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Have just installed a Zappi and notified National Grid (aka WPD) using online form.

Automated response is "approved with remedial works", no further detail given.

Can anyone say what remedial works are likely to be required and how I could/should have avoided this outcome?

Let's hope the remedial works aren't a local transformer upgrade at your expense.

sharpener wrote: ↑Fri Dec 23, 2022 7:39 pm how I could/should have avoided this outcome?

Not tell them.

Tinbum wrote: ↑Fri Dec 23, 2022 11:25 pm

sharpener wrote: ↑Fri Dec 23, 2022 7:39 pm how I could/should have avoided this outcome?

Not tell them.

Exactly this ^ ^ ^

When I asked to have an electricity supply here I was sent a spreadsheet form, with a list of appliances that we wanted to connect to the supply. This included ovens, hobs, heaters, heat pumps etc. I ticked every single box, as I really had no idea at that stage what we would really be using. At that time the Nissan Leaf and the Renault Zoe were about to hit the market (I think the Leaf already had done so), even though we were skint, I ticked the EV charger box.

Glad I did, as it means we have the highest capacity UK single phase supply available, 15kVA. Makes a big difference, as some homes not far from us have much lower capacity supplies, One about two miles away has, believe it of not, a 5kVA transformer supplying their home, and the DNO refuse to upgrade it without a massive contribution towards the cost of the new transformer and 11kV cables. The place is a farm, too, so they really have to watch their demand to stay within the safe rating of their supply.

Yes when I applied for a 3 phase supply here I ticked nearly everything and requested a 50Kva transformer. They upped it and installed a 100Kva. (Our original transformer was 5Kva single phase, though the transformer was knackered and showed signs of lightening damage ).

Oldgreybeard wrote: ↑Sat Dec 24, 2022 12:07 am

Glad I did, as it means we have the highest capacity UK single phase supply available, 15kVA.

Did you mean 50kVA?

15kVA is only fractionally more than the 13.8 you get with the assumed default 60A supply.

I left all the boxes on the online form at the default settings of 60A as I cannot see what the DNO fuse rating is.

But IIRC their distribution wiring plan shows the feed to the house as 35 Hyb, perhpas someone can say what its rating is, then I may be able to argue that my supply is adequate. The max usage (at cheap rate) will be 7.4kW for the zappi plus 1kW to charge the Pylontech ESS (no more because of fan noise) plus 500W max house loads = 40A at nom 230V, less in practice as the line voltage is more like 245.

Also in normal operation the whole installation is fed through the 50A breaker that supplies the Victron inverter, so it is limited by that to 11.5kVA. If the Victron setup dies I can bypass it but then it is not drawing any current to charge the Pylons.

My chief worry is that they will impose a G100 import limitation. I do not want to dig up the tarmac driveway but Myenergi say the harvi wireless box is not G100 compliant - though I don't see why they cannot make it failsafe by shutting down the zappi if the wireless link fails.

As a footnote I see the advice on diversity hasn't been updated since my 17th(?) edition On Site Guide, especially the 100W to be allowed for every lampholder. Including the ones in the loft space, cupboards and outbuildings this alone is 32A. A conservative calculation quickly gets me to well over 100A, allowing 27 for the cooker, 13 for the immersion and 38.4 for the two rings but clearly this is unrealistic.

sharpener wrote: ↑Sat Dec 24, 2022 6:57 pm

Oldgreybeard wrote: ↑Sat Dec 24, 2022 12:07 am

Glad I did, as it means we have the highest capacity UK single phase supply available, 15kVA.

Did you mean 50kVA?

15kVA is only fractionally more than the 13.8 you get with the assumed default 60A supply.

I left all the boxes on the online form at the default settings of 60A as I cannot see what the DNO fuse rating is.

But IIRC their distribution wiring plan shows the feed to the house as 35 Hyb, perhpas someone can say what its rating is, then I may be able to argue that my supply is adequate. The max usage (at cheap rate) will be 7.4kW for the zappi plus 1kW to charge the Pylontech ESS (no more because of fan noise) plus 500W max house loads = 40A at nom 230V, less in practice as the line voltage is more like 245.

Also in normal operation the whole installation is fed through the 50A breaker that supplies the Victron inverter, so it is limited by that to 11.5kVA. If the Victron setup dies I can bypass it but then it is not drawing any current to charge the Pylons.

My chief worry is that they will impose a G100 import limitation. I do not want to dig up the tarmac driveway but Myenergi say the harvi wireless box is not G100 compliant - though I don't see why they cannot make it failsafe by shutting down the zappi if the wireless link fails.

As a footnote I see the advice on diversity hasn't been updated since my 17th(?) edition On Site Guide, especially the 100W to be allowed for every lampholder. Including the ones in the loft space, cupboards and outbuildings this alone is 32A. A conservative calculation quickly gets me to well over 100A, allowing 27 for the cooker, 13 for the immersion and 38.4 for the two rings but clearly this is unrealistic.

