When does 3 phase supply become 230V in domestic consumer unit?

[HappyHippyDad]

I went along this morning to quote for an EVCP install.

I thought it was a domestic house but it was a B@B. It has a 3 phase supply. I always pass on commercial or 3 phase as it is outside of my remit. However, I am toying with the idea of fitting this EVCP IF I can fit it from a single phase supply.

I am unsure where to take power from. Usually I would either split the meter tails or use a spare way in the CU. I could use a spare way in an existing CU at the property but it may be better to take power from somewhere in the meter room. However, I am unsure where it is 230V and where it is 400V.

You can see in the pictures there is a 3 phase cut out, to meter, to isolator, to Henly blocks, to separate meters, then to switched fuses, then off to each area. Where would I split the tails? Where is it 230V? It must be 230V coming from the switched fuse (B) going to the single phase consumer unit in the annex (because it's a single phase board). But, another switched fuse (A) goes off to the main house which has a 3 phase board. There is no difference with regards the cables leading up to either of these switched fuses, (i.e they both have a separate meter and a single Line and neutral going to them), so how is one of them 230V and the other 400v?

 

[telectrix]

all the sub meters are single phase, ( 2 cables in and 2 cables out.) as are the isolators below them. FS 8 and 9 don't appear to have any load on them.

 

[Mikegh]

Im not sure where the main protection is in the UK

With a EVCP you'd usually branch off after main isolation and main protective devices

You'd need to be checking the suitability of the load and available capacity on each phase

Ideally loads should be 3P for balance

 

[plugsandsparks]

Well, its a lovely layout, if you can get your EVCP supply from that room, you are almost home free...
230V is from any of the phase supplies (you have 3) and Neutral (you have one).
You have two FSu not used Cider Barn and someones Shed. If you can negotiate one of those it will solve any space issues. They are both 230V supplies so all you need is a 32A fuse,

 

[plugsandsparks]

Oops just noticed those two FSUs are after the RCD, so you will need to move the meter tails over to the connection blocks prior to the RCD. You may need a larger block to accommodate the extra tails

 

[plugsandsparks]

Double Oops looks like the connection blocks to the left of the RCD have a spare way.

Anyway, it does not get easier, crack on

 

[Julie.]

Why not just fit a three phase EVCP?

if you have 3ph available it means you could charge faster if the vehicles have the capacity, if not the EVCP/vehicle charger just uses one of the phases.

 

[HappyHippyDad]

all the sub meters are single phase, ( 2 cables in and 2 cables out.) as are the isolators below them. FS 8 and 9 don't appear to have any load on them.

Why not just fit a three phase EVCP?

if you have 3ph available it means you could charge faster if the vehicles have the capacity, if not the EVCP/vehicle charger just uses one of the phases.

But at which exact point does it change from 400v to 230V? How can it decrease in voltage without a transformer? I think this last question is also the answer to your question Julie ?

ps.. I'm assuming the 3 phase CU in the picture below is fed from the switched fuse (A) (single phase). How can it be a 3 phase board? Is it a 3 phase board? It looks like it only has a 2 pole isolation switch. I'm guessing it's actually single phase?

 

[Mikegh]

There's no voltage transformation

There's a line voltage and a phase voltage on 3P supplies

 

[Mikegh]

But at which exact point does it change from 400v to 230V? How can it decrease in voltage without a transformer? I think this last question is also the answer to your question Julie ?

ps.. I'm assuming the 3 phase CU in the picture below is fed from the switched fuse (A) (single phase). How can it be a 3 phase board? Is it a 3 phase board? It looks like it only has a 2 pole isolation switch. I'm guessing it's actually single phase?

View attachment 90321

Ya that's a SP board

Ideally with 3P you distribute in 3P to sub-boards for better balance and connect 3P loads where possible

Dividing the 3P supply into 3 single phase sub-mains is a crude method used for mostly domestic I would say

 

[loz2754]

Really with 3P you distribute in 3P to sub-boards for better balance and connect 3P loads where possible

Dividing the 3P supply into 3 single phase sub-mains is a crude method used for mostly domestic I would say

I guess they've done it this way to facilitate metering of each separate switch fuse.

 

[ipf]

But at which exact point does it change from 400v to 230V? How can it decrease in voltage without a transformer? I think this last question is also the answer to your question Julie ?

ps.. I'm assuming the 3 phase CU in the picture below is fed from the switched fuse (A) (single phase). How can it be a 3 phase board? Is it a 3 phase board? It looks like it only has a 2 pole isolation switch. I'm guessing it's actually single phase?

