Single or 3 phase

[mjc55]

So how many on here have gone for 3 phase on their newbuild?

 

I haven't looked into this yet and so have no real insight as to the necessity to go for 3 phase so this may be a silly question.

 

I have a quote for a single phase connection to site and was wondering if this was increased to 3 phase, would the costs vary significantly.

[joe90]

As we are encouraged to use less with LED lights etc I can only guess it’s the amount you can sell back to the grid with PV 🤷‍♂️

Edited August 3 by joe90

[mjc55]

Just read that a fast 22 Kw car charger would require 3 phase, is that experience of others. 

[Alan Ambrose]

Fine if you can get it - not much extra install costs - it's only one cable after all. Will be expensive if there's no 3P transformer near though.

[markocosic]

If available I'd do it for vehicle charging and future PV / battery reasons.

 

Most EVs have 16A / 3.6 kW chargers. Two or three of them. If two, then max charge rate is 7.2 kW. If three, then they only use two when on single phase (to avoid melting cables), but can use three when on three phase (to charge at 11 kW) 

 

Very few can do 22 kW charge; but two 11 kW vehicles can easily.

 

Beware that smart meters may take longer to source when on 3ph in the UK.

[IanR]

3 hours ago, mjc55 said:

So how many on here have gone for 3 phase on their newbuild?

 

I have 3 phase, although only use 2 phases for the house and 3 phase in the workshop.

 

EV charging, batteries, V2H and V2G technologies are all in their infancy and will develop quickly over the next 10 years - If the connection costs around the same I'd go with 3 phase to protect for multiple EVs being charged over night with the larger battery capacities that will come along with solid state batteries.

 

It may complicate a PV & battery installation, although keeping your house on a single phase and a SMET2 3P Smart meter may mitigate most issues.

[mjc55]

51 minutes ago, IanR said:

 

I have 3 phase, although only use 2 phases for the house and 3 phase in the workshop.

 

EV charging, batteries, V2H and V2G technologies are all in their infancy and will develop quickly over the next 10 years - If the connection costs around the same I'd go with 3 phase to protect for multiple EVs being charged over night with the larger battery capacities that will come along with solid state batteries.

 

It may complicate a PV & battery installation, although keeping your house on a single phase and a SMET2 3P Smart meter may mitigate most issues.

 

Cost wise, was there much difference between going single/3 phase?

[IanR]

25 minutes ago, mjc55 said:

 

Cost wise, was there much difference between going single/3 phase?

 

I didn't get a price for single phase, as I needed (wanted) 3 phase for the workshop. My connection was around £7.5K, but included 130m of install through a duct in a trench. The 1 phase v. 3 phase difference would have been in the 100kVA pole mounted transformer that was around £2,900 of the connection price. I was told that this would have been lower for a single phase connection, but I don't remember a price. I doubt it would have made that much difference.

Edited August 3 by IanR

[Conor]

A year ago I would have said not to bother with 3 phase.

We're probably going to get a second EV within the year and I'm already struggling to see how ill be able to charge both on low rate at the same time. 

 

But good point by @markocosic, older EVs tend only to have 3.6kW charging (like our leaf) and newer ones are rarely more than 7.2.

[Jilly]

Definitely worth comparing. Also see what the offer you, there might be no choice in some locations. 

Edited August 4 by Jilly

[Dave Jones]

18 hours ago, mjc55 said:

So how many on here have gone for 3 phase on their newbuild?

 

I haven't looked into this yet and so have no real insight as to the necessity to go for 3 phase so this may be a silly question.

 

I have a quote for a single phase connection to site and was wondering if this was increased to 3 phase, would the costs vary significantly.

 

Western power dont give an option of single phase on any new builds.

 

Not to say you cant have a single phase meter (wee did) after the 3 phase cable has been connected.

[mjc55]

Just had quote back from Scottish & Southern for 3 phase.

 

So single phase quote (Last December) was £7149.29.  3 phase quote is £7723.25!  So not significantly different.

 

I expect the slight increase is just as a consequence of it being 9/10 months later.

