Builder recommending 3 phase power?

[Trw144]

1 minute ago, CalvinHobbes said:

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?

7kW I believe 

Edited February 1, 2023 by Trw144

[andyscotland]

13 minutes ago, CalvinHobbes said:

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?

Not sure how you've approached that maths?

 

UK nominal single phase voltage is 230V, current is (loosely, ignoring power factor) power divided by voltage. So 22,000W / 230V = 95.7 amps. Theoretically could just fit on a 100A supply if you turned everything else off...

[Kelvin]

22 minutes ago, CalvinHobbes said:

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?

Check your maffs. 22kW/230V = 95.6A

 

This is the reason the sparkie has said he needs 3 Phase as 3 x 7.2kW could be used simultaneously even assuming you applied diversity to everything else. 

[billt]

1 hour 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 🙂

 

Diversity is a wonderful thing (our system runs off a 6kW continuous inverter but the total potential load is well over 22kW), however diversity cannot be applied to EV chargers, for obvious reasons (they will be consuming 22kW for several hours without a break) so it looks as if your electrician is correct. If the chargers have some sort of demand reduction a reduction in supply capacity may be possible.

[andyscotland]

1 hour 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 

 

1 hour ago, joth said:

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.

 

Also, although the electrician does have a responsibility to check that the overall design load is reasonable taking account of diversity there is some wriggle room there.

 

Ultimately so long as every cable including the incoming supply is protected by a protective device adequate to the cable rating & installation method, that is the safety side of things covered IMHO.

 

And if any of the kit is cabled but not connected then it is for the electrician that eventually commissions that to sign that off.

 

It is extremely common for the total potential load on a consumer unit to be way higher than the actual maximum. Even before car chargers and the like you could easily have 2x32A ring, a 40A cooker, 16A immersion, 2x6A lighting and a 20A garage supply for a total of 152A worth of circuit breakers off a 60 or 80 Amp supply.

[andyscotland]

1 minute ago, billt said:

however diversity cannot be applied to EV chargers, for obvious reasons (they will be consuming 22kW for several hours without a break) so it looks as if your electrician is correct.

 

That's a good point (my training predates EVs!). Assuming of course the chargers are connected at this stage.

 

[Seren161]

We are at the end of our 350m2 build and we went for 3 phase.. it was a touch expensive at an initial quote of 5.6k from UK power networks but apparently this was before they realised the buried supply was much closer than they expected and we got a refund of 2k plus.. I grew up in a developing country where the housing stock is much “younger” than the UK housing stock and three phase was/is standard for average homes so that was my natural preference I guess but also wanted to have the facility for a 22kW EV charger in future and I had a pretty demanding lighting plan, plus similar to @Andehh 12kW Heat pump etc 

 

The actual 3 phase install wasn’t too bad ( done in a day ) but before they realised the supply was outside our property, they had put flyers through the neighbours’ letter boxes warning of road closure and road digging etc Add this to your building noise and building traffic and peed off neighbour x multiples is guaranteed.

 

Getting British gas to install our 3 Phase meter was a little tricky..delays of 3 weeks. 

 

They did not fit a smart meter so still waiting to see if I can get the SMETS2 3 phase smart meter. This matters especially if you have solar panels and plan to take advantage of some of the more interesting energy tariffs from providers like Octopus etc ..You can buy the smart three phase meters but not sure how that works in terms of responsibility etc..

3 phase electricity means Heat pump is three phase, Hybrid inverter for Solar array is three phase, if we decided to go for battery storage ..it would be 3phase ..The inverter was really difficult to obtain I was led to believe due to scarcity but maybe better availability in the winter?. That said I am still really pleased that we went for it but it was a rather convoluted process.

 

Unconnected to this .I have had to contact UK Power networks for some electrical upgrade work at a different location and they do seem really keen on pushing the 3 phase electric upgrade  ( they called it their preferred option) but because it is a busy fully functional location..the potential disruption means I went for a 100 amp fuse upgrade only .

