Deciding how to use our new 3 phase connection

[Ben Weston]

Hi all,

 

As part of our extensive renovation, we've had three phase installed as it wasn't much more on top of the works we were already having done. The electrician has run a single phase to the house from the kiosk, with a view to running another phase to the garage when it's built and the third phase unallocated at present. I'm now wondering if this is actually the best setup.

 

For context, we have two EVs, will be installing solar and battery storage, an air source heat pump and an induction hob. 

 

I have a garden office with a few lights, a computer and a TV in so not much load at all and currently connected to a 32amp RCD in the temporary house fuseboard.

 

I'm wondering if it might have been better to run all three phases to the house, use three phase solar/battery equipment, and then run the ASHP and induction hob on one phase, the rest of the house on another and terminate the third phase over to the garage (and on to the garden office)?

 

The garage, due to where our static caravan is currently located, will be built after we move in so the option of running all three phases to that and then splitting from there isn't an option, sadly. To complicate matters further, we still don't have a smart meter installed (have been trying for 6 months), but that will be sorted in time.

 

Any and all advice welcome as always!

Edited September 21, 2022 by Ben Weston

[JohnMo]

Do you need three phase? sounds like you don't and only got because it wasn't that expensive - are making things way more complicated than they need to be?

 

 

[joth]

How much solar? What EV / chargers?

 

What's the relative layout and effort to make changes later? I'd put 3ph into a central location that makes it easy to get to all the different places you need it (esp EV chargers, outbuildings, as well as house itself).

If the kiosk is central then what you have now is fine. 

[Ben Weston]

1 hour ago, JohnMo said:

Do you need three phase? sounds like you don't and only got because it wasn't that expensive - are making things way more complicated than they need to be?

 

Well, the total potential load is well above what one single phase 100amp supply can provide. I know not everything is run at once but 32 amp ASHP, 32 amp induction hob, 2x EV chargers, future hot tub and pool, etc; seemed the right thing to get three phase for a minimal amount more. Made sense to put it in to give the potential for future fast EV charging, etc.

 

56 minutes ago, joth said:

How much solar? What EV / chargers?

 

What's the relative layout and effort to make changes later? I'd put 3ph into a central location that makes it easy to get to all the different places you need it (esp EV chargers, outbuildings, as well as house itself).

If the kiosk is central then what you have now is fine. 

 

Yes, kiosk is relatively easily accessible between house and garage so perhaps I don't need to worry at this stage. How much solar and EV chargers largely governed by what we do with the phases. If we could get three phase to the garage, we'd have 2x 22kW chargers.

Edited September 21, 2022 by Ben Weston

[joth]

Sounds like you have too many free variables to mathematically derive an answer to the question originally posed.

I'd suggest making some decisions about what your functional requirements are, and only after that determine how to use 3ph best to fullfil them.

 

In the meantime yeah having all 3ph pulled into house and (especially) garage and wherever the EVs and the inverter will be is obviously the best future proofing, but with a centrally located kiosk it doesn't sound horrendous to change that if you come in late with those key requirement choices.

 

[Thorfun]

we have a 3-phase supply to the head in an external cabinet but could only get a single phase smart meter installed and that was hard enough to find let alone a 3-phase meter! but, that doesn't bother me as I'd always wanted just a single phase to run our entire house with the option of getting a 3-phase meter at a later date so I could charge EVs if required using 3-phase. I had our solar PV designed as a single phase inverter system and got the 10kW G99 application approved so all Solar PV can be used on any appliance in the house. I never really liked the idea of running different phases in the house for safety reasons. I'm not an electrician but I read enough posts about arcing to put me off for life!

 

We installed a TP&N switched fused isolator in the external cabinet and ran a 25mm 5 core cable from the cabinet to the comms room where it terminates in another TP&N isolator and the single phase in use is being fed to our CU. that way, if we want to add 3-phase usage in the house at a later date we can take the feeds from the isolator in the comms room. 

 

[joth]

4 hours ago, Thorfun said:

I had our solar PV designed as a single phase inverter system and got the 10kW G99 application approved so all Solar PV can be used on any appliance in the house. I

Just a small note: even if your inverter were on phase A and your house consumption on phase B you'd still get the financial benefit of self-consuming any PV generated at the time yuor appliances are in use, due to "polyphase net metering" implemented in 3 phase smart meters. You would of course need a 3ph meter to achieve that!

 

But what you have now is perfectly sensible use of a 3ph supply head too. Just slap a single phase meter on it and sit comfortable knowing you have more options in the future should you require it.

 

 

[Renegade105]

Hi, @PeterW @Thorfun

 

Sorry for the hijack but in need of some insight here.

 

We have the temporary external single-phase supply on the boundary for the build but will eventually change to a 3 phase as I will have an EV, and a very hungry ASHP plus a workshop so I will get close to the 100A easily.

 

We will have an insulated foundation KORE with an ICF house.

 

Can someone please help me in designing the underground services here? we don't have an M&E, we are relying on trades such as CVC for the design of the MVHR, ASHP etc, UFH is Wunda, Plumbing was by architect.

