240V 3 phase vs 400V 3 phase? - Page 1
Forum section: electronics / general

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: June 14, 2024, 10:51:17 pm
content: I thought 400V 3 phase had a line voltage of around 240V from neutral to each live phase.But I came across a "240V 3 phase"... It would have a line voltage of around 138V, why would a bizarre voltage standard like that exist?Or is the listed voltage actually the line voltage and not the phase sum potential?

author: Circlotron
author_rank: Super Contributor
timestamp: June 14, 2024, 11:10:53 pm
content: IMHO the degrees of phase difference are measured with respect to neutral. So 240V 3 phase would be talking about voltages WRT neutral.

author: Someone
author_rank: Super Contributor
timestamp: June 14, 2024, 11:17:04 pm
content: Leave your isolationist bubble and see the world:https://en.wikipedia.org/wiki/Mains_electricity_by_country#Table_of_mains_voltages,_frequencies,_and_plugs

author: Benta
author_rank: Super Contributor
timestamp: June 14, 2024, 11:36:13 pm
content: Quote from: ELS122 on June 14, 2024, 10:51:17 pmIt's actually 230 V phase-neutral.

author: bdunham7
author_rank: Super Contributor
timestamp: June 14, 2024, 11:51:31 pm
content: Quote from: ELS122 on June 14, 2024, 10:51:17 pmIn the US, 240V 3-phase installations typically are set up so that there is 240VAC between the phases but two of the phases are 120VAC to neutral and one of them is 208VAC. This gives you 240VAC three-phase and 240VAC split-phase from the same transformer(s).

author: Benta
author_rank: Super Contributor
timestamp: June 15, 2024, 12:00:21 am
content: Interesting.I know next to nothing about US installations, but it makes sense.Thanks.

author: Monkeh
author_rank: Super Contributor
timestamp: June 15, 2024, 12:03:05 am
content: Quote from: bdunham7 on June 14, 2024, 11:51:31 pmTo go with 120/208V 3-phase, and 277/480V 3-phase, because why not do it four different ways?

author: soldar
author_rank: Super Contributor
timestamp: June 15, 2024, 01:31:10 pm
content: Quote from: bdunham7 on June 14, 2024, 11:51:31 pmAn interesting property of delta configuration is that even ifonewinding is interrupted or disconnected all the outputs continue to supply the same output voltage. This does not happen in a star configuration where if a winding is interrupted or disconnected its output goes dead.

author: TimFox
author_rank: Super Contributor
timestamp: June 15, 2024, 04:27:57 pm
content: For standard US utility voltages:The attached pdf is an application form to the Chicago electrical utility, which lists the standard options for single and three-phase supply voltages.Commonwealth Edison Co. supplies a transformer at the commercial customer site to supply the selected voltage to the customer load.Although the connections shown by B Dunham exist on this form, a more common US connection is 208 V line-to-line, or 120 V line-to-neutral.

author: Zero999
author_rank: Super Contributor
timestamp: June 15, 2024, 05:59:41 pm
content: 240V three phase does exist. Its common in some parts of the world.A motor drive inverter run off 230V, will also give 230V three phase out. A lot of small AC motors are wound for 230V, so they can be connected in star to 400V three phase, or delta to a 230V inverter.

author: soldar
author_rank: Super Contributor
timestamp: June 15, 2024, 06:39:01 pm
content: Quote from: Zero999 on June 15, 2024, 05:59:41 pmI am not sure what you are trying to mean or imply with this or maybe I am totally misunderstanding you but I believe 230V (nominal, 240V legacy in some places) is the most common supply in Europe. Maybe single phase for residential and three phase for higher power needs.

author: Benta
author_rank: Super Contributor
timestamp: June 15, 2024, 07:23:39 pm
content: Well, there's a world outside Europe, you know...

author: soldar
author_rank: Super Contributor
timestamp: June 15, 2024, 07:41:39 pm
content: Quote from: Benta on June 15, 2024, 07:23:39 pmThe way he says it it sounds to me like he makes it sound like it is uncommon so I think I am probably missing or misunderstanding something.I believe it is probably the most common system in Europe so that by itself would make it not uncommon without regard to the rest of the world.It is also used in China where I have been many times but even if it was only common in Europe it would not be uncommon.I am trying to understand what he said. Why are we picking nits here?

