New Build Supply Issue

One of my students requested UKPN to tell him what the neutral CSA was on a supply cable so he could calculate the size of bonding he needed to install. Person comes to site and cannot answer the question and 2 weeks later gets an invoice for £300 as a standard survey charge.

Charming..!

A block of four new flats I wired went from 60K to 4K.


They have gas for space and water heating as well as gas hobs, so I submitted realistic calculations showing that the maximum demand for each flat is 40 amps each.


The maximum demand for the whole block comes out at far less than 160 amps.


Andy

Hi Andy,


In that they overestimated the true need and tried to charge for unnecessary usage?


We believe that we will need a single phase, 100A supply. We could reduce this by using LPG but that may cause some issues on the planning front. 


Surely it’s the responsibility of the DNO’s to ensure they have a network that is robust and has tolerance for new homes and an ever-increasing need for supply?


That’s likely to be a whole new thread of conversation though I imagine!

A standard connection is probably 60 amps, so straight off you have indicated that you need to have a higher than normal supply.


Assess the true requirement, not based on having increased the number of circuits beyond what is actually required.


Do a calculation for lighting, power and ovens assuming the LPG does the space and water heating, possibly also the cooking hob. You should be able to at least halve the requested supply of 100 amps in most situations.


Andy

And if the timescale for the builders to move in is weeks rather than months, to get them up and running I suggest a few phone calls to hire companies to ask about a genset suitable for building sites, and a word with the builder about what they intend to use that actually needs electricity and when they really need it - cement mixers and angle grinders can usually be be petrol/diesel or electric, so if the right models are hired, the load is small, and a lot of small tools only need a modest supply to recharge (and the thumping great music centre for the roofers of course..) - or even look into just  buying  a cheap one, almost as a consumable item it may be surprising how much can be powered off a 'burger van' size generator (you know the 3-4kW sort of thing, as seen pounding away behind a caravan in a layby near every industrial estate) depends if  with some cunning the demand can be spread suitably thin...

Just a comment on the subject of DNO service fuse size.


The design standards of each DNO (Distribution Network Operator) and IDNO (Independent DNO) may/do vary. The installation of a new single phase service, and cut-out, may be fused at a rating of either 60,80, or 100amps, respective to that particular DNO/ IDNO design standard.

However, the service fuse size does not have a direct relevance to the capacity you have declared. I.e.  if the DNO have agreed to provide you with a single phase connection of 10kva capacity to meet your declared Maximum Demand, then if that DNOs standard is to fit a 100amp fused cut-out, then that's what you will get.

Understandably, this does lead to some confusion, and I have often found customers are under the false apprehension that the size of the service fuse dictates their agreed capacity, or indeed the available capacity. 

The ramifications of this issue tends to be more of a problem in rural areas where Transformer and LV network capacity is often limited.


Kind regards


Chris

I told the DNO that the maximum demand on the flats I mentioned was 40 amps, they fused their supply at 60 amps and I fused the distribution circuit at 40 amps though the cable is sized to take the full 60 amps. No one has ever blown a fuse, I left spare 40 amp fuses cable tied to the tails just in case someone did something silly and they are still there.


I used to do some work for a central heating firm and told a customer to unplug some electric heaters they were using whilst the boiler was being replaced as they had a 40 amp DNO fuse, apparently they ignored me and the fuse blew about a hour after I left and it took the DNO around eight hours to get to them at nearly midnight. That was only because they were trying to heat rooms they weren’t actually sitting in, which was just silliness.


In the next field to where I am eating lunch there is a run 11kV two phase overhead cables with a pole mounted Tx supplying a farm. Several years ago the farmer had a firm survey for a solar PV farm, but the DNO said no because the local 11kV network is maxed out and running at near full capacity. The farmer does now have a small array of panels on a shed roof that feeds into onsite storage batteries, that’s all that could be connected to the local network.


A LPG gas tank can always be buried to supply the new house that will be built, the tank does not have to be visible.


 Andy

Hi Andy,


Thanks for the post. 


We’re very happy to change from heat pumps to LPG, as ironic as that is. 


The bigger issue right right now is that we don’t know if we can get any power at all.


We have 90 houses around us and some new as well but the surveyor reported back that the debut was showing the sub is full and when I asked him what did that mean, he casually said, you’ll have to pay for upgrades. 


We’re very happy to compromise on required supply but right now, sitting here with weeks to go before the build is due to start, we’re obviously very concerned about beginning a build with no idea on costs we could be facing for power. 


Absolutely my fault for not having a survey done prior to the land purchase but with planning already granted and houses either side, I didn’t think for a minute that it would be an issue and as a novice, don’t think it would’ve crossed my mind to find out. 


Not great that’s for sure.