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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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  1.  
    Posted By: wookeyThis project is impressively behind schedule and we'd quite like our bedroom back
    God I remember that, but it is 'nice' now and the pain gently blurring away.
    • CommentAuthorwookey
    • CommentTimeOct 15th 2022 edited
     
    Despite my last message claiming this was fixed, one of the lamps still flashed (I forget the details now, but I had more urgent things to do so stopped fiddling. Apparently I didn't leave that cap in place) so this was dealt with for 6 years by just leaving the switches in the 'not flashing' position.

    So having removed the 1960s CU and in-cavity wiring, and put an earthed upstairs lighting feed all the way to the loft about 4 years ago, I finally got round to re-doing the loft wiring properly and replaced a lot of dodgy old no-CPC braided 1960s wire. The Inner sheath is quite degraded and cracks if disturbed, so that wire is definitely past its prime. Presumably fitted in 1962 so it's done a reasonable stint. I took the opportunity to rationalise it all so all the cabling is above the fluff and it doesn't go all round the houses to every ceiling rose and back.

    I found that replacing the landing CFL with a 6W LED made it flash every 30 seconds or so when the stair switches were in the 'wrong' position. Sound familiar? Connecting up new cable that actually had an earth in it all the way back to the CU fixed that, so properly earthed cables do greatly reduce the likelihood of this problem.

    However new cabling didn't fix the flashing 1W LED discussed above in this thread. So I tried a 1.2MOhm bleed resistor across the driver. That keeps the voltage down to 38V, which is below the 50V flash threshold. It draws 0.00003A (30uA) all the time, which is about 1.2mW which is 10Wh/yr so will cost 0.5p/yr (at current prices).

    It should probably have taken me less than 6 years to get round to making this work properly

    The only problem with this fix is that, like having a neon in the circuit, it will spoil the insulation resistance test (and the resistor may not be specced for 500V either, although many are - I'll have to check.). It only has to be >1MOhm so it will pass, but not very impressively. The capacitor fix would presumably avoid this issue so long as it was rated for >500V.

    Just thought I'd post a fix having finally got round to implementing one.
    • CommentAuthorwookey
    • CommentTimeOct 15th 2022
     
    OK. And perhaps unsurprisingly a 47nF capacitor (like barney told me in the 1st place) works too. I presume that involves less leakage current than the bleed resistor, but I don't know how to do the sums to check :-)
  2.  
    If it improves the house's power factor, it might reduce the house's current consumption..!
  3.  
    Posted By: wookeya 47nF capacitor works too. I presume that involves less leakage current than the bleed resistor

    The 1.2MΩ resistor was replaced with a 47nF capacitor, with a much smaller impedance of 1/2πfC = 70kΩ. That'll pull the stray voltages down much lower (to about 2V?) and increase the leakage current a little.

    Working backward from your measurements, it looks like the stray capacitance between the cables is around 450pF (making lots of assumptions) - about what Ed and Barney estimated.

    That'll be much the biggest impedance involved, so swapping the resistor for the capacitor won't increase the leakage current by very much, less than 1%.

    It will make the leakage entirely capacitive, rather than mostly capacitive with a small resistive component. The capacitive leakage currents are out of phase with the mains voltage, so you won't be charged for any real power.

    By themselves they would increase the overall current magnitude flowing to the house (a tiny bit) so might increase I²R cable losses (a tiny bit). However they will counteract the inductive leakages from anything with a motor in it, so overall might actually reduce the current magnitude (a tiny bit) .
    • CommentAuthorwookey
    • CommentTimeOct 28th 2022
     
    Cheers Will.
    The capacitor did indeed pull the stray voltage down lower, to about 6V (vs 38V for the bleed resistor).
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