Use the link on the left to access our cable sizing application. Manage and size all your cables, from low voltage to 33 kV.
As mentioned, the adiabatic equation assumes no heat is dissipated from the cable during a fault. While putting the calculation on the safe side, in some situations, particularly for longer fault duration there is the potential to be able to get away with a smaller cross section. In these instances, it is possible to do a more accurate calculation.
Considering non-adiabatic effects is more complex. Unless there is some driver, using the adiabatic equations is just easier. Software is available to consider non adiabatic effects, however, there is a cost, time and complexity associated with this.
The IEC also publish a standard which deals with non-adiabatic equations:
The method adopted by IEC 60949 is to use the adiabatic equation and apply a factor to cater for the non-adiabatic effects:
I=ε I AD
where I - permissible short circuit current, A (or kA)
IAD - adiabatic calculated permissible short circuit current, A (or kA)
ε - factor to allow for heat dissipation from cable
The bulk of the IEC 60949 standard is concerned with the calculation of ε.