author: IanB
author_rank: Super Contributor
timestamp: June 15, 2024, 08:56:20 pm
content: Quote from: soldar on June 15, 2024, 06:39:01 pmQuote from: soldar on June 15, 2024, 07:41:39 pmIn the UK the domestic supply is 240 V AC, commonly provided from transformers that deliver 415 V phase to phase, 240 V phase to neutral. This allows bigger light industrial loads such as three phase motors in farms or factories to run off a 415 V three phase supply.When someone talks about 230 V three phase, they likely mean 230 V phase to phase, rather than 400 V phase to phase.

author: soldar
author_rank: Super Contributor
timestamp: June 15, 2024, 09:31:14 pm
content: Quote from: IanB on June 15, 2024, 08:56:20 pmI believe the domestic supply in the UK used to be 240V but now is 230 V RMS +10% -6% and has been so for quite a few many years now when it was changed also in the continent from 220 to 230 so now it is 230 V all aroundOld people in Spain still say "220" but that is just a manner of speaking and it is no longer 220 but 230. In the UK as well.So it seems we have the same delivery system. 230V phase voltage. 230 V between phase and neutral. With star configuration so neutral.When someone says "230 V" they most often mean phase voltage and if they mean anything else they are leading to confusion. If it needs clarification they might say "230 phase voltage" or, in industrial settings with 400V motors they might say "400 V line voltage" or "230/400" but this never comes up in residential settings.At any rate, I confirm residential supply in UK is exactly the same as it is in Spain: 230 V phase and neutral.Exceptionally in Spain there might still be rural areas with decades-old transformers which might supply 130/230 but they disappear as they are being replaced.

author: Monkeh
author_rank: Super Contributor
timestamp: June 15, 2024, 09:32:58 pm
content: Quote from: soldar on June 15, 2024, 09:31:14 pmMy 244.6V with a minimum seen over the last 12 months of 234.2V (and a max of 255.9!) says 230V is a manner of speaking.When you talk about voltage in the context of 3-phase use, you're talking about phase to phase voltage (U), when dealing with single phase use, phase to earth (neutral) (U₀).

author: Benta
author_rank: Super Contributor
timestamp: June 15, 2024, 09:52:12 pm
content: Quote from: soldar on June 15, 2024, 09:31:14 pmPerhaps in Spain.North of the Alps, 3-phase service is standard in private housing (L1-L2-L3-N-PE).230 V for normal outlets, yes, but 400 V for stove/oven and heating etc. Also for the hobby workshop in the basement. Or heat pump installations. Or the EV charger.

author: Benta
author_rank: Super Contributor
timestamp: June 15, 2024, 09:57:31 pm
content: Quote from: Monkeh on June 15, 2024, 09:32:58 pmPhase to Neutral, please. Earth (or rather Protective Earth or PE) should not carry any current.You need to complain about your voltage. It's way out of tolerance, and the local transformer needs to be retapped.

author: themadhippy
author_rank: Super Contributor
timestamp: June 15, 2024, 10:18:57 pm
content: QuoteJust to confuse things theirs the antiquated/confusing 415V single phase.In reality its actually 2 phases.no neutrals involved and most comonly found around welding equipment

author: Monkeh
author_rank: Super Contributor
timestamp: June 15, 2024, 11:11:53 pm
content: Quote from: Benta on June 15, 2024, 09:57:31 pmThe definition of U₀ is phase to earth. Neutral is nominally at earth potential. I'm quite aware of the difference between the various conductors - and the fact that there is no difference between the two prior to entry to my house.My voltage is not out of tolerance, excepting a very brief excursion. Nothing needs retapping.Quote from: themadhippy on June 15, 2024, 10:18:57 pmIt is a single phase load still, it just happens to be provided by two phases of a 3-phase supply. Single phase doesn't have to involve a neutral at any point. Would rather like to have 3ph available for my little welder, it's a bit of a fuse melter.

author: Benta
author_rank: Super Contributor
timestamp: June 15, 2024, 11:19:59 pm
content: Both 244.6 V and 255.9 V are out of spec.So why post "brief excursions" so sensational?

