Type A rcd . EICR coding ? etc

I've been pondering the mention of additional/supplementary protection - presumably against direct contact - so we're expecting the RCD to see a residual current that's just flowing though a person who I presume is a fair approximation to a simple resistor so we shouldn't expect any waveform distortion or d.c. components on that score - so in that respect AC type RCDs should be adequate. On the other hand we have a load that might draw distorted waveform current for its normal load - so the RCD will see distorted a.c. load current plus pure sinewave shock current flowing out in its L coil, and just the distorted N return (without the shock current) in its N coil - so the question is: can we be sure that all AC type RCDs can spot a pure sinewave residual current when both the L and N load currents equally are distorted? I.e. does the insensitivity to distorted sinewaves occur before or after summing in the toroid?


   - Andy.

Yes, whilst 10 mA and 30 mA RCDs are used for additional protection (perhaps a fault through a person), they may already be subject to complex components in residual currents downstream, and effectively "blinded" by that.


The situation with fault protection using RCDs is a little more complicated - because the fault may well be as described in A53.1.


It's also worth considering the wording in, say, some of the Part 7 sections - is the RCD providing additional protection or fault protection? Some Part 7's say "shall be protected by an RCD" - without mention of either fault protection or (in the cases where 30 mA RCDs) additional protection, or even protection against fire! Some clue may be available from the numbering of the requirements (i.e. considering which of the General Requirements in Parts 3, 4, 5, 6, or (in the case of AMD 2 DPC) 8.

I've been pondering the mention of additional/supplementary protection - presumably against direct contact - so we're expecting the RCD to see a residual current that's just flowing though a person who I presume is a fair approximation to a simple resistor so we shouldn't expect any waveform distortion or d.c. components on that score - so in that respect AC type RCDs should be adequate. On the other hand we have a load that might draw distorted waveform current for its normal load - so the RCD will see distorted a.c. load current plus pure sinewave shock current flowing out in its L coil, and just the distorted N return (without the shock current) in its N coil - so the question is: can we be sure that all AC type RCDs can spot a pure sinewave residual current when both the L and N load currents equally are distorted? I.e. does the insensitivity to distorted sinewaves occur before or after summing in the toroid?


   - Andy.

Yes, whilst 10 mA and 30 mA RCDs are used for additional protection (perhaps a fault through a person), they may already be subject to complex components in residual currents downstream, and effectively "blinded" by that.


The situation with fault protection using RCDs is a little more complicated - because the fault may well be as described in A53.1.


It's also worth considering the wording in, say, some of the Part 7 sections - is the RCD providing additional protection or fault protection? Some Part 7's say "shall be protected by an RCD" - without mention of either fault protection or (in the cases where 30 mA RCDs) additional protection, or even protection against fire! Some clue may be available from the numbering of the requirements (i.e. considering which of the General Requirements in Parts 3, 4, 5, 6, or (in the case of AMD 2 DPC) 8.