When to use your own earth rods

[Stinsy]

I agree that 2x 10.5kW electric showers is the wrong solution. They’re 90A on their own and (as above) there is no diversity allowed on the first two electric showers! A 3kW immersion and a 200L tank is a much better solution and you’ve saved 77A from your max demand calcs.

I think that more people doing property renovations should consider 3-phase. All these problems evaporate once you have 3-phase!

Funnily enough SSEN do use diversity in demand planning, the calculator with 2 showers still has only 10kVA allocated for planning purposes.

Well not ALL the problems disappear, not sure I like 415V in a domestic setting, the Germans have it better in some ways with their delta supplies but I don't like the absence of neutral either, and Victron inverters don't work with it which must be a big market closed off to them.

I think with increasing adoption of heat pumps we are going to see a massive increase in load on the whole system so use of such things as electric showers should be positiively discouraged. WPD (as was) had a policy of no longer fitting single phase supplies at all to new properties, I think this just encourages profligacy and they may come to regret it, don't know if NGED have continued this post-takeover.

The house my parents moved to on my 5th birthday had a cooker control panel with a big switch which was down for Cooker and up for Water Heater so there you are! First thing they did was to have entire house re-wired with the new fangled ring mains so it soon went. (The term "final circuit" was certainly not in use then).

I think that DNOs need to come to the realisation that we’re going to be using a lot more electricity! For decades domestic electricity consumption was dropping due to energy-efficient appliances. That is why 60A main-fuses and looped supplies became commonplace. However as we move from gas to electric for cooking, DHW, and space heating, as well as electric car charging then a standard 3-bed semi or 4-bed detached really could benefit from 3-phase.

If you have 2 or more EVs and they’re used daily then transport alone is way more than the 2300kWh a year that National Grid says an average home uses.

[AE-NMidlands]

If you have 2 or more EVs and they’re used daily then transport alone is way more than the 2300kWh a year that National Grid says an average home uses.

... which is why the decarbonisation agenda has to adopt and support active travel (much more walking, cycling and use of public transport.) It's madness to just imagine that our current 40% of emissions from transport can simply swap over to electric power. However I'm afraid there aren't any politicians in any democracies who have the spine to push this through.

(I can remember in the early 1960s as a child being taken by my Grandma by train and bus to a crossroads near my Aunt's farm where the local taxi man had been booked to collect for us that last 2-mile leg! I suppose that as they had no car they could have come out on a tractor and trailer, except that nothing was taxed for the road!)

We really do need to get used to the idea of making do with less...

[Yuff]

Not sure if this is the right thread to post this issue on, but it seems as good as any
First of all this is from my very low level understanding of electrics

We have a Rolec home smart charger, 7kw.
It’s worked fine and I switch between smart charging and dumb a fair bit of the time and have had the charger since 2020.
It is in the garage which has separate circuit and limited to 32amps. There are a few sockets etc but nothing being used whilst charging.
For the past 4-5 days the mains fuse board keeps tripping when I plug the fiat 500e’s in and the charge starts.
It doesnt trip if I plug the EQC in at anytime.
If I start the charge on the 500e at the lowest setting it dont trip, I left it on for 3 hours last night and it was fine. The fiat has 5 charge levels 1-5, 1 being the slowest.
Yesterday it tripped after 1 1/2 hours on level 4.
This morning it tripped after 50 mins on level 5 and when I dropped it to level 2 it still tripped after 5 mins.
The octopus app shows a huge spike when it trips on the usage side.
Anyone have any suggestions.
Normally it wouldn’t be an issue as I don’t need to charge the EVs that much but have had several long journeys and commutes the past week.
Going forward not so much so have time to sort this out without having to charge the 500s too rapidly.

Probably best if a mod moves this to a new thread.

There are a load of reasons why it might be tripping. The first thing to check is IR of the charging cable. Next is to do a ramp test on the RCD to see if it is too sensitive. After that you're looking at a fault within the charger (the thing on your wall is a "charging point" the "charger" is in the car).

