Jeremy Harris

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Jeremy Harris last won the day on February 27

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About Jeremy Harris

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  • About Me
    Retired scientist, made the decision to build our own home a few years before retirement, then had the good fortune to be able to retire early and start the self-build journey. Started our build in late 2013, took far longer than anticipated to finish, but have now moved in and we are enjoying having a house with no bills at all (except for the blasted Council Tax...). The house pays us a modest income from the excess energy we generate, over and above the energy we use for heating, cooling, cooking, hot water etc, so we now have a healthy retirement holiday fund.
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    Wiltshire/Dorset Border

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  1. I've seen a Twizy. More like a motorcycle than a car, with no glass in the doors, it's wide open to the elements.
  2. It's much more subtle that that, as the manufacturer's higher ratings for a cable in insulation show (and it's not just Batt, other manufacturers have their own specs and ratings). There has long been a debate about the way heat is dissipated from cables, and one factor that the rough and ready guidance in the OSG ignores is that most of the heat built up in a short insulated section of cable ends up getting conducted out of the insulated section, as the thermal resistance of the copper is massively lower than the thermal resistance of the insulation sheath and surrounding insulation. The result is that short sections of cable within insulation don't run anywhere near as warm as might be expected. The time factor is also very important, and the ratings assume continuous use at the rated current, whereas in a domestic installation it's rare for any circuit to be taking its rated current for more than a few hours, often a lot less. It's one reason why, despite it being commonplace for loft insulation to be laid over cables years after they were installed, including cables feeding things like electric showers, it's not that common to find a cable that's overheated in the middle of a run. Part of that is that the cable can safely operate at a fairly high temperature, usually higher than the stuff connected at either end (the classic being SWA, that is often rated by the manufacturer at 90°C, whereas switchgear etc is rarely rated above 70°C). It's reasonable that the guidance in the OSG errs on the side of caution, but the OSG is not regulation, or law, it's just rough and ready guidance to how the blue book might be interpreted, in short form, as an easy to reference guide. If someone chose to use, say, Table 4D5 from Batt, as they were installing Batt cable, then it would be perfectly legal to do so, as Batt have provided a clear specification for their their cable, showing that it complies with the requirements when used within their stated ratings.
  3. Looks like it, as in that last photo the tails are not connected, as there is no meter yet, they are just tucked away at the top left ready for the meter fitter to connect them to the meter. Worth noting the ownership of the various bits, as this may help. The incoming cable and head, with the company fuse, is owned by the DNO (Distribution Network Operator). The meter and the cable from the head to the meter is owned by the electricity supply company. The meter tails from the meter, and all consumer side wiring and equipment, is owned by the consumer. This is why the consumer side needs to be installed before the meter fitter arrives, as the tails need to be available, and safe, for the meter fitter to install and connect the meter.
  4. Yes, in our case it's just an indication that the Sunamp controller has turned on the power relay that allows current to flow to the heating element. When the Sunamp controller senses that the unit is fully charged, this relay opens and the LED is turned off, indicating that the Sunamp is charged.
  5. Even applying a very conservative derating factor 6mm² is fine. The cable could be buried deeply in any non-EPS insulation and not have a slightest issue with over-heating. 4mm² would be OK if only covered with 100mm of insulation, and if not covered with any insulation, but clipped direct, 2.5mm would be just about OK (not that I'd recommend going down to this small a section cable for this sort of application). I well remember chatting to a chap from Batt during a break from an LV Directive Working Group meeting years ago, who was literally getting hot under the collar at the way cables were being very conservatively derated by the IET. There's often a fairly big discrepancy between the ratings that the cable manufacturer's publish and those in the tables in the blue book. I've never been sure why (and the Batt chap didn't know either). For example, this is Table 4D5 from Batt: Note that it gives a current carrying capacity of 27 A for 4mm² T&E when covered by more than 100mm of insulation above a plasterboard ceiling. By contrast, this is Table 4D5 from the current edition of the blue book: That gives the current carrying capacity of 4mm² T&E as being only 22 A when covered by more than 100mm of insulation above a plasterboard ceiling. Given that, in general, MIs should over ride anything else, and as BS7671 isn't law, it's just guidance, there is an argument that supports the view that we should use the manufacturer's data, as they are the ones that have tested and certified their own products.
  6. Not sure, TBH. Last time I used fart mode I selected Ludicrous Mode and set it to fart on turn signal, with the default seat position for farts to be the front passenger seat. SWMBO was not amused when I indicated to pull out of our lane . . .