 

I think there is a big push to upgrade more sites to three phase as well as smart metering with a view to future proofing the functionality of the power grid as we move forward and so the cost of the three phase upgrade may well be subsidised in the near future .

Also I’m reliably informed that due to power grid constraints..having a fast ev charger doesn’t necessarily always mean a “fast” charge…..

 

 

[joth]

1 hour ago, andyscotland said:

 

That's a good point (my training predates EVs!). Assuming of course the chargers are connected at this stage.

 

But but but, 40A or smaller fuses are common place in Europe (in France you get higher standing charge the bigger the fuse) so if it's not already supported chargers will soon come with the option to shed load if import exceeds some defined cap.

It's already super common their to have contactors that automatically shut off some loads of approaching the supply limit.

 

All that said, personally I'd do the 3ph before I got vaguely serious about installing half the gear mentioned in the OP, but I don't think the OP really is and they're future proofing for things they'll never install.  Else they'd already have got 3ph without complaint.

 

[andyscotland]

9 hours ago, joth said:

But but but, 40A or smaller fuses are common place in Europe (in France you get higher standing charge the bigger the fuse) so if it's not already supported chargers will soon come with the option to shed load if import exceeds some defined cap.

It's already super common their to have contactors that automatically shut off some loads of approaching the supply limit.

 

True, it would definitely be feasible to make some sort of load management work.

 

Really, even if 3 car chargers are installed, the requirement is probably just to be able to plug three cars in at teatime and have them charged by morning, without having to go back outside to unplug one and plug in the next. Doesn't necessarily mean they have to charge simultaneously. I'm sure that will become a fairly common requirement for multi-car households so as you say if the kit isn't yet available to do that (off the shelf, I'm sure it's already doable with a Raspberry Pi, some current clamps and some contactors) it probably will be before long.

[JohnMo]

If were me and I am no electrician

 

Budget stretched

3x car chargers, you don't have a car requiring charging, pre run cable, both ends not connected. Outside end in a small waterproof box - all ready for later installation.

 

Outside garden stuff, same as above.

 

Ditch patio heaters as a waste of good electric

 

Find out why a new build needs a 12kW ASHP - use all the money you save on the above fantasies on decent insulation and air tight measures, so are installing a sensible ASHP.

 

No 3 phase required, to run a single phase house!

[andyscotland]

@Andehh thinking about it a bit more and assuming your 3 car chargers are ~7kW each rather than 22 (and given I think you said you've already bought them):

If going 3ph now isn't feasible, another short-term option might be to fit a manual 3-way changeover switch beside the consumer unit - something like this https://uk.rs-online.com/web/p/cam-switches/2937156 in a suitable enclosure, or may be possible to find IP rated ones, that was just a quick Google.

 

Then take a single supply from the CU to that switch, then your separate supplies from the switch to each charger. Fit a 3-phase-ready CU with two spare ways.

 

That would guarantee the total load on that circuit could only ever be a single charger but allow your current electrician to commission & certify all 3 - avoiding any issues about asking a later electrician to certify a concealed supply cable that was installed by someone else but left dormant.

 

Then in future when you actually have any EVs to charge you have options:

 

* Upgrade the supply to 3ph and take charger 2&3 to the spare ways on the CU, removing the switch. So basically what you'd otherwise do now, but later.

 

* Leave the supply as 1ph and fit some as-yet-to-be-determined smart tech to balance demand across the three chargers instead of the manual switch.

 

* keep the manual switch till you figure out something better, you'll still have to turn it at some point in the evening but at least you don't have to go out in the rain to unplug & replug each car 🤣

[Andehh]

Thanks everyone for the feedback & comments, very helpful indeed!

 

We haven't actually bought any vehicle chargers, but all the cabling has been installed.  We have 4 x cabled in for, with 1 x cable future proofing a battery but using same high gauge cable.

 

Certainly wouldn't say builder or electrician are forcing our hands here, but we are guilty of massive scope creep/future proofing which has come back to force our hands. The only other area we got carried away was Insulation (!) but with the electrics. Even without the Car chargers & patio haters I think we are too far gone for single phase.

