Hello fellas , Had a message from a potential customer as follows " We have 2 houses with 2 supplys and need advice on how to join the two . Main house has 3 phase supply and other house has single phase supply " Your thoughts please , Im thinking use 3 phase supply and run 25mm swa to 2nd property . Havent seen properties yet , should be visiting on friday , would like to know what you guys feel would need to be done as never came across this before . many thanks
2 houses , 2 supplys , advice on how to combine the two
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jameseye12
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If the three phase supply is big enough for the total load of the combined houses, then just use that and do away with the single phase one.
Install switchfuse from three phase head and use 25mm swa as you have suggested to take power to existing single phase board
You're on the right lines
Install switchfuse from three phase head and use 25mm swa as you have suggested to take power to existing single phase board
You're on the right lines
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remember to keep your phases balanced though.
Hoping the properties are similar size so balancing shouldnt be an issue although there was mention of outbuildings . So lets say case scenario is 1st property out balances phase due to heavy demand compared to 2nd property then we split 1st property into 2 seperate and try and equally split over 2 phases . Likelyhood of both properties being similar is unlikely if 1 has 3 phase supply but how close does the balance have to be ? Thanks not really worked on 3 phase before , domestic single phase monkey , hopefully get a bit of 3 phase experience 1 day , not easy as nobody really wants to give you a go if only know domestic . thanks guys .
Doc Hudson
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I would think a project like this needs a comprehensive design analysis of exactly what loads the customer will be needing to supply across the new property layout. Also you need to verify what is the actual rating of the existing supplies. are they 80A/100A per phase or less? Assume nothing, treat it as a blank sheet where everything must be confirmed before you start designed how you will construct the electrical installation.
Doc H.
Doc H.
DNO will not "normally" allow 2 separate supplies in a domestic.
Summation yes, 2 separate incomers not normally.
So, your first port of call would be releasing one supply.
There will be a cost especially if you need the head removing as they will need to cut the cable.
Putting 3ph in a domestic is not too much of a drama, just avoid the obvious pitfalls, sockets on different phases in the same room say.
Summation yes, 2 separate incomers not normally.
So, your first port of call would be releasing one supply.
There will be a cost especially if you need the head removing as they will need to cut the cable.
Putting 3ph in a domestic is not too much of a drama, just avoid the obvious pitfalls, sockets on different phases in the same room say.
Technician
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Had a question from a guy who does a lot of music in a
Church Hall. He asked me what manner of supply it
might be. I told him that with the floor area, possible
anticipated maximum demand it would be three phase
in all liklihood.
He asked me how he should plug his kit in and I said that
he should try to have all his kit on one phase so that
should a fault develop, the voltage would be limited to
that on a single phase.
I submit this after looking at Sidewinder's post.
Some years ago I was on a re-wire of a pub, (3 phase)
and the only way of "balancing" was to place loads as
follows;
Catering Kitchen.
Pub premises.
Upstairs flat and kitchen.
I did not sign it off by the way.
Church Hall. He asked me what manner of supply it
might be. I told him that with the floor area, possible
anticipated maximum demand it would be three phase
in all liklihood.
He asked me how he should plug his kit in and I said that
he should try to have all his kit on one phase so that
should a fault develop, the voltage would be limited to
that on a single phase.
I submit this after looking at Sidewinder's post.
Some years ago I was on a re-wire of a pub, (3 phase)
and the only way of "balancing" was to place loads as
follows;
Catering Kitchen.
Pub premises.
Upstairs flat and kitchen.
I did not sign it off by the way.
I must add that IMHO and in my experience, trying to balance a 3ph supply across single Phase circuits is virtually impossible .
You can set all your lighting out equally across RYB but if no one switches the lights on in the B area you're unbalanced straight off.
You can get near it in an industrial situation with lots of 3ph motors running and all the lights on but the offices will upset it ,depending on who and what is in there.
Really all you can do is divide the circuits up as equally as possible , and as said above, avoid 2phases of sockets in the same room etc .
You can set all your lighting out equally across RYB but if no one switches the lights on in the B area you're unbalanced straight off.
You can get near it in an industrial situation with lots of 3ph motors running and all the lights on but the offices will upset it ,depending on who and what is in there.
Really all you can do is divide the circuits up as equally as possible , and as said above, avoid 2phases of sockets in the same room etc .
