3-phase in a domestic premises

user1842

Hi,

I recently purchased an old house and it has a 3-phase supply. It needs to be fully re-wired. My electrician notes that there is no need to use the 3-phases and recommended to just use one of the phases (and neutral) connected to a standard single phase consumer unit. Basically to then run the house from just that phase (which would include a 8kW heat pump).

Any views on this?

I have been down a rabbit hole with three-phase distribution boards which nobody appears to stock and are hideously expensive.

Thanks

circadian

The only reason I could think of for keeping the 3 phase is if you were to install a large solar array. I think once the inverters go over 7KW or so then they require 3 phase.

user1842

https://www.boards.ie/discussion/comment/121941312#Comment_121941312

If I ever got an EV I could charge at 11kW or 22kW :)

Is it ok just to use one of the phases and ignore the others? if so any metering issues (it's a 3-phase meter).

circadian

Didn't realise the Zappi can do 22kwh 3 phase, that'd be handy.

tomhammer..

If you're keeping the 3 phase supply you would use all 3 phases and balance the loads across the 3

So ya the spark is wrong probably imo

meercat

I’d be inclined to keep the 3ph setup

always handy if you have

electric shower

heat pump

car charger

or if you ever put in a granny flat or home office

not sure what the difference in cost for standing charge is but it would be expensive to get 3 phase installed now or increase your M.I.C

antoinolachtnai

What your electrician recommends sounds possible but I don’t know if it would be good practice.

in particular I do not think it would be wise to install a single phase heat pump if a three phase setup was possible. It has to do with how electric motors work.

I would talk to the technical department of the heat pump vendor about this.

It may be that your electrician isn’t confident doing work on three phase and you may just need a different electrician.

Victor

What are the ESB Networks charges for three phase compared with single phase?

user1842

https://www.boards.ie/discussion/comment/121942500#Comment_121942500

Heat pump is single phase. The manufacturer does not sell the three phase version in Ireland :(

user1842

https://www.boards.ie/discussion/comment/121942113#Comment_121942113

In fairness to the electrician im not sure how much load balancing one can do in a domestic setting. Maybe heat pump on one phase, kitchen on the other and rest of the house on the last phase.

No electric shower or EV charger.

Honestly they were probably looking for the simplest and cheapest install.

I rang a few electricial suppliers and none of them do three phases distribution boards. Most of them said the electrician would need to make one up themselves with a three row board (not the most elegant solution). The majority agreed with my electrician, just use a single phase for the house.

Now im more confused than ever.

user1842

https://www.boards.ie/discussion/comment/121942313#Comment_121942313

Will definitely keep the three phase but just want to know is there any issue with using just one phase for the house.

As Tomhammer noted above, the only thing could be load balancing but does that really matter for relatively small loads.

There is also a matter of safety, im not sure how comfortable I would be having 400v in the house.

meercat

https://www.boards.ie/discussion/comment/121942915#Comment_121942915

I wouldn’t be concerned having 400v 3phase in a domestic installation.there’ll be 230v single phase at all points except the distribution board.

it'd be easy enough to make up a 3ph distribution board and as others have said, balance the load as best as possible

2011

https://www.boards.ie/discussion/comment/121942864#Comment_121942864

Then I would go with a different manufacturer.

Any 3 phase motor will be more efficient, a simpler design and more robust. Most of the cost of running a heat pump is due to the motor.

If I had a 3 phase supply available there is no way I would get rid of it.

user1842

https://www.boards.ie/discussion/comment/121943001#Comment_121943001

I think the heat pump is an inverter compressor so im not sure three-phase would make a difference.

I'm not getting rid of the three phase supply. It would just be expensive and a hassle making up a three phase distribution board. I would need at least a three row distribution board, a four pole isolator switch, four SPDs and connect everything together, then I could start with the RCBOS, very messy.

tomhammer..

https://www.boards.ie/discussion/comment/121943001#Comment_121943001

Ya i agree with all the above etc

3P supply is an asset, as meercat said keep it , unless it's cost prohibitive

Loads should be balanced and 3P equipment used where possible

Any 3P boards i fitted , I made up myself.

