Sub main supplying new build

[Deanofromthedock]

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Good morning all, long time reader first time post so looking for some help

I’m qualified as an electrician but haven’t worked as a sparky for 15 years or so. I’m just starting a self build and going to do as much as I can but over thinking that the first hurdle

New main in to the house was very expensive so going to relocate and have an external meter box instead, few k cheaper.. all new supplies for new builds in wales are 3 phase.

I’m thinking of running a 4core swa and separate earth to the plant room in the house.. I was thinking using 16mm swa to a 3 phase board and then running submains from this to the DB in the house one phase for car charging and one for pv

Does this sound ok?

Being out of the game for years it’s like starting all over again.. is 16mm sub main ok or should I look at bringing 25mm into the house?

The swa will be run in duct for 10m tray up external wall and run through posi joists about a 20m run from position of external meter box

Any advice would be much appreciated

👍🏻

 

[DefyG]

If I was to have 3phase supply I think I would balance the load across the house, 3phase 11kw or higher Ultra fast charger (capability if not actually used), and 3phase PV inverter so that energy from the panels can be utilised in the house (1 phase for PV sounds like only exporting to the grid or staorage?)

 

[pc1966]

For 3-phase SWA in duct (method D) with 90C thermosetting insulation your limits are:

• 16mm = 75A
• 25mm = 96A
• 35mm = 115A

So you need to decide what total load you expect and related supply protection used.

Chances are having a 63A fused-switch at the meter box feeding a 16mm sub-main with a separate 10mm earth in parallel is OK (assuming TN-C-S supply here so Ze low). You are probably as well putting it to a 3P board in the house (with SPD) for everything so stuff is balanced over the phase. However, check you get tolerably priced RCBO for the board as practically all domestic circuits now need RCD protection.

Also check what the PV panel and EV chargers need. 3P RCBO can be difficult to get (and almost impossible if you need a DC sensitive type B RCD characteristic) so you might end up with MCB in the panel feeding 4-pole RCD in a separate DIN style enclosure. Hager are not your cheapest choice, but they have add-on DIN boards that neatly attach to the related 3P boards for this sort of thing (also for any other electrical control & monitoring stuff you might want like contactor, bell transformer, time-switch, meter, etc).

 

[Deanofromthedock]

Thank you both.. I should of explained a bit better I think.. that was the original plan but a lot has changed.. was having ashp but scrapped that

So will be having pv as mentioned with a battery car charger will be added but not immediately hopefully not ever I like petrol..

3 phase board in to the house.. then split the phases… my plan is and you might say it’s dull.. we have 3 floors so going to put a separate DB on each floor, looking to do a floor at a time.

My plan is to run a 16mm 4 core swa with separate earth.. as you mentioned above 👍🏻 but I may price up 25mm to see the price difference

Thank you

 

[James]

If you go for 25mm 4 core, you may not need a separate earth? also it is available as 5 core.

 

[James]

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