author: Monkeh
author_rank: Super Contributor
timestamp: June 15, 2024, 11:24:28 pm
content: Quote from: Benta on June 15, 2024, 11:19:59 pmPrecisely how is 244.6V out of spec for a supply installed as 240V±6% and currently specified as 230V -6%, +10%? The maximum value is a peak value from one second of data over the last 12 months. The average of that minute (the limit of my resolution for data that old) was 245.4V. Absolutely fine. Perhaps I should store 10s averages for peaks in order to prevent unnatural twisting of foreign underwear.

author: IanB
author_rank: Super Contributor
timestamp: June 15, 2024, 11:32:40 pm
content: Quote from: Benta on June 15, 2024, 11:19:59 pmThe supply voltage in the UK is regulated to 240 V, but it can vary up and down a bit depending on the location. In towns and cities the supply is likely very stiff due to massive substation transformers and heavy gauge wiring, and will remain very close to 240 V. In more rural settings where there might be smaller pole mounted transformers and longer runs involved then you can expect more variation.That said, 255 V would not be very comfortable for 240 V incandescent bulbs. On the other hand, all recent incandescent bulbs I have seen were so called "Long Life" bulbs rated at 250 V. So 255 V would not stress them too much.

author: soldar
author_rank: Super Contributor
timestamp: June 15, 2024, 11:33:58 pm
content: Quote from: Monkeh on June 15, 2024, 09:32:58 pmIn the UK, the declared voltage and tolerance for an electricity supply is 230 volts -6%, +10%. This gives an allowed voltage range of 216.2 volts to 253.0 volts. So it is within the allowed range.Anyway, I feel we're nitpicking and arguing over semantics and nothing is to be gained by this.I just wanted to confirm service in the UK is the same as in Spain with the proviso that some older equipment is still supplying the older voltages but they are within the 230 V nominal accepted tolerance.Maybe with Brexit the UK will decide to go back to 240?

author: Monkeh
author_rank: Super Contributor
timestamp: June 15, 2024, 11:35:11 pm
content: Quote from: soldar on June 15, 2024, 11:33:58 pmJust the sort of pointless gesture they like to make, yes.

author: IanB
author_rank: Super Contributor
timestamp: June 15, 2024, 11:42:56 pm
content: Quote from: soldar on June 15, 2024, 11:33:58 pmIn the UK the supply voltage has always been regulated to 240 V, never moved from 240 V, and will likely remain at 240 V.QuoteThis is not accurate. The declared voltage is 240 V. This happens to be within the harmonized range of voltages across Europe, and should be acceptable for any appliance that conforms to European standards.The reason for this is that the entire grid and distribution infrastructure is designed around 240 V as the delivered voltage. There is no way they are ever going to change the installed infrastructure with all the costs and screw-ups that would result from that. (To give you an example, the MV distribution networks are regulated at 11 kV and other voltages like 33 kV, 66 kV and 132 kV. If you start trying to change 11 kV to 10.5 kV it would cause confusion and faults all along the way.)

author: themadhippy
author_rank: Super Contributor
timestamp: June 15, 2024, 11:47:25 pm
content: QuoteNo its not,and hasnt been since 1994.

author: Monkeh
author_rank: Super Contributor
timestamp: June 15, 2024, 11:53:28 pm
content: Quote from: IanB on June 15, 2024, 11:42:56 pmThe fact that existing supplies didn't require modification to fit in the new specified range does not change that the legal standard has been 230V for quite some time. There's no need to conflate LV supply with HV distribution, and absolutely zero issue in leaving an established 240V supply alone while installing supplies which are not merely nominally 230V, but actually are 230V.If you wish to continue down this path of 'always' and 'never', may I suggest you (and Benta) read the relevant legislation:https://www.legislation.gov.uk/uksi/2002/2665/regulation/27For bonus points:https://www.legislation.gov.uk/uksi/1994/3021/made

