Calculation Results
Recommended Cable Size: -
Current Carrying Capacity: - A
Voltage Drop: - V (-%)
Power Loss: - W
Derating Factor: -
Short Circuit Capacity: - kA
Voltage Drop Visualization
Calculation Details
The cable size is determined based on:
- Current carrying capacity requirements
- Allowable voltage drop (typically limited to 5% or less)
- Short circuit withstand capacity (if selected)
- Derating factors for installation conditions
The calculation follows IEC 60364-5-52 and BS 7671 standards.
Voltage drop occurs due to the resistance of the cable and is calculated using:
Voltage Drop = (I × R × L × √3) / 1000 (for three phase)
Voltage Drop = (I × R × L × 2) / 1000 (for single phase)
Where:
- I = Current (A)
- R = Resistance (Ω/km)
- L = Length (m)
Derating factors account for conditions that reduce a cable's current carrying capacity:
- Ambient Temperature: Higher temperatures reduce capacity
- Cable Grouping: Multiple cables together increase temperature
- Installation Method: Buried or insulated cables have different heat dissipation
- Harmonics: Non-linear loads can increase heating
Electrical Engineering Context
Why Proper Cable Sizing Matters
Selecting the correct conductor cross-sectional area (mm²) is fundamental to electrical safety and system performance. Undersized cables can lead to:
- Excessive temperature rise: Violating insulation thermal limits (PVC: 70°C, XLPE: 90°C)
- Voltage regulation issues: Excessive drop affecting motor starting and equipment operation
- Fire hazard: Increased risk from sustained overload conditions
- Energy inefficiency: Higher I²R losses increasing operational costs
- Premature insulation degradation: Reduced cable lifespan
This tool implements the iterative design process used by electrical engineers: checking current capacity, voltage drop, and short-circuit withstand in sequence.
Engineering Formulas & Variables
ΔV = (√3 × I × L × ρ) / (A × 1000)
Current Carrying Capacity (Derated):
Iz = It × Ca × Cg × Ci × Cd
• ΔV: Voltage drop (V)
• I: Load current (A) - RMS value for AC circuits
• L: Cable length (m) - one-way distance for single-phase, actual route length for three-phase
• ρ: Resistivity (Ω·mm²/m) - 0.0172 (Cu), 0.0282 (Al) at 20°C
• A: Conductor cross-sectional area (mm²)
• Iz: Derated current capacity (A)
• It: Tabulated current rating (A) from IEC 60364-5-52
• Ca: Ambient temperature correction factor
• Cg: Grouping correction factor
• Ci: Thermal insulation correction factor
• Cd: Harmonic correction factor (typically 0.8-0.9 for nonlinear loads)
Safety & Application Notes
Important Safety Disclaimer
This tool is for educational and preliminary design purposes only. Final cable sizing for installations must be:
- Verified by a qualified electrical engineer or licensed electrician
- Compliant with local electrical codes (NEC, CEC, BS 7671, AS/NZS 3000, etc.)
- Validated against manufacturer's specific cable data sheets
- Considered alongside protective device coordination (OCPD sizing)
Never use online calculators as sole justification for electrical installations affecting life safety.
Common Engineering Scenarios
Example 1: Motor feeder cable - Consider starting current (5-7× FLC), voltage drop during start (≤15%), and overload protection coordination.
Example 2: PV array wiring - DC calculations with different derating (NEC 690.8), consider temperature coefficients for outdoor exposure.
Example 3: Harmonic-rich loads - Data centers with >30% THD may require neutral conductor upsizing and K-factor transformers.
Frequently Asked Questions
Q: Why does cable grouping reduce current capacity?
A: Multiple cables in proximity reduce heat dissipation capability. The thermal derating factors in IEC 60364-5-52 account for reduced convection and radiation cooling paths. For example, 3-6 cables touching typically require 30% derating (Cg = 0.7).
Q: Should I use copper or aluminum conductors?
A: Copper offers 61% better conductivity (1.68 vs 2.65 μΩ·cm), smaller cross-section for same current, better corrosion resistance, but higher cost. Aluminum is lighter, cheaper, and common for large feeders (>70 mm²). Consider termination methods—aluminum requires antioxidant compound and specific torque procedures.
Q: What voltage drop limits should I follow?
A: Typical limits are 3% for feeders, 5% total from service to load (NEC 210.19). For sensitive equipment or motor starting, stricter limits (1-2%) may apply. UK regulations (BS 7671) recommend ≤5% for lighting, ≤4% for other uses.
Q: How does temperature affect calculations?
A: Conductor resistance increases approximately 0.4% per °C for copper. The calculator adjusts both resistivity (ρ) and derating factors. At 70°C, copper resistance is ~1.23× its 20°C value, increasing voltage drop proportionally.
Tool Limitations & Assumptions
- Steady-state conditions: Calculations assume continuous maximum load, not transient or cyclic loads
- Standard conductors: Based on IEC cable construction, not specialty or high-temperature cables
- Balanced three-phase: Assumes equal loading on all phases
- Power factor: Voltage drop calculations assume unity PF; inductive loads increase apparent voltage drop
- Skin & proximity effects: Neglected for cables below ~185 mm² at 50/60 Hz
- Earth return paths: Not considered for single-phase calculations
- Protective devices: Does not verify coordination with fuses, breakers, or RCDs
Last formula review: September 2025. Based on IEC 60364-5-52:2020 and BS 7671:2022.
Data Privacy & Technical Trust
This calculator performs all computations locally in your browser—no electrical parameters are transmitted to external servers. The algorithms implement industry-standard methods per:
- IEC 60364-5-52: Selection and erection of electrical equipment - Wiring systems
- BS 7671: Requirements for Electrical Installations (UK Wiring Regulations)
- IEEE Std 141: Recommended Practice for Electric Power Distribution
For mission-critical applications, always cross-reference with cable manufacturer datasheets and perform detailed studies using specialized software (ETAP, SKM, Amtech).