When to use your own earth rods

[cojmh]

My comments:

• You need to do max-demand calculations! Very doubtful that you'd get away with 2x electric showers...

• THe circuits you're referring to are not "ring mains" they are "ring finals".

• IMO you've got way too much on the UPS/EPS CU. No need to have all your sockets powered in the event of an outage. Lights I agree with, and you'd want your wifi router, TV, and a few strategically-places sockets for phone/laptop charging, but think carefully before adding anything else.

• I wouldn't put the outbuilding on the EPS/UPS supply either. Just fit an emergency light with a self-contained battery, and use a UPS to power your CCTV via a PoE switch.

• Soalr thermal isn't worth it these days, just fit more PV.

• Convention states that you should list circuits from biggest to smallest.

Thanks for the thoughts

My thoughts are (for what their worth)

1. I am acutely aware of max power .... currently there are two electric showers in the house which were there we we bought it. I hate them but not had a chance to do much about them because I couldn't take a bathroom out of commission to deal with them. With our new wet room coming before Christmas we will be able to take one bathroom out of commission at a time when funds allow and redo them. They were replaced with lower power units which is all I have done so far with them. They will be gone in the next couple of years and that will be before other big things like the EV. I have watched our power consumption for over a year and we have never gone over 8KW at any given time. That might change though as the kids get older.

2. Sorry - Electrical terminology is not my strong point (and the official terminology is confusing to compound that issue!).

3. There is an additional reason for a lot on the UPS/EPS - my switch over gear also allows for generator input which is more than capable of running everything in the house excluding kitchen/showers etc. So rather than separate 3 ways this seemed like the more sensible way to do things. My switch over gear is also fully manual. So if we go to Solar EPS then I can switch things off manually before switching over. If we go to generator then we don't need to. Most critical stuff is on UPS to allow for this manual change over (if I am there!).

4. The reason for the garage to have a single spur for critical things was because of the generator being available as opposed to UPS (which critical things are already on). I can always rejig this in the future if I don't use it or need it (working on the better to have and not need than need and not have strategy).

5. The problem with adding more PV is that I only have the FIT system at the moment and my intention to add more solar will be big and on the out building. I have just added a sloped roof to the porch and it is only big enough for one PV panel (just!) or the solar tubes so I have gone with solar thermal. From my understanding they are much more efficient (80ish percent) and we use more hot water than the average household due to my mother in law, so I am still thinking this will be useful to us.

6. Yeah - fair point ... it would make it easier for others to read!


Thanks for all of the help

[AGT]

Just fit 2 boards
1 essential 1 non essential
Everything you want to work off the UPS goes on the essential and is fed from the UPS circuit you just need to acknowledge the limitation
That’s what I’m planning on doing on the 8kW inverter
However I am using my existing generator changeover switch which will become redundant to switch between the UPS and the mains supply in the event there is an issue with the inverter and I have no mains from it

My 7 kW EV Charger, PV Fit Circuit, 10.8kW electric shower, and a couple other things will all be off the non essential

[cojmh]

Just fit 2 boards
1 essential 1 non essential
Everything you want to work off the UPS goes on the essential and is fed from the UPS circuit you just need to acknowledge the limitation
That’s what I’m planning on doing on the 8kW inverter
However I am using my existing generator changeover switch which will become redundant to switch between the UPS and the mains supply in the event there is an issue with the inverter and I have no mains from it

My 7 kW EV Charger, PV Fit Circuit, 10.8kW electric shower, and a couple other things will all be off the non essential

Makes absolute sense .

I have ordered two BG Fortress consumer units (with up to 10 RCBOs each) .... just need to sort getting them fitted.

[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.

[Stinsy]

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).

[sharpener]

My comments:

• You need to do max-demand calculations! Very doubtful that you'd get away with 2x electric showers...

there is a very useful calculator here https://www.ssen.co.uk/our-services/too ... alculator/

• THe circuits you're referring to are not "ring mains" they are "ring finals".

ooh, that's a bit picky!

• Convention states that you should list circuits from biggest to smallest.

and put the biggest nearest the main switch to reduce the voltage drops in the busbars

[Stinsy]

My comments:

• You need to do max-demand calculations! Very doubtful that you'd get away with 2x electric showers...

there is a very useful calculator here https://www.ssen.co.uk/our-services/too ... alculator/

• THe circuits you're referring to are not "ring mains" they are "ring finals".

ooh, that's a bit picky!

• Convention states that you should list circuits from biggest to smallest.

and put the biggest nearest the main switch to reduce the voltage drops in the busbars

That might be how the DNO works out max demand if you're planning a housing estate. However, the correct way to do it for a single dwelling is as follows:

(You calculate everything in Amps)

• Electric showers: 100% of the two largest then 25% of the rest.

• Electric Cookers: 100% of the first 10A + 30% of the rest + 5A if there is a socket.

• Immersion heaters, Storage heaters, other electric heaters: 100%

• EV charging points: 100%

• Heat pumps: 100%

• Lighting: add up all the bulbs then 66% of that.

• Sockets circuits: 100% of the first/largest then 40% of the rest.

