# 6. Permissible short-circuit current(1)

```Calculation of thermally
Permissible short-circuit
current
Standard reference
IEC 60949 : 1988
( 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
πΌπ΄π·
π‘ = πΎ 2 π 2 ln
0.6/1 kV CV 95 sq.mm
ππ = 3.45 &times; 106 π½/πΎπ3
π½ = 234.5 πΎ
πΎ=
ππ π½ + 20 &times; 10−12
π20
πΎ=
3.45 &times; 106 234.5 + 20 &times; 10−12
= 225.669
1.7241 &times; 10−8
π20 = 1.7241 &times; 10−8 Ωπ
π = 95 ππ2
ππ = 250 β
ππ = 90β
π‘ = 1π
ππ + π½
ππ + π½
2
πΌπ΄π·
&times; 1 = 225.6692 &times; 952 ln
πΌπ΄π· = 13.6 ππ΄
250 + 234.5
90 + 234.5
IEC 60949 : 1988
IEC 60949 : 1988
IEC 60949 : 1988
IEC 60949 : 1988
IEC 60949 : 1988
Example
πΌπ΄π· = 13.6 ππ΄
0.6/1 kV CV 95 sq.mm
π = 0.41
πΌ = π &times; πΌπ΄π·
π‘
π‘
+π
π
π
π=
1+π
π=
1
1
1 + 0.41
+ 0.12
= 1.021
95
95
π = 0.12
πΌ = 1.021 &times; 13.6 = 13.9 ππ΄
Example 22 kV
Duration of short circuit 1 sec
```