310.60 Conductors Rated 2001 to 35,000 Volts
Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0 m (10 ft) or 10 percent of the circuit length calculated at the higher ampacity, whichever is less.
Informational Note: See 110.40 for conductor temperature limitations due to termination provisions.
Tc = conductor temperature (°C)
Ta = ambient temperature (°C)
ΔTd = dielectric loss temperature rise
Yc = component ac resistance resulting from skin effect and proximity effect
Rca = effective thermal resistance between conductor and surrounding ambient
Informational Note: The dielectric loss temperature rise (ΔTd ) is negligible for single circuit extruded dielectric cables rated below 46 kV.