View attachment 90321

The board's not 3 phase, although it is designed for it. They do Kits for altering 3 phase board to single. It looks like a conversion.

Found a replacement 24w 3phase MEM in a school once, converted to single phase. There was actually a 400v supply at installation origin...seems like they didn't fancy running a 3phase supply, or whatever. The main incomer was melting tar on one phase.

 

[loz2754]

I guess they've done it this way to facilitate metering of each separate switch fuse.

Which raises an important question - which metered supply is the EVCP to be connected to?

 

[ipf]

Ya that's a SP board

Ideally with 3P you distribute in 3P to sub-boards for better balance and connect 3P loads where possible

Dividing the 3P supply into 3 single phase sub-mains is a crude method used for mostly domestic I would say

What do you mean? What's crude about it? You've got to split somewhere.
All single phase supplies originate from 3 phase.
How do you connect a 3ph load when only single is required.
Any block of flats, for instance, is fed similarly, with single phase to each property. Balancing phases is a job for the designer.
Obviously, millions of single phase circuits come from 3 phase boards.
What's wrong with a single phase board in a factory, say, where required?

 

[ipf]

I went along this morning to quote for an EVCP install.

I thought it was a domestic house but it was a B@B. It has a 3 phase supply. I always pass on commercial or 3 phase as it is outside of my remit. However, I am toying with the idea of fitting this EVCP IF I can fit it from a single phase supply.

I am unsure where to take power from. Usually I would either split the meter tails or use a spare way in the CU. I could use a spare way in an existing CU at the property but it may be better to take power from somewhere in the meter room. However, I am unsure where it is 230V and where it is 400V.

You can see in the pictures there is a 3 phase cut out, to meter, to isolator, to Henly blocks, to separate meters, then to switched fuses, then off to each area. Where would I split the tails? Where is it 230V? It must be 230V coming from the switched fuse (B) going to the single phase consumer unit in the annex (because it's a single phase board). But, another switched fuse (A) goes off to the main house which has a 3 phase board. There is no difference with regards the cables leading up to either of these switched fuses, (i.e they both have a separate meter and a single Line and neutral going to them), so how is one of them 230V and the other 400v?

View attachment 90311

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View attachment 90315

Is the job for the property owner? If so, you could always install a small single phase CU as a 'Landlord's supply'. Doesn't seem to be one, from the photo.

 

[loz2754]

To original poster-

Three phase is by no means beyond you.
Maybe you should read up on it a little so you can get an understanding of the differences.

But simply put, UK power generation and transmission is generally all 3 phase.
The nominal voltage U, is the voltage between one phase and one of the other 2 phases. This is 400 volts.
The nominal voltage U0, is the voltage between any one phase and earth. This is the line voltage, and is 230 volts.
As the neutral is connected to earth, the line to neutral voltage is also 230 volts.

In a 3 phase distribution board, there can be both 3 phase circuits and single phase circuits.
A 3 phase circuit will have a 3 pole circuit breaker, whereas a single phase circuit will generally have a single pole circuit breaker.
The single phase circuit may be connected to either of the 3 busbars within the DB.

In a row of houses in a street, fed by 3 phase underground cables, usually each house will be fed from 1 of the phase conductors and the neutral conductor. So house 1 from phase 1, house 2 from phase 2, house 3 from phase 3, house 4 from phase 1 etc. Thus the load is roughly balanced across all 3 phases.

I hope this helps, and that I'm not trying to teach you how to suck eggs....

 

[Strima]

Any spare ways on the MG board, just above the intake? If possible I would seriously consider fitting a 3ph EVCP if the facility is there for future expansion and rapid charging.

Three phase is easy enough to work on you just need to remember the full safe isolation process which has a few more steps than single phase.

3 Phase installations test to confirm that there is no voltage between:

• L1 and L2
• L1 and L3
• L1 and Neutral
• L1 and Earth
• L2 and L3
• L2 and Neutral
• L2 and Earth
• L3 and Neutral
• L3 and Earth
• Neutral and Earth

When energised you should see voltage between earth and neutral:

L1 - 230V
L2 - 230V
L3 - 230V

Line to line you should see:

L1 - L2 - 400V
L1 - L3 - 400V
L2 - L3 - 400V

To get single phase from three phase all you do is connect to one of the phases and use the neutral.