 

I assume you guys would recommend on installing an external floor mounted kiosk somewhere near this temp site, what size would you advise for the 3Phase electric kiosk? I am happy mounting this to the outside of the house too as it will only be a few meters away from the temp site anyway (appx 4m). Does then the Gas meter get installed here in its own external kiosk too?

 

For the house, I suppose everything internally can be run on single phase, but how would you suggest the setup for the ASHP and the garage and the EV. I can see us having 2 in the future (fund allowing).

do you need a 100A TP&N isolator in the kiosk after the meter, and then a 5 core cable run underground in conduit and up and into the house at the utility, to another 100A TP&N isolator and then wire up a single phase to the CU? What about getting 3 phase to the garage etc?

 

Here is my site plan and house, ALL of my plant room essentials will be in the Utility room.

 

As ever, many thanks.

 

[PeterW]

31 minutes ago, Renegade105 said:

3 phase as I will have an EV, and a very hungry ASHP plus a workshop so I will get close to the 100A easily.

Whats “very hungry”, who specced it and why are you going ASHP when you’ve got gas available ..??

 

Workshop - not on the plans, do you mean the garage..? 3Ph kit (mill / lathe etc) or just thinking you need a lot ..?

 

32 minutes ago, Renegade105 said:

Can someone please help me in designing the underground services here? we don't have an M&E, we are relying on trades such as CVC for the design of the MVHR, ASHP etc, UFH is Wunda,

Who’s plugging that lot together ..?? Is it you..? As…. It’s not that easy, and you need a decent plan on how it works - wired vs wireless for stats etc, multiple switch scenarios for heat and so on. 
 

33 minutes ago, Renegade105 said:

Plumbing was by architect.

Would have been better asking the milkman, but let’s move on …

 

34 minutes ago, Renegade105 said:

We will have an insulated foundation KORE with an ICF house.

what’s your heat loss calculation as this doesn’t match with the ASHP requirements

 

35 minutes ago, Renegade105 said:

do you need a 100A TP&N isolator in the kiosk after the meter, and then a 5 core cable run underground in conduit and up and into the house at the utility, to another 100A TP&N isolator and then wire up a single phase to the CU? What about getting 3 phase to the garage etc?

ask your electrician - this is not something you need to make a mess of as it could / will be expensive to correct.

 

Personally - and now seeing the plans - I would run a pair of phases to the side of the garage externally and then run the car chargers off a phase each. If you’re desperate to go 3Ph charging as you find the money for a Tesla that’s a different issue, but tbh I’m struggling to see how you’re above 100A on a phase here.

 

38 minutes ago, Renegade105 said:

Does then the Gas meter get installed here in its own external kiosk too?

Is this only for cooking..?? If so.. just go get an induction hob, and save yourself about £10k on install costs. 

[Thorfun]

19 hours ago, PeterW said:

 

20 hours ago, Renegade105 said:

Plumbing was by architect.

Would have been better asking the milkman, but let’s move on …

😂

 

19 hours ago, PeterW said:

 

20 hours ago, Renegade105 said:

do you need a 100A TP&N isolator in the kiosk after the meter, and then a 5 core cable run underground in conduit and up and into the house at the utility, to another 100A TP&N isolator and then wire up a single phase to the CU? What about getting 3 phase to the garage etc?

ask your electrician - this is not something you need to make a mess of as it could / will be expensive to correct.

 

+1 to this. my electrician told me what to buy and just came and fitted it. I wouldn't like to give advice that might be wrong on a subject like this!

 

20 hours ago, Renegade105 said:

I assume you guys would recommend on installing an external floor mounted kiosk somewhere near this temp site, what size would you advise for the 3Phase electric kiosk?

the DNO told me what size kiosk to buy and where to site it after discussions during the initial site survey. each DNO may have different requirements. but, I would suggest bigger is better as it seems to fill up pretty quickly especially if you do need a TP&N isolator as they're rather large!

 

here's what we did (note: this is not a recommendation of what to do as it might not work for you!)

 

we installed a W750xD400xH1250 kiosk and the DNO (UKPN) came and installed the 3-phase head. our groundworkers ran a 110mm twinwall duct from the cabinet to the plant room in the basement which we pulled through a 25mm 5-core cable (which is bloody heavy!). our electricity supplier then came and installed a single-phase smart meter to one of the phases at the head. our electrician then wired the tails and the 5-core 25mm cable in to our TP&N switched fused isolator in the kiosk. he then terminated that into another TP&N isolator in the comms room to allow for future expansion to run a 3-phase supply to the garage for EV charging (if required). he then took a single phase and terminated it in the CU.

 

so we are running our whole house off a single phase but have the capability of 3-phase later on if required. e.g. if we ever built a pool house we could run a cable through the ducting I've installed to the comms room and tap in to the TP&N isolator there. or could run a 3-phase connection to the garage etc.

 

my advice with underground work is to try and think where you might need power and/or network as it's a lot easier to run it at build stage rather than after. I know as I've just had to dig 50m of trench to fit 4 x 63mm ducts for power and network to the proposed chicken house and pool house! glad I did it now though rather than have to dig up the garden and patios etc to run it later. the pool house ducts will just be left underground and can be dug up if we ever need them.