Unusual MCB

Thanks for the further pictures. I have never come across such things in the UK - interesting!


Now, thinking on the comment "without the inclusion of an instantaneous trip mechanism", I start to be curious about whether they do some clever trick like having a deliberately bad balance on the RCD core so that high overcurrents - even though non-residual - cause the RCD part to trip, or some other sensing. I admittedly can't see any other way of sensing in the picture, and can't imagine how a core and wires looking like this could have a reliable level of imbalance. (Sometimes the designers of these things have cunning tricks: for example, a chip commonly used for plug-in RCDs (RV4145) includes a rather neat detection of downstream N-E faults described on p.5, end of first section, which is wanted because these faults in a TN system can make the RCD much less sensitive to L-E faults by creating in effect a short-circuited turn through the core.)  


Else, perhaps the thermal trip anyway manages to be within the 0.1 s that still persists as the "instantaneous" requirement in IEC standards although all the manufacturers seem to make them so quick that they're even current-limiting (<0.01 s). 

Thanks for the further pictures. I have never come across such things in the UK - interesting!


Now, thinking on the comment "without the inclusion of an instantaneous trip mechanism", I start to be curious about whether they do some clever trick like having a deliberately bad balance on the RCD core so that high overcurrents - even though non-residual - cause the RCD part to trip, or some other sensing. I admittedly can't see any other way of sensing in the picture, and can't imagine how a core and wires looking like this could have a reliable level of imbalance. (Sometimes the designers of these things have cunning tricks: for example, a chip commonly used for plug-in RCDs (RV4145) includes a rather neat detection of downstream N-E faults described on p.5, end of first section, which is wanted because these faults in a TN system can make the RCD much less sensitive to L-E faults by creating in effect a short-circuited turn through the core.)  


Else, perhaps the thermal trip anyway manages to be within the 0.1 s that still persists as the "instantaneous" requirement in IEC standards although all the manufacturers seem to make them so quick that they're even current-limiting (<0.01 s).