 

Its a large bungalow with 6 bedrooms, 2 studies then the normal assortment of rooms. We also have an existing single garage & new external garage that are wired in, then 3 x large external AC units. The Electrician gave me a verbal run down of this and we quickly blew through 80amps.

 

Waiting for pricing from DNO which worries me (ben chasing them daily), and also further feedback from Builder/Electrician on what could be done to bring us down to 80 - 100amp loads.

 

Ill keep the thread updated!

 

 

[andyscotland]

Ah, that does sound like you will be snug even without cars and patios.

 

If you manage to get down to the point the car supplies make the difference, another option might be to just terminate those cables into say 6A MCBs and leave the other end without anything on it (or say a 5A lighting socket, though that would be a bit odd). Or take them to a single 16a MCB, stick a single 13A socket on each, and treat them as a radial.

 

There's no reason a protective device can't be less than the theoretical current carrying capacity of the cable (in fact it's quite common if eg a cable is oversized due to voltage drop).

 

That might again allow the electrician to certify everything he's installed including the cabling runs. And then be less drama for a future electrician to consider just upgrading the protective device and installing a charger on the other end knowing the cable run was inspected & signed off previously.

 

It'd be a bit "thinking outside the box" but I think compliant, and if it saved you putting in 3 phase now to commission 5 empty cables then worth a bit of oddity!

 

[Andehh]

Thanks for all the support!

 

After a really good chat with a wonderful women at National Grid (previously Western Power) she confirmed it'd be an estimate of £1950 for the 3 phase installation, including meter, and two holes dug in the verge. Builder just needs to the dig 3-4m trench to where the meter will be installed.

 

Very happy chap here! Just need to be mindful of future proofing for a 3 phase Solar Inverter etc, but a problem for another day! 

[SteamyTea]

On 01/02/2023 at 17:02, saveasteading said:

can't remember the term, for not all machines and appliances being used at once

Diversity.

 

Patio heating, FFS.

As if climate change is not enough.

Be cheaper to drive down to Spain every 2 months.

[Andehh]

If its good enough for pub beer gardens, it's good enough for us to try out! If it makes you feel any better we have 3.99Kw of solar going in to counter act the environmental harm.

[CalvinHobbes]

On 01/02/2023 at 22:11, Seren161 said:

3 phase electricity means Heat pump is three phase, Hybrid inverter for Solar array is three phase, if we decided to go for battery storage ..it would be 3phase ..

 

 

Darn, there is a 3 phase pole beside us (stay in our garden) and we are thinking of getting it. We have been recommended a 11kw ashp, electric shower and 5 showers (don't ask). Hadn't thought of the heat pump having to be 3 phase. Is there a big cost difference? 

[Andehh]

We're still working through this. 

 

Our ASHP is single phase 12kw Samsung. Solar inverter is an old old one, but also single phase. 

 

Reality is one phase will have PV, ASHP, and house. Other phase double garage and garden and final phase single garage and chargers. 

 

So PV sits in the main phase we will draw it from. 

 

Electrician says he will fit a diverter that will switch PV to whatever phase needs it... Not sure if that exists without being expensive, need to look into it more. 

[crispy_wafer]

1 hour ago, Andehh said:

Electrician says he will fit a diverter that will switch PV to whatever phase needs it... Not sure if that exists without being expensive, need to look into it more. 

  Ooh, sounds like something I could need further info on as my 3ph setup will be broadly similar.  Please report any findings either way.

[saveasteading]

10 hours ago, CalvinHobbes said:

Hadn't thought of the heat pump having to be 3 phase. 

I dont think it does unless huge.

3 phase makes big machines run better in factories.

 

But the point here,  I  think, is of using one phase as a dedicated supply, just like a  second mains. 

You seem to have enough power in a normal supply. The ashp will be about 3kW. Electric showers, pump not heating, not a lot.

The cooker will potentially use more.