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RCD types

Farmboy
Regarding RCD types, AC, A, F, etc. Do these classification/types apply only to RCD's installed in CU's/DB's, or to RCD's incorporated in RCD sockets and fused connection units as well? A manufacturer is getting back to me about their products later in the week, and I'd like to have something to compare their answer to.


F
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    As the type (AC, A, B, etc) describes the type of residual waveform the RCD will recognise (and/or be disabled by) then logically they apply to all types of RCD (although conceivably other standards may describe the same thing differently).


    But given that the 18th Ed seems not to recognise RCD sockets and RCD FCUs (to BS 7288) any more (only BS EN 61008 series, BS EN 61009 series and BS EN 62423 are listed as acceptable, at least in installations used by ordinary persons) then it might be a mute question anyway.


      -  Andy.
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    or moot if we believe the reg writers really intended this, - but not a daft question to ask in any case .

    Most plug in RCDs for example are designed as AC type, but do still respond to lumpy DC (as A type) but need rather more of it to trip them.

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    AJJewsbury:

    As the type (AC, A, B, etc) describes the type of residual waveform the RCD will recognise (and/or be disabled by) then logically they apply to all types of RCD (although conceivably other standards may describe the same thing differently).


    But given that the 18th Ed seems not to recognise RCD sockets and RCD FCUs (to BS 7288) any more (only BS EN 61008 series, BS EN 61009 series and BS EN 62423 are listed as acceptable, at least in installations used by ordinary persons) then it might be a mute question anyway.


      -  Andy.




    ...logically they apply to all types of RCD... Quite so, which is why I was bemused when the manufacturers tech dept told me that as far as they were aware, the types only apply to RCD's in CU's/DB's.


    ...the 18th Ed seems not to recognise RCD sockets and RCD FCUs (to BS 7288) any more... Which is why I asked them why they state in their advertising that their new range of units 'Conforms to BS7288:2016, BS1363-2, and meets latest Wiring Regulations'.


    F

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    mapj1:

    or moot if we believe the reg writers really intended this, - but not a daft question to ask in any case .

    Most plug in RCDs for example are designed as AC type, but do still respond to lumpy DC (as A type) but need rather more of it to trip them.

     




    Which is along the lines of why I asked them that given that their new advertising states that their new range of RCD sockets and fused conn. units 'Continues to protect with lost neutral / pulsating DC earth fault'., are they stating that these new units are type A's (whereas a couple of years ago they stated their range were AC's, but oddly, now say that they think the type classification only applies to RCD's in cu's/db's). They also think they may have to pull their new advertising however as it may be misleading. I hope to know more from them by the end of the week.


    F

  • Former Community Member
    0 Former Community Member

    AJJewsbury:

    As the type (AC, A, B, etc) describes the type of residual waveform the RCD will recognise (and/or be disabled by) then logically they apply to all types of RCD 




    Hi Andy, could you give a link to any evidence on that theory? I would be interested to know of any manufacturers willing to declare that their product will disable probably the most widely used general type AC RCD :)

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    I would be interested to know of any manufacturers willing to declare that their product will disable probably the most widely used general type AC RCD :)



    In terms of manufacturer's declaring that their product is intended to disable an RCD the only one I can think of are the loop testers with the old 'D-Lok' function (but that at least does demonstrate the underlying physics).


    I think in terms of ordinary appliances I think it's more of a case of the industry gradually realizing that there's a problem that even fault-free RCDs might not trip when they should, rather than appliance manufacturers jumping up and down to draw anybody's attention to the fact. EVSE equipment manufacturers are probably the most open at the moment.


      -  Andy.
  • Former Community Member
    0 Former Community Member

    AJJewsbury:




    I would be interested to know of any manufacturers willing to declare that their product will disable probably the most widely used general type AC RCD :)



    In terms of manufacturer's declaring that their product is intended to disable an RCD the only one I can think of are the loop testers with the old 'D-Lok' function (but that at least does demonstrate the underlying physics).


    I think in terms of ordinary appliances I think it's more of a case of the industry gradually realizing that there's a problem that even fault-free RCDs might not trip when they should, rather than appliance manufacturers jumping up and down to draw anybody's attention to the fact. EVSE equipment manufacturers are probably the most open at the moment.


      -  Andy.

     




    Thanks for the reply Andy, is the industry you refer to the manufactures of RCDs who are the only source of the rumour that some connected consumer appliances WILL render the most widely used RCD type useless :O

  • 0
    Changing the design of an AC to an A is a fairly small change, in many cases no design change at all.

    To make a B type is a more significant step, involving a new DC sensing part, either a Hall effect device or in the case of ABB a flux gate, where a magnetic  core is driven to saturation alternately in both polarisations by an audio frequency AC, and the DC field is deduced from the asymmetry of the current waveform relative to the voltage.

    If I was a maker and I had produced a device, be it a DIN rail RCD that meets an IEC spec or not,  that met a harder spec than the previous model, and covered a wider range of fault cases, I'd be declaring it, even if not using the nomenclature AC A or B; which given we already have B and C curves for MCBs is a pretty stupid classification anyway ( but that is committees that don't talk to each other.)


    edit - an  example of a flux gate  DC current sensor as a hobby project,  albeit a rather deaf one to give a feel for the complexity.
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    Farmboy:

    Regarding RCD types, AC, A, F, etc. Do these classification/types apply only to RCD's installed in CU's/DB's, or to RCD's incorporated in RCD sockets and fused connection units as well? A manufacturer is getting back to me about their products later in the week, and I'd like to have something to compare their answer to.




    BS 7288 RCDs may be type A or AC. Paragraph 4.3.

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