or 3-phase configuration, simply because there is enough market for them in both systems. This would be a physical configuration option when selling the car to a specific market, not usually something end-user can easily configure.Can be achieved the same way as the stoves/ovens/cooktops I mentioned above: with 3 charger modules which do not depend on 120deg phase shift (but can accept it), wired in either parallel for 1-phase, or separately for 3-phase.There is an even simpler way found in some EVs: just design it with a single-phase charger, but make it accept and operate at wider voltage range up to 400V nominal. Then it can be wired between two phases of a true 3-phase system, and run at 400V instead of 230V, obviously getting more power for the same amps. And utilizing 2 of the 3 phases, much better than just 1, although not as good as balanced current over all phases. Now this does depend on the 120deg phase shift to get the better power per ampere, so counts as a modern example of true household 3-phase usage.And then again, my Nissan Leaf just has a single-phase charger of max. 30A. With 25A main fuses, I have no chance running it at full power. But at 25A I can charge with; I have moved almost every other load to other two phases. But oven is still in the same phase as the car, so I depend on the fuse protection mode of the energy management box; it reduces charging current to 8A when it detects sustained overcurrent close to blowing up a fuse. No need to think about stupid stuff like this in the UK or US.Heck, we already had fuse protection automation in 1980's sold for households!

author: Zero999
author_rank: Super Contributor
timestamp: March 20, 2025, 08:15:45 am
content: I thought most EVs accept up to 700V: 690V is a common industrial three phase voltage.I don't see why anyone would want a three phase domestic supply in the UK. If it's for a home machine shop, then most smaller AC motors can run off a three phase 230V supply, generated from 230V single phase with an inverter, which is much cheaper than paying for a three phase service.

author: tom66
author_rank: Super Contributor
timestamp: March 20, 2025, 08:32:22 am
content: Most EVs only accept 100-250V ac across 1-3 phases. My ID.3 has 3 x 3.6kW modules on board. For single phase charging it uses two of these in parallel, for three-phase charging it uses all modules, one for each phase. The speed increase on 11kW charging is not really that important for overnight usage but it can be good if stopped in a parking garage for a few hours for instance.For DC charging, the voltage has to match the battery pack, as the contactors connect it directly to the charge port. The BMS will then ask the external DC charger to provide 'X' amps or 'Y' volts within a tight tolerance. EV batteries range from 250V nominal (Dacia Spring) to 350-450V nominal (ID.3, Tesla, most other EVs) to 800-900V nominal (some BYD cars, Taycan, Ioniq5, etc). In theory the higher voltage allows for faster charging with smaller external conductors; but it doesn't really benefit the car that much unless it really needs to push for performance. The GM pickup truck platform can put the battery pack into an 800V configuration for charging, but switches back to 400V for driving.I'm not aware of any EV that can accept over 250V ac on the input, possibly some electric buses can do it, but it wouldn't be part of the Type 2 standard as that calls for max. 250V ac.

author: themadhippy
author_rank: Super Contributor
timestamp: March 24, 2025, 12:27:27 pm
content: Quotewere? in the uk 415v is standard and you might find 11kv on large sites but 690v?

author: Siwastaja
author_rank: Super Contributor
timestamp: March 24, 2025, 01:53:26 pm
content: Quote from: themadhippy on March 24, 2025, 12:27:27 pmI would be also interested in hearing how common it really is. "690V is very popular voltage in industrial settings" is some kind of mantra I have heard numerous times, but it seems nearly ungooglable - spending 5 minutes only results in meta discussions (the mantra itself, or discussions that question the validity of the mantra).I'm sure it is used somewhere, like any other voltage, but howcommonis it? In which countries it is popular, and in what types of industries?I can see it being useful to reduce copper in some certain motor size/power level, maybe a few hundred kW or so, before going to truly high-voltage motors. And in an industrial setting you would have your own transformer from HV grid (say, e.g. 11kV) anyway, so could use any voltage you choose. Motors can be wound for any custom voltage, but of course it makes sense to have "popular standard options" available. But how popular is exactly this 690V (referring to 400V line-to-neutral, I guess)?Or is the image of popularity exaggerated by the existence of AC induction motors marked as 400/690V? (Random example:https://adajusa.fr/en/three-phase-electric-motors-3000-rpm-flange-b3-foot-car-aluminum-ie1-ie2-ie3/977-three-phase-motor-55kw-75hp-400-690v-3000-rpm-ie1-flange-b3-foot-8435532809777.html) If that, then remember these motors would be most likely used wired in delta in 400/230VAC system, and only rarely wired in wye on a 690/400V system.

author: Xena E
author_rank: Frequent Contributor
timestamp: March 24, 2025, 04:34:24 pm
content: The dual voltage motors ≈690/400 are traditionally used on 400 Volt supplies in lighter plant, 10's to 100's of kW with star delta starting to reduce maximum starting loads on soft supplies.690~ 3ø was a thing but long obsolete for general industry... perhaps some Specialist application now only?X

author: Zero999
author_rank: Super Contributor
timestamp: March 24, 2025, 09:44:27 pm
content: I just thought 690VAC was common, due to the fact motors and transformers with 690V primary windings are common. I haven't seen it in the UK, but assumed it was more popular in Europe or the US.https://www.larsonelectronics.com/product/281032/1-kva-control-transformer-690v-input-voltage-120-240v-output-voltage?srsltid=AfmBOop1ZdTI7_U0KGBkMJ4CyCPiQoV7YZZxxWkjoxYhi2yAKRl1otkOhttps://www.radwell.eu/uk/buy/moeller-electric-sti1-6-690-230/23307478.html?source=GoogleShopping&IgnoreRedirect=true&ItemSingleId=119952195&srsltid=AfmBOoriRQgvswvIazgeVoPqadBKmNzER-3RUe0fjjRqpIGoST_XDL6ODpMMennekes also make 690V connectors.https://www.mennekes.co.uk/products/industrial-plugs-and-sockets/product-specific/extended-versions/600-v-690-v/I'm surprised no one here has encountered 690VAC in real life.

