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New Grid Connection

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Firstly I'd like to start by saying I have read a number of the other forums covering this topic which have been very useful but I'm hoping for some specific advice on the particular circumstances we have on site. 

We are converting some old stone barns into a new home which will have PV panels, MVHR, ASHP and EV charger. Our DNO (Northern Powergrid) have told us we need a new connection and that this will require "work to our high voltage network" so requires an initial £800 design fee. Before they come on site I'm trying to get my head  around what is actually required so have drawn a schematic below, which is very basic but hopefully conveys the salient points.





Power comes in over the 2 phase high voltage (HV lines, 2 cables, I think that means 11kV) to the transformer about 100m from the house. This is a 15kVA transformer which connects to the low voltage lines (230V) which connect to the cottage up the hill (on our site) and 3 buildings (2x cottages and 1x small pastoral farm) over the road. All of the lines and poles etc are on our land. My understanding of what needs to happen is this: the newly converted farm buildings will need their own LV connection (currently comes off the cottage as shown by the dotted line) and given the increased power demands from the converted barns the existing transformer needs to be upgraded.


My questions are as follows:

What capacity should the transformer be? Given 15kVA has been fine for the existing setup (total of 3 cottages and a farm), I would assume that upgrading to 50kVA would be more than sufficient however if we want all houses to have their own 80A circuit then at most you would need a 100kVA transformer (5 circuits x  80A x 230V = 92kVA). Given realistic load demands this is very conservative but if I have understood correctly that is a realistic worst case scenario.

Does the 2 phase (2 cable) HV line need upgrading? My hope is that it wont but I have no idea here. The closest 3 phase (from which our 2 phase branches off) is probably 400m away.

Does the LV cable coming from the transformer need upgrading? Again I have no idea here. 

Can the connection for the new buildings come from the existing pole? This I imagine also ties into the question above but can we connect from that pole to the house by way of underground cables?

Sorry for such a long post but I would be so grateful for the thoughts of those more experienced than me!

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32 minutes ago, charlieroper said:

What capacity should the transformer be? DNO will work this out based on your supply requirements. If an upgrade is required, it will be at their cost

Does the 2 phase (2 cable) HV line need upgrading? Again, the DNO will work this out, and if anything needs to change, it will be at their cost

Does the LV cable coming from the transformer need upgrading? DNO will advise. It sounds like you will just need a new supply cable to the converted buildings. 

Can the connection for the new buildings come from the existing pole? The DNO will advise on the best route. There are regulations relating to cable heights etc., so they may suggest an underground route, especially if the existing cables may be damaged by construction work. If you're lucky, they may want to put it all underground at their cost, but you'd need to be very lucky for this one... But you do own the land, so it might be something to consider...



See comments above, but also check out 

for some information on how the charging structure for connections changed from the 1st April 2023 and the differences between reinforcement assets (things the DNO pay for) and extension assets (your connection that you pay for).

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Thanks @garrymartin


Perfect timing as the DNO called me half an hour ago and you are bang on! They think the transformer upgrade will be their expense so we just need to pay for the new connection and dig the underground trench from the final pole to the new house which is through a flat field which is a great result. 

Annoying that I have to pay £800 for them to confirm what I already knew but frankly I'm so relieved I don't have to pay for HV/transformer works that I'll take it!

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