If that is over the fuse rating then you need to reduce it or apply to the DNO to fit a bigger main fuse or upgrade to 3-phase.

The regs do stipulate other methods that you might choose to make the calculation and the spark is supposed to use common sense and apply professional judgment. And it is generally understood that the above is excessively conservative for the modern world with energy-efficient devices.

For example, there might be an extension with 2x guest bedrooms on a 32A ring with only a bedside lamp and a phone charger in each, total load way under 1A, so 40% of 32A (12.8A) is probably too much. However, on the other hand, you're supposed to take into account how the house might be used when the current owners sell it on. For example, student houses can be problematic because a bunch of girls all tend to get ready for a night out at the same time with hair driers and straighteners blasting simultaneously.

Similarly for lighting, so long as you've checked it is all-LED then 1A for the whole house is likely to be plenty for max demand calcs even if there are loads of 6A circuits.

A lot of the above is fiddling with small numbers though. It is the: electric showers, EV charging points, and heat pump that are the big immovable objects. Modern demand-limiting EV charging points are a big help too but more than one electric shower should wave a red flag that max demand probably hasn't been accounted for.

I get that I can be picky with terminology. However I strongly believe that helping someone use the correct terminology is also helping them to understand the underlying situation as well as helping them describe it correctly. There are two types of people: intelligent people are usually happy to be corrected even on minor points and are eager to take on the new information. Dim people generally get stroppy and defensive.

People will argue as to whether putting the biggest circuits next to the main switch is required, certainly there is no harm, but voltage drops are relevant over distances measured in tens of metres not a few cm. When listing circuits it is handy to put them biggest-to-smallest so that all the important stuff is grouped together which makes it easier to do a quick reckoning at a glance.

[sharpener]

The SSEN calculator seems to be just as valid an approach for 1 dwelling as 100. (As you increase the # of properties on the first line from one it makes some reasonable and increasing allowances for inter-property diversity.) I mentioned it bc it is (a) quick and easy to use (b) has the imprimatur of at least one DNO (c) is not so pessimistic as the IET-derived process you quote.

Yes I had to consciously switch the garage to "bypass" last night but that was bc I wanted to run the HP hard during the Cosy cheap period in the small hours and charge the car and the house battery as well. And then only bc the battery inverter is limited to 50A, not on account of the total load on the supply.

Adopting your "common sense and apply professional judgment" maxim suggests that I do not need to allow for immersion heater simultaneously with the HP, or allow 24A for using the cooker 0400 - 0700, not least because the AGA is lit at the moment.

I see my On-Site Guide has a handwritten note that the full rules expressly allow you to "take account of the operating time profile of the loads and the extent to which they will coincide with other loads and seasonal demands".

So all-in-all it is IMO a much more realistic method, and more importantly gives a result that both NGED and I am happy with, which is that I do not need to upgrade the meter tails - which go by an unknown route through a 600mm stone wall - to allow for the fuse to be increased from 80A, despite all the kit I possess.

But then I also consider 2 x 10kW showers to be the work of the devil. Even one of them with the OP's other stuff results in the dreaded message

Based on the information you provided, your connection may require a split or third phase which is probably the correct answer!

[Stinsy]

The SSEN calculator seems to be just as valid an approach for 1 dwelling as 100. (As you increase the # of properties on the first line from one it makes some reasonable and increasing allowances for inter-property diversity.) I mentioned it bc it is (a) quick and easy to use (b) has the imprimatur of at least one DNO (c) is not so pessimistic as the IET-derived process you quote.

Yes I had to consciously switch the garage to "bypass" last night but that was bc I wanted to run the HP hard during the Cosy cheap period in the small hours and charge the car and the house battery as well. And then only bc the battery inverter is limited to 50A, not on account of the total load on the supply.

Adopting your "common sense and apply professional judgment" maxim suggests that I do not need to allow for immersion heater simultaneously with the HP, or allow 24A for using the cooker 0400 - 0700, not least because the AGA is lit at the moment.

I see my On-Site Guide has a handwritten note that the full rules expressly allow you to "take account of the operating time profile of the loads and the extent to which they will coincide with other loads and seasonal demands".

So all-in-all it is IMO a much more realistic method, and more importantly gives a result that both NGED and I am happy with, which is that I do not need to upgrade the meter tails - which go by an unknown route through a 600mm stone wall - to allow for the fuse to be increased from 80A, despite all the kit I possess.

But then I also consider 2 x 10kW showers to be the work of the devil. Even one of them with the OP's other stuff results in the dreaded message

Based on the information you provided, your connection may require a split or third phase which is probably the correct answer!

Some professionals will insist that the logic of: two devices are unlikely to be used simultaneously as being moot. (eg as you say: it is unlikely that you’ll be cooking during the cheap period when your storage heaters are cranking, and the backup resistive heating is unlikely to be used at the same time as the primary HP). They say that unless a device such as a timer or priority switch is in place to prevent them being used simultaneously you cannot apply this. I take a more measured approach: YOU being unlikely to use the devices simultaneously is irrelevant, if I can imagine NO ONE using the devices simultaneously then I’d apply it. However the max demand calcs just got a lot more complicated…

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!

[sharpener]

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).