DNO electrician installed wrong main fuse

[yessuz]

Ok, this is a strange one.

Last year we had an emergency at home where main fuse had to be removed ( by DNO electrician). Once issue was rectified - they came in and installed a new one.

All was good until today I checked something and realized that instead of 100A main fuse 80A was installed.

So total capacity is reduced by 20%...
So in theory now I could max it out with 19 kw load rather than 24 kw

Has anyone faced such situation and hiw much of chance I have to persuade my DNo to revert change?

I do have picture of BEFORE when fuse was 100A.

It is 2014 built property and while I might not need full 24 kw load now, with car + solar batteries charging up I am already at 10-11 kw and with any additional load (kettle + oven + iron) I might be exceeding 19 kw...

And I was thinking about getting induction hob...

Any ideas what should I do?

P.s. already sent email to DNO with "guys, wtf!?" Type of email but since it is weekend I have 48 hrs to wait (the least)

 

[Fursty Ferret]

Are you absolutely sure it was a 100A fuse, and not just the fuse carrier, which often states 100A on it?

You can overload an 80A fuse for a considerable period before it blows. They’re there to protect against direct shorts and long-term overload. For example, a 60A (well, they’re 63A now) fuse will tolerate 100A for four minutes.

Unless you have multiple EV chargers without load balancing and several electric showers going at once while you cook dinner, run the immersion heater, and dry your hair, you won’t have a huge problem.

 

[MrBadger]

Off top of my head, when you have electricity work carried out, part of the electrician’s paperwork has space for earthing and fuse size.

May be worth checking paperwork from when you had charge point/EVSE and batteries installed, especially since charge point install is likely to have specified calculations for loading. I would refer to those calculations if any dispute as they would have helped justify any charge point max load.

As @Fursty Ferret says, the fuse carrier will often state max load of the fuse carrier (eg 100A) which may well differ from the actual fitted fuse.

 

[linkandnavi]

Are you absolutely sure it was a 100A fuse, and not just the fuse carrier, which often states 100A on it?

You can overload an 80A fuse for a considerable period before it blows. They’re there to protect against direct shorts and long-term overload. For example, a 60A (well, they’re 63A now) fuse will tolerate 100A for four minutes.

Unless you have multiple EV chargers without load balancing and several electric showers going at once while you cook dinner, run the immersion heater, and dry your hair, you won’t have a huge problem.

Ok, this is a strange one.

Last year we had an emergency at home where main fuse had to be removed ( by DNO electrician). Once issue was rectified - they came in and installed a new one.

All was good until today I checked something and realized that instead of 100A main fuse 80A was installed.

So total capacity is reduced by 20%...
So in theory now I could max it out with 19 kw load rather than 24 kw

Has anyone faced such situation and hiw much of chance I have to persuade my DNo to revert change?

I do have picture of BEFORE when fuse was 100A.

It is 2014 built property and while I might not need full 24 kw load now, with car + solar batteries charging up I am already at 10-11 kw and with any additional load (kettle + oven + iron) I might be exceeding 19 kw...

And I was thinking about getting induction hob...

Any ideas what should I do?

P.s. already sent email to DNO with "guys, wtf!?" Type of email but since it is weekend I have 48 hrs to wait (the least)

It was a policy decision by National Grid in 2023. All domestic cutouts would now be 80amp instead of 100, for both new installations and replacement of existing 100amp fuses. See the link here.

My layman's understanding is that 100a fuses were put in at a time when a heavy load was likely to be a one off, short term burst. But with the advent of things like solar panels, heat pumps and EV chargers the load can be both very high and sustained over a long period of time. That means the 100a cutout is less suitable as it will allow a greater load on the house's circuits for too long a time which those circuits aren't designed for.

I think though that the National Grid simultaneously amended the guidance on how to calculate diversity (the likely maximum load on a house at a given time from the ratings of the installed circuits) to allow more on an 80a circuit which brings it closed to the old 100a diversity max.

(I have a 100a fuse. When my EV charger was installed in November 2022, the electrician failed to put the cutout back in properly so it burnt out and the DNO had to come to replace it. He told me that he should be replacing it with an 80a but because it was already 100a and he had one in the van, he'd just put another in - he basically told me he wasn't supposed to though but couldn't be bothered with the admin).

 

[Js1977]

See what they come up with but to put it into perspective, Ive got a 100A fuse but more chance to overload than you.