author: soldar
author_rank: Super Contributor
timestamp: June 16, 2024, 12:07:27 am
content: https://www.legislation.gov.uk/uksi/2002/2665Statutory Instruments2002 No. 2665ELECTRICITYThe Electricity Safety, Quality and Continuity Regulations 2002Coming into force 31st January 2003The Secretary of State, in exercise of the powers conferred on her by sections 29, 30(3) and 60 of the Electricity Act 1989M1, hereby makes the following Regulations:—Declaration of phases, frequency and voltage at supply terminals27.—(1) Before commencing a supply to a consumer’s installation, or when the existing supply characteristics have been modified, the supplier shall ascertain from the distributor and then declare to the consumer—(a)the number of phases;(b)the frequency; and(c)the voltage,at which it is proposed to supply electricity and the extent of the permitted variations thereto.(2) Unless otherwise agreed in writing between the distributor, the supplier and the consumer (and if necessary between the distributor and any other distributor likely to be affected) the frequency declared pursuant to paragraph (1)shall be 50 hertz and the voltage declared in respect of a low voltage supply shall be 230 volts between the phase and neutral conductors at the supply terminals.(3) For the purposes of this regulation, unless otherwise agreed in writing by those persons specified in paragraph (2), the permitted variations are—(a)a variation not exceeding 1 per cent above or below the declared frequency;(b)in the case of a low voltage supply, a variation not exceeding 10 per cent above or 6 per cent below the declared voltage at the declared frequency;

author: soldar
author_rank: Super Contributor
timestamp: June 16, 2024, 12:08:36 am
content: Quote from: Monkeh on June 15, 2024, 11:53:28 pmHa ha, simulpost!

author: soldar
author_rank: Super Contributor
timestamp: June 16, 2024, 12:12:51 am
content: Quote from: themadhippy on June 15, 2024, 11:47:25 pmSame in Spain and yet a lot of people still say "220" out of habit ( I sometimes do it). Those of us who know what we mean know what we are talking about but you still come across someone who's been living in a cave and didn't hear the news and he'll argue "how can you say its not 220 when everybody says 220".

author: IanB
author_rank: Super Contributor
timestamp: June 16, 2024, 12:14:10 am
content: Quote from: themadhippy on June 15, 2024, 11:47:25 pmQuote from: Monkeh on June 15, 2024, 11:53:28 pmThanks for the information. I consider myself educated.However, on the practical side, no UK resident on this forum has ever posted an actual supply voltage other than 240 V. So I suspect there are practical reasons to keep it that way, even if the regulations say that a lower voltage is permissible.

author: vk6zgo
author_rank: Super Contributor
timestamp: June 16, 2024, 01:11:31 am
content: Quote from: IanB on June 15, 2024, 11:32:40 pmFor many years, for complicated historical reasons, the standard single phase mains voltage in Western Australia was 250v, whilst in the rest of Australia, it was 240v.Incandescent 240v lamps made in Australia had very long lives both on their designed voltage & at 250v.The "new breed" of management came along & decided it was much cheaper to import 240v lamps, & get rid of those pesky workers.The imported lamps were barely adequate on 240v, but on 250v, were significantly reduced in life."All good" quoth the importers, we will import 260v lamps & sell them at ---ahem, a small premium, win-win for everybody!"The "260v" lamps were a little better, but not much, so soon,"a great bewailing arose in the land".According to the media & a "tame" EE, it was all the fault of WA's iniquitous 250v system!!After much agitation, the mains voltage was reduced to a nominal 240v at great cost, but the imported lamps were still crap.Again, "a great bewailing arose in the land".Forgetting that locally made lamps lasted much longer, it was all the fault of incandescent lamps, so we must all install compact fluorescents!

author: jmelson
author_rank: Super Contributor
timestamp: June 16, 2024, 01:58:22 am
content: Bdunham7's drawing is a center-grounded delta system. There is also corner-grounded delta, which was popular a long time ago and two pole breakers could be used, and you got two 240V feeds that had one wire grounded. These could be fed with just two single-phase transformers, that was called open delta.In the US, a very common system is a 120/208 V Wye system, often found in office buildings, stores, commercial parks, etc. These have a neutral with 3 120 V phases that are 120 degrees apart in phase angle. You get 209 V RMS between any hot wire. This allows lots of 120 V outlets, and 3 phase power for air conditioners and other larger loads.A 240 V line-line delta system would give 138 V line-neutral, but that is generally not done. A 480 V (L-L) system can give 277 V line-neutral, this is often seen in commercial building lighting systems.Jon