 

[loz2754]

Any spare ways on the MG board, just above the intake? If possible I would seriously consider fitting a 3ph EVCP if the facility is there for future expansion and rapid charging.

Three phase is easy enough to work on you just need to remember the full safe isolation process which has a few more steps than single phase.

3 Phase installations test to confirm that there is no voltage between:

• L1 and L2
• L1 and L3
• L1 and Neutral
• L1 and Earth
• L2 and L3
• L2 and Neutral
• L2 and Earth
• L3 and Neutral
• L3 and Earth
• Neutral and Earth

When energised you should see voltage between earth and neutral:

L1 - 230V
L2 - 230V
L3 - 230V

Line to line you should see:

L1 - L2 - 400V
L1 - L3 - 400V
L2 - L3 - 400V

To get single phase from three phase all you do is connect to one of the phases and use the neutral.

Simpler than my attempt!

 

[pc1966]

Who is paying for the use of the EV charger?

I ask as there are lots of meters, and it is not obvious who pays for what. It is probably the site owner who pays the main 3-phase meter bill on the right, but after that?

Even if it is that person, if there is a spare single meter & fused-switch that can be used they might like the visibility of the EV use to be shown.

 

[loz2754]

Any spare ways on the MG board, just above the intake? If possible I would seriously consider fitting a 3ph EVCP if the facility is there for future expansion and rapid charging

A good suggestion. Just to bear in mind the additional isolation precautions needed when working on a DB with solar PV in it.

 

[HappyHippyDad]

Which raises an important question - which metered supply is the EVCP to be connected to?

I don't think the owner would be too fussed which meter it comes off, but I would certainlt discuss it before making a decision.

Is the job for the property owner? If so, you could always install a small single phase CU as a 'Landlord's supply'. Doesn't seem to be one, from the photo.

Yes, its for the owner. What do you mean 'landlords supply'? Actually, I may not be understanding your question properly. It is for the owner, but it will be used by the customers.

Any spare ways on the MG board, just above the intake? If possible I would seriously consider fitting a 3ph EVCP if the facility is there for future expansion and rapid charging.

Three phase is easy enough to work on you just need to remember the full safe isolation process which has a few more steps than single phase.

3 Phase installations test to confirm that there is no voltage between:

• L1 and L2
• L1 and L3
• L1 and Neutral
• L1 and Earth
• L2 and L3
• L2 and Neutral
• L2 and Earth
• L3 and Neutral
• L3 and Earth
• Neutral and Earth

When energised you should see voltage between earth and neutral:

L1 - 230V
L2 - 230V
L3 - 230V

Line to line you should see:

L1 - L2 - 400V
L1 - L3 - 400V
L2 - L3 - 400V

To get single phase from three phase all you do is connect to one of the phases and use the neutral.

I do understand safe isolation of 3 phase, but when you guys start talking about 'out of phase, star and delta etc' I am lost. If I don't understand something as basic as that I don't think I should be adding to the 3 phase part of it. However, it does sound as though a 3 phase EVCP would be a better option for the owner. I'll make him aware of that so he can look elsewhere if he chooses.

 

[pc1966]

Generally it looks a neat and well done installation.

The 300mA RCD for agriculture areas (special area for fire protection, don't have regs to hand) is not needed for your EV supply, but if for any reason you are taking the power from one of those unused fused-switches you need at least a 30mA A-type RCD as well so it is selective with the up-fornt RCD (I am assuming here it is a delay type, it should be...). But check if the EV model need a B-type for DC leaks.

 

[HappyHippyDad]

Who is paying for the use of the EV charger?

I ask as there are lots of meters, and it is not obvious who pays for what. It is probably the site owner who pays the main 3-phase meter bill on the right, but after that?

Even if it is that person, if there is a spare single meter & fused-switch that can be used they might like the visibility of the EV use to be shown.

The owner would be paying. The EVCP would be for use by the customers.
Looking at the spare meters, they look like a good choice! if indeed they are spare, and the cables are not hidden behind. I wish I'd taken a peek.

 

[HappyHippyDad]

Generally it looks a neat and well done installation.

The 300mA RCD for agriculture areas (special area for fire protection, don't have regs to hand) is not needed for your EV supply, but if for any reason you are taking the power from one of those unused fused-switches you need at least a 30mA A-type RCD as well so it is selective with the up-fornt RCD (I am assuming here it is a delay type, it should be...). But check if the EV model need a B-type for DC leaks.

