Cable Derating Calculator
Calculate cable current capacity based on environmental and installation factors
Cable Derating Calculator
Compliant with IEC 60364 Standards
Results:
Total Derating Factor: 0.000
Cable Derated Current (A): 0.00
How to Use the Calculator
Step 1: Initial Current
- Enter the initial current rating of the cable (e.g., from manufacturer data or standard tables).
- This is the current the cable can carry under ideal conditions.
Step 2: Select K-Factors
- k1 (Ambient Temperature): Choose the factor based on the surrounding air temperature.
- k2 (Grouping): Select the factor based on the number of cables or circuits grouped together.
- k3 (Thermal Insulation): Account for the thickness of any thermal insulation around the cable.
- k4 (Depth of Burial): For buried cables, select the factor based on the burial depth.
- k5 (Soil Resistivity): For buried cables, choose the factor based on the thermal resistivity of the soil.
- k6 (Harmonics): Select the factor based on the Total Harmonic Distortion (THD) in the system.
- k7 (Cable Type): Use the factor specific to the cable insulation type (e.g., PVC, XLPE).
Step 3: Calculate
- Click the "Calculate" button to determine the total derating factor and the derated current.
- The derated current is the maximum safe current the cable can carry under the specified conditions.
Cable Derating Fundamentals
What is Cable Derating?
Cable derating is the process of reducing the current-carrying capacity of a cable to account for environmental and installation conditions that can affect its ability to dissipate heat. Factors like ambient temperature, grouping with other cables, and installation methods can cause a cable to overheat if not properly derated, leading to insulation damage or fire hazards.
Key Derating Factors Explained
- k1 (Ambient Temperature): Accounts for the surrounding air or ground temperature. Higher temperatures reduce a cable's ability to dissipate heat, thus reducing its current capacity.
- k2 (Grouping): Applies when multiple cables are grouped together in conduits, trays, or bundles. Heat generated by adjacent cables accumulates, requiring a reduction in individual cable capacity.
- k3 (Thermal Insulation): Used when cables are installed in or near thermal insulation, which impedes heat dissipation.
- k4 (Depth of Burial): For buried cables, deeper burial can affect heat dissipation, especially in conjunction with soil properties.
- k5 (Soil Thermal Resistivity): For buried cables, the thermal resistivity of the surrounding soil impacts how effectively heat can escape from the cable.
- k6 (Harmonics): Non-linear loads can introduce harmonic currents, which increase the effective RMS current and cause additional heating in cables.
- k7 (Cable Type): Different insulation materials (e.g., PVC, XLPE) have varying thermal properties and maximum operating temperatures, which can influence the derating factor.
Key Formulas:
Total Derating Factor = k1 × k2 × k3 × k4 × k5 × k6 × k7
Cable Derated Current = Initial Cable Current × Total Derating Factor
Calculation Formulas
Total Derating Factor:
DF = k1 × k2 × k3 × k4 × k5 × k6 × k7
Cable Derated Current:
I_derated = I_initial × DF
All k-factors are multiplied to determine the overall reduction in current capacity.
Example Calculation
Consider a cable with an initial current rating of 100A.
Initial Cable Current (I_initial): 100 A
Ambient Temperature (k1): 35°C (Factor = 0.96)
Grouping (k2): 4 Circuits (Factor = 0.65)
Thermal Insulation (k3): 0 mm (Factor = 1.00)
Depth of Burial (k4): 0.5 m (Factor = 1.00)
Soil Thermal Resistivity (k5): 1.0 K·m/W (Factor = 1.00)
Harmonics (k6): 0% THD (Factor = 1.00)
Cable Type (k7): Standard (Factor = 1.00)
Total Derating Factor (DF) = 0.96 × 0.65 × 1.00 × 1.00 × 1.00 × 1.00 × 1.00 = 0.624
Cable Derated Current (I_derated) = 100 A × 0.624 = 62.4 A
The cable can safely carry 62.4 Amps under these conditions.
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