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So , how does it work for example in a block of flats where you have 3 phase incoming , where to balance you would need flats in multiples of 3 ( 3 , 6 , 9 , 12 flats etc ) . If you had 7 flats how do you equally balance them over a 3 phase supply ?
The neutral would balance a set of flats.
AndyGuinness
AndyGuinness
sidewinder , can you explain in more detail why and how to balance ( 2 seperate consumer units in 2 different properties , does that mean all circuits would need to be calculated and distributed between 3 consumer units ?)
---------- Post Auto-Merged at 22:38 ---------- Previous post was made at 22:34 ----------
So why wont the neutral balance the 2 properties , is the principle not the same ? if not can you please explain , not had much experience of 3 phase , thanks .
---------- Post Auto-Merged at 22:59 ---------- Previous post was made at 22:38 ----------
Why avoid 2 phases of sockets in the same room?
---------- Post Auto-Merged at 22:38 ---------- Previous post was made at 22:34 ----------
So why wont the neutral balance the 2 properties , is the principle not the same ? if not can you please explain , not had much experience of 3 phase , thanks .
---------- Post Auto-Merged at 22:59 ---------- Previous post was made at 22:38 ----------
Why avoid 2 phases of sockets in the same room?
philbas
Well-known member
I'll have a go at this 
1) I think it's unlikely you can balance a 3 phase domestic split over 2 properties, you can asses the likely needs of each property, this could change, is the smaller one a Granny Flat or a Tennage hang out, just look at the likely split, could be the smaller on will use more.
2) The neutral doesnt Balance it, it takes away the imbalance, if its perfectly balanced the current in the neutral is 0.
3) We have a potential difference of 415v between sockets in the same room.
1) I think it's unlikely you can balance a 3 phase domestic split over 2 properties, you can asses the likely needs of each property, this could change, is the smaller one a Granny Flat or a Tennage hang out, just look at the likely split, could be the smaller on will use more.
2) The neutral doesnt Balance it, it takes away the imbalance, if its perfectly balanced the current in the neutral is 0.
3) We have a potential difference of 415v between sockets in the same room.
Hi all,
Just my "newbie" opinion here!!
Sounds a completely daft idea to me to be honest.... Firstly, how you going to balance it all?? If you are going to run a Three phase submain to the second house, you will have some chance, but then you are going to have to completely re-design and rewire the installation in possibly both houses to try to balance the loads, and all without having things in close proximity on separate phases.. Not easy....
Say you just run a single phase to the second house; You got no chance then.. Say they have their shower and possibly an electric cooker on in the second house, and this is then added to whatever the same phase is supplying in the first house, at some stage or other the phase balance will be terrible..
Do not suppose it matters overly much though, as long as you do not overload the one phase, but you will have high neutral currents as a result of the imbalance. Not sure the effect this will have, but it is undesirable in any case.
Second, metering; How you going to do this? The people in the second house will have to have their own "sub meter" i suppose you would call it, and "chip in" to the first houses bill.
Lets say that the property owners have in mind that with their [To their mind] hugely powerful three phase installation in the one house, that running it to the second house with be a useful "upgrade" to the second house as it were. Ummm, wrong.. As has been pointed out, the DNO will not allow two supplies to the same house, so they will have to pay to have the first, existing supply removed, and I expect they will find that this will cost more than having an entirely new "beefed up" [if this is what they are after] supply to to the second house installed properly, especially considering all the additional alterations and expense to try to balance everything properly if they go for "plan A" !!
Apart from this; What type of supply has the first house got? [from the point of view of earthing] This will all add to the fun!!!!
john...
Just my "newbie" opinion here!!
Sounds a completely daft idea to me to be honest.... Firstly, how you going to balance it all?? If you are going to run a Three phase submain to the second house, you will have some chance, but then you are going to have to completely re-design and rewire the installation in possibly both houses to try to balance the loads, and all without having things in close proximity on separate phases.. Not easy....
Say you just run a single phase to the second house; You got no chance then.. Say they have their shower and possibly an electric cooker on in the second house, and this is then added to whatever the same phase is supplying in the first house, at some stage or other the phase balance will be terrible..
Do not suppose it matters overly much though, as long as you do not overload the one phase, but you will have high neutral currents as a result of the imbalance. Not sure the effect this will have, but it is undesirable in any case.
Second, metering; How you going to do this? The people in the second house will have to have their own "sub meter" i suppose you would call it, and "chip in" to the first houses bill.