Thanks Stinsy

It’s tethered cable.
I spoke to Rolec this afternoon and they think it sounds like the circuit breaker might be at fault as I suspect it’s 32amps and they recommend a 40amp circuit breaker.
I may need to get Dan electrician round.
They said that’s the cheapest part to replace first and a good place to start

[Stinsy]

If you have 2 or more EVs and they’re used daily then transport alone is way more than the 2300kWh a year that National Grid says an average home uses.

... which is why the decarbonisation agenda has to adopt and support active travel (much more walking, cycling and use of public transport.) It's madness to just imagine that our current 40% of emissions from transport can simply swap over to electric power. However I'm afraid there aren't any politicians in any democracies who have the spine to push this through.

(I can remember in the early 1960s as a child being taken by my Grandma by train and bus to a crossroads near my Aunt's farm where the local taxi man had been booked to collect for us that last 2-mile leg! I suppose that as they had no car they could have come out on a tractor and trailer, except that nothing was taxed for the road!)

We really do need to get used to the idea of making do with less...

Well this has drifted a bit off-topic!

To some extent I agree. We do need to give the traveling public alternatives to traveling by car where practical to do so.

I am (and always will be) fiercely protective of personal transport. I think there is too much demonisation of cars and car drivers. I have a young family, I live in a semi-rural area, and we holiday in the UK. There is no way to get the kids to their sporting activities without owning and using a car, we couldn’t possibly holiday in the same way we do without our own car, etc.. I cannot think of a single journey we take by car where public transport could possibly be used instead even if it did exist. We do of course use electric cars

I’m taking child no2 to the Natural History Museum on Wednesday. An anytime return train ticket for one adult is £305.80! I don’t understand why train ticket prices aren’t a bigger scandal. I saw a guy on Twitter who bought a train ticket from the UK to Venice, every leg on the continent was a tenth of the price of similar UK legs. This is after the UK taxpayer donating £26.8bn in subsidies (https://www.statista.com/statistics/298 ... 0transport.). I really don’t see how either taxpayers (particularly those who don’t use the train) or the traveling public can possibly be getting value for money.

Child no1 gets a bus to high school, the ticket cost us £600, child no2 walks to primary school.

[cojmh]

Main Consumer Unit

• PV - 32A

• Eddi - 16A

• Outbuilding - 40A

• Zappi Charger - 32A - This is a future install but I need to maintain the spot

• AC 1 - 16A - This is a next year install

• AC 2 - 16A - This is an install probably 2-3 years down the line

• Shower 1 - 40A - This will be removed next year and I am pretty sure the shower is about 5KW

• Shower 2 - 40A - This will be removed in a couple of years and I am pretty sure the shower is about 5KW

• Kitchen/Cooker - 40A

Switchable Consumer Unit

• Exterior lighting - 6A

• Ring Main Downstairs -32A

• Ring Main Upstairs -32A

• Ring Main Lofts - 32A

• Lighting Downstairs - 6A

• Lighting Upstairs - 6A

• Outbuilding- 16A - This is mainly to provide lights and CCTV in a power cut

• Solar Thermal - 6A - To be added next year

• Front External Plug 16A

I think I should qualify the above a bit which I will do below just to sense check that we are not overloading the system.

I am always happy to be corrected on things I have got wrong - as you say it is the way to learn - my only caveat is that it is done constructively without being condescending (which to be fair I have almost always found everything on the forum to be respectful and constructive)

Main Consumer Unit

• Shower 1 - 40A - This will be removed next year and I am pretty sure the shower is about 5KW - So this is closer to 22A real world use

• Shower 2 - 40A - This will be removed in a couple of years and I am pretty sure the shower is about 5KW - So this is closer to 22A real world use

• Kitchen/Cooker - 40A - This is probably accurate when we do celebratory meals (Christmas/Easter etc.)

• Outbuilding - 40A - At this point I don't know what I will have in the outbuilding. The plan is to run it as a workshop I don't foresee having more than 3KW (13A) running at the same time. Perhaps I should downsize this?

