Afternoon all,

I have a 4 core 95mm2 xlpe/lsf/swa cable, protected by a 160amp mccb which runs 135 metres clipped direct to a wall to a sub distribution board. The external EFLI is 0.05 and based on my cals this is what i get-

Zs = Ze + l x (R1+R2)
Zs = 0.05 + 135 x (0.26m/ohms + 1.1m/ohms)
Zs = 0.23 ohms

Fault current = V/Z

230/0.23 = 1000Amps

Am i correct in doing my calulation, as the maximum allowable earth loop impedance according to the manufactures data for 5 sec is:-
Min - 0.20ohms
Max - 0.12 ohms

Thanks CPC

Hi CPC , I have a slightly different result to yours.

I have 135 x 0.193 x 1.2 / 1000 = 0.031 , thats for R1.

Then 135 x 1.1 x 1.18 / 1000 = 0.17 , thats for R2.

Result is 0.20 so I think it will comply with your maximum allowable Zs.

Also the cable will probably not be fully loaded so there is a calculation you could do with reduced temperature but that is beyond me .

Regards