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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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    For example will a type A (or “better”)  trip at low enough DC currents such that an upstream type AC won't be blinded by DC currents low enough to be passed?

    A-types aren't guaranteed to trip at all on pure d.c. - their only guarantee is that they'll still operate within spec if the pure d.c. component of the residual current happens to be below 6mA.

    B-types will trip on pure d.c. but need a considerable pure d.c. residual current to do so - over 60mA for a 30mA (nominal a.c.) rated device I believe - so won't be blinded by pure d.c. and will trip for very significant d.c. faults, but pretty useless for protecting upstream A (or AC) types from being blinded if there's any possibility of a d.c. fault (or leakage) producing a d.c. component of the residual current between 6mA and 60mA.

    There are devices that are intended to look for d.c. residual currents and trip if they exceed 6mA - RDC-DDs - Residual d.c. detecting devices - which are good for protecting upstream A-type RCDs (provided there are no other sources of d.c. residual currents) - as mentioned in 722.531.3.101 in AMD1.  Sometimes they're sold combined with an A-type RCD as an “EV” type.

       - Andy.

     

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  • 0

    For example will a type A (or “better”)  trip at low enough DC currents such that an upstream type AC won't be blinded by DC currents low enough to be passed?

    A-types aren't guaranteed to trip at all on pure d.c. - their only guarantee is that they'll still operate within spec if the pure d.c. component of the residual current happens to be below 6mA.

    B-types will trip on pure d.c. but need a considerable pure d.c. residual current to do so - over 60mA for a 30mA (nominal a.c.) rated device I believe - so won't be blinded by pure d.c. and will trip for very significant d.c. faults, but pretty useless for protecting upstream A (or AC) types from being blinded if there's any possibility of a d.c. fault (or leakage) producing a d.c. component of the residual current between 6mA and 60mA.

    There are devices that are intended to look for d.c. residual currents and trip if they exceed 6mA - RDC-DDs - Residual d.c. detecting devices - which are good for protecting upstream A-type RCDs (provided there are no other sources of d.c. residual currents) - as mentioned in 722.531.3.101 in AMD1.  Sometimes they're sold combined with an A-type RCD as an “EV” type.

       - Andy.

     

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