• PV - 32A - I consider this item to be pretty much zero as it is a generator rather than consumer. I understand there will be a little to keep it running when there is no sun but I think in the context we are assessing it that it will be negligible

• Zappi Charger - 32A - I currently don't have one so this is zero at the moment but will be in this Consumer unit when it is installed (after showers are removed)

• Eddi - 16A - I consider this item to be pretty much zero too as it is only there to consume surplus power from the PV system. Again there will be a little use to stay running when not diverting but again I consider it to be negligible

• AC 1 - 16A - This is a next year install - This is currently not installed and will not be until after showers removed

• AC 2 - 16A - This is an install probably 2-3 years down the line - Same as above

Based on the house at the moment this consumer unit will run 22+22+40 = 84A Maximum (everything on)

Based on where I will end up this consumer unit will run 40+13+32+16+16 = 117A Maximum (everything on)



Switchable Consumer Unit

• Ring Main Downstairs -32A - About the biggest thing we run is the vacuum cleaner ... which is max 2KW or 8.7A

• Ring Main Upstairs -32A - Nothing much upstairs maybe a couple of modern TVs and the hair dryer - so again assumer 2KW or 8.7A

• Ring Main Lofts - 32A - Server Gear up here so maybe 0.8KW or 3.5A

• Outbuilding- 16A - This is mainly to provide lights and CCTV in a power cut - This an estimate at 300W or 1.3A

• Front External Plug 16A - Very little we run outside - maybe the vacuum cleaner for the car or the pressure washer so 2KW or 8.7A

• Solar Thermal - 6A - To be added next year - This is just to run the pump so about 50W which is 0.25A

• Exterior lighting - 6A - I have a total of 6 outside lights (total of 60 Watts) so 0.26A

• Lighting Downstairs - 6A - There are probably 24 light fittings averaging about 5W per fitting - 120W which is 0.5A

• Lighting Upstairs - 6A - There are probably 12 light fittings averaging about 5W per fitting - 60W which is 0.25A

Based on where I will end up this consumer unit will run 32A Maximum (everything on) But this is extremely unlikely

We are currently on an 80A supply and three phase is not an option as I know they would need to run it across the road at high expense.

Whilst everything on will overload the supply - we have never got anywhere close so far.

I suppose the only thing we could do is move to gas for cooking but I think that would be a step backwards

[Stinsy]

I think I should qualify the above a bit which I will do below just to sense check that we are not overloading the system.

I am always happy to be corrected on things I have got wrong - as you say it is the way to learn - my only caveat is that it is done constructively without being condescending (which to be fair I have almost always found everything on the forum to be respectful and constructive)

Main Consumer Unit

• Shower 1 - 40A - This will be removed next year and I am pretty sure the shower is about 5KW - So this is closer to 22A real world use

• Shower 2 - 40A - This will be removed in a couple of years and I am pretty sure the shower is about 5KW - So this is closer to 22A real world use

• Kitchen/Cooker - 40A - This is probably accurate when we do celebratory meals (Christmas/Easter etc.)

• Outbuilding - 40A - At this point I don't know what I will have in the outbuilding. The plan is to run it as a workshop I don't foresee having more than 3KW (13A) running at the same time. Perhaps I should downsize this?

• PV - 32A - I consider this item to be pretty much zero as it is a generator rather than consumer. I understand there will be a little to keep it running when there is no sun but I think in the context we are assessing it that it will be negligible

• Zappi Charger - 32A - I currently don't have one so this is zero at the moment but will be in this Consumer unit when it is installed (after showers are removed)

• Eddi - 16A - I consider this item to be pretty much zero too as it is only there to consume surplus power from the PV system. Again there will be a little use to stay running when not diverting but again I consider it to be negligible

• AC 1 - 16A - This is a next year install - This is currently not installed and will not be until after showers removed

• AC 2 - 16A - This is an install probably 2-3 years down the line - Same as above

Based on the house at the moment this consumer unit will run 22+22+40 = 84A Maximum (everything on)