Yep, happy with all the RCD requirements. That's one thing I do understand. More so after your 'blinding' experiment. ?

 

[buzzlightyear]

What do you mean 'landlords supply'? Actually, I may not be understanding your question properly. It is for the owner, but it will be used by the customers.

Plane and simple he who calls the piper
Pays for tunes, separate meter for him
And the rest for the porpers.

 

[pc1966]

The owner would be paying. The EVCP would be for use by the customers.
Looking at the spare meters, they look like a good choice! if indeed they are spare, and the cables are not hidden behind. I wish I'd taken a peek.

Check with the owner about the meter use in case not all are wired up.

You probably have space to the left to add another meter (if owner wants one), wiring is much as they are done already and probably a spare way or two on the existing Henley blocks for putting in the new L & N tails. Ideally try to get the same makes & models so it all looks consistent and works in the same sort of way.

Just be very sure you don't use two of the L blocks or you will see 400V! As explained above L-L is nominally 400V and L-N nominally 230V so it is which pair of cables you use.

Edit to add: The tails look colour coded with tape, but the N blocks are obvious as there are two cascaded to have enough holes to fill (oh-err) as 6 single phase means 2 per phase and 6 per neutral block. Might be worth checking with a clamp meter or looking at loads to select a phase that is lower loaded to keep the 3 in a better balance when EV on.

 

[HappyHippyDad]

Check with the owner about the meter use in case not all are wired up.

You probably have space to the left to add another meter (if owner wants one), wiring is much as they are done already and probably a spare way or two on the existing Henley blocks for putting in the new L & N tails. Ideally try to get the same makes & models so it all looks consistent and works in the same sort of way.

Just be very sure you don't use two of the L blocks or you will see 400V! As explained above L-L is nominally 400V and L-N nominally 230V so it is which pair of cables you use.

Edit to add: The tails look colour coded with tape, but the N blocks are obvious as there are two cascaded to have enough holes to fill (oh-err) as 6 single phase means 2 per phase and 6 per neutral block. Might be worth checking with a clamp meter or looking at loads to select a phase that is lower loaded to keep the 3 in a better balance when EV on.

Thanks PC. That all makes sense. Yes, it is obvious which is the neutral, plus I can test to make certain.

 

[buzzlightyear]

hope this helps, and that I'm not trying to teach you how to suck eggs....

Try a ostrish one that you mind.

 

[ipf]

A 'Landlords supply' is separate from all the tenants, who have their own meters. It is generally used for essential circuits in multi tenanted buildings like stair case lighting, outside lighting or other maintenance/cleaning facilities, available. Maybe even fire alarm supply or emergency lighting.

I don't think you'd have much problem picking up for a single phase DB.
That MG board might be interesting, Solar involved but it has a mains 3 phase supply, by the looks.

Remember, even if it's for the tenants, one of them won't want to pay for it, if it's for all.

 

[Yozza19]

But at which exact point does it change from 400v to 230V? How can it decrease in voltage without a transformer? I think this last question is also the answer to your question Julie ?

ps.. I'm assuming the 3 phase CU in the picture below is fed from the switched fuse (A) (single phase). How can it be a 3 phase board? Is it a 3 phase board? It looks like it only has a 2 pole isolation switch. I'm guessing it's actually single phase?

View attachment 90321

Wow if you honestly don’t know how to get single phase from a 3 phase supply you shouldn’t be let loose near electrics

btw the isolator in the db is only 2 pole so my gues would be that it is a 3 phase db with a single phase conversion kit

 

[HappyHippyDad]

Wow if you honestly don’t know how to get single phase from a 3 phase supply you shouldn’t be let loose near electrics

btw the isolator in the db is only 2 pole so my gues would be that it is a 3 phase db with a single phase conversion kit

Nice one chap, useful stuff as always.

 

[marconi]

HHD: I think you would enjoy slides 1-20 of this set - those after 21 quickly dive into technicalities I reckon you ought for now to leave for 'later':

https://www.bu.edu.eg/portal/upload...es/Cir2_Lect_8_Introduction_to_Poly_Phase.pdf

 

[Julie.]

