Builder recommending 3 phase power?

[Andehh]

Hi all,

 

Slight surprise when builder calculated our electrical load and now recommends we go 3 phase. Seems kind of obvious now that I think about it, but with everything else going on never occurred. 

 

Our budget is massively constrained (as per tradition), but having paid for 3 x Car chargers, 12kW ASHP, 2 x hardwired elec patio heaters, 2 x 16amp supplies for garden potentials (long runs, hot tubs, etc etc - long term potentials) and 4kW on roof (but designed to extend to 8kW) it seems a shame to not connect them one day.

 

The house has the 100amp mains cable from meter to fuse box loose installed, and electrician is recommend running 2 more 'positive' cables between meter & fuse box, that could be connected up to a 3 phase meter one day. Then ducitng under the driveway to the incoming supply to enable DNO to make the run if/when we decide to upgrade it.

 

Does this sound sensible? Any experience of going 3 phase from people?

 

The house opposite (30m away) has 3 Phase installed, if that makes any difference? We are with Western Power, village location.

Edited January 28, 2023 by Andehh

[nod]

It doesn’t sound like your budget is massively constrained 

If it is Id ask myself do I really need three car chargers and hard wired patio heaters They cost a fortune to run 

[Kelvin]

Do all the prep work for it while the build is going on as it won’t cost much and much harder and costlier to do afterwards. Contact your DNO and get a budget estimate for adding 3 phase. There’s normally a form you fill in. 3 phase can obviously complicate your electrics especially PV and battery storage. 
 

Ditch the electric patio heaters and buy some warm blankets. 

Edited January 28, 2023 by Kelvin

[Marvin]

5 minutes ago, nod said:

It doesn’t sound like your budget is massively constrained 

If it is Id ask myself if I really need three car chargers and hard wired patio heaters They cost a fortune to run 

+1. with @nod

 

However in my humble opinion if you are going to use all the listed items and general house use then 3 phase will be the way to go. In fact probably sooner rather than later...

[Andehh]

Thanks all, the short version is it is all being wired 'for' but not 'with'. Lots of cable tucked out of sight until the time we choose to use them. Due to a bungalow with warm roof, there is no chance of ever routing future cables!!

 

We don't own an electric car now, but in 10 years time i'm confident we will have a couple of them + visitors traveling from afar. Patio heaters etc were an easy choice with the extra cable on the drum we were having for the car chargers...again few £100 to install for it, whether we chose to use it is up to us long term. Have to admit, the ease of knocking them on for an hour as we sit on the patio is nice to have the option of.

 

It's our forever home & 4 young kids mean we are trying to keep options open going forwards!

 

Welcome any further experience/starters for considering 3 phase. I presume with PV etc you need the correct inverter for 3 phase v single phase? Same as per battery?

Edited January 28, 2023 by Andehh

[ProDave]

I would certainly bury the appropriate cable to allow a 3 phase upgrade later.  (not an option for us the nearest 3 phase is about a mile away)

 

But worth considering how the DNO would get a new cable in.  If it means digging up your garden or driveway I would be looking at getting that done now rather than later.

 

No harm in asking the DNO for a quote so you will find out the cost and how they would actually do it. 

[Dave Jones]

all new builds are 3 phase now, you need a deeper recessed box to fit it all in mind.

 

You can always get 3 phase cable and then use a single phase meter.

[saveasteading]

We had 3 phase just 20m away but the transformer would need changing . £15k.

Advice from many sources (incl here) was that it was very unlikely that we would have it all running.

And yes, 3 electric cars may need charging, but charging systems/ timing systems will come too. And we will have more solar panels.

 

What some people were getting wrong was that a 12kW ashp uses about 3kW, that being the whole point of them

 

So we will have 350m2 off single phase.

[Jilly]

1 hour ago, Kelvin said:

Ditch the electric patio heaters and buy some warm blankets. 

I think heating the garden is an anathema to many of us on here…

[Temp]

6 hours ago, Andehh said:

3 x Car chargers, 12kW ASHP, 2 x hardwired elec patio heaters, 2 x 16amp supplies for garden potentials (long runs, hot tubs, etc

 

Is that 3 x 7KW chargers = 21kW = 90 A ?

 

12kW ASHP with COP of 3ish would be about 15A

 

 

[Andehh]

Thanks very much all. Electrician on site has grave concerns at single phase, to the point where he is really not willing to certify it. Looks like our hand is being forced. I am annoyed this wasn't pointed out to us until the last minute, but even removing the car chargers he still said with 2 garages (existing/previous and a new one), some 10mm for out building future proofing etc etc we have backed ourselves into a corner into needing one. Wish I'd been told this 12 months ago!!!!!!

 

Just waiting...hoping...praying the DNO isnt unreasonable for the connection. Village edge location, with Neighbour opposite wired for 3 phase, but otherwise not many high power homes in the vicinity.

 

here's hoping!!!

[Kelvin]

You might be fine. It depends in whether they need to do any reinforcement works which can be really expensive. That said there was a post on here a while back about a change to policy whereby the poor self-builder doesn’t need to fund the reinforcement. Worth searching for it. 

[saveasteading]

Probably already said above, I haven't reread.

If you need a new cable, an option is to put in an oversized one now. If you don't eventually need it, you haven't unnecessarily committed to higher fees for ever. 

Then you can upgrade to 3 phase when it suits, if ever.

All you need to do is tell your sparks that one car charging us enough.

I can't remember the term, for not all machines and appliances being used at once....is it divergence? It is a significant proportion.

[IanR]

On 28/01/2023 at 08:45, Andehh said:

We don't own an electric car now, but in 10 years time i'm confident we will have a couple of them + visitors traveling from afar.

