Storage Heaters

[Oldgreybeard]

That's my storage heater path complete. Installed three hive plugs and a final 1.7kW unit this morning. Had a count around the house, we are as follows

6x850W upstairs
10x850W downstairs

That's 13.6kW with a 7 hour charging capacity. 95.2kWh potential storage capacity!

We are currently on a five hour charging window, falling to four hours at Hogmanay and rising to six hours when IO opens to me.
Nowty, please adjust my storage capacity when you have a moment. This has been an excellent wee journey and I'll happily have the ability to shift the charging window from Turkey at New Year.

I absolutely do not want to be a merchant of doom, but this set up does worry me a great deal. Ring circuits were never intended to be used to carry this sort of load for long periods, storage heater circuits were always wired as radials from a separate consumer unit, in part to mitigate the issues associated with high loads on rings (rings are a complete and utter bodge, in my view, and often present significant risks when highly loaded).

If the house has two rings, one upstairs, one downstairs, then the absolute maximum capacity of each will be either 30A (if fused) or 32A (if protected with MCBs or RCBOs.

The actual cable used in each ring will be rated at between about 22A and 27A, depending on how it is routed (it can carry less when running inside walls and floors that it can when clipped to the outside of a wall). The cables in a ring tend to share current, although this sharing is always uneven, due to the varying lengths from the common point (at the consumer unit) to each outlet. The shorter legs from the consumer unit to an outlet will always carry more current than the longer lengths.

6 x 850W gives 5,100W, so a nominal load on the upstairs ring of 22A, with no other loads running from any other outlet.

8 x 850W gives 6,800W, so a nominal load on the downstairs ring of 29.6A, with no other loads running from any other outlet.

The downstairs ring is getting a bit marginal, TBH. I'd not want to leave the house unattended with that sort of load and would want to go around and check things, especially all the wiring terminations in the outlets and the consumer regularly, just in case.

The total load of 11.9kW leaves only a small margin for other loads, too. At the very most you may have a 15kVA single phase supply (which will be fused at 100A for short circuit protection of the cable), many homes only have a 13.8kVA supply (which will be fused at 80A, again for short circuit protection of the cable).

We are lucky enough to have the highest rated single phase supply SSE PD can provide, with a 100A fuse, so we can draw up to an absolute maximum long duration load of 15kVA. Sounds like a lot, but with 3kW charging the hot water, 7.4kW charging the car, 3kW charging the battery , around 1.5kW running the heat pump and around a 200W background load for the MVHR, water disinfection and treatment plant aeration air pump we are slightly over the limit, 15.1kW. That's without the ~45 minute overnight filter backwash every fourth night, which uses around another 600W.

My fix has been to turn the car charger down to 6kW and turn the house battery charger down to 2.5kW, just to keep the electrical installation safe. The very last thing I want is to have an electrical fire at night, when we are sound asleep, as that's when our demand is always at it's very highest.

[Joeboy]

That's my storage heater path complete. Installed three hive plugs and a final 1.7kW unit this morning. Had a count around the house, we are as follows

6x850W upstairs
10x850W downstairs

That's 13.6kW with a 7 hour charging capacity. 95.2kWh potential storage capacity!

We are currently on a five hour charging window, falling to four hours at Hogmanay and rising to six hours when IO opens to me.
Nowty, please adjust my storage capacity when you have a moment. This has been an excellent wee journey and I'll happily have the ability to shift the charging window from Turkey at New Year.

I absolutely do not want to be a merchant of doom, but this set up does worry me a great deal. Ring circuits were never intended to be used to carry this sort of load for long periods, storage heater circuits were always wired as radials from a separate consumer unit, in part to mitigate the issues associated with high loads on rings (rings are a complete and utter bodge, in my view, and often present significant risks when highly loaded).

If the house has two rings, one upstairs, one downstairs, then the absolute maximum capacity of each will be either 30A (if fused) or 32A (if protected with MCBs or RCBOs.

