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High protective conductor currents - Deletion of 543.7.1.204

AJJewsbury

543.7.1.204 - the one about duplicate c.p.c.s needing to be 'terminated independently of each other' - has gone.

Does anyone understand the thinking behind this? It seems a bit odd to me.

Given that (in my experience) more problems occur at terminals rather than along cable runs, if we need the c.p.c.s to be duplicated, it seems like a bit of a flaw that one single loose connection can make them both useless simultaneously. I can see that in some instances (e.g. a terminal on a socket on a ring) that losing a single terminal carries a limited immediate risk (as the leakage current from a single socket should be small and all other sockets are still connected to a c.p.c.) but in other instances - say the connection of both c.p.c.s to the earth bar in a DB - that single fault could be very significant.

   - Andy.

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  • gkenyon said:
    the vast majority of circuits complying with 411.3.3, would be required to have a maximum protective conductor current of 9 mA

    Assuming this is from 531.3.2 which 411.3.3 references in Note 2. The 9mA (30% of 30mA) seems to be only one of a number of suggested solutions to the problem of unwanted tripping which should be "considered", so not really a requirement for all circuits with RCDs. And if a requirement, where does this leave circuits with pc currents of between 9 and 10mA?

  • in reply to OlympusMons
    OlympusMons said:
    And if a requirement, where does this leave circuits with pc currents of between 9 and 10mA?

    > 9 mA and < 10 mA has no special consideration (except for the fact that you can't power the load straight from a circuit protected by 30 mA RCD without nuisance tripping. The following would be recommended for protective conductor currents exceeding 9 mA

    • If the protective conductor current is caused by more than one load, more final circuits are necessary, and 30 mA RCDs can be used.
    • If the protective conductor current is caused by one load alone, then that load should be installed considering the product standard and manufacturer's instructions (which may include additional earthing, e.g. as described in BS EN 60204-1, or BS EN 62368-1, or by the adoption of BS EN 50310).
      In BS 7671 terms, consideration might be needed for the use of particular wiring systems or routes to avoid the use of 30 mA RCDs ...

    Simples.

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  • in reply to OlympusMons
    OlympusMons said:
    And if a requirement, where does this leave circuits with pc currents of between 9 and 10mA?

    > 9 mA and < 10 mA has no special consideration (except for the fact that you can't power the load straight from a circuit protected by 30 mA RCD without nuisance tripping. The following would be recommended for protective conductor currents exceeding 9 mA

    • If the protective conductor current is caused by more than one load, more final circuits are necessary, and 30 mA RCDs can be used.
    • If the protective conductor current is caused by one load alone, then that load should be installed considering the product standard and manufacturer's instructions (which may include additional earthing, e.g. as described in BS EN 60204-1, or BS EN 62368-1, or by the adoption of BS EN 50310).
      In BS 7671 terms, consideration might be needed for the use of particular wiring systems or routes to avoid the use of 30 mA RCDs ...

    Simples.

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