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My war against dual rcd boards

Newfutile
As each (RCD) Residual Current Device must not have more than 30% leakage current on it.
It's hard to see how dual (RCD) Residual Current Device boards can be fitted at all these days.
i come across so many dual rcd boards with solar, evse and heat pumps on them, these have all been recently installed.
i wonder if BS7671 should state: Dual (RCD) Residual Current Device boards shall not be fitted, unless it can be shown (and documented) that they are suitable for the combined leakage currents expected .
otherwise developers will keep specifying them and i will have keep educating them on the many reasons a type A rcd should not be shared with other equipment!.
maybe manuafactuers instructions should also state : not suitable for a shared rcd, for certain equipment.
  • in reply to Sparkingchip

    The gas discharge car lights are indeed a marvel of HV tech, but in a car, with enough petrol to put the driver into orbit, 25kV sparks to ignite that fuel, and red hot catalyst glowing in the exhaust, in a single skin metal box that does up to 70mph, (honestly officer), the additional risk is actually 'small beer'. If they were indoors, they'd probably be banned Relaxed.

    Mike.

  • in reply to mapj1

    Mike, many thanks for the explanation - most interesting!

  • in reply to Chris Pearson

    no probs, but be aware it is only skating over quite a lot of extra detail, several heavy books have been written on the subject of LEDs and mixed semiconductors more generally..

    The biggest operational problem for an LED compared to a normal lamp is that the internal resistance of many LEDs  has a negative temperature slope. A series resistor, or more likely, some current controlling electronics that emulates one,  is then required,  as if connected to a constant voltage, with nothing to throttle the voltage and limit the current from rising, there would be a tendency for things to either not turn on at all, or then to warm up and run away to self destruction.... (the one off noise emitting diode is not supposed to be a thing...)

    Mike.

  • in reply to mapj1

    Well, yes but LEDs have come on in leaps and bounds.

    Time was you had those rather feeble ones which could be used as indicators and they had to be treated with the same respect as ordinary diodes and transistors. Now they have all gone miniature.

    Recent developments in car headlights are extraordinary. Mine (2019 build) dance around and cut out the upper right quadrant to avoid dazzling oncoming traffic. The current model claims a 650 m range and can project images on to the road or, I assume, adjacent buildings. There are 84 LEDs per side and they use micro mirrors (but hopefully not smoke) to do the fancy stuff.

    (How's this for thread-drift? :-) )

  • If you were to do a Type A RCD test on the RCDs installed in the consumer unit, what test current does the installation tester deliver?

  • in reply to Sparkingchip
    Sparkingchip said:
    If you were to do a Type A RCD test on the RCDs installed in the consumer unit, what test current does the installation tester deliver?

    Would that not depend on whether you were '. . . doing a Type A RCD test' or '. . . testing a Type A RCD in accordance with BS 7671 (643.7.1) and/or (643.8)' ?

    In the former case it would be an AC waveform with superimposed pulsed DC whilst in the latter case it would be an AC waveform.

     - Ross

  • in reply to Ross C

    As in the photo, what amperage is the pulsed DC current test current that the tester will deliver for a X1 30 mA Type A RCD test?

  • in reply to Sparkingchip

    A multiplier of 1.4 comes to mind, so with the instrument set as in the photo (30 mA × 1 × 1.4) = 42 mA ?

    - Ross

  • in reply to Ross C

    1.414 the square root of 2, so 42.42 mA.

  • in reply to Sparkingchip

    I thought that A type RCDs only needed to cope with 6mA of d.c.?

       - Andy.

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