NEC – Cable Temperature Calculation

Step – I Cable Temperature (If total calculated de-rating Cd <=1

0 = A + ( [R - A] * [I0 / IR * Ct* Pc ]2 )

Where:

I0 = operating current, in amperes

IR = rated current of cable, in amperes

0 = operating temperature of cable when carrying I0, in degrees Celsius

R = rated or maximum operating temperature determined from Table 1 when carrying IR, in degrees Celsius

A = ambient air or soil temperature, in degrees Celsius

Ct = ambient temperature de-rating factor (De-rating factor for Ambient Temperature (Cat))

Pc = number of cables in parallel

Then set qA = 40

Else set qA = 30

IR = Max. Current:

I0 = Design Current: This is the Cable Current column.

qR = Conductor Temperature:

Pc = No. of Cables:

Step – II Cable Temperature (If total calculated de-rating Cd >1

0 = A + ( [R - A] * [I0 / IR * Cd * Pc]2 )

Where:

I0 = operating current, in amperes

IR = rated current of cable, in amperes

0 = operating temperature of cable when carrying I0, in degrees Celsius

R = rated or maximum operating temperature determined from Table 1 when carrying IR, in degrees Celsius

A = ambient air or soil temperature, in degrees Celsius

Cd = total calculated derating

Pc = number of cables in parallel

Step – III Cable Temperature Conversion

If cable temperature is defined in degrees F, then the following equation for cable temperature is used:

C = 5/9 * (F–32)

Where:

C = ambient temperature in degree Celsius

F = ambient temperature in degree Fahrenheit