Based on where I will end up this consumer unit will run 40+13+32+16+16 = 117A Maximum (everything on)



Switchable Consumer Unit

• Ring Main Downstairs -32A - About the biggest thing we run is the vacuum cleaner ... which is max 2KW or 8.7A

• Ring Main Upstairs -32A - Nothing much upstairs maybe a couple of modern TVs and the hair dryer - so again assumer 2KW or 8.7A

• Ring Main Lofts - 32A - Server Gear up here so maybe 0.8KW or 3.5A

• Outbuilding- 16A - This is mainly to provide lights and CCTV in a power cut - This an estimate at 300W or 1.3A

• Front External Plug 16A - Very little we run outside - maybe the vacuum cleaner for the car or the pressure washer so 2KW or 8.7A

• Solar Thermal - 6A - To be added next year - This is just to run the pump so about 50W which is 0.25A

• Exterior lighting - 6A - I have a total of 6 outside lights (total of 60 Watts) so 0.26A

• Lighting Downstairs - 6A - There are probably 24 light fittings averaging about 5W per fitting - 120W which is 0.5A

• Lighting Upstairs - 6A - There are probably 12 light fittings averaging about 5W per fitting - 60W which is 0.25A

Based on where I will end up this consumer unit will run 32A Maximum (everything on) But this is extremely unlikely

We are currently on an 80A supply and three phase is not an option as I know they would need to run it across the road at high expense.

Whilst everything on will overload the supply - we have never got anywhere close so far.

I suppose the only thing we could do is move to gas for cooking but I think that would be a step backwards

I’ve never heard of a 5kW shower, the lowest I’ve seen are 7.5kW but they’re pretty rare, 9.5kW or 10.5kW are the most common. You’re supposed to go off of the breaker rating prima facie, because you’re supposed to be able to do max demand calcs simply by looking at the CU. You can do further investigations and modify your calculations but you need to have a good answer as to why a 20A device is protected by a 40A breaker it is doubtful that would comply with MIs!

You need to at least provide lip service to the formal method of calculating max demand! You can deviate from that with justification but it needs to be your starting point! What actually is connected to sockets circuits isn’t as relevant as what might be connected by another user. Therefore you need a very good reason if you’re going to deviate from the standard methods and should consider changing the breaker size.

Here goes!

Main Consumer Unit: DB1

• Shower 1 - 40A - 40A

• Shower 2 - 40A - 40A

• Cooker - 40A -10+9+5=24A (assuming a socket)

• Outbuilding - 40A - DB3 (circuits listed separately)

• PV - 32A - 0A (negligible demand (assuming no battery))

• Zappi - 32A - 0A if installed with wired CT and set to cap max demand

• Eddi - 16A - 0A if installed with wired CT and set up to cap max demand.

• AC 1 - 16A - 16A

• AC 2 - 16A - 16A

DB1 total: 136A

Basically you’re way over already, with two more DBs to consider! Once the showers are removed then DB1 drops to 56A.

Switchable Consumer Unit: DB2

• Downstairs Ring - 32A - 32A

• Upstairs Ring - 32A - 32*0.4=12.8A

• Loft Ring - 32A - 32*0.4=12.8A

• Outbuilding - 16A - 16*0.4=6.4

• Front External Plug -16A -16*0.4=6.4

• Solar Thermal - 6A - 0A (single hardwired device with negligible demand)

• Exterior lighting - 6A - 1A (to cover all lighting circuits)

• Lighting Downstairs - 6A - 0A

• Lighting Upstairs - 6A - 0A

DB2 Total: 71.4A

Outbuilding: DB3

• Sockets Ring - 32A - 32x0.4=12.8A

• Lights 6A - 0A

DB3 Total: 12.8A

GRAND TOTAL: 219.8A

So you’re way WAY over. If you’re taking out the 80A of showers then this drops to 139.8A (only after they’re out!) which is still over. And I’ve rated the 32A EV charging point and the 16A immersion at 0A because I’m assuming they are installed with a compliant method of max demand management. To do this they must be formally certified, have wired CTs, and there must be no method to override the max demand with a “boost” function or similar.

