Calculation of thermally Permissible short-circuit current Standard reference IEC 60949 : 1988 ( IAD ) ( Ρ) ( I) IEC 60949 : 1988 IEC 60949 : 1988 IEC 60949 : 1988 IEC 60949 : 1988 IEC 60364-5-54 : 2011 IEC 60364-5-54 : 2011 IEC 60949 : 1988 Example 2 πΌπ΄π· π‘ = πΎ 2 π 2 ln 0.6/1 kV CV 95 sq.mm ππ = 3.45 × 106 π½/πΎπ3 π½ = 234.5 πΎ πΎ= ππ π½ + 20 × 10−12 π20 πΎ= 3.45 × 106 234.5 + 20 × 10−12 = 225.669 1.7241 × 10−8 π20 = 1.7241 × 10−8 Ωπ π = 95 ππ2 ππ = 250 β ππ = 90β π‘ = 1π ππ + π½ ππ + π½ 2 πΌπ΄π· × 1 = 225.6692 × 952 ln πΌπ΄π· = 13.6 ππ΄ 250 + 234.5 90 + 234.5 IEC 60949 : 1988 IEC 60949 : 1988 IEC 60949 : 1988 IEC 60949 : 1988 IEC 60949 : 1988 Example πΌπ΄π· = 13.6 ππ΄ 0.6/1 kV CV 95 sq.mm π = 0.41 πΌ = π × πΌπ΄π· π‘ π‘ +π π π π= 1+π π= 1 1 1 + 0.41 + 0.12 = 1.021 95 95 π = 0.12 πΌ = 1.021 × 13.6 = 13.9 ππ΄ Example 22 kV Duration of short circuit 1 sec