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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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    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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  • 0

    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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