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?

 

[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