Bigger work there would be an assembler supplying them

Lenar3556

https://www.boards.ie/discussion/comment/121941377#Comment_121941377

Note however that 11KW is as fast as most EV’s can charge on AC.

(Renault Zoe & Tesla I think can utilise 22KW)

2011

https://www.boards.ie/discussion/comment/121943796#Comment_121943796

....and BYD

The Ging and I

I have 3ph and as other posters have advised spread the connections across the 3. Do not put it all on one.

2011

https://www.boards.ie/discussion/comment/121943146#Comment_121943146

A three phase inverter type compressor is more efficient than a single phase unit.

https://givenergy.co.uk/three-phase-inverters-what-are-they-how-do-they-work-and-what-are-their-benefits/#:~:text=Simply%20put%2C%20three%2Dphase%20inverters,performance%20of%20your%20electrical%20system.

I have built and designed many 3 phase boards, it really is not that complicated. Certainly not cost prohibitive. A larger enclosure is required but these are not expensive. The difference in cost between a 2 pole and 4 pole isolators and SPD's is not that much either. The single phase RCBO's are the same, they just use a 3 or 4 pole busbar.

user1842

Thanks all,

I think what I will do is see if the heat pump can be changed to 3-phsae and if so then get the electrician to build a 3-phase distribution board.

If not, and this is probable, then just use a single phase board for the house (have to go with the cheaper option here as single phase boards comes pre-built).

I cannot see any requirement for a domestic premises to load balance so I don't see any issue with feeding the house from just a single phase (neutral is suppled and it the same diameter as the phase).

In the future, if I get an EV, I can pull the 3-phases from the meter (already located in the garage) to small distribution board to feed the EV.

meercat

If you have a 3ph supply then you’ll need a 3ph board anyway with main isolation and surge protection

it’ll be simpler and not much dearer to build a complete 3phase distribution board

user1842

https://www.boards.ie/discussion/comment/121945938#Comment_121945938

Not necessarily, nothing wrong in taking one phase from the customer main overcurrent device at the meter and running that to a single phase distribution board.

Unfortunately there is a significant difference in cost between a pre-built single phase consumer unit and a three phase unit that the electrician would need to put together (im not sure why people on here are saying otherwise). Budget is very tight.

tomhammer..

https://www.boards.ie/discussion/comment/121946208#Comment_121946208

Maybe make your mind up what you want

3P supply you fit a 3P board and use 3P equipment(if available )and balance the loads

meercat

https://www.boards.ie/discussion/comment/121946208#Comment_121946208

Ah here

do the job right or not at all

at least run the 3 phases to the distribution board

just put a 3 phase isolator in it( minimal cost)

theres really no difference cost wise between a 3ph board and single phase

tomhammer..

https://www.boards.ie/discussion/comment/121946208#Comment_121946208

Dunno us there anything in the esbn code of practice on that

It's not standard practice anyhow to use 1 phase only on a 3P metered supply

As said above the only difference is the 4 pole isolation and SPDs

2011

https://www.boards.ie/discussion/comment/121946314#Comment_121946314

Exactly this.

2011

https://www.boards.ie/discussion/comment/121946208#Comment_121946208

"Unfortunately there is a significant difference in cost between a pre-built single phase consumer unit and a three phase unit…"

In the broader context, there isn't a substantial variance in cost. Perhaps you need to shop around.

It's crucial to consider the long-term savings that come with a more efficient 3 phase heat pump. Eventually, you'll likely value having a 22kW car charger, and even if you don't, it could significantly enhance the appeal of your home to potential buyers down the line if you decide to sell.

Personally, I would strive to install a substantial solar array in the future, one that exceeds what's allowed with a single-phase supply.

Tax The Farmers

Fun fact: Three phase domestic supplies while unusual in Ireland are quite frequently encountered in some European mainland countries where three phase electric cookers are a thing.

We may start to see more of them here as electric cars become more popular ?

cnocbui

3 phase is standard in Australia. I really miss instant hot water heaters that do away with the need for a cylinder, timers, corrosion prone immersion elements…