The actual cable used in each ring will be rated at between about 22A and 27A, depending on how it is routed (it can carry less when running inside walls and floors that it can when clipped to the outside of a wall). The cables in a ring tend to share current, although this sharing is always uneven, due to the varying lengths from the common point (at the consumer unit) to each outlet. The shorter legs from the consumer unit to an outlet will always carry more current than the longer lengths.

6 x 850W gives 5,100W, so a nominal load on the upstairs ring of 22A, with no other loads running from any other outlet.

8 x 850W gives 6,800W, so a nominal load on the downstairs ring of 29.6A, with no other loads running from any other outlet.

The downstairs ring is getting a bit marginal, TBH. I'd not want to leave the house unattended with that sort of load and would want to go around and check things, especially all the wiring terminations in the outlets and the consumer regularly, just in case.

The total load of 11.9kW leaves only a small margin for other loads, too. At the very most you may have a 15kVA single phase supply (which will be fused at 100A for short circuit protection of the cable), many homes only have a 13.8kVA supply (which will be fused at 80A, again for short circuit protection of the cable).

We are lucky enough to have the highest rated single phase supply SSE PD can provide, with a 100A fuse, so we can draw up to an absolute maximum long duration load of 15kVA. Sounds like a lot, but with 3kW charging the hot water, 7.4kW charging the car, 3kW charging the battery , around 1.5kW running the heat pump and around a 200W background load for the MVHR, water disinfection and treatment plant aeration air pump we are slightly over the limit, 15.1kW. That's without the ~45 minute overnight filter backwash every fourth night, which uses around another 600W.

My fix has been to turn the car charger down to 6kW and turn the house battery charger down to 2.5kW, just to keep the electrical installation safe. The very last thing I want is to have an electrical fire at night, when we are sound asleep, as that's when our demand is always at it's very highest.

I appreciate the thought and time taken here, thank you. The system is split evenly across 3 x 32A ring mains. The EV is on its own Spur and breaker off of the incoming from street post smart meter and the charger is current limited. I have built the system slowly over time and almost every electrical connection in this house has been in my hands at one time or another through my life here. Your points are all valid and anyone pursuing SH's should take note and understand. I also keep the max load of house under 90A. Beyond that,I sleep fine. , 21A is max on any of the 3 32A circuits.

[Oldgreybeard]

90A is pretty big overload, though. At the most your supply will be rated to deliver 15kVA, as there are no UK single phase domestic supplies rated at more that that for long duration loads. 15kVA is about 65A continuous. so 90A is an overload of about 38%.

I would very, very strongly suggest that no one emulates this without being fully aware that they are taking a very significant risk, are exceeding their supply maximum continuous rating by a big margin and that there may well be significant risks, especially on an older electrical installation that hasn't been recently tested and inspected, along with all sorts of possibly unpleasantries from insurers etc if, heaven forbid, something were to go awry as a consequence of deliberate abuse of the supply maximum rating.

Luckily we do have significant safety margins built in to the system, so modest overloads can often be tolerated with few ill effects, but the other point to consider is the impact on other homes in the area and on the local distribution system. There is also one exception to this at the moment. Western Power Distribution have opted to increase the single phase power limit per home recently, and are rolling out a supply upgrade programme, with new transformers and cabling. This is only in some parts of the West country for now, but I'm sure that other DNOs will follow suit before long, and we may all get slightly higher rated supplies over the next decade or so.

The very largest pole mounted transformer used in the UK at the moment is typically rated at 100kVA. Often that will supply around 20 to 30 local properties. It will be fed from an 11kV overhead line in all probability, and each outgoing phase will most probably have a a 400A, perhaps 800A, fuse, to protect the cables, that will have a nominal working current (on the LV side) of about 145A per phase. Each 145A, 230V, nominal single phase supply from the sub-station may well be supplying half a dozen houses or more.