 

The quote numbers were the same so I expect they just did a bit of a cut and paste for the 3 phase quote.

 

This is of course for a connection to an external (temporary) meter box close to the front of the site.  What happens when the house is complete and we want to then put meter etc. in the plant room in the house.  Do they junction the cable underground or is there a requirement to pull another (longer) cable through the ducting so that it is one piece of cable?

Edited August 30 by mjc55

[LnP]

I went for 3 ph in a new free standing meter box in its final position, adjacent to a side boundary. I used this calculator from SSEN to decide how big the supply needed to be.

[Mr Blobby]

We have a 3-phase connection to our on-going build.  We want 2 EV 3-phase chargers for two EVs (Tesla charge 11KW 3 phase if ever needed).  We also also want to charge simultaneuosly off peak and maybe charge batteries simultaneously so the house load will be quite high. I think we have 3 100 amp fuses which the DNO had no problem with, so lots of headroom. 

Also 3P means its easy to install solar PV > 3.6kw limit without any hassle.

 

For us the cost was only slightly more than single phase because of our location to the pole and cables. 

 

We are running all 3 phases into the house and balancing them and running a 3-phase hybrid inverter.  Will be interesting.

 

If the cost is not prohibitive then go 3-phase.  Its more interesting too.

 

 

[Alan Ambrose]

>>> Its more interesting too.

 

Ho ho ho. By all means have 3P if you want and if there’s little additional cost. You can always use just one phase for the house if you like. There is a bit of an anomaly though - you want the 1000hp of a Bugatti veyron while supposedly running a passivehouse which is sipping energy like a Prius? There will also be additional cost and less choice and more complexity for 3P inverters, batteries etc - if you decide you need them.

 

I think it’s possible also that we might all end up paying a premium for peak loads - it’s that that impacts the capital expenditure on the grid after all. France has this kind of arrangement in a basic form - with higher payment for a higher main fuse (and therefore peak load). Also, that’s how your fixed line internet works - you pay for higher max bandwidth. Once you have a smart meter, then all sorts of innovative charging schemes can by created with very simple software changes at your electricity supplier.

[mjc55]

i was going to ask the question this morning about the possible downsides of 3 phase supply @Alan Ambrose has certainly started the ball rolling!

[mjc55]

1 hour ago, Alan Ambrose said:

>>> Its more interesting too.

 

Ho ho ho. By all means have 3P if you want and if there’s little additional cost. You can always use just one phase for the house if you like. There is a bit of an anomaly though - you want the 1000hp of a Bugatti veyron while supposedly running a passivehouse which is sipping energy like a Prius? There will also be additional cost and less choice and more complexity for 3P inverters, batteries etc - if you decide you need them.

 

I think it’s possible also that we might all end up paying a premium for peak loads - it’s that that impacts the capital expenditure on the grid after all. France has this kind of arrangement in a basic form - with higher payment for a higher main fuse (and therefore peak load). Also, that’s how your fixed line internet works - you pay for higher max bandwidth. Once you have a smart meter, then all sorts of innovative charging schemes can by created with very simple software changes at your electricity supplier.

I'm not sure I understand your reasoning here.

 

You can control the use of electricity in your house by various means, most obviously in heating costs etc.  A passive house by definition would require less input.  Why would having a 3-phase supply change what you actually use?  Surely input is down to requirement not the availability of supply?

 

Am I missing something?

[JohnMo]

My thoughts on the whole thing, if you need to draw more than 23kW (100A) at a time, you need to step back and really ask your why - especially in a new build.

 

Most people on this forum seem to want to build low energy houses on one hand, while on the other want a dedicated power station feeding it. Who needs 69kW, who wants to pay a bill that warrants that electric demand.

 

 

[mjc55]

3 hours ago, JohnMo said:

My thoughts on the whole thing, if you need to draw more than 23kW (100A) at a time, you need to step back and really ask your why - especially in a new build.

 

Most people on this forum seem to want to build low energy houses on one hand, while on the other want a dedicated power station feeding it. Who needs 69kW, who wants to pay a bill that warrants that electric demand.

