Advice on long SWA cable run and new supply

[jim payne]

Hi,
I have a house with a standard mains supply coming down a pole in the front garden to a brick meter housing.
I also have a bungalow that is 350 metres away and is also supplied from my existing mains supply via an underground SWA cable (7 strand 1.1-1.4mm so 10A I think max) 50 metres past that is another building which is to be replaced by a new house.
I have ordered 2 new 5KVA supplies which will also come down the pole and terminate in 2 new utility cabinets which will house the meters on either side of the existing brick built one.
I then intend to run 2 x 16mm 2 core SWA cables underground to replace the old SWA cable to the bungalow and supply a new supply to the new house. The new house will have 5kw solar panels and possibly a Tesla powerwall and be very low energy requirements.
Couple of questions...
1) I intend to put earth spikes on each end of each cable connected to the armouring, is this ok?
2) Is there any reason I can't run the two cables in one 63mm dia twin duct? (I mean is there an issue with capacitance or something)
3) The cable run is across my own land, garden, field, driveway I assume I just use common sense approach as to cable depth and include tape above it?
4) Best place to buy the SWA cable from?
Regards
Jim

 

[DPG]

I don't know the best answer to this, but 2 questions come to mind:
Why the spike at each end of the SWAs?
What earthing system do you have?

 

[Spoon]

What has the electrician, who will be testing the new circuits, said?

 

[buzzlightyear]

I'm holding my breath on this one !

 

[buzzlightyear]

go on give us a clue is a TT system with totem poles in garden!

 

[Octopus]

Pop corn at the ready...

 

[buzzlightyear]

get the barbecue out it is going to be a long night .

 

[buzzlightyear]

What has the electrician, who will be testing the new circuits, said?

there isn't one !

 

[Spoon]

there isn't one !

We will see what the OP says..... If he gets back to us....

 

[buzzlightyear]

may be he has one of these .

 

[Octopus]

Back to the op on a more serious note, I very much doubt the supplier will connect anything without a test cert from a sparky.....

 

[jim payne]

I don't know the best answer to this, but 2 questions come to mind:
Why the spike at each end of the SWAs?
What earthing system do you have?

Hi,
The existing SWA is earthed at the far end only, it was installed in 1970's
So, it seems logical to me to earth each end?
At this stage I am only concerned with running the cables in correctly, neither supply will be connected for some time (house not got planning yet)
Regards
Jim

 

[jim payne]

What has the electrician, who will be testing the new circuits, said?

Hi,
House hasn't got planning yet so I'm along way off appointing an electrician. All I need to do at this stage is run the cables in, the supplies, won't be used for some time to come.

 

[jim payne]

Back to the op on a more serious note, I very much doubt the supplier will connect anything without a test cert from a sparky.....

Hi, the supplier is only putting the mains supply in, they are not connecting to anything. Once they are in I choose a meter provider who installs just the meters.
Regards
Jim

 

[jim payne]

Back to the op on a more serious note, I very much doubt the supplier will connect anything without a test cert from a sparky.....

Hi,
They aren't connecting to anything, just putting the supply in.

 

[Spoon]

Hi,
House hasn't got planning yet so I'm along way off appointing an electrician. All I need to do at this stage is run the cables in, the supplies, won't be used for some time to come.

Yet you are asking questions regarding the installation of power cables to regulations....
Can't have one without the other..

 

[DPG]

Yet you are asking questions regarding the installation of power cables to regulations....
Can't have one without the other..

As above ^^^. I would have thought all you can do at this stage is get some trenches ready.

 

[Octopus]

^^ where do you think the meters will be?

 

[Octopus]

^^ where do you think the meters will be?

 

[Pete999]

Pop corn at the ready...

Or Freddos

 

[telectrix]

5KVA seems pathetic for a dwelling. I'd do the 3 D's (dig, duct, drag rope ) then leave it at that till things have been finalised and calculations completed.

 

[Leesparkykent]

The design sounds wrong from the start....5KVA are you sure? The second building is 400 meters from the meter position? The second building is going to have PV? The recommended Volt drop for PV is <1%..If the run is that long you are looking at a big CSA.

 

[Leesparkykent]

Put it this way....If the supply is only 5KVA (which as said above is pathetic) and IMO unrealistic. The cable you would require to achieve <1% volt drop would cost in the region of £11500 and that's without any other material required.The cable would weigh about 2 and a 1/4 ton which you are never pulling through a duct for love or money. I think you best get an electrician involved sharpish if you're serious about it.

 

[suffolkspark]

I normally keep quiet on these sort of threads, but why oh why do people think, oh I can just chuck a cable in, I mean anybody can do that?! ill just make it up as I go along, cooorrrr I duno lets stick a 2 core armoured in and some stakes, that'l do,! just literally please STOP IT get an electrician in and get him to design it.

 

[jackhammerJIM]

it might be 5 KVA after the electric board have calculated diversity . In our world its a 100 amp supply .

If you going to use 16mm swa on the 400meter run your getting 89 volts of volt drop at a design current of 80 amps .This will leave you with an undesirable 141 volts to play with in the house .

 

[telectrix]

it might be 5 KVA after the electric board have calculated diversity . In our world its a 100 amp supply .

