Electricity Connection...

[Mulberry View]

We're building a 4-bed ICF 'forever home'. We plan to have MVHR, ASHP/GSHP, PV/Car Charging etc.

 

I had quotes to go for 3ph for the Mains connection after several people recommended we do, but my sparky (a good friend) disagrees. He says that the likelihood of me surpassing the capacity of a 100a 1ph connection is almost non-existent and doesn't stack up against the clumsiness of having things on different phases which don't play well with the PV.

 

I have 2 poles I could connect to. Pole 346 is the first pic is in the back of a Church Hall. 20m of trenching is needed and legal complications mean I cannot dig it, UKPN must This factor adds a good chunk of money to any connection that uses that pole. However, this pole is a bit closer to the house. (the plan doesn't really properly represent where the box will go)

 

Pole 345 is only about 18" into the garden of a private homeowner, thus no expensive UKPN trenching. However, it is about 15m further from the property.

 

3ph from Pole 346 is £4300

3ph from Pole 345 is £2700

 

Firstly, should I go 1ph or 3ph? Secondly, which connection would be best from the viewpoint of performance/voltage drop and can I make up any weakness in the cable that goes from the boundary box to the house?

 

They have also offered a 'Mains extension', but I guess this will be fiercely expensive.

 

 

[TonyT]

If costs aren’t too crazy

I would go for 3 phase to allow you to maximise PV over 3 phases.

 

helpful for balancing other loads too, particularly EV charging

 

there is no clumsiness in using 3 phase

 

[ProDave]

Re which pole, if the land owner with pole 345 gives consent without contest or conditions I would go for that, and even ask them if you (or your contractor) could dig the short bit of trench on their land as that would be cheaper then the DNO doing it.  There is little to choose between the options from a technical point.

 

You could get 3 phase to future proof yourself but only use 1 phase (to simplify solar PV self use) to start with knowing if you really need more power (multiple simultaneous EV charging for example)

[Mulberry View]

3 phase appears to be making about £500 difference.

 

My sparky tells me that it'll make an immediate impact in terms of having to use 5-core cable from the boundary box to the house, but also additional equipment/boards etc. I like the option to futureproof, but need to consider if we'll 'ever' need it?

 

So there's no real issue in the extra distance the cheaper pole is from the house?

[TonyT]

£500. Best £500 you will spend.

 

5/10/15/ 20 years time when the family all have EV and you are looking for multiple charging points! For just one example.

 

 

[ProDave]

9 hours ago, Mulberry View said:

3 phase appears to be making about £500 difference.

 

My sparky tells me that it'll make an immediate impact in terms of having to use 5-core cable from the boundary box to the house, but also additional equipment/boards etc. I like the option to futureproof, but need to consider if we'll 'ever' need it?

 

So there's no real issue in the extra distance the cheaper pole is from the house?

It is true that a 3 phase board cost a lot more than a single phase board, but the way I would tackle it is just fit a single phase board now.  you can add a second or change to a 3 phase board later if you need to.

[TonyT]

I would fit the 3 phase board now, why spend money twice to swap out and have to pay an electrician twice.

 

deal with the grief once

[SteamyTea]

Yes, fit the 3P now.

You will loose a bigger difference in timber offcuts and dropped screws during the build.

 

And if you like making things in a workshop, 3P machines are cheaper.

[Mr Punter]

I understood that a 3ph supply and board is not considered appropriate for a temporary builders supply.

[TonyT]

Never heard that before

[markc]

Me neither, yes you have 440v between phases as opposed to 240v phase to earth but no reason for site staff to access the panel

[Mr Punter]

My son mentioned it.  He is an electrical engineer designing building services.  Maybe it is a best practice thing for H & S?

 

I have often seen people accessing the fuse board on small sites.

[joth]

15 hours ago, Mulberry View said:

My sparky tells me that it'll make an immediate impact in terms of having to use 5-core cable from the boundary box to the house, but also additional equipment/boards etc. I like the option to futureproof, but need to consider if we'll 'ever' need it?

 

Terminate the three phase in the boundary box and run a spare duct with pull cord from that to the house. If you ever need additional phases you can pull them through at a later date. 

[Mulberry View]

Thanks for your help everyone. I think that's the decision made regarding 3-phase.

 

As an additional point, is it worthwhile shopping around for the connection? We've had UK Power Networks quote for everything so far...