3.91
W/m
195.5
W
13.69
°C
43.69
°C
0.01955
Ω
3.91
W/m
195.5
W
13.69
°C
43.69
°C
0.01955
Ω
The Cable Temperature Rise Calculator determines how much a cable's conductor temperature increases above ambient when carrying a specified load current. Conductor temperature rise is a central parameter in cable engineering: it governs the selection of insulation material, determines maximum permissible current (ampacity), drives cable derating in high-ambient or bundled installations, and directly affects the conductor's resistance and therefore its voltage drop and power losses.
Every current-carrying conductor dissipates energy through resistive (Joule) heating at the rate P = I² × R watts per unit length. This heat must flow outward through the insulation, bedding, sheath, and ultimately to the surrounding environment before steady-state temperature is reached. The thermal resistance of the cable system — measured in kelvin-metres per watt (K·m/W) — quantifies how readily heat can escape. The temperature rise is then: ΔT = P_loss/m × T_thermal where P_loss/m is the heat generated per metre and T_thermal is the overall thermal resistance per metre.
Thermal resistance is a composite property. For a single-core cable, it includes the insulation layer (which depends on insulation material and geometry), the outer sheath, and the external thermal resistance (air, duct, direct burial, or water). Typical values range from about 1 K·m/W for a water-cooled bus duct to over 6 K·m/W for a small cable buried in dry soil. IEC 60287 provides detailed methods for computing each component.
The insulation material sets the absolute maximum permissible conductor temperature: PVC insulation is rated to 70 °C, XLPE (cross-linked polyethylene) to 90 °C, EPR to 90 °C, and XLPE/EPR under emergency conditions to 105 °C. High-temperature cables with silicone or PTFE insulation may be rated to 150–200 °C. Exceeding these limits degrades insulation, shortens cable life, and can ultimately lead to insulation failure and fire.
Derating is the practice of reducing a cable's rated current when installation conditions are more severe than the standard reference. Key derating factors include: elevated ambient temperature (each 1 °C above the 30 °C reference reduces allowable current approximately 0.5–1%), grouping of cables (mutual heating reduces each cable's ampacity — IEC 60364 and AS/NZS 3008 provide correction factors), installation in thermal insulation (heat cannot escape freely), and depth of burial (soil moisture and thermal resistivity vary with depth).
This calculator uses a simplified model appropriate for steady-state design checks and comparative studies. It computes total I²R losses along the cable, heat generated per metre, the resulting temperature rise, and the final conductor operating temperature. For regulatory compliance calculations (NEC, IEC 60287, BS 7671), consult the full standard which accounts for dielectric losses in high-voltage cables, proximity effects, and detailed soil thermal models.
In data centre design, cable temperature rise is a first-order concern. High-density server racks draw enormous currents, and cable routes are often congested. Engineers carefully model thermal rise to avoid exceeding XLPE ratings and to maintain adequate cooling airflow. Similarly, in automotive and aerospace wiring harnesses, weight constraints prevent oversizing cables, so precise thermal modelling is essential to safe design.
Renewable energy installations — particularly solar PV string cabling and battery interconnects — operate in high-ambient environments (rooftop, battery enclosures) where conservative ampacity ratings are essential. The combination of high ambient temperature and reduced convective cooling can more than double the effective thermal resistance, mandating significant derating of cable current capacity.
The calculator applies the fundamental thermal-electrical analogy:
The thermal resistance T_thermal (K·m/W) can be estimated from cable data sheets or computed per IEC 60287. For reference: 4 mm² PVC cable in free air ≈ 3.5 K·m/W; 16 mm² XLPE cable direct buried ≈ 2.5 K·m/W. Resistance per metre values are available in cable manufacturers' catalogues (e.g., Nexans, Prysmian) or computed from conductor cross-section and resistivity.
Compare the calculated conductor temperature against the insulation rating: below 70 °C for PVC, below 90 °C for XLPE/EPR. If the calculated temperature exceeds the insulation rating, the cable is overloaded — increase conductor size, reduce current, improve cooling, or use higher-rated insulation. A temperature rise above 40 °C above ambient is generally a warning sign for standard installations. The I²R loss figures are also useful for energy efficiency audits and calculating annual energy cost of cable losses.
Inputs
Results
At 200 A the conductor reaches 49.3 °C — well within the 90 °C XLPE limit. Total I²R loss of 772 W represents an annual energy cost that should be factored into life-cycle analysis.
Inputs
Results
At 50 A in a 40 °C ambient, the conductor reaches 79.1 °C — exceeding the 70 °C PVC limit. Either reduce current, upgrade to 10 mm², or use XLPE insulation.
Thermal resistance (K·m/W) quantifies how much the conductor temperature rises per watt of heat generated per metre of cable length. Lower values mean heat escapes more easily. It depends on insulation material, geometry, and installation environment (air, duct, buried).
Resistance per metre is listed in cable manufacturer datasheets (e.g., Nexans, Prysmian, Belden) or can be calculated as ρ/A, where ρ is conductor resistivity (1.72×10⁻⁸ Ω·m for copper, 2.82×10⁻⁸ Ω·m for aluminium) and A is cross-sectional area in m². IEC 60228 also tabulates standard values.
When cables are bundled, each cable's heat cannot dissipate as freely because neighbouring cables are also generating heat. The effective thermal resistance increases, raising conductor temperature for the same current. IEC 60364-5-52 provides grouping correction factors to account for this effect.
Common ratings: PVC 70 °C, XLPE 90 °C, EPR 90 °C, Silicone 150 °C, PTFE 200 °C. For emergency conditions, XLPE is sometimes rated 105 °C short-term. Always verify the specific cable's rating from its datasheet or IEC 60502/60245 standard.
Yes, but for three-phase cables you should use the resistance of one conductor and the current in that conductor. In a balanced three-phase system, the neutral conductor carries little current, so heating is primarily from the three phase conductors. For unbalanced or harmonic-rich loads, also consider neutral and earth conductor heating.
The model is accurate for steady-state conditions with constant current. It does not account for cyclic loading (which allows partial thermal recovery), dielectric losses in HV cables, magnetic losses in steel-armoured cables, or transient fault heating. For full compliance calculations, use IEC 60287 or a validated cable sizing software package.
Dry soil has thermal resistivity of about 2.5 K·m/W, while moist soil is approximately 1.0 K·m/W. Higher soil resistivity means more temperature rise. IEC 60287 uses a standard of 1.5 K·m/W for buried cable ampacity tables. In hot, dry climates, cable ampacity must be derated accordingly.
Roboculator Team
The Roboculator Team explains calculations, planning tools, and practical formulas in clear language for real-life situations.
How helpful was this calculator?
Be the first to rate!
Conductor Resistance at Temperature Calculator
Conductor & Material Properties Calculators
Resistivity and Conductivity Calculator
Conductor & Material Properties Calculators
Skin Depth Calculator
Conductor & Material Properties Calculators
Busbar Current Carrying Capacity Calculator
Conductor & Material Properties Calculators
AWG to mm² SWG Converter
Conductor & Material Properties Calculators
