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RCD x 5

lyledunn
apologies if you are already aware of this but with respect to the x5 or greater test current introduced in the 18th, Hager have advised that their RCBO units are manufactured to the 2017 amended version of BSEN61008/9 which permitted disconnection within 40ms at 250mA. Thus they advise testing at x 5 on both sides with the instrument set for 50mA on the variable range.
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    My personal take is that it is not tripping at large fault currents that is the case that needs a test, such as a short inside  some class 1 equipment from L to the CPC .

    The far harder test to pass, and the thing that could be the life and death moment, is the one where someone has a dog or lawnmower chewed extension lead in one hand,  and walks out onto the sightly damp lawn in sandals.


    That updated guidance from Hagar seems to be basically the same as their earlier, and is to me clear what they think about a 30mA test.

    The 1x test is no longer a requirement but could of course be carried out. ...




    The problem I see is that as the advice as written it may well be possible to have an RCD that does meet 40ms at some arbitrary  high current but would not do the required  at 30mA.

    I have a sneaking suspicion that what was lost in translation should have been  more like
    40 ms when tested at currents equal to AND  higher than.

    So that would mean that it must make 40ms at 5 times, and must not respond more slowly at any higher currents. It is hard to see why that failure mode would occur however, and that is sadly not what it says.

     


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    Actually shock currents can be very low, especially in winter time when skin is dry, as opposed to slightly sweaty, and folk are wearing more clothing. Also small area contact shocks like finger in the lamp socket stupidity. But a healthy person can pull away from a shock of 10mA or so , and just feel rather shaken. It is quite possible for that sort of  poor contact L-E shock not to trigger an RCD, but then equally it is not such a health risk. Note that 10mA is still the best part of 25 watts, and as most of the heat is where most of the resistance is, namely the outer skin, it will leave a burn mark similar in size  to a match or soldering iron tip.


    As an aside, although things like TENS machines use higher currents (up to 100mA on some models if the labelling is to be believed ),  and have a high open circuit voltage, maybe a few hundred V, falling under load, the pulses are very short - a few hundred microseconds, and repeated only at a few tens of Hz, so the average current and also joule heating is low. It does not mean these level would be safe for longer exposure.
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    The problem I see is that as the advice as written it may well be possible to have an RCD that does meet 40ms at some arbitrary  high current but would not do the required  at 30mA.



    Indeed - if for instance someone mistakenly installed a 100mA (non-delayed) unit instead of a 30mA one - chances are it would pass if only subjected to a 40ms/250mA test - yet it would hardly provide adequate additional protection.


      - Andy.
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    Something must have been lost in the translation.


    Testing at 250mA would not be RCD x 5, would it?  It would be 8.33 x IΔn of a 30mA RCD.
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    And therein lies my gripe, because the rules say must operate in 40ms or less testing at 5 times or higher

    Then that must be ok as testing 250mA is (one example of)  a test at a higher current, albeit one I think gives the RCD an easy ride and is  pretty feeble test of its safety function.

    Equally testing at 5 amps would also be 'higher than' and they did not pick that, so perhaps I should be grateful for small mercies.

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    Something must have been lost in the translation.


    Testing at 250mA would not be RCD x 5, would it?



    That's the point - it seems the standards have changed so that 5x IΔn is no longer the requirement. You might have noticed that all the requirements for a 30mA RCD used for additional protection to have 'an operating time not exceeding 40ms at a residual current of 5 IΔn'  vanished completely from the 18th Ed - the requirement is simply for a 30mA RCD now. We seem to be discovering why....


    I'm trying to imagine why such a change would have been thought a good idea - after all we certainly have the technology to achieve 40ms at 150mA - maybe it's to allow the RCD to ignore the sort of transients that can lead to 'unwanted tripping' or some such.


        - Andy.
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    The cynic in me wonders if lobbying took place because somewhere there was a warehouse bulging with not quite compliant RCD mechanisms waiting for a rule change to allow them to be unloaded on the unsuspecting muggins. There is some precedent for this in other industries.
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    Mike


    I think you are close to the truth there!


    Andy


    Yes the standard has changed a bit but BS 7672 had not changed the test requirement. The requirement in the 17th in Chapter 41 did change and the 5 times requirement now appears as a Note in Part 6 and as we all know Notes in BS 7671 are not Regulations. The "or higher" in my mind is just a test for the mechanical operation of the device. It is not a test to verify if the device will operate to save life where say 50mA ( or higher) coursing through a person for an indefinite period.


    These weasel words in Part 6 apply to Aditional Protection and there are ambiguous words for a RCD provided for Fault Protection.


    The advice us Stroma tutors give on the 18TH Edition courses is you don't need a shiny new 18the Edition meter your old meter is just fine provided it complies with BS EN 61557. Carry on doing the 5 tests as you did before and refer to Table 3A in Appendix 3 of BS 7671 for the standard. If the X1 test fails then the RCD is defective and should be replaced. I would say the "softer" RCD test is the more important test than the X5 test.
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    But John how can you fail it if the manufacturer has complied with the requirements of the relevant standard?

    the x 1 test is not required by 7671 and since you are testing to 7671 and not 61008, I fail to see the justification other than a possible noteworthy item.
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    AJJewsbury:




    Something must have been lost in the translation.


    Testing at 250mA would not be RCD x 5, would it?



    That's the point - it seems the standards have changed so that 5x IΔn is no longer the requirement. You might have noticed that all the requirements for a 30mA RCD used for additional protection to have 'an operating time not exceeding 40ms at a residual current of 5 IΔn'  vanished completely from the 18th Ed - the requirement is simply for a 30mA RCD now. We seem to be discovering why....


    I'm trying to imagine why such a change would have been thought a good idea - after all we certainly have the technology to achieve 40ms at 150mA - maybe it's to allow the RCD to ignore the sort of transients that can lead to 'unwanted tripping' or some such.


    BS EN 61008 has allowed testing at 250 mA instead of 5 x IΔn since at least 2001 (1995:Amd3) for RCDs with an IΔn <= 30 mA, so nothing new there. Perhaps it was felt that BS 7671 should be brought into line with the standard for the devices?

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