If just a few of those properties choose to start drawing over 20kVA at the same time then that transformer is going to quickly overload. When that happens it increases the likelihood of a power failure, probably a prolonged one, as a PMT replacement is an all day job, perhaps longer in inclement weather. The time such an overload is most likely to happen is during cold weather, when lots of people may be pulling a fair bit of power. The consequences of having no power in very cold weather for some people could be serious, and to be quite open and honest I would not want that on my conscience.

We must all make our own judgement as to what is both safe, and what is least likely to cause harm or inconvenience to others from our actions. I'll leave it at that.

[Joeboy]

I think you are overcautious and now edging into preaching territory in how I/we should live. You are right to leave it at that.

[Oldgreybeard]

I think you are overcautious and now edging into preaching territory in how I/we should live. You are right to leave it at that.

I'm not preaching at all, especially not to you, you can do as you wish as can anyone else taking an informed risk as you have - you know what you are doing, some do not. My comments are aimed fairly and squarely at those that might decide to take an uninformed risk, as they are unaware of both the nature of the risk or ways to mitigate it.

We see examples of people asking for advice here every day, as they aren't as well informed about safety as some others here. I'm just trying to present some balance to those with little or no experience who may be reading this.

I've seen the consequences of overloads many times over the years, almost all in an industrial setting. Most have been minor and little more than an inconvenience, several have been pretty grim, and one caused a significant loss of life. Most of the time lady luck prevails and the erosion of safety margins causes little or no harm, but it's not something I feel should be promoted to others as sensible practice. I spent a fair portion of my career trying to make things less prone to being accidentally abused by well-meaning people, trying to get their job done, but who didn't fully appreciate the risks involved in some of the things they were trying to do. Some of those risks were pretty subtle and far from obvious, so very easy to overlook, even for very bright and competent people

It is those that are not as informed as yourself, and perhaps not so capable of judging what is an acceptable risk, to whom my observations are addressed. There are a lot of inexperienced people that read this forum and some choose to follow the advice of prominent members. That is a large part of what makes this place so very useful and helpful. It's also a sad fact that there a lot of hidden, or little known, risks around, in every home in the land.

For example, a lot of ring mains in UK homes are not actually rings, so cannot ever safely carry the 26A maximum working current that a 32A protected ring can accept. It is very, very common to find broken rings, and sadly not many people realise that they are supposed to get them tested and inspected at least every ten years (5 years if they are in a rented place, or at any change of tenant). It's an insidious risk, as a broken ring very often works just fine - there is no outward sign that the ring is broken at all until it is tested (and is why I absolutely hate them!).

Our last house was a good example, ten year old electrical installation and I wanted to re-tile the kitchen. Every single outlet I took off the kitchen wall had at least one wire that had fallen out of its terminal. There was no ring integrity at all, all the outlets were working as radials, with cable rated at 20A (2.5mm² inside capping in the wall) with unsafe overload protection (a 32A MCB). Some had no protective earth, either, as that was the wire that had fallen out the back! No one was ever hurt by the lack of an earth or the underrated cable, we'd been living there about 4 years at the time, and those outlets were unsafe all of that time I suspect, but that was just luck, and we are fortunate that luck often works in our favour. I would not want to always rely upon it though!

Sorry for any completely accidental personal offence, that was very definitely not my intent at all. My defence is that human life is worth a great deal more to me than some words posted on a forum, and if my views on safety are seen as out of order, then please take whatever action you feel is needed.

[Joeboy]

I think you are overcautious and now edging into preaching territory in how I/we should live. You are right to leave it at that.

I'm not preaching at all, especially not to you, you can do as you wish as can anyone else taking an informed risk as you have - you know what you are doing, some do not. My comments are aimed fairly and squarely at those that might decide to take an uninformed risk, as they are unaware of both the nature of the risk or ways to mitigate it.

We see examples of people asking for advice here every day, as they aren't as well informed about safety as some others here. I'm just trying to present some balance to those with little or no experience who may be reading this.

