kW to Cable Size Calculator
Determine the precise cable size for any electrical load. Our calculator ensures safety, prevents overheating, and accounts for voltage drops and derating factors according to IEC standards.
Power Load to Wire Size Finder
How to Use the kW to Cable Size Calculator
Follow this beginner-friendly step-by-step guide to determine the correct wire size for your project.
- Load (kW): Enter the total power consumption of your equipment.
- System type: Select either single-phase (homes) or three-phase (industrial).
- Voltage (V): Input your system's operating voltage.
- Power factor (PF): Typically 0.8 for motors or 1.0 for heaters.
- Cable length: Distance between the power source and the load in meters.
- Conductor material: Choose between Copper (efficient) or Aluminum (cost-effective).
- Insulation type: Select PVC (70°C) or XLPE (90°C) based on your cable specification.
- Installation method: Choose how the cable is laid (conduit, air, or buried).
- Ambient temperature: Select the surrounding air or soil temperature.
- Grouped cables: Specify if the cable runs alone or with others in a conduit.
After clicking calculate, you will receive results for current, adjusted current, cable size, voltage drop percentage, and IEC compliance status.
Essential Derating Factors in Cable Sizing
Derating factors are multipliers that reduce the current-carrying capacity of a cable based on environmental conditions. Ignoring these can lead to overheating and fire hazards.
Ambient Temperature Factor
Cables generate heat. If the surrounding temperature is high, the cable cannot shed this heat effectively.
- 25°C → 1.03 (Higher capacity)
- 30°C → 1.00 (Standard)
- 40°C → 0.87 (Reduced capacity)
- 50°C → 0.71 (Significant reduction)
Grouping Factor
When multiple cables run together, they share heat, reducing each cable's ability to stay cool.
- 1 cable → 1.00
- 3 cables → 0.70
- 7–9 cables → 0.60
Installation Method (IEC 60364)
The environment (air vs. conduit vs. soil) drastically changes how a cable cools down. Method C (clipped direct) usually allows more current than Method A (in insulation).
Real-Life Step-by-Step Calculation Guide
Let's look at a practical example for an industrial motor.
- Load: 30 kW
- Voltage: 400 V (3-phase)
- PF: 0.8
- Length: 60m
- Temp: 40°C
- Installation: In conduit (Method B)
Step 1: Convert kW to Current
For a 3-phase system: I = (kW × 1000) / (√3 × V × PF)
I = (30 × 1000) / (1.732 × 400 × 0.8) = 54.13 Amps
Step 2: Apply Derating Factors
Find factors: Temp (40°C) = 0.87. Installation Factor = 0.9 (approx).
Adjusted Current = 54.13 / (0.87 × 0.9) = 69.13 Amps
Step 3: Select Cable Size
Based on IEC tables, a 16 mm² copper cable handles up to 76A. We select 16 mm².
Step 4: Voltage Drop Check
Using 16 mm² (approx 2.8 mV/A/m): VD = (2.8 × 54.13 × 60) / 1000 = 9.09V.
VD % = (9.09 / 400) × 100 = 2.27% (Well within the 5% limit).
Final Result:
16 mm² Copper XLPE cable is safe for this application.
Voltage Drop and Thermal Withstand
Understanding Voltage Drop
Voltage drop is the loss of electrical pressure across a cable due to resistance. If the drop is too high, equipment may fail to start or operate inefficiently. IEC limits permit 3% for lighting and 5% for power circuits.
Thermal Withstand Capability
During a short circuit, cables experience massive heat surges. The calculator ensures the selected cross-section is large enough to handle these brief thermal stresses without melting the insulation.
kW to Cable Size Conversion Chart (Copper/Typical)
Practical reference values for 400V 3-phase systems at 30°C.
| Load (kW) | Current (A) | Copper Size (mm²) | Aluminum Size (mm²) |
|---|---|---|---|
| 5 kW | 9 A | 1.5 mm² | 2.5 mm² |
| 11 kW | 20 A | 2.5 mm² | 4 mm² |
| 18 kW | 32 A | 6 mm² | 10 mm² |
| 30 kW | 54 A | 16 mm² | 25 mm² |
| 45 kW | 81 A | 25 mm² | 50 mm² |
IEC Standards and Reliability
We build our tools based on international engineering standards to ensure global compliance and safety.
- IEC 60364: Electrical installations of buildings.
- IEC 60287: Calculation of current rating.
- IEC 60502: Power cables with extruded insulation.
Frequently Asked Questions (FAQs)
It is a specialized tool that converts electrical power (kW) into the required cable cross-section (mm²) based on voltage, distance, and environmental factors.
They account for heat build-up from external sources like high ambient temperatures or grouping with other cables, ensuring the cable doesn't overheat.
Multiply the load current by the cable's resistance factor and length. Our calculator automates this using standard millivolt-drop tables.
Undersized cables overheat, causing insulation failure, voltage drops that damage machinery, and significantly increasing the risk of electrical fires.
Copper is a better conductor and allows for thinner cables. Aluminum is much lighter and cheaper but requires larger sizes to handle the same current.
No. When multiple cables run in one duct, they heat each other up. Ignoring this leads to cables operating above their design temperature.
Sizing only for the load current and ignoring voltage drop over long distances. A cable might be safe thermally but fail due to poor voltage stability.
Yes, it supports three-phase systems, XLPE insulation, and IEC installation methods typically used in industrial and commercial projects.
Use PVC for standard indoor wiring (70°C). Use XLPE for higher efficiency, industrial power systems, and outdoor/underground use (90°C).
Yes, the logic follows standard IEC 60364-5-52 current capacity and voltage drop principles for safe electrical installation sizing.