Cable Temperature Calculator – IEC

Accurately estimating cable temperature ensures safety, optimal performance, and compliance with modern international electrical standards.

The IEC Cable Temperature Calculator evaluates conductor heat under varying load, ambient temperature, and installation-specific conditions.

Cable Temperature Calculator – IEC

Common Values Table: Cable Temperature (IEC Guidelines)

Below is a comprehensive, user-friendly table showing common parameters and values used in IEC-based cable temperature calculations. This reference is essential for design engineers, electrical contractors, and installers.

Table 1: Common Parameters for IEC Cable Temperature Calculations

Formulas Used in Cable Temperature Calculations – IEC

IEC standards (especially IEC 60287-1-1) provide a structured methodology to calculate the temperature of power cables under continuous load conditions.

1. Power Loss (Joule Heating)

Where:

  • P= power loss per meter (W/m)
  • I= current through conductor (A)
  • R(T)= conductor resistance at temperature T (Ω/m)

Note: Resistance increases with temperature using the following relation:

  • R20= resistance at 20°C
  • α= temperature coefficient (Cu: 0.00393/°C, Al: 0.00403/°C)
  • T= conductor temperature (°C)

2. Temperature Rise of the Conductor

  • ΔT= temperature rise (°C)
  • P= power loss per meter (W/m)
  • G= total thermal conductance (W/°C·m)

Thermal conductance G is defined as:

Where:

  • Te= external thermal resistance (°C·m/W)

Therefore:

3. Overall IEC-Based Temperature Equation

Using all the above:

This equation can be iteratively solved, as R(T) depends on T.

4. Cable Ampacity Based on Max Temperature

Solving for I:

Where:

  • Tmax= permissible temperature of insulation (°C)

Real-World Application #1: Underground XLPE Cable in Dry Soil

Problem Statement

An engineer must determine the operating temperature of a 3-core 150 mm² copper XLPE-insulated cable buried at 0.5 m depth in dry soil (thermal resistivity = 2.5 °C·m/W). The cable carries 350 A continuously. Ambient temperature is 30°C.

Step 1: Input Data

Step 2: Calculate Resistance at Target Temperature (~85°C guess)

Convert to per meter:

Step 3: Calculate Power Loss

Step 4: Calculate Temperature Rise

Step 5: Final Conductor Temperature

Exceeds XLPE max limit of 90°C → Cable not suitable for 350 A in this condition

Solution

To stay within safe limits, recalculate the safe ampacity:

Seems contradicting. Why? Because resistance increases with actual temp. Must iterate for accuracy.

Real-World Application #2: Tray Installation in Industrial Plant

Problem Statement

A 70 mm² aluminum conductor cable with EPR insulation (max 105°C) is installed in a cable tray exposed to 40°C ambient in a high-load industrial setting. The expected continuous current is 200 A. Determine if the cable will exceed its temperature limit.

Step 1: Input Data

Step 2: Estimate Conductor Temp

Assume T=95

Safe temperature well below EPR limit

External Authoritative References

For accurate application and compliance, consult the following official sources:

Pro Tip: Always use local amendments to IEC standards, such as NTC (Colombia), UNE (Spain), or DIN VDE (Germany), for compliance in national installations.

Key Takeaways

  • Cable temperature rise is governed by Joule heating, conductor resistance, and thermal resistance to the environment.
  • IEC formulas require iteration due to the temperature dependence of resistance.
  • Soil conditions, installation method, and insulation material have major impacts on temperature.
  • Proper cable selection ensures thermal integrity, safety, and long-term reliability.
  • Field installations must always consider correction factors from IEC 60364-5-52.

Need an Online Cable Temperature Calculator?

You can use online calculators to simulate these calculations with adjustable parameters, including conductor size, material, soil type, and load current.

Recommended calculators:

However, for safety-critical applications, manual validation using IEC formulas remains best practice.