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?

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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.