240V 3 phase vs 400V 3 phase?

[ELS122]

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?

[Circlotron]

IMHO the degrees of phase difference are measured with respect to neutral. So 240V 3 phase would be talking about voltages WRT neutral.

[Someone]

Leave your isolationist bubble and see the world:
https://en.wikipedia.org/wiki/Mains_electricity_by_country#Table_of_mains_voltages,_frequencies,_and_plugs

[Benta]

I thought 400V 3 phase had a line voltage of around 240V from neutral to each live phase.

It's actually 230 V phase-neutral.

[bdunham7]

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?

In 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).

[Benta]

Interesting.
I know next to nothing about US installations, but it makes sense.
Thanks.

[Monkeh]

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?

In 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).

To go with 120/208V 3-phase, and 277/480V 3-phase, because why not do it four different ways?

[soldar]

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?

In 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).

An interesting property of delta configuration is that even if one winding 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.

[TimFox]

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.

[Zero999]

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.

[soldar]

240V three phase does exist. Its common in some parts of the world.

I 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.

[Benta]

Well, there's a world outside Europe, you know...

[soldar]

Well, there's a world outside Europe, you know...

The 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? 

[IanB]

240V three phase does exist. Its common in some parts of the world.

I 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.

The 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.

In 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.

[soldar]

In 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.

I 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 around

Old 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.

[Monkeh]

In 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.

I 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 around

Old 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.

My 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).

[Benta]

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.

Perhaps 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.

[Benta]

My 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).

Phase 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.

[themadhippy]

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).

Just 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

[Monkeh]

My 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).

Phase 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.

The 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.

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).

Just to confuse things theirs the  antiquated/confusing  415V single phase.
https://d1hu4133i4rt3z.cloudfront.net/attachments/693/693192-4ae526381bed2011eaeeb4e3150e1f93.jpg

In reality its actually 2 phases.no neutrals involved and most comonly found around welding equipment

It 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.

[Benta]

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

[Monkeh]

Both 244.6 V and 255.9 V are out of spec.
So why post "brief excursions" like you do?
 

Precisely 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.

[IanB]

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.

[soldar]

My 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.

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. 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?

[Monkeh]

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

Just the sort of pointless gesture they like to make, yes.