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Type A R.C.D. 6mA tolerant.

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Can I really be confident in the use of a Type A R.C.D. that will tolerate up to only 6mA D.C. current and still operate?

I have a box of old Pifco torch bulbs as used in battery motorists' lanterns. They are filament bulbs rated at 6.2V 0.5 Amp. Their current draw is 500mA. And that for a not very bright torch bulb. That current is supplied via dry cells.

So, the Type A R.C.D.s can only work reliably with a D.C. current of up to 6mA. That is a piddly low current.

Comments please.

Z.

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    We fit 30mA RCD protection to final circuits as a personnel protection measure as additional protection against direct contact.

    Agreed (for TN systems) - so we're not talking about earth faults of negligible impedance at or before the appliance, more screwing a utensil rail into a concealed cable kind of thing - where we really do want the RCD to trip out normally (well within 300ms at 30mA or 40ms at 150mA kind of thing) and even a small reduction in the RCDs performance could be very significant.

    So bearing in mind that an RCD might be covering half the house (or even the entire house) and someone screws/drills into a cable, is there anything about any of the electronic appliances downstream of the same RCD that could reduce it's effectiveness? Either an uncleared fault (d.c. → N perhaps) in  one of the appliances, or just cumulative leakage currents? Many electronic devices are renowned for high leakage currents (everything from induction hobs to PCs) with the filtering trying to stop nasty spikes escaping the equipment as much as protecting the equipment from incoming noise - can we be sure that there are no non-sinusoidal components to the leakage current? As the residual current seen by the RCD will be the sum of the shock current and the leakage currents from connected equipment, there seems to be a possibility there to my mind.

            - Andy.

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  • 0

    We fit 30mA RCD protection to final circuits as a personnel protection measure as additional protection against direct contact.

    Agreed (for TN systems) - so we're not talking about earth faults of negligible impedance at or before the appliance, more screwing a utensil rail into a concealed cable kind of thing - where we really do want the RCD to trip out normally (well within 300ms at 30mA or 40ms at 150mA kind of thing) and even a small reduction in the RCDs performance could be very significant.

    So bearing in mind that an RCD might be covering half the house (or even the entire house) and someone screws/drills into a cable, is there anything about any of the electronic appliances downstream of the same RCD that could reduce it's effectiveness? Either an uncleared fault (d.c. → N perhaps) in  one of the appliances, or just cumulative leakage currents? Many electronic devices are renowned for high leakage currents (everything from induction hobs to PCs) with the filtering trying to stop nasty spikes escaping the equipment as much as protecting the equipment from incoming noise - can we be sure that there are no non-sinusoidal components to the leakage current? As the residual current seen by the RCD will be the sum of the shock current and the leakage currents from connected equipment, there seems to be a possibility there to my mind.

            - Andy.

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