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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
    I'd very much agree, given the natural variation of ground resistances and so on, it is a brave fellow who omits RCDs in a TT system, or maybe one who has not realised the full significance of it being TT.


    Perhaps they are saved from total failure by the fact that a lot of TT systems in buildings with bonds to the main water pipes etc, are actually neutral connected as someone on the same substation, and same water main, has PME or TNS. I fully appreciate this is not how it is supposed to work.
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  • 0
    I'd very much agree, given the natural variation of ground resistances and so on, it is a brave fellow who omits RCDs in a TT system, or maybe one who has not realised the full significance of it being TT.


    Perhaps they are saved from total failure by the fact that a lot of TT systems in buildings with bonds to the main water pipes etc, are actually neutral connected as someone on the same substation, and same water main, has PME or TNS. I fully appreciate this is not how it is supposed to work.
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