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. You can estimate these long-term expenses using our energy savings calculator to compare cable options.
  • 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
Voltage Drop Calculation (Three-Phase):
ΔV = (√3 × I × L × ρ) / (A × 1000)

Current Carrying Capacity (Derated):
Iz = It × Ca × Cg × Ci × Cd
Variable Definitions:
• 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. For help with complex systems, our load flow analysis tool can provide deeper insights.
  • Considered alongside protective device coordination (OCPD sizing). Use our fuse and circuit breaker size calculator for this critical step.

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. The motor starting current calculator helps estimate these inrush values.

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. Check our harmonic analysis tool to assess distortion levels.

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).