 

EV A/C charging at 22kW  will become more common in the 5 - 10 year future, as battery capacity increases. If you don't install 3 phase initially, make it an easy upgrade in the future so you're not stuck with 7kW charging at home, otherwise you'll find yourself paying a premium for DC fast charging at public charging points more often as you can't get enough charge at home - epically with multiple EVs in a household.

[Kelvin]

39 minutes ago, IanR said:

 

EV A/C charging at 22kW  will become more common in the 5 - 10 year future, as battery capacity increases. If you don't install 3 phase initially, make it an easy upgrade in the future so you're not stuck with 7kW charging at home, otherwise you'll find yourself paying a premium for DC fast charging at public charging points more often as you can't get enough charge at home - epically with multiple EVs in a household.

I’m unconvinced by this argument. What you need to install is very much dependent on the miles you drive every day. The average daily mileage in the UK is relatively small and getting less with each passing year. Therefore the vast majority of people don’t need to charge their cars every day. You also don’t charge to 100% generally either. Therefore a typical 2/3 car household could easily survive with one 7kW charger given that you probably can get away charging each car 1-2 times per week. We’ve done 29,000 miles in ours in 18 months and get by with the slow mobile charger. Sure multiple 7kW or a 22kW would make life easier but I don’t agree that not fitting either would necessarily mean visiting DC chargers more frequently as we don’t do that today. 

Batteries might get bigger but it’s more likely they won’t for your average EV if say solid state batteries become the norm. They could offer similar density to current batteries that are smaller and lighter making the car smaller and lighter improving efficiency and range for a smaller footprint. We’ll still see larger batteries in the luxury end of the market. 

 

Of course by all means future proof your house. I made the decision not to install 3 phase due to cost but did put in ducting to the kiosk that could accommodate it in the future. 

Edited February 1, 2023 by Kelvin

[IanR]

21 minutes ago, Kelvin said:

I’m unconvinced by this argument.

 

The industry is already responding to the need for 22kW home charging, having listened to their customers. It may take time for some brands to introduce them as it often pushes the need for a different cooling strategy for improved efficiencies, so may not be easy to upgrade.

[Kelvin]

Sure but I’d question the ‘need’ for 22kW charging at home. The vast majority of home owners won’t be able to accommodate it because it requires 3 phase and that’s not typically readily available. 22kW isn’t fast enough for en-route charging either so there’s not much advantage there. It is less expensive for companies to install a 22kW AC charger vs a fast DC charging point so there’s some advantage for destination chargers to offer it. I’m not suggesting that future EVs won’t be able to charge at 22kW AC but I am struggling to see that the demand for this is being driven by folk wanting to install  it at home. 

Edited February 1, 2023 by Kelvin

[Wil]

1 hour ago, saveasteading said:

I can't remember the term, for not all machines and appliances being used at once....is it divergence? It is a significant proportion.

 

Diversity. Don’t add up all your loads and assume the worst case is all on at the same time- apply diversity to each load.  And then an overall diversity factor of 0.7 to the total to allow for you over-egging the first set of diversity 🙂

[joth]

15 minutes ago, Wil said:

 

Diversity. Don’t add up all your loads and assume the worst case is all on at the same time- apply diversity to each load.  And then an overall diversity factor of 0.7 to the total to allow for you over-egging the first set of diversity 🙂

It's worse than that, the electrician appears to be adding up a lot of equipment that hasn't been bought and won't be installed for many years.

If you put the oversized wires in but don't connect them into your consumer unit (which you really shouldn't anyway if the other end is just dangling in the air) then it's just a bit of dead burried copper. There's literally nothing there for the electrician to certify.

I'm all for ppl installing 3ph when they have the option, but this seems to be bullying you into it over hypothetical possible future scenarios. Seems mad to mad. 

[saveasteading]

On 28/01/2023 at 08:04, Andehh said:

builder calculated our electrical load 

Don't assume that the builder or electrician understand all or any if this. I have employed many who may be good at installation, may be qualified to sign it off, but don't know much theory.

And I have met some who know how to connect a socket, and have a source of certificates.

There are plenty of good ones too.

Ask them to explain what 3 phase is. (More power is the wrong answer)

Ask them to explain how a 2 way switch doesn't short.

Ask them to explain diversity....actually this one might do on its own.

[Kelvin]

All you need to ask the electrician is to show you his working to calculate your load. 

[Trw144]

Might not be applicable to you but I have asked for 3 phase supply for the new house (development of two) and received a quote a few months back for it. I called this week to go ahead and it was suggested to me I would be better waiting until April as they are changing the way they charge. Costs of upgrades required being absorbed by a central pool of money (ie. Put on everyone's bill) rather than charged to the individual 

[Wil]

3 minutes ago, Trw144 said:

Might not be applicable to you but I have asked for 3 phase supply for the new house (development of two) and received a quote a few months back for it. I called this week to go ahead and it was suggested to me I would be better waiting until April as they are changing the way they charge. Costs of upgrades required being absorbed by a central pool of money (ie. Put on everyone's bill) rather than charged to the individual 

Does that apply to all DNOs? Do the Wild Western Thieves come under this as our T/X is well under powered? (Western Power)

[Trw144]

Too be honest, I could nt find a lot on it (but admittedly only had a quick google search). I'm a western power area.

 

Did find this (not sure how if a self builder and developer would be treated as the same)... https://www.premierenergy.co.uk/blog/electricity-connection-charges-good-news-from-april-2023/

[CalvinHobbes]

What is the fastest charge you can get from single phase? Like if you have a 100 amp supply then is a 22kw not running at 32 amps? Or is that just wishful thinking?