  7. @TerryE is referring to the way he's using some homemade smart stuff to both control his heating and to use local weather forecast data to predict how much heat needs to be put into his slab for the following day. A rough translation: The "240 V stuff . . . needs to be part P compliant" refers to the fact that all electrical work of this type must be undertaken by a competent person that is registered with one of the Part P accreditation cartels. Most electricians will be. The alternative is to get the installation inspected and tested by a building control body, but that may not always be that easy, as in some areas building control don't have anyone competent to undertake third party inspection and test. The electrical installation will need to have a part P IEC lodged on the database, as it's a legal requirement. My guess is that your electrician will be able to do this, as most can. @TerryE uses a microcontroller to switch the Willis heaters, using solid state relays (SSRs) that have an isolated low voltage input and are able to switch a high AC current. Crydom is just a well-respected manufacturer of these. IoT refers to "internet of things", and specifically in this case to the many cheaper "smart" switches that are around that may not be able to handle the high continuous load presented by a Willis heater. "TTL outputs" refers to a 5 V logic level output that can often be used to switch an SSR directly. The Raspberry Pi General Purpose Input/Outputs (RPi GPIO) operate at 3.3 V, so may not be able to directly control an SSR. A level shifter is a simple electronic circuit that converts 3.3 V logic levels to 5 V logic levels, usually in both directions. The MCP23008 is an integrated circuit that can interface with any microcontroller than has an Inter-Integrated Circuit (abbreviated to I²C) serial interface. It has a higher current drive capability than the GPIO ports on a Raspberry Pi, so can drive an SSR directly.
  8. Yes, it does. Failure to make it vapour tight can lead to it getting waterlogged and very soggy over time. I used closed cell neoprene insulation around our intake and exhaust[1] ducts. PITA to fit and tape up, but I can be reasonably confident that it won't end up as a soggy mess. [1] The reason for doing the exhaust duct is only because the Genvex MVHR we have can exhaust air at about -5° C if it's ever run in heating mode.
  9. Easy to see the savings on running cost for something like an electric bus. I worked out my "fuel" running cost, assuming I always charge at home overnight, which isn't always the case, I charge from the PV system when there's enough generation. My car costs about 2p/mile for the electricity used to charge it. My wife's Toyota Yaris hybrid does about 50mpg and costs around 11p/mile, in fuel, to run. With that sort of fuel cost saving it probably doesn't take very long for a bus operator to recover the additional cost of purchase.
  10. TBH, I doubt anyone could tell that it's a budget basin from B&Q. When it comes to ceramic bathroom stuff it's hard to see the difference between some of the budget stuff and some of the high end stuff. I've never been sure where the money goes on the high end stuff, either, as I can't see how a £200 ceramic basin can possibly cost more to manufacture than a £50 one.
  11. One for both is more than big enough, even if buried in insulation.
  12. If that much heat was leaking out somehow then it would be pretty noticeable, the case of the Sunamp would be getting pretty warm. The Eddi has no way of knowing the state of charge of the UniQ at all, this is one of the major issues with the Sunamp, that it's impossible to tell the state of charge, or even know whether the thing is charged at all (unless you take the lid off the controller and see if the call for heat LED is on). If I had to guess, knowing that there have been a few issues with the firmware in the Eddi controller, I'd say it's more likely to be an erroneous display on the Eddi than anything else, and may possibly be related to the way the Eddi senses power. The Eddi can only very roughly guess what the Sunamp state of charge is, and can only possibly know one state, which is fully charged (it can probably work this out because the Sunamp controller will stop accepting power). we boost our 9 kWh Sunamp with E7 every night as a matter of course. We have a 6.25 kWp PV array, but it's rare that we get enough generation to provide hot water in winter. Today is one day when we have fully charged the Sunamp from PV, but it's the first day for a week or so that this has happened, and I only know that the Sunamp is charged because mine has the controller cover removed, so the LED is visible (I don't suggest doing this, as there are live terminals exposed with the cover off).
  13. You can always just increase the cable size to 6mm² to be absolutely safe, although the cable ratings in the blue book are very conservative. The reality is that the middle runs of cables very rarely suffer from overheating, most of the time it's the terminations at the ends of cables that cause problems.
  14. Firstly, I'm most definitely not a "Tesla fanboy", whatever that is. The company has some serious shortcomings, as I've highlighted in another thread here very recently, for example the hassle in getting hold of customer service, their intrinsically broken IT systems that cannot even deal with email, their failure to get the basics, like sending a customer an accurate invoice (I had eleven invoices before they got it right, believe it or not). Their "no dealership" model is a serious embuggerance if you need service, too, and their pre-delivery inspection is virtually non-existent. The car is, however, superb, and it's really hard to find fault with it. That's just the way it is. It's well designed, well built and doesn't have any of the issues you've highlighted, like cheap or poor quality interior materials. I'm not a fan of the Cybertruck, either. Not at all my thing, and way too big to be practical around the narrow lanes where I live. Whether it gets delivered or not I really don't know, but if I had to guess I'd say it almost certainly will, if only because the big truck market in the US is a big segment. VAG aren't comparable to Tesla, you're right. So far, VAG have been proven, beyond any doubt, to be a company that has cheated and lied to their customers on a massive, global, scale for years, so far Tesla has done neither.
  15. I suspect that those in rural areas, where taxis are expensive and public transport has been in decline for years, may well have a long wait until such services become profitable. I doubt very much that I'll live long enough to see the end of private car ownership, TBH, although it does seem very likely that those living in cities will be able to give them up fairly easily. A friend of mine lives in Regent's Park, and pays four times the cost of our electricity bill just to park his car outside his house.