I’m also concerned that the outbuilding has its own DB but there is a circuit within the outbuilding that isn’t controlled by the DB. There needs to be very good signage on the DB and the non-DB3 accessories explaining such. It’d be easy for a future spark to get a shock incorrectly thinking that DB3 isolates the whole outbuilding.

How can you get this down?

What is the actual current draw of the AC units? A typical 3.5kW AC might be rated at 5A.
Does the outbuilding “switchable” circuit need to be 16A can it not be 6A? And you really, really should consider doing away with this. It is loads of added complexity and safety concerns to solve a problem that would be better solved with a UPS.
Does the attic sockets circuit need to be 32A? You could you downrate this to 16A? You could possibly justify, listing the actual devices and explaining that it is unlikely anything else will be powered by this circuit. Particularly if there is only a single double-socket up there and you clearly label it “computer equipment only” or similar.

Maybe you can scrape under the 100A but you really should consider getting a quote for a 3-phase supply.

[cojmh]

I’ve never heard of a 5kW shower, the lowest I’ve seen are 7.5kW but they’re pretty rare, 9.5kW or 10.5kW are the most common. You’re supposed to go off of the breaker rating prima facie, because you’re supposed to be able to do max demand calcs simply by looking at the CU. You can do further investigations and modify your calculations but you need to have a good answer as to why a 20A device is protected by a 40A breaker it is doubtful that would comply with MIs!

You need to at least provide lip service to the formal method of calculating max demand! You can deviate from that with justification but it needs to be your starting point! What actually is connected to sockets circuits isn’t as relevant as what might be connected by another user. Therefore you need a very good reason if you’re going to deviate from the standard methods and should consider changing the breaker size.

Here goes!

Main Consumer Unit: DB1

• Shower 1 - 40A - 40A

• Shower 2 - 40A - 40A

• Cooker - 40A -10+9+5=24A (assuming a socket)

• Outbuilding - 40A - DB3 (circuits listed separately)

• PV - 32A - 0A (negligible demand (assuming no battery))

• Zappi - 32A - 0A if installed with wired CT and set to cap max demand

• Eddi - 16A - 0A if installed with wired CT and set up to cap max demand.

• AC 1 - 16A - 16A

• AC 2 - 16A - 16A

DB1 total: 136A

Basically you’re way over already, with two more DBs to consider! Once the showers are removed then DB1 drops to 56A.

Switchable Consumer Unit: DB2

• Downstairs Ring - 32A - 32A

• Upstairs Ring - 32A - 32*0.4=12.8A

• Loft Ring - 32A - 32*0.4=12.8A

• Outbuilding - 16A - 16*0.4=6.4

• Front External Plug -16A -16*0.4=6.4

• Solar Thermal - 6A - 0A (single hardwired device with negligible demand)

• Exterior lighting - 6A - 1A (to cover all lighting circuits)

• Lighting Downstairs - 6A - 0A

• Lighting Upstairs - 6A - 0A

DB2 Total: 71.4A

Outbuilding: DB3

• Sockets Ring - 32A - 32x0.4=12.8A

• Lights 6A - 0A

DB3 Total: 12.8A

GRAND TOTAL: 219.8A

So you’re way WAY over. If you’re taking out the 80A of showers then this drops to 139.8A (only after they’re out!) which is still over. And I’ve rated the 32A EV charging point and the 16A immersion at 0A because I’m assuming they are installed with a compliant method of max demand management. To do this they must be formally certified, have wired CTs, and there must be no method to override the max demand with a “boost” function or similar.

I’m also concerned that the outbuilding has its own DB but there is a circuit within the outbuilding that isn’t controlled by the DB. There needs to be very good signage on the DB and the non-DB3 accessories explaining such. It’d be easy for a future spark to get a shock incorrectly thinking that DB3 isolates the whole outbuilding.

How can you get this down?