I've seen the consequences of overloads many times over the years, almost all in an industrial setting. Most have been minor and little more than an inconvenience, several have been pretty grim, and one caused a significant loss of life. Most of the time lady luck prevails and the erosion of safety margins causes little or no harm, but it's not something I feel should be promoted to others as sensible practice. I spent a fair portion of my career trying to make things less prone to being accidentally abused by well-meaning people, trying to get their job done, but who didn't fully appreciate the risks involved in some of the things they were trying to do. Some of those risks were pretty subtle and far from obvious, so very easy to overlook, even for very bright and competent people

It is those that are not as informed as yourself, and perhaps not so capable of judging what is an acceptable risk, to whom my observations are addressed. There are a lot of inexperienced people that read this forum and some choose to follow the advice of prominent members. That is a large part of what makes this place so very useful and helpful. It's also a sad fact that there a lot of hidden, or little known, risks around, in every home in the land.

For example, a lot of ring mains in UK homes are not actually rings, so cannot ever safely carry the 26A maximum working current that a 32A protected ring can accept. It is very, very common to find broken rings, and sadly not many people realise that they are supposed to get them tested and inspected at least every ten years (5 years if they are in a rented place, or at any change of tenant). It's an insidious risk, as a broken ring very often works just fine - there is no outward sign that the ring is broken at all until it is tested (and is why I absolutely hate them!).

Our last house was a good example, ten year old electrical installation and I wanted to re-tile the kitchen. Every single outlet I took off the kitchen wall had at least one wire that had fallen out of its terminal. There was no ring integrity at all, all the outlets were working as radials, with cable rated at 20A (2.5mm² inside capping in the wall) with unsafe overload protection (a 32A MCB). Some had no protective earth, either, as that was the wire that had fallen out the back! No one was ever hurt by the lack of an earth or the underrated cable, we'd been living there about 4 years at the time, and those outlets were unsafe all of that time I suspect, but that was just luck, and we are fortunate that luck often works in our favour. I would not want to always rely upon it though!

Sorry for any completely accidental personal offence, that was very definitely not my intent at all. My defence is that human life is worth a great deal more to me than some words posted on a forum, and if my views on safety are seen as out of order, then please take whatever action you feel is needed.

Ah, not going to leave it at that then, still going? There is no offence taken yet you do continually cry doom on this subject. It has become boring. I look back through the thread and you pop up time and again stating the same over and over increasing the potential outcome. I've not bothered with it, today though, that last one...Ramming stick anyone?
Trot on Chicken Little. Kids, be safe when you play with electricity, ok? If you can't be safe, that's on you.

[nowty]

That's my storage heater path complete.

6x850W upstairs
10x850W downstairs

That's 13.6kW with a 7 hour charging capacity. 95.2kWh potential storage capacity!

Nowty, please adjust my storage capacity when you have a moment. This has been an excellent wee journey and I'll happily have the ability to shift the charging window from Turkey at New Year.

Done.

That's quite some uplift in thermal capacity.

[Joeboy]

That's my storage heater path complete.

6x850W upstairs
10x850W downstairs

That's 13.6kW with a 7 hour charging capacity. 95.2kWh potential storage capacity!

Nowty, please adjust my storage capacity when you have a moment. This has been an excellent wee journey and I'll happily have the ability to shift the charging window from Turkey at New Year.

Done.

That's quite some uplift in thermal capacity.

Thank you Nowty, majority of it is theoretical limits of the gear. If We ever ran it up to full capacity we would have to open the windows for hours on end. Used as 4 to 5 hour storage capacity distributed system though it is absolutely excellent and good down to minus 6 so far. Can re-set the timers via Hive from anywhere and drop down to a couple of hours charging as we move towards Spring. I hope your folks are doing well? Cheers!

Assuming you got back down the road hassle free?

[AGT]

Grabbed 2 dimplex XL12 heaters today, so that’s good and got a confirmed date for the smart meter install of mid January so things are progressing

[nowty]

Grabbed 2 dimplex XL12 heaters today, so that’s good and got a confirmed date for the smart meter install of mid January so things are progressing

Is that on top of another unit about half the size as I already have something down for you in thermal storage ?