But at which exact point does it change from 400v to 230V? How can it decrease in voltage without a transformer? I think this last question is also the answer to your question Julie ?

ps.. I'm assuming the 3 phase CU in the picture below is fed from the switched fuse (A) (single phase). How can it be a 3 phase board? Is it a 3 phase board? It looks like it only has a 2 pole isolation switch. I'm guessing it's actually single phase?

View attachment 90321

As has been said previously, the normal supply in the uk is 230/400V

Each of the three lines is 230V when measured between line and earth/neutral
BUT measure between lines you will get 400V.

This is part of your basic training, you probably ought to re-familiarise yourself with it if you are dealing with a site which has three phase.

If you have a 32A supply available, you could fit a single phase EVCP connected to any one of the three phases and neutral - this would charge at 32A or 7.4kW, obviously you would need a supply cable - either 2 or 3 core SWA usually (3c if you need the earth at the charge point).

If you use a three phase charge point this would charge at 32A per phase, so 22kW in total, in this case you would need a 4 or 5 core SWA (5c if you need the earth at the charge point). A 3ph charge point is around £100 more expensive than a single phase, but can charge up to 3x as fast.

Look in the standard charge cable connector - there are 5 main contacts and two small - the 5 main are the three phases, neutral and earth (be it from the supply or a specific TT for the EVCP).

The vehicle charger itself (in the vehicle) determines from the two small contacts what the maximum charge current is and then takes up to the limit of the charge point or the charger itself.

So some cars have a max of 6.6kW

• if you connect it to a 16A 1 ph EVCP it would charge at 3.6kW
• if you connect it to a 32A 1 ph EVCP it would charge at 6.6kW
• if you connect it to a 32A 3 ph EVCP it would charge at 6.6kW

Some other cars have a max of 11kW

• if you connect it to a 16A 1 ph EVCP it would charge at 3.6kW
• if you connect it to a 32A 1 ph EVCP it would charge at 7.4kW
• if you connect it to a 32A 3 ph EVCP it would charge at 11kW

Some other cars have a max of 22kW

• if you connect it to a 16A 1 ph EVCP it would charge at 3.6kW
• if you connect it to a 32A 1 ph EVCP it would charge at 7.4kW
• if you connect it to a 32A 3 ph EVCP it would charge at 22kW

I would always try for the largest I could, because more and more cars will be able to handle the larger values as time goes on.

The work is exactly the same - run the cable connect in the EVCP end and connect (Via a RCD/RCBO if specified) into the supply - usual methods be it single or three phase.

 

[ipf]

As has been said previously, the normal supply in the uk is 230/400V

Each of the three lines is 230V when measured between line and earth/neutral
BUT measure between lines you will get 400V.

This is part of your basic training, you probably ought to re-familiarise yourself with it if you are dealing with a site which has three phase.

If you have a 32A supply available, you could fit a single phase EVCP connected to any one of the three phases and neutral - this would charge at 32A or 7.4kW, obviously you would need a supply cable - either 2 or 3 core SWA usually (3c if you need the earth at the charge point).

If you use a three phase charge point this would charge at 32A per phase, so 22kW in total, in this case you would need a 4 or 5 core SWA (5c if you need the earth at the charge point). A 3ph charge point is around £100 more expensive than a single phase, but can charge up to 3x as fast.

Look in the standard charge cable connector - there are 5 main contacts and two small - the 5 main are the three phases, neutral and earth (be it from the supply or a specific TT for the EVCP).

The vehicle charger itself (in the vehicle) determines from the two small contacts what the maximum charge current is and then takes up to the limit of the charge point or the charger itself.

So some cars have a max of 6.6kW

• if you connect it to a 16A 1 ph EVCP it would charge at 3.6kW
• if you connect it to a 32A 1 ph EVCP it would charge at 6.6kW
• if you connect it to a 32A 3 ph EVCP it would charge at 6.6kW

Some other cars have a max of 11kW

• if you connect it to a 16A 1 ph EVCP it would charge at 3.6kW
• if you connect it to a 32A 1 ph EVCP it would charge at 7.4kW
• if you connect it to a 32A 3 ph EVCP it would charge at 11kW

Some other cars have a max of 22kW

• if you connect it to a 16A 1 ph EVCP it would charge at 3.6kW
• if you connect it to a 32A 1 ph EVCP it would charge at 7.4kW
• if you connect it to a 32A 3 ph EVCP it would charge at 22kW

I would always try for the largest I could, because more and more cars will be able to handle the larger values as time goes on.

