The adiabatic equation assumes that no heat is dissipated from the cable during a fault. This is normally conservative, but for longer fault durations it may be possible to account for heat dissipation and use a more accurate calculation.
Considering non-adiabatic effects is more complex than using the adiabatic equation. Unless there is a clear design reason, the adiabatic method is usually simpler and more conservative.
IEC 60949 approach
IEC 60949, Calculation of thermally permissible short-circuit current, taking into account non-adiabatic heating effects, deals with non-adiabatic short-circuit current calculations.
The method uses the adiabatic equation and applies a correction factor to allow for heat dissipation from the cable:
| I | Permissible short-circuit current, A or kA |
| IAD | Adiabatic calculated permissible short-circuit current, A or kA |
| ε | Factor allowing for heat dissipation from the cable |
The bulk of IEC 60949 is concerned with calculating ε. Specialist software is often used where non-adiabatic effects need to be considered, because the method adds cost, time and complexity to the calculation.