@njt That situation does seem very strange. Usually, the DNO assesses the appropriate fuse rating based on the expected load and safety standards for each property, so it’s odd that your neighbour had a 100A fuse replaced with an 80A, especially since a 100A fuse would generally allow for more electrical load capacity, which is what we need more of and delivers the opposite message from the very same DNO when we interviewed them less than two years ago. I'll reach out to them for comment:

@editor 

That would make my situation easier, but they were adamant they will only fit 80A max. If I want more I'll have to pay to have 3 phase fitted, along with the tarmac drive dug up, and that isn't happening. 

I've yet to hear back from octopus about the supposed amp overload at my property. 

I've emailed about diversity calculations which I think/hope they didn't use which would help my cause.

Posted by: @gunboatdiplomat

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Found this which may explain what is going on: https://connections.nationalgrid.co.uk/news-and-events/latest-news/standardisation-of-fusing-to-80a#:~:text=National%20Grid%20Electricity%20Distribution%20(NGED,a%20cutout%20fused%20at%20100A  

I read that UKPN is still doing 100A fuses.

NGED are clearly concerned about high sustained loads. We know that ASHPs should be operated 'low & slow' and, most likely, few would be considered a high load and even then, only in very cold weather.

More generally, I've not (yet) got a ASHP but I have a recently refurbished kitchen & utility with 2 ovens, a microwave, washing machine, dryer, dishwasher and hot-tap (in addition to fridges, freezers, IT kit around the home, etc, etc).  I also have a 7kW EV charger and 6kW home battery. However, in practice:

a) 'Diversity' dictates that not all will be 'ON' at the same time

b)My EV charger monitors the grid and reduces charging if grid import is too high (and I could configure my home battery similarly)

c) An 80A fuse will carry 100A for a long time.

Is NGED just being over-cautious?

@ianmk13

It could be that NGED are trying to encourage consumers to pay them to install a 3 phase supply, which would be financially advantageous for NGED, and also help reduce the phase to phase imbalance.

@derek-m   I think I'll pass 😊 

Can you get the electric shower disconnected as it would be far cheaper to use the water heated by the ASHP anyway? The stance on 80A fuses seems bonkers when it cropped up last summer and I’ve seen a strong reaction against it from the industry and the energy policy sector so hopefully it’s short-lived… 

@dougmlancs 

I'll have to go down that route I suspect. 

If octopus ever get back to me again, I'll suggest taking it out of the calculations then disconnect fully when heat pump is installed. 

If i have to have it all removed first then a problem occurs with the heat pump install and it never gets fitted, I'll be in more of a mess.

@njt did the DNO ever give you any calculations for your property that lead them to the 80A limit?

This is quite an interesting read on the subject: https://richardlowes.com/2024/05/31/blowing-a-fuse-electricity-distribution-networks-need-to-drive-clean-heating-currently-they-are-slowing-it/

@editor 

Hi Mars,

Very interesting read. 

An 100A fuse would have made my life much easier.

I just applied to the DNO for a fuse upgrade as octopus after their heat pump survey said I needed one. 

Getting in contact with the DNO was easy and fuse upgraded within days for free but stated their policy will only allow up to 80A fuse.

As I've already mentioned they removed neighbours 100A fuse and replaced it with an 80A

MCS again!

Fingers crossed I think we're on our way. 

After a few emails to octopus they have supposedly sent a revised application for a heat pump to the DNO today.

We don't used the 9kw shower in main bathroom, only use the en suite one,  so will be removing that for a normal bar type one saving about 40A which will be within total 80A limit. 

Hopefully get things moving with the install before cold weather creeps in.

At least your installer flagged it as an issue before the installation. My ECO4 installer never bothered to inform the DNO that they'd installed a 12kW heat pump on my 60A fuse, nor the 3.6kW solar array that I had to notify them of to get the DNO approval letter for the SEG payments. They just went ahead anyway under permitted development despite not meeting the criteria for install and notify, and then failed to notify! I wonder how many installations are out there that the DNOs have no knowledge of.

The DNO were not best impressed when I requested an 80A fuse upgrade due to the installed heat pump - I only really requested it as sometime we do hammer the supply when Agile has negative pricing and 80A is sufficient for us. To be fair, once they had the retrospective application, they were quick to do the upgrade.

During the process I came across the ENA heat pump database which lists the Maximum Demand of many heat pumps. My own Samsung 12kW model is listed as 6.44kW (28A) which matches the spec sheet for 55C flow temps at -5C. The spreadsheet database was available here:

https://www.energynetworks.org/links

When completing the form, I think I specified a Maximum Demand of 74A, but in reality if everything is turned on at once we'd exceed that. The heat pump could conceivably draw a combined 41A in DHW mode with the immersion on too for a legionella cycle, then hop in the 40A electric shower at the same time Sunday roast is cooking in the 13A cooker and someone turns on the 13A kettle, and we are well over 100A