The step value of the conductor transient current is the new load current applied as a step function to a system with given current operating conditions.

It can be the emergency load current $I_2$ which may subsequently be applied for time $τ$ so that the conductor temperature rise above ambient at the end of the period of emergency load is θmax, which is the sustained (100% load factor) for rated current $I_R$ for the conductor to attain, but not exceed, the standard maximum permissible temperature.

Symbol
$I_{\mathrm{R}}$
Unit
A
Used in
$h_{\mathrm{1}}$
$h_{\mathrm{2}}$
$I_{\mathrm{2}}$