The work is exactly the same - run the cable connect in the EVCP end and connect (Via a RCD/RCBO if specified) into the supply - usual methods be it single or three phase.

I know what you're saying but there's no doubt, with his experience, HHD should know the vast majority of that. Let's face it, he's been a forum member for 10 years.

 

[HappyHippyDad]

I know what you're saying but there's no doubt, with his experience, HHD should know the vast majority of that. Let's face it, he's been a forum member for 10 years.

As in the first post, I have stuck rigidly to domestic electrics. I have always declined any work to do with 3 phase because, as a domestic installer, we should not be touching commercial/industrial 3 phase etc. My instinct was to immediately decline this job, however I thought I'd chat through with you guys and see if if there was a simple way to use 230V (which it seems there is). This I understand.

I may yet still walk from this one, but I'm now erring towards doing it as it seems it will all se 230V.

 

[ipf]

As in the first post, I have stuck rigidly to domestic electrics. I have always declined any work to do with 3 phase because, as a domestic installer, we should not be touching commercial/industrial 3 phase etc. My instinct was to immediately decline this job, however I thought I'd chat through with you guys and see if if there was a simple way to use 230V (which it seems there is). This I understand.

I may yet still walk from this one, but I'm now erring towards doing it as it seems it will all se 230V.

To tell you the truth, I don't see where 3 phase comes into it. You're installing single phase.
It seems the problem, from your point of view, is whether it is 'domestic' or not....the very first point you made.
It's down to you, but knowing, to some extent, the way you seem to regard your position and work, I wouldn't object in the slightest to you carrying the installation.
If you're worried, have a look at your company insurance, maybe.

 

[plugsandsparks]

As in the first post, I have stuck rigidly to domestic electrics. I have always declined any work to do with 3 phase because, as a domestic installer, we should not be touching commercial/industrial 3 phase etc. My instinct was to immediately decline this job, however I thought I'd chat through with you guys and see if if there was a simple way to use 230V (which it seems there is). This I understand.

I may yet still walk from this one, but I'm now erring towards doing it as it seems it will all se 230V.

No dont walk unless the route from that room to the charge point is full of Bramble and thistle, lol - seriously you have fallen on a gem. 3 Phase is generally 4 wires, 3 X Line, 1 X Neutral, you only get 400 (actually more like 420V if you put you tester between 2 of the lines, you get 240V between any of the lines and Neutral.
So when you come to start if not sure what is what test the voltages and polarity which you would do anyway for a Sp install. Typically the Phase lines are coloured Brown, Black, Grey. Neutral is Blue (dont ask, its a long story) or if you still cannot figure it out, follow the cables from the service head. The three on the left above the fuse carriers are the lines and the one on the right which does not have a fuse is the Neutral.
Seriously man, TP does not get easier than this install, you gotta start somewhere

 

[HappyHippyDad]

It does all sound pretty straight forward now thanks to you lot. ?

 

[Resu]

Not sure if it's been said before but the only real worry you should have with the 3 phase in this scenario is which phase to use. A quick check on the main tails (around main meter/isolator) with a clamp meter should give you an idea.

Whether to come off of one of the already metered (& seemingly unused) supplies or come direct from the henleys and possibly include your own seperately metered supply is a question you'd need to put to the client.

Yet to come across a farm electrical system as well laid out as this, with plans too!

 

[Lucien Nunes]

HHD: I'll recommend a simple exercise to consolidate your visualisation of the voltage relationships: Draw a phasor diagram for yourself.

Mark a point in the middle of a piece of paper. That will be the neutral point.

Draw three lines radiating from it in a Y, 120 degrees from each other (the angles need to be fairly accurate.) These are the phasors that stand for the voltages of the three supply lines - L1, L2 and L3 - relative to the common neutral point.

The 120 degree angles represent the phase angles between the sine waves of the three phases. In essence, how far through a cycle of the sine wave L1 has got, by the time L2 starts, and so on. Because it is a 3-phase system, three times the phase angle makes one complete circle of 360 degrees, i.e. the phases are 120 degrees apart.

The length of each phasor represents the voltage from line to neutral. so make them represent 230V using some convenient scale such as 100V per inch, (which would make the phasors 2.3 inches long.)

Now measure the distance between the ends of any two phasors, representing the voltage between any two line conductors of the 3-phase system. Convert the length back to volts using the same scale.

That's where the 400V comes from.