gkenyon:

ProMbrooke:


However, when all is said and done, I think table 41.1 needs to be re-visited again. 

But is that based on the fact that RCDs can't be trusted?


Table 41.1 is dry condition only.


Other than reliance on RCDs to achieve 40 ms disconnection time for additional protection, is IEC 60364 deficient in any other respect?

If all disconnection times are reduced to 0.2 s, what do you propose we do about circuits > 63 A (sub-mains etc.) that currently have disconnection times of 2 s and 5 s (and do NOT align in any way, shape or form to IEC 60479)? How will we achieve disconnection times and selectivity for these circuits?


If Table 41.1 is revisited for these reasons, other parts must be also ... would be good to hear your recommendations and reasoning on these other circuits?

In my opinion, an RCD can fail, and thus are just one layer of the onion.


There is also the fact RCDs are 30ma devices, where the no let go current starts at 10ma. It is possible (in theory) to end up frozen to the source, yet not trip the RCD. For this reason US GFCIs trip around 6ma.


In any case 6ma GFCI, or a even 30ma RCD, may trip large equipment due to leakage current. Even if/where steady state leakage current is under 6 or 30ma, Xc=1/2pifC can cause tripping from a sharp rising edge or spike in the sine wave. For this reason medical equipment, freezers, refrigerators, process equipment and the like should not be protected by an RCD due to the possible inadvertent tripping causing a greater risk such as food poisoning. Rather BS7671 should offer either an exception where the CPC is not likely to become compromised (like a home refrigerator that is typically rarely moved) or in the case of commercial kitchens and factories allow for other means such as an earth proving unit. The earth proving unit will not power the equipment unless the CPC is intact, and of course a 0.2 or 0.4 second disconnection time will take care of the rest.


US GFCIs tripping on AC units: 


   https://www.mikeholt.com/newsletters.php?action=display&letterID=2339  



There are many aspects of IEC 60364 that I would like to changed, clarified or added to. Or in the case of AFDDs have their mention tossed out altogether. However I think going into more detail on those other aspects would complicate this thread.


I do not believe all disconnection times should be reduced to 0.2 seconds, just wet locations. 0.4 can remain. 5 seconds for circuits over 63 amps, 10 seconds for circuits over 400 amps 15 seconds for circuits 1,200 amps and over. 30-60 seconds for select DNO cables.


Fault on larger circuits cause voltage drop on the output terminals of the transformer, resulting in lower touch voltage, and as such disconnection times can be longer. Typical transformer sizes, DNO runs, sub/final circuits and MCB/fuse trip times should be evaluated across the globe in order to establish reasonable values for each country.

gkenyon:

ProMbrooke:


However, when all is said and done, I think table 41.1 needs to be re-visited again. 

But is that based on the fact that RCDs can't be trusted?


Table 41.1 is dry condition only.


Other than reliance on RCDs to achieve 40 ms disconnection time for additional protection, is IEC 60364 deficient in any other respect?

If all disconnection times are reduced to 0.2 s, what do you propose we do about circuits > 63 A (sub-mains etc.) that currently have disconnection times of 2 s and 5 s (and do NOT align in any way, shape or form to IEC 60479)? How will we achieve disconnection times and selectivity for these circuits?


If Table 41.1 is revisited for these reasons, other parts must be also ... would be good to hear your recommendations and reasoning on these other circuits?

In my opinion, an RCD can fail, and thus are just one layer of the onion.


There is also the fact RCDs are 30ma devices, where the no let go current starts at 10ma. It is possible (in theory) to end up frozen to the source, yet not trip the RCD. For this reason US GFCIs trip around 6ma.


In any case 6ma GFCI, or a even 30ma RCD, may trip large equipment due to leakage current. Even if/where steady state leakage current is under 6 or 30ma, Xc=1/2pifC can cause tripping from a sharp rising edge or spike in the sine wave. For this reason medical equipment, freezers, refrigerators, process equipment and the like should not be protected by an RCD due to the possible inadvertent tripping causing a greater risk such as food poisoning. Rather BS7671 should offer either an exception where the CPC is not likely to become compromised (like a home refrigerator that is typically rarely moved) or in the case of commercial kitchens and factories allow for other means such as an earth proving unit. The earth proving unit will not power the equipment unless the CPC is intact, and of course a 0.2 or 0.4 second disconnection time will take care of the rest.


US GFCIs tripping on AC units: 


   https://www.mikeholt.com/newsletters.php?action=display&letterID=2339  



There are many aspects of IEC 60364 that I would like to changed, clarified or added to. Or in the case of AFDDs have their mention tossed out altogether. However I think going into more detail on those other aspects would complicate this thread.


I do not believe all disconnection times should be reduced to 0.2 seconds, just wet locations. 0.4 can remain. 5 seconds for circuits over 63 amps, 10 seconds for circuits over 400 amps 15 seconds for circuits 1,200 amps and over. 30-60 seconds for select DNO cables.


Fault on larger circuits cause voltage drop on the output terminals of the transformer, resulting in lower touch voltage, and as such disconnection times can be longer. Typical transformer sizes, DNO runs, sub/final circuits and MCB/fuse trip times should be evaluated across the globe in order to establish reasonable values for each country.