What is the actual current draw of the AC units? A typical 3.5kW AC might be rated at 5A.
Does the outbuilding “switchable” circuit need to be 16A can it not be 6A? And you really, really should consider doing away with this. It is loads of added complexity and safety concerns to solve a problem that would be better solved with a UPS.
Does the attic sockets circuit need to be 32A? You could you downrate this to 16A? You could possibly justify, listing the actual devices and explaining that it is unlikely anything else will be powered by this circuit. Particularly if there is only a single double-socket up there and you clearly label it “computer equipment only” or similar.

Maybe you can scrape under the 100A but you really should consider getting a quote for a 3-phase supply.

Thank you, that is super useful - I am basically going from what is already in the existing consumer units as a start point and looking to add/replace as per what I have said already to get to where I want to be. Nothing currently has changed under my ownership other than a physical swap of the shower unit and switching to LED lighting. I will dig deeper into the shower units though as I am now intrigued

With respect to the two different circuits in the outbuilding - I was intending to have two consumer units next to each other (like DB1 and DB2 are within the house). Clearly labelled on the consumer units what they are. Would this be enough to allay your concerns or do recommend other steps?

Using your calculations:

Main Consumer Unit: DB1

• Shower 1 - 40A - 0A To be deleted ASAP

• Shower 2 - 40A - 0A - To be deleted ASAP

• Cooker - 40A -10+9+5=24A (assuming a socket)

• Outbuilding - 40A - DB3 - Down grade this to 20A - which I think would still be adequate

• PV - 32A - 0A (negligible demand (assuming no battery)) - This does have batteries but can only be charged from the DC side

• Zappi - 32A - 0A if installed with wired CT and set to cap max demand

• Eddi - 16A - 0A if installed with wired CT and set up to cap max demand. - I thought the Eddi just took surplus power that was being fed to the grid and hence not a consumer?

• AC 1 - 16A - 16A - I based this on specs from the retailer

• AC 2 - 16A - 16A - I based this on specs from the retailer

DB1 current total: 136A

Ultimately I should be able to get DB1 to 76A (and that includes 20A for the outbuilding at 100%).

Switchable Consumer Unit: DB2

• Downstairs Ring - 32A - 16A - I think this can be dropped to 16A safely without any issues for us

• Upstairs Ring - 32A - 16*0.4=6.4A - I think this can be dropped to 16A

• Loft Ring - 32A - 6*0.4 =2.4A - I think this can be dropped to 6A

• Outbuilding - 16A - DB4 - 6*0.4 =2.4 - I think this can be dropped to 6A

• Front External Plug -16A - 6*0.4=2.4 - I think this can be dropped to 6A

• Solar Thermal - 6A - 0A (single hardwired device with negligible demand)

• Exterior lighting - 6A - 1A (to cover all lighting circuits)

• Lighting Downstairs - 6A - 0A

• Lighting Upstairs - 6A - 0A

Updated DB2 Total: 30.6A

DB3 Total: This was already included in DB1 above at 20A
DB4 Total: This was already included in DB2 above at 2.4A

Ultimate GRAND TOTAL: 106.6A

I accept that the calculations need to be done based on what others people might do (not me and my family specifically) but if we can get to the 106.6A or lower then I hope we are squeezing in .... just.

I have spoken to National Grid about 3 Phase as I had them in to move my incoming electrical supply and I explored the 3 Phase option as that seemed like a good opportunity. The cost indication from the representative I spoke to was too large to stomach so I am going to have to figure out how to make do with the single phase connection I have

Just on a side note - I have purchased the new consumer units (BG Fortress with space for up to 10 RCBOs and it comes with 8 pre-populated). The eight RCBOs that are present are 1*40A, 3*32A, 1*16A, 3*6A giving a total of 170A with space for 2 more RCBOs. Now as we have already discussed - not everything is going to be running at 100% concurrently - but it gives the capacity to until you blow the main incoming fuse.

Thank you again for all of your help

[cojmh]

As an additional thought - I think the only other area to approach is the AC units - as you pointed out.

