Advice on long SWA cable run and new supply

[jim payne]

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.

Hi, thanks for some constructive points, as you say some people are missing the point to the point of being offensive.
The two supplies were ordered as two new domestic supplies (the 5kva is what SSE have marked on the map) I know there is limited capacity locally on the network.
I have limited spare capacity on my own supply to cater for these two properties.
The cost of these new supplies is £400 each I then have the cabling costs. This compares with £40,000 to provide new supplies directly to the properties!
If I have a Tesla Powerwall (or equiv) and 5kw PV the internal AC supply would be supplied by this, the new supply would charge the Powerwall if there was insufficient from the PV, the new supply could also power MVHR , LPG boiler etc. The new house will be built to Passivhaus standards but not necessarily certified to that standard, but will be compliant with current building regulations.
I have some trenching information from SSE so I don't see any issues that I can't resolve trench wise. I am aware of voltage drop calculations etc but as I mentioned earlier the bungalow is currently on the end of a 350 metre 10mm SWA fused at 20A and has been for about 30 years!
Regards Jim

 

[suffolkspark]

Look whatever you choose to do you still need an electrician on board at this early stage because you could do all of this yourself and find nobody will sign it off, some electricians can do third party certification, some can't, and some choose not too.

 

[jim payne]

Look whatever you choose to do you still need an electrician on board at this early stage because you could do all of this yourself and find nobody will sign it off, some electricians can do third party certification, some can't, and some choose not too.

Hi, I do have a qualified electrician on board who has given me some guidance re trenching, is supplying the cable and will be terminating both ends.
Regards
Jim

 

[Wilko]

Hi, I do have a qualified electrician on board who has given me some guidance re trenching, is supplying the cable and will be terminating both ends.
Regards
Jim

Good news - get them to do the design and you work under their supervision as an instructed person to install it. They will need to inspect at stages, then test, certify and obtain Building Approval.

 

[marconi]

Will there be any motors (of non trivial power output) supplied by this long run of cable? eg; vacuum cleaners, fridge/freezers...

 

[alasdairp]

Hi, thanks for some constructive points, as you say some people are missing the point to the point of being offensive.
The two supplies were ordered as two new domestic supplies (the 5kva is what SSE have marked on the map) I know there is limited capacity locally on the network.
I have limited spare capacity on my own supply to cater for these two properties.
The cost of these new supplies is £400 each I then have the cabling costs. This compares with £40,000 to provide new supplies directly to the properties!
If I have a Tesla Powerwall (or equiv) and 5kw PV the internal AC supply would be supplied by this, the new supply would charge the Powerwall if there was insufficient from the PV, the new supply could also power MVHR , LPG boiler etc. The new house will be built to Passivhaus standards but not necessarily certified to that standard, but will be compliant with current building regulations.
I have some trenching information from SSE so I don't see any issues that I can't resolve trench wise. I am aware of voltage drop calculations etc but as I mentioned earlier the bungalow is currently on the end of a 350 metre 10mm SWA fused at 20A and has been for about 30 years!
Regards Jim

The fact that cable has been there 30 years does not even mean you could replace it with like-for-like. Regulations have tightened a lot since then. Make sure that your electrician belongs to a Approved Scheme / Organisation that the local authority recognise as able to sign off new work. I am a professional electrical engineer with some 45 years practical experience, including supervising teams of electricians, but as I am not a practising member of an Approved Scheme I can't now sign off any domestic-related electrical work that needs local authority approval.

 

[alasdairp]

Hi, thanks for some constructive points, as you say some people are missing the point to the point of being offensive.
The two supplies were ordered as two new domestic supplies (the 5kva is what SSE have marked on the map) I know there is limited capacity locally on the network.
I have limited spare capacity on my own supply to cater for these two properties.
The cost of these new supplies is £400 each I then have the cabling costs. This compares with £40,000 to provide new supplies directly to the properties!
If I have a Tesla Powerwall (or equiv) and 5kw PV the internal AC supply would be supplied by this, the new supply would charge the Powerwall if there was insufficient from the PV, the new supply could also power MVHR , LPG boiler etc. The new house will be built to Passivhaus standards but not necessarily certified to that standard, but will be compliant with current building regulations.
I have some trenching information from SSE so I don't see any issues that I can't resolve trench wise. I am aware of voltage drop calculations etc but as I mentioned earlier the bungalow is currently on the end of a 350 metre 10mm SWA fused at 20A and has been for about 30 years!
Regards Jim

The fact that cable has been there 30 years does not even mean you could replace it with like-for-like. Regulations have tightened a lot since then. Make sure that your electrician belongs to a Approved Scheme / Organisation that the local authority recognise as able to sign off new work. I am a professional electrical engineer with some 45 years systems design, including maintenance, and loads of practical hands-on experience, including supervising teams of electricians, but as I am not a practising member of an Approved Scheme I can't now sign off any domestic-related electrical work that needs local authority approval.