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JSHarris last won the day on September 7

JSHarris had the most liked content!

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About JSHarris

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    Advanced Member

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  • About Me
    <p><a href="<fileStore.core_Attachment>/monthly_2016_05/573eec7b190c1_Croppedpictureforavatar-1.jpg.ddce6c04bada76e7f9084efdd5664dff.jpg" class="ipsAttachLink ipsAttachLink_image"><img data-fileid="11" src="<fileStore.core_Attachment>/monthly_2016_05/573eec7b3c539_Croppedpictureforavatar-1.thumb.jpg.82bf4596124b669fa8c295c37295ec21.jpg" class="ipsImage ipsImage_thumbnailed" alt="Cropped picture for avatar - 1.jpg"></a></p>
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    Wiltshire/Dorset Border

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  1. JSHarris

    Pitched roof thickness and insulation

    We have 302mm deep I beam rafters, with an added bit of stud timber nail plated spaced 10mm off the lower I beam edge, giving a total rafter depth of about 401mm, The outer face of the rafters is clad with OSB, to provide sarking and containment for the insulation, the inside has a layer of Isover VCL membrane, held in place by 50mm x 50mm battens across the underside of the rafters, which also provides a service void. The space between the rafters is filled with ~400mm of cellulose, which in reality is a bit thicker than this on average, as the pressure under which it's blown in has slightly quilted the membrane on the underside. The advantage of this method is that the ~400mm layer of cellulose provides a reasonable level of insulation, but more importantly, it has a reasonably long decrement delay. An unexpected advantage is that it also provides a very good degree of acoustic insulation, so the house is very quiet inside, and we can't hear rain on the roof, for example.
  2. JSHarris

    Marking wires and cables

    Colour is a funny thing to me. I think in colour, and every word has a specific colour, or sequence of colours, which made memorising resistor colours codes easy. I don't consciously translate colour bands into numerical values, but just "see" the value from the colour. My late mother used to make me do party tricks by asking me the colours of words like the days of the week, or numbers. It does mean I remember phone numbers and credit card numbers/PINs easily, because they are just colours. For years it was just a bit of a curiosity, one of those odd things that didn't seem at all significant, but around 25 years or so ago there was an article in New Scientist, or maybe a paper in Nature, describing exactly the way I think in colour. Apparently it's not that unusual; it's even got a name and is in Wikipedia: https://en.wikipedia.org/wiki/Synesthesia In my case I lived for the best part of 40 years keeping quiet about it most of the time, although I invariably got quizzed by my mother, trying to catch me out, as I don't think she ever really understood that I think in colour and have to actively translate colours to words, with often subtle colour shade differences (for example Wednesday is a dark green, but Thursday is a sort of muddy green). I think the only advantage it's given me is being able to remember facts a bit better than most, which certainly helped when doing exams, otherwise it's just a bit of a curiosity.
  3. JSHarris

    Flat panel LED lights

    Yes, it's SELV. These LED panels qualify as the driver is separate and mains powered, but connected by a low voltage cable to the light itself.
  4. JSHarris

    Marking wires and cables

    I've always just used the Brother stuff, and not had any issues with labels coming off. Perhaps some of the clones of the Brother label tape that are around may have adhesive that's not as good? Years ago I used to print paper labels and cut them up and poke them under clear heatshrink as cable markers, but it was a real faff and I needed power to run the small heat gun, so stopped doing this when I bought the labelling machine.
  5. JSHarris

    Marking wires and cables

    A cheap Brother label printer works fine. The labels can be either stuck to T&E, or wrapped around individual wires. I used to use different coloured electrical tape, but so much of the stuff has really nasty adhesive now that I stopped using it. A sharpie works OK too, at least on the outside of T&E, but I prefer using the Brother labelling machine, as it has the option to make wire wrap-around labels.
  6. JSHarris

    My underfloor heating

    The regs are pretty clear with regard to what's required, and have been for decades. When I used to teach apprentices decades ago, switches and FCUs were often supplied with engraved labels on the front, describing the circuit that they controlled (something like "immersion" or "heater"). This is something that has "gone out of fashion", but the requirement to identify circuits and switches where it's not obvious (and light switches and switches in outlets are considered obvious) has existed for as long as I can remember. What's happened is that the economics of supplying so many variations of the same basic switch has meant that manufacturers have saved costs by removing the built-in labels, with the possible exception of cooker switches. This has switched responsibility to the installer, and there are far too many monkey's out there who have never bothered to read and understand the regs - read through any of the electricians forums and you'll find a LOT of electricians asking really basic questions where they should have already known the answers as a part of their training.
  7. JSHarris

    decrement delay - what is that?

