311.60 Ampacities of Conductors
Exception: Where different ampacities apply to portions of a circuit, the higher ampacity shall be permitted to be used if the total portion(s) of the circuit with the lower ampacity does not exceed the lesser of 3.0 m (10 ft) or 10 percent of the total circuit.
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|
|Rdc||= dc resistance of conductor at temperature, Tc|
|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 kilovolts.