2 Phase supply to barn

[dunny]

I will hopefully be lucky enough to be buying a barn that was previously part of a farm. The barn is partially completed although the electrics are approaching a first fix stage but not quite there yet. In fact I think, given that the whole place is just a shell, it might be worth taking them out and starting again.

It appears to have a 2 phase supply in and it currently is shared with the farmhouse next door via overhead cables. I will need to get a separate supply put in and was wondering whether a building of this size (4350 sq ft) would require a 2 phase supply??

Are the cables that bring the supply in the same as a normal domestic supply (I assume they are different given the additional voltage they carry)??

Is 2 phase more expensive to install?

Any info on this topic would be great.

D

 

[Chri5]

The general rule of thumb for the DNO is 100 amp limit on a single phase.

Do you think that the barn will require more power than 100 amp.

I would suggest you look at what you intend to use electricity for within the property and calculate from there.

Simple things like:-

Heating- Electric or gas
Cooking- Electric or gas
Showers- Electric or gas CH HW
Rooms- How many
Outbuildings- What will they need
Kitchen / Laundry room kit and electrical demands

Lifestyle- Do you stay indoors (retired or home working)

At 4500 sq ft, you have a large footprint and you need to decide if the overall demands of the site will require a large supply than 100 amp single phase

 

[Adam_151]

Supplies are normally 3 phase (for anything above the smallest commerical concern) or single phase (for most houses), two phase does exist and it may be two phases from a three phase system (where the area is pretty urban and has a three phase transformer and the client doesn't actually need all three), or split phase in more rural areas where a single 11kv phase is brought down to a centre grounded transformer, you still get 230v between phase/neutral and phase/earth, but they are 180 apart instead of 120 and so phase/phase is 460v instead of 400v

Neither 2 phases from a three phase system, nor split phase are much good if you want to use motors, etc

Anyway, are you sure you have more than one phase, and not that the DNO hasn't just brought two phases off the pole and given one to the farmhouse and one to you? or do you only have one meter between you and have some kind of submain involved? I'm not entirely sure what you have, any chance of some photos?

Anyway, you house is a bit bigger than normal, but if you heat by gas I'm not sure you'd have problems with 100A single phase... could always approach the DNO and see what they say about installing a three phase supply, how much it'll cost etc..... but shouldn't this have been sorted out prior to the electrical design stage

A regards to cables, yes they are obviously insulated to the highest voltage present (phase-phase on a 120 spaced 3 phase is 400v), the biggest difference to single phase supply cables are the extra cores...

 

[dunny]

We are a family of four , the kids still young (7 and 3). I also work from home and we will have reasonable demands once things like security lighting, electric gates, electric garage door, outside lighting etc is in place.

Heating will be oil or gas.
Showers will need to be at the high end (pumps maybe??)
Cooker will likely be electric/gas
There will be oodles of rooms - 4 double beds, huge bathroom, 3 ensuites, large kitchen diner, large formal diner, lounge, large office, wetroom and a gym - plus utility , outside toilet, store.

There are huge lights on columns in the garden and other floodlights here and there - as well as CCTV.

Sound maybe getting near a domestic limit??

Regards

D

 

[dunny]

Anyway, you house is a bit bigger than normal, but if you heat by gas I'm not sure you'd have problems with 100A single phase... could always approach the DNO and see what they say about installing a three phase supply, how much it'll cost etc..... but shouldn't this have been sorted out prior to the electrical design stage

To be honest Adam I am not sure there has been a 'design stage'. The guy who owned the farmhouse also owned the barn. There is a single supply at present which comes in from the farmhouse. This needs to be split as part of the obligations of the vendor (that means me for the barn).

I looked inside the barn and there are cables running all over the place clipped to beams and I think at present only provide light and maybe a couple of temporary sockets. I think all of this needs to be stripped out and started again. There are no ceilings in place and no plaster on the walls so its a blank canvas really.

When I looked at where the supply came in there was a huge grey steel box with a big chrome on/off switch (in fact I think there was more than one) and it gave me the impression that it was more than a usual domestic supply. Given that the barn used to be part of a working farm and outside has got huge floodlights on poles etc I assumed it would be more than a single phase.

What I am not sure about is whether I need more than a single phase or not...

 

[JohnD]

You can run a pretty big house on a single-phase 80A supply, inluding a big electric cooker, a tumble drier, washing machine and dishwasher.
Lighting loads are not significant, even if you have outdoor lighting (anyway, you should be using energy saving bulbs/CFLs).

100A should be plenty.

The things that eat electricity are:

Electric showers
Electric heaters
Electric hobs
Electric swimming pool heaters

Which are much more expensive to run than gas or electric ones anyway.
Are you expecting to have (m)any of them?

 

[dunny]

The things that eat electricity are:

Electric showers
Electric heaters
Electric hobs
Electric swimming pool heaters

Which are much more expensive to run than gas or electric ones anyway.
Are you expecting to have (m)any of them?

Electric showers - NO
Electric heaters - NO
Electric hobs - maybe as part of the cooker.
Electric swimming pool heaters. not yet at least - maybe a hot tub though...

D

 

[JohnD]

Then I see no reason why single phase should not be enough. I believe UK hot tubs are usually only 13A.

Try to get a gas hob, they're better than electric.

You will need a big hot water store with all those bathrooms. A place I stayed at a while ago (in Australia) had a hot water cylinder for each bathroom, a good idea, as it prevents one or two extravagant people using it all up. They supplemented the boiler with Solar. May need a bit of advanced HVAC design though. Preferably you could turn off the ones for guest rooms when unoccupied.

 

[plugwash]

Neither 2 phases from a three phase system, nor split phase are much good if you want to use motors, etc

if i'm not very much mistaken if you have two of the three phases and a neutral then it should be possible to put together a transformer combination that gives 3 phase.