I have 2 chargers at 32A each, Powerwall at 21A, Kettle at 13A, Oven at 15A, toaster at 8A, Immersion at 13A... then there is the usual other bits like blow dryer, washing machine, dishwasher, and tumble drier etc plus 300w base load plus 2nd Powerwall incoming.

They apply what is called diversity as to allow all these things.

Plus dont forget about your CT clamps since your charger If it has one fitted will also reduce power, Your battery/inverter will have this for sure.

 

[linkandnavi]

It was a policy decision by National Grid in 2023. All domestic cutouts would now be 80amp instead of 100, for both new installations and replacement of existing 100amp fuses. See the link here.

My layman's understanding is that 100a fuses were put in at a time when a heavy load was likely to be a one off, short term burst. But with the advent of things like solar panels, heat pumps and EV chargers the load can be both very high and sustained over a long period of time. That means the 100a cutout is less suitable as it will allow a greater load on the house's circuits for too long a time which those circuits aren't designed for.

I think though that the National Grid simultaneously amended the guidance on how to calculate diversity (the likely maximum load on a house at a given time from the ratings of the installed circuits) to allow more on an 80a circuit which brings it closed to the old 100a diversity max.

(I have a 100a fuse. When my EV charger was installed in November 2022, the electrician failed to put the cutout back in properly so it burnt out and the DNO had to come to replace it. He told me that he should be replacing it with an 80a but because it was already 100a and he had one in the van, he'd just put another in - he basically told me he wasn't supposed to though but couldn't be bothered with the admin).

To follow up on my own post (I knew I had read an article on this somewhere but have only just found it), there's an article here on the decision here. Largely critical of it I think, although it does note that 100a was an absolute max but 80a can sustain 100a for up to four hours so the average person is unlikely to actually see a difference.

Anything above 80a fuse requirements will require 3-phase (which I always assumed was 3 80a connections but according to National Grid is actually 3 60a connections).

I have solar panels, batteries and an EV charger. I want a heat pump as it's my last step to completely cutting the gas connection to my house. Have been told that I'd likely need 3 phase. Quoted about £7k for the National Grid work, plus then hiring an electrician privately to do the interior house stuff. Would need the microbore piping replaced at least in part plus the cost of the pump. Even with the Government heat pump grant, cost would come to almost £20k from my pocket which I just can't do.

They don't half make doing the environmentally right things hard. I've done what I can with EVs, solar and moving the cooking to all electric but how people in less fortunate financial positions than me are supposed to do anything while being constantly lecturered by those in charge about doing so is beyond me...

 

[Hurricane]

This day an age it’s really not hard to reach and breach 100A. We have a 22KW Andersen charger and three 10.8KW showers. Run all these together and the load is more than 230A. We have a three phase supply and luckily the fuses are 100A each so we still have some spare capacity for all the other usual domestic items.

 

[yessuz]

Are you absolutely sure it was a 100A fuse, and not just the fuse carrier, which often states 100A on it?

You can overload an 80A fuse for a considerable period before it blows. They’re there to protect against direct shorts and long-term overload. For example, a 60A (well, they’re 63A now) fuse will tolerate 100A for four minutes.

Unless you have multiple EV chargers without load balancing and several electric showers going at once while you cook dinner, run the immersion heater, and dry your hair, you won’t have a huge problem.

100%

I have pics AND at least few electrical certificates from the works carried over past few years (i e. Installation of Pod-Point, or solar oanels)

 

[yessuz]

Off top of my head, when you have electricity work carried out, part of the electrician’s paperwork has space for earthing and fuse size.

May be worth checking paperwork from when you had charge point/EVSE and batteries installed, especially since charge point install is likely to have specified calculations for loading. I would refer to those calculations if any dispute as they would have helped justify any charge point max load.

As @Fursty Ferret says, the fuse carrier will often state max load of the fuse carrier (eg 100A) which may well differ from the actual fitted fuse.

Yup, have few which states 100A

 

[yessuz]

I mean I agree I might not need it now ..

But let's model the situation:
Car is charging at 30 A. 16 A is for house batteries. This is a sustained load over few hrs...

Another 7 A for oven. Washer + dryer + dishwasher another 13 (easily
That os 66 A already

Add iron, kettle and if I upgrade to induction hob (32 A this one alone) and we are heading into the pop territory.

But the point is - why they derating the property when all logic (EVs, heat pumps etc) should be that it should be heading another direction

I KNEW it was 100A and my behavior with power load was based on the known info that it is 100A .

 

[Js1977]

I mean I agree I might not need it now ..

