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Can this device be installed in an installation and comply with B.S. 7671?

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Can this gadget be B.S. 7671 compliant?

https://www.tdk-electronics.tdk.com/en/2487672/products/product-catalog/emc-components/leaxield?wt_mc=gaw_LeaXieldEnglish_rccb&gclid=EAIaIQobChMI8vfs-tTi5gIVFODtCh0I3gl5EAMYASAAEgL6uvD_BwE


More about it.....

https://www.youtube.com/watch?v=42g6Mawr3s4




Z.
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    So long as the parts of the installation that are RCD blinded are wired accordingly - SWA or SY and no sockets would probably do.

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    Humm. Presumably it attempts to generate a leakage current that's equal in magnitude but opposite in polarity to the imbalance it senses. I can't help thinking that it'll risk hiding real earth fault currents in the same way - so defeating the RCD not only for unintentional tripping, but intentional as well. I realise it claims only to work for frequencies above 150Hz and for a limited current (a few amps) so simple earth faults before the inverter is likely not to be fully cancelled and so the RCD should hopefully still trip - but what of earth faults after the inverter or where the residual current has additional (higher frequency) components due to the downstream electronics? The fact they don't suggest that shock protection isn't compromised isn't reassuring.


    If the idea is that shock protection from faults only before the device is reliable, then I can't help thinking that a simpler answer might be to use double/reinforced insulation for the supply and just omit the RCD altogether.


    As for BS 7671 I can't think of a regulation that would expliciity prohibit its installation - but clearly some 'engineering judgement' (good workmanship at the design stage?) should be applied and might caution against such things.


      - Andy.
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    There is no reason why you should not use such a technique to defeat additional protection for part of an installation downstream of an RCD if you wish to do so - in effect the system injects current in the NE loop, to match and cancel the current in the L-E loop. It is not much more complex than an audio power amplifier and a sense coil. The power amplifier part only needs to deal with a few volts, maybe 10s at most, and current equal to those to be cancelled.


    As the problem with EMC filters is that they allow L-E current to flow, injecting counter current  in this way is a good way of reducing currents in RCDs and earth rods when no fault is present

    Would you put one of these filters

    Lindgren 6000 series fixed installation filters

    Leakage Current at 250 VAC 50 Hz​  <10% of Rated Current




    In a TT system without something to tame the earth leakage ? - the leakage on a 60A filter is not to be sneezed at.

    Even these N900 series manage to leak the best part of an amp to earth in normal use.

      The usual wheeze is to trim the capacitances from the 3 phases, so that the resultant leakage is near zero, but this active approach should allow results that are as almost  as good on a single phase system, or a system where only 2 phases are used.


    The key thing however is to be very clear about how the part that is not under RCD protection is to be kept safe -  if it is all in the one box, and the effect is that a piece of closed class 1 equipment has a low earth leakage, no one will question how this is achieved, but this technique allows the wiring that is after the active current cancellation to be part of the fixed wiring, and that is I think a novel step.

    I'd want to see the bulk of the installation being low leakage and RCD protected, so the magic current injection box as close as possible to the filters, and those in turn close to the inverter - and all of that, I'd like to be enclosed,  such that additional protection by RCD is not really needed, as it may not have it.


    I agree if you do not allow cancellation at 50Hz, then the load side circuitry is still RCD projected to a degree, but then the dominant leakage current is not being ameliorated either, which sort of defeats the best point of the technique somewhat.


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    I can’t think of any industrial installations that I have been in where RCD protection would have been required for circuits supplying motors. Recently did a large dairy farm    with a fair amount of VSD kit but we were able to design out any issues arising from the TT earthing requirements. 

    Is this another one of these situations where a solution to a unique problem is being hailed as a solution to a manufactured general problem?
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    Perhaps 536.4.203 original manufacturer equipment integrated according to BS EN 61439 series

    I was also thinking of a reg that prohibited introducing voltages(?) to an RCD other than those required for periodic testing by an approved testing device, but cant find it ATM.
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    I was also thinking of a reg that prohibited introducing voltages(?) to an RCD other than those required for periodic testing by an approved testing device, but cant find it



    I suspect you're thinking of 531.3.1.202 - but the wording is rather too specific - "It is not permissible to introduce an external connection for the purpose of intentionally creating a residual current to trip an RCD."


      - Andy.
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    That's it, thanks Andy. Agreed, too specific.
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    I cannot see anything wrong with the device, but I cannot really see many applications either. A typical one which may come to mind is an EMC test enclosure (cage) with mains sockets and an operative inside. However the solution to this is simply to put the RCD after the very high attenuation mains filters used for such an application, which may pass considerable current to Earth, for additional protection and to meet BS7671 "socket outlet" regulations. I can see very little reason to fit one to VSDs, because they do not usually drive socket outlets, although there may be a case if the supply is TT, but 30mA protection is very unlikely to be required. The question is probably whether the device adds risk under the proposed use, or reduces it. The fact that it doesn't reduce 50Hz "leakage" suggests that its real purpose is to reduce possible EMC cases with certain types of VSDs, but if so it is probably well behind the design curve of modern power factor corrected drives.
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    davezawadi:

    . . . I can see very little reason to fit one to VSDs, because they do not usually drive socket outlets, although there may be a case if the supply is TT, but 30mA protection is very unlikely to be required. . . 




    The manufacturers instructions state that the device should be used on 3 phase TN systems, and talks about a maximum leakage current of 1A. 


    Regards,


    Alan. 

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