Suggestions - 3 Phase v Single Phase for Domestic Dwelling

Joined
10 Jul 2007
Messages
7
Reaction score
0
Country
United Kingdom
Hi

I would be grateful for suggestions/advice regarding this -

We have a plot of land to which there is a 3 phase supply, the supply comes into a distribution box sited on an exterior wall (it was sited before any building was erected).

On the site there is now a small 2-room brick building and a wagon (like a caravan) both wired Single Phase fed from the distribution box, each has its own consumer unit.

There is now a 2-bed house being erected and we have to choose how to connect this up. We have 2 options -

1. Move the distribution box into the house, re-connect to main supply, re-route cables to brick building and wagon and wire up the house off the distribution box 3 phase

2. Leave the distribution box where it is (no change needed to cables to brick building and wagon) run a cable from distribution box into a consumer unit located in the house and wire up the house Single Phase.

Originally the idea was to move the distribution box into the house but we are unsure if this is actually the best option.

Does anyone have any suggestions as to which option is best or doesn't it matter?

Thanks

Kevin
 
Sponsored Links
how are you planning to use this house, is it going to be rentend out to a long term tennant? used for holiday letts? used by the same people who use the existing facilities? sold on? something else?

is this distribution box after the meter (which would indicate you own it) or before multiple meters (which would indicate the leccy co own it)?

is this box appropriately waterproof?

what are the main fuse ratings for the 3 phase supply?

got any pictures?
 
Thanks for your reply

how are you planning to use this house, is it going to be rentend out to a long term tennant? used for holiday letts? used by the same people who use the existing facilities? sold on? something else?

Probably holiday letts

is this distribution box after the meter (which would indicate you own it) or before multiple meters (which would indicate the leccy co own it)?

After the meter - we definitely own it. The site is cabled from a local sub-station (our very expensive cable) and metered at the sub-station. There should be enough main cable to run to the house.

is this box appropriately waterproof?

Good point! and probably not as it was supposed to be a temp site for it but if we go with keeping it 'outside' we will replace the existing box and fully weatherproof it

what are the main fuse ratings for the 3 phase supply?

Sorry don't know but it was supposed to be sufficient to supply the whole plot - originally 4-bed house plus outbuildings

got any pictures?

Not scanned ones

PS This site is outside the UK but it is the basic principle 3 v 1 phase I am asking for opinions on.

Thanks

Kevin
 
If outside the UK you need to ask the local electricity supply company what is usual practice.
 
Sponsored Links
securespark said:
If outside the UK you need to ask the local electricity supply company what is usual practice.

We are building in the Ukraine, either option will be ok
 
The downside i see of having the main DB inside the house and using it to directly supply the stuff in the house is firstly the space it will take up and secondly the access arrangements. You don't want the house tennants to be able to turn off the other properties and yet you also don't really want them to have to call you if a lighting breaker trips (which happens all too often when bulbs blow). You also don't really want to have to intrude into the house because the breaker for someone else tripped.

The downside i see of putting the house (which i assume will be a much larger load than the small building and wagon) on one phase is that if the main fuses are too small and the house has lots of large electric loads then you may have issues with the main fuse that covers the house blowing.

another option would be to leave the main DB where it is and take a 3 phase feed from it into the house.
 
another option would be to leave the main DB where it is and take a 3 phase feed from it into the house.

Brilliant idea, plugwash. can you please tell me roughly what this would entail? I am not going to do this myself but would like to know so I am not dupped (again).

Would this option require something like -

Install new 3-phase distribution box in house

Run 5-core armoured cable from external DB (one connected to each phase, plus neutral and earth) to house DB. If so I guess we would need a MCB on each phase of the existing and house DB's ie if we assume (for the moment) the house will have a max demand of say 120A would we need say a 50A MCB on each phase (3 * 40A = 120A needed plus a margin)

If this is correct, Am I right in thinking we would then only need to size a cable that will handle 50A per core?

Thanks

Kevin
 
Domestic 3-phase is handy in countries that have long cables runs and substantial voltage drops.


In Oz it is quite common to have 3-phase cookers and air con in quite small houses. It's also handy if you have large machinery, smelting furnaces, pottery kilns or large electric heating (uncommon).


Is that the way it's done over there?

There are additional risks in having multiple phases in a single room, as the voltage between phases is greater so electric shocks are worse. In a large building you sometimes use a different phase for each floor which spreads the load with reduced risk.
 
JohnD said:
Domestic 3-phase is handy in countries that have long cables runs and substantial voltage drops.


In Oz it is quite common to have 3-phase cookers and air con in quite small houses. It's also handy if you have large machinery, smelting furnaces, pottery kilns or large electric heating (uncommon).


Is that the way it's done over there?

There are additional risks in having multiple phases in a single room, as the voltage between phases is greater so electric shocks are worse. In a large building you sometimes use a different phase for each floor which spreads the load with reduced risk.