But let's model the situation:
Car is charging at 30 A. 16 A is for house batteries. This is a sustained load over few hrs...

Another 7 A for oven. Washer + dryer + dishwasher another 13 (easily
That os 66 A already

Add iron, kettle and if I upgrade to induction hob (32 A this one alone) and we are heading into the pop territory.

But the point is - why they derating the property when all logic (EVs, heat pumps etc) should be that it should be heading another direction

I KNEW it was 100A and my behavior with power load was based on the known info that it is 100A .

Yep...and you will be doing all this at about 11:30pm like clockwork

 

[yessuz]

Yep...and you will be doing all this at about 11:30pm like clockwork

At least car + house batteries. Some other stuff might spread.. might not.

 

[Js1977]

At least car + house batteries. Some other stuff might spread.. might not.

I do both cars plus battery at the same time and my battery has higher draw than yours. Not a problem at all plus is your battery is setup properly it will curtail draw as well as your charger if it has a ct clamp as to prioritise the house.

I used to think like you but honestly dont worry about it. You should have a trip switch that will actually safeguard your main fuse but you would have to be trying hard to trip it.

 

[yessuz]

I do both cars plus battery at the same time and my battery has higher draw than yours. Not a problem at all plus is your battery is setup properly it will curtail draw as well as your charger if it has a ct clamp as to prioritise the house.

I used to think like you but honestly dont worry about it. You should have a trip switch that will actually safeguard your main fuse but you would have to be trying hard to trip it.

This is not about a worry.

It is in principle that someone decides to downgrade your property without informing about it or providing justification (not even talking about letting you know)

So now I have a situation where I have shitload of certificates all stating 100A and in reality it is 80A...

I mean Heat Pump is at least 7 kw. Same as car. And will be running HP during winter at same time as changing your car)
These two alone are already 60 out of 80 A...

 

[Js1977]

You never said you had a heat pump and even then it won't be a problem. When it comes to your next installation of hob or whatever the fuse might be upgraded but like I said, Your battery and charger will manage the draw as to make sure you dont get up to a cold house and there is plenty time left to fill your car and battery even a slower rate at a guess.

 

[yessuz]

You never said you had a heat pump and even then it won't be a problem. When it comes to your next installation of hob or whatever the fuse might be upgraded but like I said, Your battery and charger will manage the draw as to make sure you dont get up to a cold house and there is plenty time left to fill your car and battery even a slower rate at a guess.

I do not. But there will be no new boiler installations and when boiler will fail I WILL switch to Heat Pump as most of UK in future

but again, it is not about possible upgrade in the future. It is about UNWANTED and UNANNOUCED Downgrade. As well as now all my Electrical certificates ARE NOT CORRECT

 

[Js1977]

I hope you get it sorted to your liking

 

[Zilla91]

Had the same thing happen to me before I got my charger installed.

Chap from the DNO who was doing the pre-install checks didn’t like that I had a 100 amp fuse installed so he downgraded it to 60/80 amps (I’m on a looped supply) without saying anything. The old 100 amp fuse is now sat on a shelf in my office.

 

[MrBadger]

This is not about a worry.

It is in principle that someone decides to downgrade your property without informing about it or providing justification (not even talking about letting you know)

So now I have a situation where I have shitload of certificates all stating 100A and in reality it is 80A...

I mean Heat Pump is at least 7 kw. Same as car. And will be running HP during winter at same time as changing your car)
These two alone are already 60 out of 80 A...

It sounds like from an earlier post that the diversity calculation has changed to accommodate the lower fuse, ie the previous calculation gives a higher load.

Its the diversity calculation result that effectively governs what you can draw not the physical size of the fuse.

So if the previous diversity calculation calculated the load you can draw from the 100A fuse, and the new diversity calculation allows you to draw the same theoretical load but from an 80A supply, then you are no worse off.

Diversify takes into account that all loads will not be drawing full power continuously, and that fuse ratings are not quick blow but would allow a significant ’overload’ to occur for significant periods of time, so would therefor allow a higher load to be theoretically drawn from a smaller fuse when the reality is that all loads will not be drawing continuously for many circuits.

eg I have a large electric oven with many induction rings, yet because of diversification of the loads, the recommended fuse for the circuit is significantly less than the sum of all the components.

 

[yessuz]

I will get some response from DNO tomorrow and will keep updated.

My concern is that potentially, all my Electrical certificates are wrong now. which in THEORY might lead into some issues if I sell the house, as documents supplemented will not be correct.