Cable length limit from table 7.1

[wattsy]

Evening all

Hopeully someone can help me get my head around this.

I'm looking at table 7.1 OSG. For the 1361/3036 45A radials on a TN-S system the limiting factor is sc, which means its limited by the line to neutral loop impedance (short circuit). But the TNC-S it isn't. Can't see what the difference between L - N fault on TNC-S and TN-S?

Can somebody please explain this to me in detail please i'm confused
Many Thanks

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[telectrix]

poss to do with the different values of Ze between TNS and TNCS. the Ze will influence your Zs

 

[wattsy]

poss to do with the different values of Ze between TNS and TNCS. the Ze will influence your Zs

What is the relationship between L -N fault and the Ze?

 

[telectrix]

bugger all i think. Ze is the impedance between phase and earth of the supply.