I wonder if they're looking to upgrade your fuse to 100A with associated remedial works. I assume you're not on a looped supply.

You would only get a max 23 kVA supply on a single phase

AGT wrote: ↑Sat Dec 24, 2022 10:23 pm You would only get a max 23 kVA supply on a single phase

There are (or were when I applied to SSEPD in 2012-13 - I believe WPD are now offering slightly higher rated supplies) only two single phase supply options available. An 80A fused supply rated at 13.8kVA (being phased out even then) or a 15kVA supply fused at 100A (which is what most people in houses built in recent years will most probably have). The fuse rating is always higher than the supply rating, it's only there for short circuit protection. Same principal as the power circuits in a house, a ring circuit is rated at 26A continuous but over-current protected by either a 30A fuse or a 32A circuit breaker. A power outlet is the same, they are rated at 10A continuous but fused at 13A.

There seems a lot of confusion about fuse rating and and power ratings. Having a 100A main fuse doesn't mean you have a 100A supply, most likely (unless you have one of the newer supplies WPD are rolling out to homes that need more power) then your supply will have a 65A continuous current rating. This is why chargers with load limiting (like the Zappi) come with that load limit set to 65A as the default setting, I believe, as that is now probably the most common maximum for single phase homes.

The logic of this carries through to the supply network. Our house has a new 15kVA supply, fed, along with about dozen or more other homes from a 100kVA transformer. Obviously we can't all even draw the 15kVA rating we have at the same time, if we did then the 100kVA transformer would be well overloaded, perhaps around double its rated power. 100kVA is the largest pole mounted transformer available usually, so the system replies on diversity to remain safe, the assumption that not everyone will have high loads on at the same time.

That worked fine until car chargers, heat pumps and home batteries came along, when there is a higher probability that more homes will draw their full rated power at the same time - overnight during a short cheap rate period. This is why the DNO needs to know about high loads, so it can plan upgrades to allow the network to cope with them, or impose restrictions, like insisting that a load limiting charger be installed (and that in turn is why companies like Myenergi have made the Zappi load-limiting).

Final bit of trivia about fuses. I believe that newer transformers are input fused, rather than output fused (the combined pole operated MV or HV fuse disconnects make maintenance easier). The fuses are on the output side of our old 100kVA transformer, and are rated at 800A each. Doing the sums, that means that if all three phases exceeded the 800A fuse rating by enough to cause the fuse to blow, that 100kVA transformer would be running at over 550kVA - A pretty massive overload. The reality is that, just like every other fuse or over-current device the fuse is ONLY there to protect the cable it is supplying if there is a short circuit downstream. The 800A fuses on the output side of our supply transformer are there to stop the cables catching fire if a pole comes down and there is a short - saves fires starting around grossly overloaded cables.

sharpener wrote: ↑Sat Dec 24, 2022 6:57 pm

Oldgreybeard wrote: ↑Sat Dec 24, 2022 12:07 am

Glad I did, as it means we have the highest capacity UK single phase supply available, 15kVA.

Did you mean 50kVA?

15kVA is only fractionally more than the 13.8 you get with the assumed default 60A supply.

No, very definitely 15kVA.

As above, unless you are lucky enough to have one of the uprated supplies that WPD started rolling out a couple of years or so ago (no idea if other DNOs are doing the same) them the max will be 15kVA, so around 65A. I'm not sure what the newer, higher rated, supplies are, I've heard rumours that WPD are either offering 18kVA or 20kVA, but haven't seen anything in writing about this, it all seems a bit vague. There is scope in some areas for the DNO to use discretion to increase the 15kVA rating, without a fuse change, but to do that they need to know the local demand, and there are, apparently large areas of the UK where the DNOs have no form of LV demand measurement and reporting, hence the reason they ask for the size of loads on the form, seems to be the only way they have of knowing how much power local users may be drawing.

The chaps that were working on our local 100kVA transformer when running in our new supply mentioned that some of the newer installations now have telemetry so the DNOs have a better picture as to what the loads are across their network, rather than only relying on the MV and HV load measurements they have from sub-stations. I found chatting to that team from SSEPD both educational and a bit worrying when I counted up the houses that transformer feeds and did the sums. It seems that the diversity rules the DNOs use are wildly different from those used by domestic electricians.

One reason for this, I think, is that an overloaded transformer takes a fair time to overheat, and can probably carry more power in cold weather than it can in hot weather. May well be that being run with a hefty overload for half an hour or so in freezing weather may be fine. I think chargers are causing concern because they will most likely be on for many hours at a time, and with cheap rate electricity on EV tariffs and the like then there's a pretty fair chance that everyone will be charging at the same time.