If you going to use 16mm swa on the 400meter run your getting 89 volts of volt drop at a design current of 80 amps .This will leave you with an undesirable 141 volts to play with in the house .

he can always buy some american gear.

 

[jackhammerJIM]

he can always buy some american gear.

Good idea Tel . He can use a smaller swa t get down to 120 . Its a free step down transformer

 

[Toneyz]

Or Freddos

What are these Freddos ?

 

[Leesparkykent]

If you worked on a design current of 63A and <1% volt drop, had a couple of cables in parallel, had a trench dug to proper depths, 50mm bed of sand, cables laid in trench, 150mm of sand on top, warning tape, trench back filled, OCPD/earth fault protection installed, termination at far end and so on I don't think you would see any change out of 20K. That's just for the cables to the furthest building....you still have the cable to get to the 1st building. If the cables followed the same route your still looking at least another 10K.

 

[telectrix]

they're little frogs. very strong.they can pull 95mm SWA down a 400m duct wihtout using a pull through. no wonder they'reexpensive.

 

[freddo]

Couple of LV-MV transformers back to back.

 

[jim payne]

^^ where do you think the meters will be?

^^ where do you think the meters will be?

Hi, the meters will be in the new cabinets at the supply (not the other end of the cable)

 

[jim payne]

5KVA seems pathetic for a dwelling. I'd do the 3 D's (dig, duct, drag rope ) then leave it at that till things have been finalised and calculations completed.

Hi,
I'm not trying to provide a 5kva supply to the house, the house will be built to use minimal electriciy, there will be a 5 kw solar and a tesla powerwall, and the elecrical system will be designed around the availiable supply. The cost of supplying 5kva to both properties is horrendous and dearer than going off grid. This is a compromise which should provide 2kw with a <4% drop, sufficient to supply charging current to the powerwall if needed.
The bungalow which is currently running on 10mm SWA 350 metres long doesn't have any issues with insufficient power so to change to 16mm can only improve the situation, the bungalow has a PV system but no battery storage at the moment.

 

[jim payne]

If you worked on a design current of 63A and <1% volt drop, had a couple of cables in parallel, had a trench dug to proper depths, 50mm bed of sand, cables laid in trench, 150mm of sand on top, warning tape, trench back filled, OCPD/earth fault protection installed, termination at far end and so on I don't think you would see any change out of 20K. That's just for the cables to the furthest building....you still have the cable to get to the 1st building. If the cables followed the same route your still looking at least another 10K.

 

[Pete999]

I normally keep quiet on these sort of threads, but why oh why do people think, oh I can just chuck a cable in, I mean anybody can do that?! ill just make it up as I go along, cooorrrr I duno lets stick a 2 core armoured in and some stakes, that'l do,! just literally please STOP IT get an electrician in and get him to design it.

Answer to your question, the mindset of the average Joe Public is shot to pieces,

 

[jim payne]

Hi, I'm not working on 63A supply at the property, probably nearer 10A. The electrical system will be designed to allow for this, yes, agree with trench procedure, but can I put two cables side by side in the same trench?

 

[jim payne]

it might be 5 KVA after the electric board have calculated diversity . In our world its a 100 amp supply .

If you going to use 16mm swa on the 400meter run your getting 89 volts of volt drop at a design current of 80 amps .This will leave you with an undesirable 141 volts to play with in the house .

Hi, I am not trying to supply 80A at the property, the electrical system will be designed around a much smaller supply, probably nearer 10A

 

[Pete999]

Being blunt Jim, I think you are playing around with something you know next to nothing about, for goodness sake get someone in to design this installation properly.

 

[Spoon]

Hi, I am not trying to supply 80A at the property, the electrical system will be designed around a much smaller supply, probably nearer 10A

Why will you not take the advice of people here. I don't understand you......

If you want these circuits designed to current regulations then you need an electrician.
If you are not bothered about doing it properly and safely then just bung some cable into a trench and job done....... ( I do not recommend the latter )

 

[alasdairp]

Hi, I am not trying to supply 80A at the property, the electrical system will be designed around a much smaller supply, probably nearer 10A

Having been somehat involved in low-power off-grid and alternatives for 50 years, I think some people here are missing the point - although I absolutely agree that you do need to get this properly designed and the overall design formally approved before starting work or you may find the whole thing condemed when you try to get it connected. Two suitable cables in one suitable trench should be fine, but that is a trivial issue compared with what you are trying to do. I am not clear how you can "order 2 x 5kVA" supplies for use in dwellings. What you need, it seems to me, is effectively the equivalent of a private caravan site supply for 2 caravans from your main electricity supply. Those supplies can be privately metered and charged for by you and can be limited to 16 A or whatever - provided the right protection and voltage drop and required impedances are met. I would be surprised if they have been agreed to by the DNO (Scottish and Southern) as separate supplies for 'human dwellings'. Also, if people are to be living in them, they will also have to meet the Part P building regulations if the bungalow and the other house are to have internal 230 volt AC power supplied by these cables. I would suggest DC wired power only inside the two properties and the AC just to an external supplementary charger unit that only supplies DC to the buildings. It should be do-able, but in my opinion you need to get the whole scheme professionally designed and formally approved in detail before doing anything else!
p.s. the IET have a Code of Practice for LV and ELV Direct Current Power Distribution in Buildings, published in 2015, that you should probably read.