Boundary box - voltage drop

[James94]

Hi all,

 

I’ve had northern power quote me £3700 for an electricity connection, or £1300 to a boundary box and then I build a kiosk, supply the cable and pay an Electrican to wire it up from there.

It will be a single phase 18Kva connection with a 80amp fuse I believe.

 

Now I’m just trying to calculate how much savings are to be had if I go down the boundary box route.  The total distance from boundary box to consumer unit is roughly 75m, I can check exact measurement later.

 

I’m trying to work out what size cable is required, taking voltage drop into account. As on the original design it showed 50 meters of 95mm wavecon and then a 35mm service cable into the meter. 

 

I will attach the Original plan.

 

Thanks James

72B Humberston Ave plan.pdf

[TonyT]

Well the dno don’t have to comply with BS7671 so their installation will end at the box.

 

you will then need a switch fuse and a SWA run to the house

 

lots of variables regarding earthing etc

 

http://www.doncastercables.com/technical-help/

 

cable sizing calculator link above.

 

 

[ProDave]

I am surprised the quotes vary so much.  Is that them doing all the work?  If you are digging trenches on your land then I would expect the quotes to vary by little more than the cost of the extra 75M of cable.

 

How about a half way house, still go for an outside kiosk but closer to the house so the cable you supply is shorter and hence smaller, try and get to within 25M of the house?

[James94]

Have used the calculator and it’s saying 25mm SWA will be ok to use for a 75m run. 
 
Both quotes are for me to dig and reinstate on my land, they connect up to the meter points. They was quoting for 50 meters of wavecon 95 which is around £50 a meter so that’s a big chunk of the £3700.

 

The gas meter is situated at the top of the driveway so I thought it would be easier having them together.

[PeterW]

28 minutes ago, James94 said:

Have used the calculator and it’s saying 25mm SWA will be ok to use for a 75m run. 

What amperage/power did you select ..? It’s borderline for 80A with the voltage drop at that distance so you may want to price up 35mm

[James94]

Correct me if I’m wrong here, but it’s a 18Kva connection so that is 78.261 amps. I believe we will just use an 80 A fuse?

[PeterW]

So at 80A you are absolutely on the borderline of the 5% drop for 25mm cable. Make it 75.1m and it needs lifting to 35mm cable. In likelihood the DNO will install a 100A fuse anyway. It’s why they have specced a 35mm service cable not 25mm. It’s slightly more expensive but the distance you are talking about the voltage drop is the major factor. 
 

 

 

[ProDave]

Our supply is technically only rated at 12kVA but is still has the same 100A fuse and 35mm cable feeding it as any other house.

 

[James94]

Thanks for the help guys, 35mm it is.

[TonyT]

 

 

what earthing arrangement are the DNO leaving you?

Edited November 15, 2020 by TonyT

[James94]

I have no idea, is there a standard arrangement for this scenario? The original design with the connection to the house showed a earth rod 50m down the drive. Is there anything I will have to put in place for earthing?