I have looked at two multi split units which would manage every area in the house - but there are a couple of realities:

1. Not every room in the house will always be occupied - during the day I would expect down stairs to be cooled and not so much upstairs and vice versa at night. I accept that cooling might be left on by accident somewhere - but it is very very unlikely for both system to be running at max.
2. As the house has been significantly up graded in terms of insulation - this should also reduce the demand on the AC. From reading what others have achieved it seems this is likely?

Would this be adequate reasoning to apply a reduction factor on the power consumption by AC1 and AC2? Even a 20% reduction would bring the total under 100A?

[Stinsy]

If max demand calcs come out at 106A then any spark would let that through with a roll of their eyes and a sigh…

However I have some problems with your methodology…

• Having DB3 and DB4 next to eachother in the outbuilding (similar to DB1 and DB2 in the house) is fine. Disregard my earlier concerns.

• The Eddi controls your immersion heater. You’re required to put this circuit as 100% if there is any way to manually activate the immersion heater as in some kind of “boost” function. If the IH can only be activated via diverted export then you can downrate the IH to 0A for max demand calcs.

• What is the outbuilding? I have a garden office, it is on a 32A, but 20A would be fine. Having a workshop or something on a 20A might cause nuisance tripping.

• AC units usually require a higher breaker rating than their running power because of the startup. EG a typical 3.5kW model might require a 16A breaker but only consume 5A when running (at max power). I heat a whole 5-bed house with a single “7kW” AC unit. You really don’t need one in every room! (Although two smaller units would be better!)

• You need to think really carefully before dropping the downstairs ring to 16A. What about the: washing machine, dishwasher, kettle, toaster, air frier, microwave, etc.? Nowadays it is common to put the kitchen/utility on one 32A ring and the rest of the downstairs on another.

• Having the other sockets circuits on 16A circuits is fine so long as you give it some thought. Will there really never be several high-power devices running simultaneously?

• I really don’t think it is sensible to put the outside socket on a 6A. People tend to plug high power devices into these (lawnmower, granny cable, etc.). Having any sockets circuit on a 6A is a bit unusual but permissible if it powered a single outlet intended and clearly labelled for a specific device only.

Let’s do max demand calc for a typical installation using that BG board you’ve bought:

40A cooker - 10+9+5=24A
32A ring - 32A
32A ring - 32*0.4=12.8A
32A ring - 32*0.4=12.8A
16A outside socket - 16*0.4=6.4A
6A lights - 1A (for all lights)
6A lights - 0A
6A smokes - 0A

Total: 89A

So totally fine!

(BTW buy the nice BG din-rail blanks rather than the crappy ones that come with the board https://www.screwfix.com/p/british-gene ... lank/5390p)

[Stinsy]

As an additional thought - I think the only other area to approach is the AC units - as you pointed out.

I have looked at two multi split units which would manage every area in the house - but there are a couple of realities:

1. Not every room in the house will always be occupied - during the day I would expect down stairs to be cooled and not so much upstairs and vice versa at night. I accept that cooling might be left on by accident somewhere - but it is very very unlikely for both system to be running at max.
2. As the house has been significantly up graded in terms of insulation - this should also reduce the demand on the AC. From reading what others have achieved it seems this is likely?

Would this be adequate reasoning to apply a reduction factor on the power consumption by AC1 and AC2? Even a 20% reduction would bring the total under 100A?

Basically no. You can’t use this as justification to apply diversity. In very cold weather or when you return to a cold house you have to assume it’ll be cranking at the maximum power.

If the house is well-insulated then fit a smaller AC/HP system. As I said above you really don’t need one in every room. Here is a 4-head “7kW” multi-split that requires a 20A breaker but draws 9.2A running at full chat. You could install 4x 3.5kW internal units with it so you can direct all your heating/cooling to either upstairs or down as you wish: https://cooleasy.co.uk/cdn/shop/files/M ... 4618322948

2-units up and 2-units down really should be plenty!