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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:
    The other (possibly more important question) is how do currents at higher frequencies affect the human body

    Afraid that all this talk of various frequencies makes my eyes glaze over, but v. high frequencies are used in diathermy. Bipolar is easy to understand - the current passes between the tips of a pair of forceps and cooks the tissue, which stops any bleeding. Rather more old-fashioned monopolar diathermy has a large "earth" plate attached e.g. to a buttock where the current density is low, and a pointy instrument where the current density is high, and accordingly, able to coagulate (stop bleeding) or cut.

    Then you have things like cardioablation, where the electrode is poked into yer heart tissue and the current fries it, so clearly HF currents can have very beneficial effects. :-)

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  • AJJewsbury said:
    The other (possibly more important question) is how do currents at higher frequencies affect the human body

    Afraid that all this talk of various frequencies makes my eyes glaze over, but v. high frequencies are used in diathermy. Bipolar is easy to understand - the current passes between the tips of a pair of forceps and cooks the tissue, which stops any bleeding. Rather more old-fashioned monopolar diathermy has a large "earth" plate attached e.g. to a buttock where the current density is low, and a pointy instrument where the current density is high, and accordingly, able to coagulate (stop bleeding) or cut.

    Then you have things like cardioablation, where the electrode is poked into yer heart tissue and the current fries it, so clearly HF currents can have very beneficial effects. :-)

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