author: bdunham7
author_rank: Super Contributor
timestamp: March 24, 2025, 11:50:42 pm
content: Quote from: Zero999 on March 24, 2025, 09:44:27 pmI think it is just the updated version of 380/660. But the only place I've seen either of them was in imported made-in-Italy (or other western European country) equipment that had to be adapted to a US installation. And IIRC they were all connected at 380V, never actually seen 660 either, although I didn't work with such stuff very much. Many systems here will stick with 480V until the power requirements are so big they just go to a >1000V medium voltage installation. However, there are 575 and 990V systems as well for certain applications where you have long runs but for some reason they just don't want to go up to medium voltage. Mines, maybe? So maybe the new 690V is only found in select situations.

author: TimFox
author_rank: Super Contributor
timestamp: March 24, 2025, 11:58:30 pm
content: Quote from: bdunham7 on March 24, 2025, 11:50:42 pmAgain, from the Commonwealth Edison document I posted above (and elsewhere), the three-phase choices available in Chicago are120/240 (the 240 V line-line leg of one delta winding is center-tapped)120/208 (common for commercial customers)277/480 (higher power commercial/industrial customers)480 ungrounded (delta secondary)

author: bdunham7
author_rank: Super Contributor
timestamp: March 25, 2025, 12:17:39 am
content: Quote from: TimFox on March 24, 2025, 11:58:30 pmOur installation had the first type, but 380V or other setups would be done with customer equipment (transformers). We had 240V because at least some of the imported equipment could be configured to use 240V but not 208. And somehow nobody seemed to worry about 50 to 60Hz. But I'm sure those voltages you list are just the common options you can get with a standard form, there have to be options for medium voltage, etc.

author: TimFox
author_rank: Super Contributor
timestamp: March 25, 2025, 02:04:29 am
content: Those are the relevant standard ordering options. When configuring our large x-ray systems for customers, we tried to stay with that list.ComEd can supply others after their engineering department consults with the customer.(Presumably, standard secondary connection options from transformer manufacturers are quicker and cheaper to supply.)

author: Xena E
author_rank: Frequent Contributor
timestamp: March 25, 2025, 02:16:20 am
content: Quote from: bdunham7 on March 25, 2025, 12:17:39 am50Hz eqipment on 60 isn't usually a problem, however the other way can run into saturation problems with marginally specified line frequency transformers.

author: bdunham7
author_rank: Super Contributor
timestamp: March 25, 2025, 03:35:30 am
content: Quote from: Xena E on March 25, 2025, 02:16:20 amI know, but one of the applications was a motor driving a very large grinding wheel. Not something you'd want to overspeed by too much even if it was mostly enclosed in a 1/2" welded steel cage. I don't recall how that was dealt with, but only one wheel was ever blown up and that was due to a different error.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 25, 2025, 08:31:43 am
content: Quote from: Zero999 on March 24, 2025, 09:44:27 pmAs I said, that could contribute to the idea of 690VAC supply being common. Motors marked nominally as 400/690 are indeed very common, but what that really means is that you can configure them for use in 400VAC(phase-phase) or 690VAC(phase-phase) systems. From the existence of these motors you can't know in what proportion they are installed in 400V or 690V systems.When little starting torque is required, these motors can be started in wye (in "690V mode") in a 400V system, i.e. undervoltaged, to reduce inrush current. So the wiring configurability is a useful feature anyway, and it comes for nearly free, just with access to the junction box where those connections would need to be done anyway.So this popularity of 690V might be a similar misconception like the "US has 115VAC voltage" based on seeing this number commonly on labeling.

author: Zero999
author_rank: Super Contributor
timestamp: March 25, 2025, 10:40:26 am
content: Quote from: Siwastaja on March 25, 2025, 08:31:43 amBut what about the transformers and connectors? Click on the links I posted above. They're only rated for 690V and there appear to be easy to find.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 25, 2025, 12:18:59 pm
content: Quote from: Zero999 on March 25, 2025, 10:40:26 amWell yeah, those would be used in a true 690VAC system, sure. Specifically the plug is a variation of the usual CEE plug with different "key" position to prevent insertion into wrong-voltage socket. Seehttps://www.klibo.com/cee-connectors-code-colours- the usual CEE plug we have here is red, with 6 o'clock key, rated to 400V systems, and those 690VAC plugs would be black, with 5 o'clock key.So clearly there is existing market for them. How popular and where, I have no idea.

author: floobydust
author_rank: Super Contributor
timestamp: March 26, 2025, 02:25:19 am
content: I use this old table to better understand the common five types of mains power systems, if you are doing (global) product design.Once I had a product with 690V requirement which can get ugly with the required creepage/clearances in the 1,000V club.