Zs values recorded results.

[westward10]

Was this a teacher or work colleague.

 

[Julie.]

When I noticed that I was surprised! It seems simply wrong that you can have an acceptable system where you get a L-N fault and not even disconnect if no risk of fire, etc, but sure enough that is the case.

Of course it is an odd/pathological system arrangement where that is possible, but it is still possible to achieve.

Something I would try and avoid if possible by OCPD choice, even if not strictly required.

The reason is that ADS is all designed around protection of the individual in the event of contact (nail into a cable shorting to earth/cpc sort of thing) this determines the duration of fault (and to some extent the voltage - which should be less than 2/3 × 230V [due to the higher cross section of live conductors to cpc])

Hence why the time is specified.


There is still a requirement for proper design in terms of operation for L-N faults, it just doesn't have to meet the ADS times.

So yes, the OCPD must have sufficient breaking capacity for the maximum fault level, the cables/equipment must withstand the FLC for normal operation AND for fault conditions - that would be both line to earth (Zs) faults and line to neutral - although they could have different fault levels and duration to each other.