    The easiest to understand description is on this website, I think: http://www.greenspec.co.uk/building-design/decrement-delay/
  8. JSHarris

    My underfloor heating

    It's not just in the CU that labels are a requirement, they are required wherever there could be doubt as to what a switched circuit controls, or there needs to be a diagram/adequate description located close to the CU or distribution board such that anyone looking at the system can understand how it's wired. Apart from being something that saves time (and so should save cost) for any subsequent inspection and test, it also makes it a lot easier to resolve the sort of issues that @lizzie is now, unfortunately, experiencing.
  9. JSHarris

    Spray foam insulation

    It's slightly longer than EPS, and a fair bit shorter than blown cellulose. However, it depends very much on what the outer skin of the house is made from. If the outer skin is brick, block or stone, then that will substantially increase the overall decrement delay. It's also a bit site-specific. Our location is such that the house gets sun from sunrise to sunset, so decrement delay has a potentially big impact. It was one reason we opted to use pumped cellulose. If we'd had a stone outer skin than I'd not have been so concerned, and may well have opted for something like PIR insulation.
  10. JSHarris

    My underfloor heating

    There's a requirement in the wiring regs to ensure circuits are adequately identified. It's an issue that should be flagged during an inspection and test, and has been for years (although it's something often ignored). If I was inspecting a system that didn't have labels or an adequate description of the installation that was clear enough to inform me of the details of each circuit I'd mark it down as a C3 (Improvement Required). Bearing in mind that every domestic electrical installation should be inspected and tested at least every ten years (another thing that's very widely ignored) and that an inspection and test is a hell of a lot easier if things are properly labelled and that either the original data from the installation tests, or the previous EICR (Electrical Installation Condition Report) is available (and it makes the EICR cheaper, as it takes less time), then there's every reason to make sure that documents are retained and everything is properly labelled. It's worth noting that the guidance for conducting an EICR is that there should be minimal exposure to live parts. This means that if there is an existing description of the installation, with the results of the tests that were conducted, then many of the EICR tests can be conducted with least disturbance to the installation, provided that an inspection of the installation doesn't give rise to concern. Mind you, I bet that 90%+ of domestic electrical installations rarely get any inspections at all. SWMBO has always been a bit annoyed with me for spending a couple of hours every few years checking our electrical installation. My obsession with inspection and testing comes from having seen some pretty grim installations in houses we've bought over the years. Arguably, this has made me go a bit OTT with our new build, with an all-RCBO CU, cables that are generally one size up from what's just about OK and labels everywhere. My workshop even has E stop buttons and contactors controlling the two 20 A radials that supply the main power circuits, so banging a button kills all the power (but not the lights) if something goes awry.
  11. JSHarris

    Paint for concrete floor?

    I've used non-slip epoxy floor paint from Reactive Resins and it was really good, but sadly I see they have now gone into liquidation. There are plenty of other suppliers of epoxy floor paints though, and generally they are all pretty similar, and if applied as at least two coats would probably meet any food safety issues OK. They are hard work to apply, in my experience, as to get the required build thickness they tend to be quite thick and need a lot of work to brush or roller out. Worth it though, as there's simply no comparison between ordinary floor paint and the epoxy stuff - it's far more hard wearing and gives a really nice looking finish.
  12. JSHarris

    My underfloor heating

    As an example, this is our heating and hot water control box, with labels on every relay and LEDs on them so anyone can see at a glance what's on and what's off. Under the centre blanking strip there are three connections from the thermostats, so when the lid's off anyone can see which connection goes where:
  13. JSHarris

    My underfloor heating

    There are supposed to be labels on damned near everything now, so why the electrician who wired it didn't label it I don't know. There's also supposed to be a description or diagram of the whole installation somewhere by the consumer unit, although that's a rule that's more often than not ignored. I spent ages going around labeling stuff, so every switch and box has a label on letting anyone who looks at it know what it does. It should be standard practice, especially as labeling machines are pretty cheap and it's a lot easier to label stuff as you go, rather than do it all at the end when you may well have forgotten what some of the things do, or connect to.
  14. JSHarris

    Supply from mains or from tank?

    3.3 kW at the UK nominal supply voltage of 230 VAC = 14.35 A, so it can't be connected to a FCU, as they only go up to 13 A. The maximum power that can be drawn from a 13 A supply is 13 A x 230 V = 2.99 kW. If it's a resistive load, like a heating element, then it will probably deliver more than this power, as in reality the UK mains supply voltage is still really 240 VAC. When we harmonised with the EU, it was agreed that our nominal supply would be stated as 230 VAC, but we were allowed to have a tolerance of +10%, -6%, which conveniently allowed us to keep our 240 VAC supplies without changing anything, because they are within the allowable tolerance (minimum supply voltage is 216.2 VAC, maximum is 253 VAC).
  15. Here's a cross section through our house, showing the detail: The gap was created when the rafters were put together in the factory, by nailplating a bit of timber to the lower member of the I beam with a small gap.