Type A rcd . EICR coding ? etc

AJJewsbury:

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?

That is a pretty fair summary. In other words, might a fault in the boiler "blind" a type AC RCD?


The manufacturer's instructions don't require that this particular boiler be RCD protected so in a TN installation, ADS should provide shock protection for a fault inside it. Whether or not a distorted load current would trip a type AC RCD becomes irrelevant. So that leaves a fault in the supply cable (which need not require additional protection) or in the many cables which control the heating system, which are buried in walls < 50 mm from the surface, and which I assume are at mains voltage.


So to my mind, it is all about blinding. I await a response from the manufacturer.

AJJewsbury:

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?

That is a pretty fair summary. In other words, might a fault in the boiler "blind" a type AC RCD?


The manufacturer's instructions don't require that this particular boiler be RCD protected so in a TN installation, ADS should provide shock protection for a fault inside it. Whether or not a distorted load current would trip a type AC RCD becomes irrelevant. So that leaves a fault in the supply cable (which need not require additional protection) or in the many cables which control the heating system, which are buried in walls < 50 mm from the surface, and which I assume are at mains voltage.


So to my mind, it is all about blinding. I await a response from the manufacturer.