Hi

I don't think 3-phase for domestic dwellings is common in the Ukraine except for the larger properties - probably much like the UK. The voltage is slightly lower at 220V and the distances from sub-stations is generally not too far. Our plot is perhaps 300m away but we have a huge main cable running from sub-station to the plot. I cannot remember the exact cable capacity but it is about 300A

The biggest problem in the part of the Ukraine where we are is that everyone is after money and they lie, cheat, over-spec, over-charge, etc to make as much as they can get from any job. Getting genuine impartial advice is near to zero.

Yours

Kevin
 
If you have 300A per phase available, there's no need to give the house 3-phase. Just use 1 phase, with a 100A SPN Switchfuse in your distribution cabinet.

(which by the way I would rebuild in brick with a strong locked door to prevent interference, or buy a steel street cabinet and fit your own internal locks)

If you have 100A per phase, that's still ample for a 2-bed house, and you only need 1 phase. Again, a 100A SPN switchfuse in the cabinet. Supply the other building and caravan pitch from the other phases.

Run underground cable ducts of good size to each position, and leave loops of polyurathene rope inside them so you can draw in a larger cable if at some time you need it. For example, one day you might decide to put machinery in the outbuilding.

BTW I have a house of reasonable size, and my suppliers fuse (although the holder says 100A) is only 60A, this is quite common, and unless you use two big electric showers at the same time is more than enough. Big electric cookers cycle the rings and ovens on and off thermostatically, so hardly ever take full load for even a few minutes.
 
JohnD said:
If you have 300A per phase available, there's no need to give the house 3-phase. Just use 1 phase, with a 100A SPN Switchfuse in your distribution cabinet.

(which by the way I would rebuild in brick with a strong locked door to prevent interference, or buy a steel street cabinet and fit your own internal locks)

If you have 100A per phase, that's still ample for a 2-bed house, and you only need 1 phase. Again, a 100A SPN switchfuse in the cabinet. Supply the other building and caravan pitch from the other phases.

Run underground cable ducts of good size to each position, and leave loops of polyurathene rope inside them so you can draw in a larger cable if at some time you need it. For example, one day you might decide to put machinery in the outbuilding.

BTW I have a house of reasonable size, and my suppliers fuse (although the holder says 100A) is only 60A, this is quite common, and unless you use two big electric showers at the same time is more than enough. Big electric cookers cycle the rings and ovens on and off thermostatically, so hardly ever take full load for even a few minutes.

That's good to hear. The possible sticking point would be water heating and air con. If we can install gas for water heating that maybe fine otherwise it may mean a couple of instantaneous water heaters - kitchen and bathroom, in addition to 1 shower. Air Con will be installed but these vary quite a lot in power I am assuming (until we check it out) we could run these off the normal ring circuits, still using power though.

The other sticking point is lighting. The wife wants halogens in both bedrooms, bathroom and kitchen. The bedrooms are quite big and we are working to 8 lamps per room, kitchen will be similar, bathroom maybe 4 lamps. At 50W per lamp this is quite a lot.

In the hot summer evenings I can easily foresee lots of lights on, 4 air con units blasting away, someone cooking and washing up, someone else having a shower. So I am a little worried of usage keeping under 100A

If we were to install a cable of say 50A capacity per phase and run that from the DB to a 3 phase DB in the house, I am right in thinking this would give us 50A per phase in the house ie a total upto 150A - we would have to balance the loading of course.

If this is correct what size of cable would we need - the box is about 10m from the house

Thanks

Kevin


Thanks

Kevin
 
I think 10mm 4-core 3-phase armoured copper. (It's 58A clipped direct but I can't see correction factors for underground duct.)

2-core single phase is 25mm for 118A (subject to correction factors)

Someone will know.

There is also a voltage drop depending on length, at 10m that would be 38mv/A and 15 mV/A respectively (less than 2v at max load)

Fixed air con should not be taken of the socket circuit.

Most countries outside UK do not use ring circuits for sockets.

You should be looking at energy-saving lamps.
 
JohnD said:
I think 10mm 4-core 3-phase armoured copper. (It's 58A clipped direct but I can't see correction factors for underground duct.)

2-core single phase is 25mm for 118A (subject to correction factors)

Someone will know.

There is also a voltage drop depending on length, at 10m that would be 38mv/A and 15 mV/A respectively (less than 2v at max load)

Fixed air con should not be taken of the socket circuit.

Most countries outside UK do not use ring circuits for sockets.

You should be looking at energy-saving lamps.

Thanks JohnD thats great info and will give me something to check those Ukrainian electrician suggestions against when we go over in 3 weeks time.

Virtually all of the air con units over there in shops, etc are all 'plug in' types maybe they are smaller powered than those in the UK and at around £200 fitted they are certainly cheaper. No reason why we couldn't provide individual circuits for them though

I don't know if it is possible to get energy-saving lamps there, and somewhat doubt it

Thanks again

Kevin
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top