 

 

But isn't more to do with how much you can draw at one time, especially given that electric car charging is coming more and more into the equation?

 

And why are some suppliers only offering 3 phase?

 

Note that I am not disagreeing with you just wanting to further my knowledge in an area that I am lacking in by the way.

[Marvin]

4 hours ago, mjc55 said:

But isn't more to do with how much you can draw at one time, especially given that electric car charging is coming more and more into the equation?

Yes and going forward it's the capability of electricity companies being able to dump energy into your EVs - trials recently being carried out....

[Mr Blobby]

5 hours ago, mjc55 said:

if you need to draw more than 23kW (100A) at a time, you need to step back and really ask your why

 

Because we want the option to charge two EVs at the same time in an off-peak time-frame at 11 KW each if we need to.  That's the 22kW gone.  And then we may also want to heat the water in the same off-peak window.  And maybe charge the batteries connected to the inverter as well.

This isn't about using more electricity, its about being able to time-shift higher loads into an off-peak window, something that is cheaper and greener and better for network stability.

Edited August 31 by Mr Blobby

[Mr Blobby]

On 30/08/2024 at 17:31, mjc55 said:

This is of course for a connection to an external (temporary) meter box close to the front of the site.  What happens when the house is complete and we want to then put meter etc. in the plant room in the house.  Do they junction the cable underground or is there a requirement to pull another (longer) cable through the ducting so that it is one piece of cable?

 

We have a temporary supply inside our boundary.  The DNO laid the 3-phase cable into the temporary cabinet and a single phase is split off into the temporary meter in the temporary cabinet. 

 

In a few months time when we get the meter installed in the cabinet on the side of the house (which must be bigger than a standard permali box) then the DNO will joint underground to the cable already inside the boundary.  No further excavation by the DNO required.

 

For us the initial connection that required DNO excavation outside the boundary (which is typical of course) cost way more, about 2/3 total connection cost.  If you can pay for it all up front in one bill then do so.  The initial connection is vat free as a new connection but the second DNO bill to connect to the house is a change of existing supply and is not zero-rated for VAT.

 

 

Edited August 31 by Mr Blobby

[mjc55]

2 hours ago, Mr Blobby said:

 

We have a temporary supply inside our boundary.  The DNO laid the 3-phase cable into the temporary cabinet and a single phase is split off into the temporary meter in the temporary cabinet. 

 

In a few months time when we get the meter installed in the cabinet on the side of the house (which must be bigger than a standard permali box) then the DNO will joint underground to the cable already inside the boundary.  No further excavation by the DNO required.

 

For us the initial connection that required DNO excavation outside the boundary (which is typical of course) cost way more, about 2/3 total connection cost.  If you can pay for it all up front in one bill then do so.  The initial connection is vat free as a new connection but the second DNO bill to connect to the house is a change of existing supply and is not zero-rated for VAT.

 

 

 

Thanks for that.  Makes complete sense.

 

As an aside, Is it still a requirement to have meter in an external cabinet?  They wont be coming to take a reading and it makes more sense to install the meter in the plant room!

[mjc55]

2 hours ago, Mr Blobby said:

 

Because we want the option to charge two EVs at the same time in an off-peak time-frame at 11 KW each if we need to.  That's the 22kW gone.  And then we may also want to heat the water in the same off-peak window.  And maybe charge the batteries connected to the inverter as well.

This isn't about using more electricity, its about being able to time-shift higher loads into an off-peak window, something that is cheaper and greener and better for network stability.

 

This is what I had assumed.

 

(pedantic note - sorry) It wasn't me you were responding to it was JohnMo!

[JohnMo]

6 hours ago, mjc55 said:

 

(pedantic note - sorry) It wasn't me you were responding to it was JohnMo!

Yes it was, I read it. First thing I thought, our van and car never get refueled at the same time and it's several weeks between refueling generally. Even if you did charge both cars every night and you did a 1000 miles in each car, every month, the charge time each night (for each car) would be 0.8hrs using an 11kW charger assuming the car is doing around 3.5kWh per mile.