Add RCD to Shed supply and update

Discussion in 'Electrics UK' started by northbank_dom, 2 Sep 2021.

  1. flameport

    flameport

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    The standard states they are only suitable for use where the circuit already has RCD protection.
    That makes them useless.
    They could still be used, but the reason for using them is then undefined in BS7288, and not recognised by BS7671.

    Compliance with BS7671 and any other standard isn't mandatory, but is generally accepted to be a suitable method of ensuring safety.
    Not complying with BS7671 means it can't be relied on as evidence of safety or compliance with Part P or the EAWR.
     
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  3. JohnD

    JohnD

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    So not "explicitly forbidden."
     
  4. JohnW2

    JohnW2

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    If that's correct, then this presumably means that you don't believe that what was posted in ....
    .... (apparently from a 'NICEIC magazine') is telling the truth, since it said ...

    upload_2021-9-4_0-15-51.png

    Do you believe that to be untrue ?

    Kind Regards, John
     
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  5. yorkspark

    yorkspark

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    That is not true and is niceic wishful thinking, in fact there is no mention of srcd's in the dpc of amendment 2

    As an aside, this is the position of srcd's

    So what does BS 7288 say?
    The residual current device at socket-outlet level is normally intended to be installed by skilled or instructed persons. It can be operated several times per day. The isolation function is not necessary since pulling out the plug from the socket-outlet is recognized as providing effective isolation. The absence of permanently connected long conductors downstream of the RCD, together with a limited number of powered appliances, justifies reduced EMC levels. Residual current devices covered by this standard are intended for additional protection in case of direct contact only. These particular features having been considered, it was recognized that a dedicated standard for socket-outlet residual current devices (SRCDs) was necessary.

    This part of the introduction to the document highlights that these devices provide additional protection for direct contact only. The device itself does not achieve sufficient isolation in it's operation as it is considered that isolation can be verified with simple removal of the plug or isolation of the fcu.

    Isolation is a requirement for additional protection as suggested in 415.1 of BS 7671, yet BS 7288 considers removal of the plug as isolation. This difference in consideration allows for devices to be installed in SRCDs with a much smaller clearance gap within their devices.

    Manufacturers may also claim that their device complies with BS 7671, but BS 7671 has nothing to do with the construction of equipment or devices, just their selection and installation. So it is important to identify if your SRCD or other accessory, such as an FCU actually comply with the requirements of the standards mentioned within BS 7671 in Regulation 531.3.6.

    So what does BS 7288 say?
    This British Standard applies to residual current-operated devices (RCD) incorporated in, or specifically intended for use with, single pole and neutral and single pole and switched neutral and double pole socket-outlets, with provision of earthing of the socket-outlet for household and similar uses (SRCD:socket-outlet residual current devices). SRCDs, according to this standard, are intended to be used in single phase systems such as phase to neutral. SRCDs are only intended to provide supplementary protection downstream of the SRCD. SRCDs are intended for use in circuits where the fault protection and additional protection are already assured upstream of the SRCD.

    SRCDs are neither intended to provide an isolation function nor intended to be used in IT systems.

    It is clearly mentioned here that SRCDs are only to be considered for supplementary protection to the equipment connected downstream and fault protection and additional protection, as required under Regulation 415.1, shall be provided by another device upstream

    The comment of additional protection is key and as we have already mentioned, BS 7288 mentions that additional protection is required upstream.

    The problem is the contact separation within the BS 7288 devices is inadequate, and thus cannot meet the requirements for safe disconnection.

    For compliance with the requirements of BS 7671 and other associated standards, to allow them to be used for isolation and emergency disconnection, and automatic disconnection in the event of a fault will require an update to BS 7288 and a modification to every product.

    It does not look like this is forthcoming at the moment.

    Thus BS 7288 devices must have an upstream 61008/9 or 62423 to meet the requirements of BS 7671.
    Therefore it is not a deviation to install a BS 7288 device for additional protection, it is an outright non-compliance with BS 7671.
     
  6. EFLImpudence

    EFLImpudence

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    We can certainly see the cause of the confusion.

    What rubbish.
     
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  7. flameport

    flameport

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    Yes, as that is just what some magazine writer cobbled together from scraps of rumours they may have heard from someone who assumed various things and didn't even bother to check what BS7671 and BS7288 actually said.

    That particular item is a reply to a Q&A section in Connections magazine, Autumn 2019 edition.
    The draft of BS7671:2018 AMD2 wasn't available until September 2020. There is absolutely no way anyone could have known what would be in it a full year previously - and that is only the draft version, not the final publication.
     
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  9. JohnW2

    JohnW2

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    As EFLI has said, this all seems to be very confused/confusing and (at least to my mind) more than a little silly.

    The material you quote seems to imply that the main issue is that SRCDs do not (or may not) have a large enough contact gap to be adequate as a means of isolation. You write:
    ... but where does that come from? 415.1 says nothing about isolation, all it actually says being:
    .... and, in turn, "Sections 411 to 414"relate to ADS, Double or Reinforced Insulation, 'Electrical Separation' and ELV respectively - so not relevant to this discussion.

    Even the preamble about 'additional protection' says nothing about a 'requirement for isolation' ...
    Not to mention the fact that 'additional protection' does not only relate to RCDs ...
    ... and "supplementary protective equipotential bonding" clearly does not include any 'requirement for isolation'.

    ... and then we get (with my emboldening) ...
    'Additional protection' is bad enough, since it has both an everyday meaning and a poorly-defined (well, hardly at all defined) specific meaning in BS7671, but what on earth is "supplementary protection" (a term which exists nowhere in BS7671) ??

    It's obviously only a personal opinion, but this seems to me to be a complete mess.

    ... and I think one keeps on coming back to the question of why SRCDs exist (and still exist) and, in particular, why there is a Standard relating to them, if, in themselves (per BS7288), they seemingly serve no particularly useful purpose other than redundancy (which is not a requirement of BS7671), and the fact that they are usually (always?) 'active' RCDs.

    Kind Regards, John
     
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  10. davelx

    davelx

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    Both types readily available from TLC.
     
  11. EFLImpudence

    EFLImpudence

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    ...and also some (I obviously don't know about all) will not work unless the CPC is connected as they use it for the test button circuit - an additional additional protection.
     
  12. JohnW2

    JohnW2

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    Indeed - as you say, an 'additional additional' protection.

    Also, I seem to recall from experiments I undertook a year or three ago (and reported here) that, with at least some of them, unless an 'effective earth' is connected, one cannot 'reset' (i.e. 'switch on') the device (so maybe 'additional additional additional' protection!) - although I'm not sure how that is achieved.

    Kind Regards, John
     
  13. EFLImpudence

    EFLImpudence

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    Yes, that's what I meant by 'will not work' - i.e. switch on.

    I do not know exactly how they do it.
     
  14. JohnW2

    JohnW2

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    Fair enough - and, yes, as I said, it's not easy to see 'how they do it'.

    Whatever method they use, I would suspect that it probably involves deliberately putting a little current through the CPC (when connected, and an 'effective path to earth') - since, otherwise, I can't see how absence of an effective earth connection could be made to prevent the mechanism resetting.

    However they do it, it does seem to represent a useful element of 'protection' (be that 'additional additional additional' or whatever!) - and, indeed, a feature which one might argue could perhaps be more generally 'desirable' in relation to RCDs.

    Kind Regards, John
     
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