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Definition of high protective conductor currents

AJJewsbury

I'm currently installing a heat pump and noticed that some of the manufacturer's information says of the RCDs to be used with it:

...now requires the use of a Type B RCD/RCBO with the following specification:

  • Minimum detection capability up to 20 kHz
  • Minimum trip threshold of 150 mA above 1 kHz

and looking at the devices the manufacturer suggests, these seem to be nominally 30mA types.

So it seems to me these suggested devices may trip at 15-30mA at 50Hz, but may tolerate more than 150mA above 1kHz.

My first thought was where does this leave me with respect to section 543.7 (equipment having high protective conductor currents)? Can I assume that the 10mA limit only applies to 50Hz currents? or given the way the words are written should it be read as applying to all frequencies?

The other (possibly more important question) is how do currents at higher frequencies affect the human body - if I have a device that maybe doesn't trip until over 150mA (at 1kHz) do I still have additional protection? I think I recall that 50 or 60Hz is about the worst possible choice of frequency for shock considerations, but can currents at higher frequencies be safely ignored entirely?

I guess similar considerations might potentially arise anywhere we have power inverters .. so my heat pump might be just the tip of the iceberg,

   - Andy.

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  • AJJewsbury said:

    now requires the use of a Type B RCD/RCBO with the following specification:

    • Minimum detection capability up to 20 kHz
    • Minimum trip threshold of 150 mA above 1 kHz

    To me, that reads as the requirement being a 300 mA Type B RCD.

    The current is presumably a mix of alternating, pulsating DC and pure DC? If it is, don’t forget to multiply by the square root of two as required when considering the leakage currents and testing.

  • in reply to Sparkingchip

    To me, that reads as the requirement being a 300 mA Type B RCD.

    You might very well think so ... but all the examples of the recommended "B HP" devices I can find are 30mA ones - e.g.https://hager.com/uk/search?q=heat+pump

       - Andy.

  • in reply to Sparkingchip
    Sparkingchip said:
    To me, that reads as the requirement being a 300 mA Type B RCD.

    I do not think that can be correct at all - in that case you would have no additional protection.

    In BS EN 61008-12012+A12:2017, the "preferred value of the rated frequency is 50 Hz" (5.3.7) and I think that must mean that IΔn is the value at 50 Hz (or 60 Hz) unless stated otherwise.

    The distinguishing feature, and reason for the eye-watering price of HP RCDs, seems to be that IΔn is frequency dependent.

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  • in reply to Sparkingchip
    Sparkingchip said:
    To me, that reads as the requirement being a 300 mA Type B RCD.

    I do not think that can be correct at all - in that case you would have no additional protection.

    In BS EN 61008-12012+A12:2017, the "preferred value of the rated frequency is 50 Hz" (5.3.7) and I think that must mean that IΔn is the value at 50 Hz (or 60 Hz) unless stated otherwise.

    The distinguishing feature, and reason for the eye-watering price of HP RCDs, seems to be that IΔn is frequency dependent.

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  • in reply to Chris Pearson

    Yes; and that it's a 'new' set of test criteria (even if existing unmarked devices might actually pass the tests anyway). In time it'll be simply the norm.

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