Lets say that the property owners have in mind that with their [To their mind] hugely powerful three phase installation in the one house, that running it to the second house with be a useful "upgrade" to the second house as it were. Ummm, wrong.. As has been pointed out, the DNO will not allow two supplies to the same house, so they will have to pay to have the first, existing supply removed, and I expect they will find that this will cost more than having an entirely new "beefed up" [if this is what they are after] supply to to the second house installed properly, especially considering all the additional alterations and expense to try to balance everything properly if they go for "plan A" !!
Apart from this; What type of supply has the first house got? [from the point of view of earthing] This will all add to the fun!!!!
john...
Technician
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Two sockets in the same room means that there are two
simultaneously accessible exposed conductive parts within
one room connected between two live conductors. The
fault current would be large, and the potential shock voltage
would be in excess (big style) of the 230 line to neutral
voltage.
It is a primary requirement of three phase installations that
this situation is avoided as Sidewinder stated.
Evans makes the point that if most of the load is three phase
motors, balancing is easy. I have worked on installations where
the three phase load was over 95% balanced, but these are not
common.
simultaneously accessible exposed conductive parts within
one room connected between two live conductors. The
fault current would be large, and the potential shock voltage
would be in excess (big style) of the 230 line to neutral
voltage.
It is a primary requirement of three phase installations that
this situation is avoided as Sidewinder stated.
Evans makes the point that if most of the load is three phase
motors, balancing is easy. I have worked on installations where
the three phase load was over 95% balanced, but these are not
common.
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Wsoppitt , I would'nt worry about balancing if I were you .
Just do your design , if its two very large houses from one supply, high expected load then keep the 3Ph .
Sockets on two phases in a child's room say, loads of games and computers and printers and TV and Hi-Fi and Mobile chargers all plugged in and mixed up together ............ voltage between flexes ...415V.... not the best situation .
Just do your design , if its two very large houses from one supply, high expected load then keep the 3Ph .
Sockets on two phases in a child's room say, loads of games and computers and printers and TV and Hi-Fi and Mobile chargers all plugged in and mixed up together ............ voltage between flexes ...415V.... not the best situation .
Hello fellas , turns out the property has a 3 phase supply , of which the existing consumer unit is connected to 1 phase via a single phase meter , so cannot split over the phases anyway . Turns out 2nd property is basically 2 small rooms downstair and 1 small room and bathroom upstair so will just run as submain from main consumer unit in 16mm t+e .
ring 1 ( 4 sockets)
ring 2 ( 6 sockets)
radial ( 2 socket + outside light )
lights up ( 4 )
lights down ( 3 )
lights outside ( 3 )
as you can see small installation , 16mm just incase electric shower needed in future is my logic .
Also customer asked about bonding of copper bath , i told him not necessary as dual rcd consumer unit is fitted , but for peace of mind he can fit bonding between all pipework and electrics within what will be a bath in a bedroom ( no room in bathroom ) . Told about zoning with regards to existing sockets within room . The question i have is what are your thoughts on bonding do or dont and would the bedroom now require an extractor ?
ring 1 ( 4 sockets)
ring 2 ( 6 sockets)
radial ( 2 socket + outside light )
lights up ( 4 )
lights down ( 3 )
lights outside ( 3 )
as you can see small installation , 16mm just incase electric shower needed in future is my logic .
Also customer asked about bonding of copper bath , i told him not necessary as dual rcd consumer unit is fitted , but for peace of mind he can fit bonding between all pipework and electrics within what will be a bath in a bedroom ( no room in bathroom ) . Told about zoning with regards to existing sockets within room . The question i have is what are your thoughts on bonding do or dont and would the bedroom now require an extractor ?
Its now become a "Special Location " so its a bathroom with a bed in it . The criteria of low skin resistance applies IMHO. Sockets need to be moved out of zones etc. And a fan would be required under building regs.
If main bonds are in place and all bathroom electrics are on an RCD bonding can be ommitted.
If main bonds are in place and all bathroom electrics are on an RCD bonding can be ommitted.
Technician
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Yes Evans; true; AND the disconnection times have to be met.
Doc Hudson
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Has the copper bath got a metal waste pipe going directing into the ground? in which case it may be an extraneous part and require bonding. If it has a plastic waste pipe then it could be just a piece of metal that is neither part of the electrical installation nor likely to introduce and earth potential. In which case bonding is not needed. I would suggest doing a quick continuity test between the bath and electrical earth to help decide if it is required or not.
Doc H.
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