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