240V 3 phase vs 400V 3 phase?

[IanB]

Maybe with Brexit the UK will decide to go back to 240?

In the UK the supply voltage has always been regulated to 240 V, never moved from 240 V, and will likely remain at 240 V.

In 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.

This 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.)

[themadhippy]

This is not accurate. The declared voltage is 240 V.

No its not,and hasnt been since 1994.

[Monkeh]

Maybe with Brexit the UK will decide to go back to 240?

In the UK the supply voltage has always been regulated to 240 V, never moved from 240 V, and will likely remain at 240 V.

The 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/27

For bonus points: https://www.legislation.gov.uk/uksi/1994/3021/made

[soldar]

https://www.legislation.gov.uk/uksi/2002/2665

Statutory Instruments
2002 No. 2665

ELECTRICITY
The Electricity Safety, Quality and Continuity Regulations 2002

Coming into force 31st January 2003

The 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 terminals

27.—(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;

[soldar]

The 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.

Ha ha, simulpost!

[soldar]

This is not accurate. The declared voltage is 240 V.

No its not,and hasnt been since 1994.

Same 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".

[IanB]

No its not,and hasnt been since 1994.

The 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/27

For bonus points: https://www.legislation.gov.uk/uksi/1994/3021/made

Thanks 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.

[vk6zgo]

Both 244.6 V and 255.9 V are out of spec.
So why post "brief excursions" so sensational?
 

The 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.

For 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!

[jmelson]

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