Undersized earth?

[rumplestiltskin]

6mm2 main earth, TN-S, 100a BS1361 main fuse, 1610A measured fault current.
I tried this on the adiabatic equation, and compared to fuse curve and it seems to just be large enough. However I've been known to make mistakes! Can anyone confirm if this seems correct please? (I used 115 for k but not sure if this is correct either)

 

[RF Lighting]

Where did you get your k value from?

I'm looking at table 54.2, which lists k as 143.

 

[Adam_151]

Sounds good to me, I have a feeling it might be 143 for k if its not in a sheath and not bunched with others (which it probably is... the tails?), but it works out ok with 115 and I get a mimimum of 5.44mm²

Using the figures of 1400A will disconnect in 0.2 seconds, and with a fuse the higher fault current will result in a lower I²t let-through (only holds true with fuses, not mcbs)[/i]

 

[GaryMo]

115 is for a protective conductor incorporated in a cable.
143 is the figure you require if the earthing conductor is separate.

 

[rumplestiltskin]

yeah I got k a bit out... guess I got a bit blinded with tables and curves, thanks guys.