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Why switch neutral on TN SP but not TPN supplies?

Farmboy
Regulation 462.1.201 requires that in single phase TN supplies, a main switch operated by ordinary persons interrupts line and neutral conductors. So why just for SP supplies but not TPN operated by ordinary people as well?

GN 2 (2018) offers no help, with e.g. table 4.1 saying of isolation requirements of the neutral - Not Applicable, because ordinary persons would not normally be operating TPN systems.

However, new TPN supplies are still being installed in domestic settings and used by ordinary people, so should the neutral be switched as well on TN-S & TN-C-S systems?

The regulation suggests no, but presumably the logic of requiring it for SP supplies would also apply to TPN in such settings.


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    I agree with the above, but would add that it's not just the design of the timing of the switch contacts that's the issue but the reliability of the switching mechanism - moving parts being inherently less reliable than static solid joint. So even a switch that's designed to open N last and close N first could allow N to be opened when L is closed should a moving contact break open (N) or weld close (L).

       - Andy.
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    I agree with the above, but would add that it's not just the design of the timing of the switch contacts that's the issue but the reliability of the switching mechanism - moving parts being inherently less reliable than static solid joint. So even a switch that's designed to open N last and close N first could allow N to be opened when L is closed should a moving contact break open (N) or weld close (L).

       - Andy.
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