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table 41.1 max. disconn. times and the extra notes

psychicwarrior
good day folks


"Where in TT systems the disconnection is achieved by an overcurrent protective device and the protective equipotential bonding is connected with all extraneous-conductive-parts within the installation in accordance with Regulation 411.3.1.2, the maximum disconnection times applicable to TN systems may be used."


Does this [also] imply that where protective equipotential bonding is not needed, then TN times can be used ?


And what reasons might there be for no similar relaxation of effectively 411.3.2.4 to 411.3.2.3  (1s to 5s  for other circuits not covered in 411.3.2.2 and in the light of the above extracted note to 411.3.2.2 Reg ) ?


Regards

Habs


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  • 0
    So when the earth rod resistance is really low, then an MCB or fuse will be as fast as an RCD.


    Presumably the thinking is that during an L-E fault the touch voltage is not as high, with say a 5 ohm electrode as it would be with a 100 ohm electrode resistance, so a longer break time is OK.


    To meet safety of life with a lower voltage is only applicable to the breaking times of half a heartbeat or so, where we can stand 100volts for almost twice as long than we can stand 200V for the same death wish, 1 second or 5 seconds are all about fire/ overheat so the exposed voltage during fault is not such an issue.
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  • 0
    So when the earth rod resistance is really low, then an MCB or fuse will be as fast as an RCD.


    Presumably the thinking is that during an L-E fault the touch voltage is not as high, with say a 5 ohm electrode as it would be with a 100 ohm electrode resistance, so a longer break time is OK.


    To meet safety of life with a lower voltage is only applicable to the breaking times of half a heartbeat or so, where we can stand 100volts for almost twice as long than we can stand 200V for the same death wish, 1 second or 5 seconds are all about fire/ overheat so the exposed voltage during fault is not such an issue.
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