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WHAT WOULD YOU DO?

John Peckham
Today's job inspect and test a domestic installation in a sheltered housing flat. TN-C-S earthing system. Main protective bonding correct. 


Wet room for disabled occupant. Electric shower and extract fan supplied from a Wylex 2 way consumer unit  with BS EN 61008 30mA RCD main switch. Recently installed.


RCD does not trip on X1 RCD test but does trip on X 5 and operation of test button. RCD does not tip on a second and third test after X 5 test and operation of the test button.


Thinking about the Note to Regulation 643.8 are you content with this installation as there are no other observations recorded and prepared to issue a "Satisfactory" EICR?


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    John Peckham:

    The changes relating to this requirement were the move of the 40ms at 150mA from Chapter 41 to Part 6. 


    The big change I strongly object to is testing RCDs only at x5 or higher. The higher bit is just stupid! I have heard one manufacturer recommending a test at 250mA. What is the purpose of this test is it to get the RCD to trip? Or should it be a test the RCD at a potentially lethal current and verify it will disconnect the supply in a safe time.


    Graham Kenyon posted a very good table on the old forum for testing of RCDS that I think should appear in the future AMD1 to the 18TH.


    I note that the sad posts by Zoom of a double fatality concerning a shower and GB post of a fatality in rented premises could have been prevented by RCD protection.




    Does the move from Ch 41 to Part 6 make finding it any easier or not?


    For me, the problem is that the reduction in the number of columns in the generic schedule encourages testing to be limited to one value.


    Testing an RCD 5 times (on auto) instead of 3 (or one?) is so little effort that I cannot understand why anybody would avoid doing it. The corollary is that if any of the values is a fail, then a remedy needs to be provided.


    I am a bit wary of the notion that the above fatalities could have been avoided if (functioning) RCDs were present. They are, after all, in a TN installation additional to ADS and not in place of it.

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    The question is why the need for change. It would be interesting to have the RCD that John condemned tested by Wylex for compliance with BSEN 61008.    Is this perhaps the problem? RCDs being tested for parameters that might be difficult to assess when tests are conducted on site then being condemned when they don't meet those parameters? Did the manufacturers have any sway with the JPEL64 committee, perhaps arguing that the 61008/9 parameters should be their responsibility?

    Absolutely no arguement with JPs reasoning, but like many, I would love to know the actual reason for the change rather than just speculate.
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    What were we taught twenty years ago about testing RCDs, some of us are old enough to have installed consumer units where the requirements for RCDs of anything other than TT installations was basically none existent. New houses built on estates in the 1980’s that had TN installations had a socket with a built in RCD in the garage for outdoor use and that was it.


    So what were we taught about testing RCDs twenty years ago when split load consumer units were becoming the norm .


    Andy
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    Well according to B.S. 7671 15th Edition 1981 including Amendments up to June 1987.


    613-16. "Where protection against indirect contact is to be provided by a residual current device its effectiveness shall be verified by a test simulating an appropriate fault condition and independent of any test facility incorporated in the device (see Item 6 of Appendix 15)."


    Appendix 15. 6.1 With all loads disconnected the test is carried out with tester leads connected to the load L of the R.C.D. and the C.P.C. of the circuit. The test current is limited to one second maximum.


    Note. "Where the circuit breaker has a rated tripping current not exceeding 30mA and has been installed to reduce the risk associated with direct contact as indicated in Reg. 412-14 (ii) a residual current of 150mA should cause the circuit breaker to open within 40ms."


    The test button was also to be used to confirm correct operation.


    Z.






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    Interestingly in B.S. 7671 16th Edition of 2001 in 713-13-01 it just says: "Where protection against indirect contact or supplementary protection against direct contact is to be provided by a residual current device, its effectiveness shall be verified by a test simulating an appropriate fault condition independent of any test facility incorporated in the device". No figures specified.


    Although 412-06-02 specifies an R.C.D. of 30mA to operate at 5X its rating within 40 ms as provided for by BS 4293, BS 7071 BS 7288, BS EN 61008-1 or BS EN 61009-1


    Z.
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    Sparkingchip:

    What were we taught twenty years ago about testing RCDs, some of us are old enough to have installed consumer units where the requirements for RCDs of anything other than TT installations was basically none existent. New houses built on estates in the 1980’s that had TN installations had a socket with a built in RCD in the garage for outdoor use and that was it.


    So what were we taught about testing RCDs twenty years ago when split load consumer units were becoming the norm .


    Andy 


    No RCDs in sight and all rewireable fuses - did charred bodies litter the pavements back then? No, it was normal to us.

    When RCDs first came in fashion it was for a dedicated new circuit (say shower) or more often a front ender either on tails to consuimer unit or as the mainswitch of a consumer unit itself.


    In fact wylex changed their rocker switch colours when down for ON started to lose out in favour of up for ON.

    Happy days?




     

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    Could it be that for additional protection, the max trip time at 5 IΔn is appropriate, but for ADS in a TT system, it is the max trip time at IΔn which is important?



    Disconnection times for  IΔn (for non-delayed RCDs) need only be ≤300ms - which isn't adequate for ADS on most final circuits on TT systems where a 0.2s disconnection time is required, Hence we should be designing circuits for a minimum earth fault current of at least 2x IΔn to meet ADS requirements. Testing at  IΔn and getting a result within the BS EN spec doesn't necessarily directly prove that ADS requirements have been satisfied. It's all a bit of a mess really.

       - Andy.

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