Cable Sizing Calculator

Cable sizing must comply with IEC 60364-5-52 (Electrical installations – Selection and erection of equipment) and local regulations like the UK’s BS 7671 or the US NEC Article 310. IEC 60364-5-52 mandates voltage drop limits (typically ≤3% for final circuits, ≤5% for distribution) and requires derating for ambient temperature, grouping, and installation method (e.g., buried vs. in air). Current-carrying capacity (Iz) is derived from tables in IEC 60287 or manufacturer datasheets, accounting for conductor material (Cu/Al), insulation (PVC/XLPE), and thermal conditions. Our calculator applies IEC-based voltage drop formulas (e.g., ΔU = b × ρ × L × I / A) and assumes standard reference conditions—always verify against project-specific derating factors and local authority requirements.

Voltage drop (ΔU%) is inversely proportional to cable cross-sectional area (A): ΔU% ∝ I × L / A. Halving the allowable drop (e.g., 5% → 3%) demands ~67% larger A to maintain the same current and length—since A must scale linearly with the inverse of the allowed drop. For example, a 5 kW load at 400 V over 100 m drops from ~2.1% (with 10 mm² Cu) to ~3.5% if undersized; enforcing 3% may require upgrading to 16 mm². This reflects real-world trade-offs: tighter voltage regulation improves equipment performance (e.g., motor torque, LED dimming) but increases cost and installation complexity. Always prioritize the stricter limit where sensitive loads or long feeders are involved.

No—the calculator assumes copper conductors by default, using resistivity ρ = 0.0184 Ω·mm²/m at 20°C (IEC 60228). Aluminium has ~56% higher resistivity (ρ ≈ 0.0283 Ω·mm²/m), so for identical geometry, it delivers ~56% higher voltage drop and lower current rating. To use aluminium safely, manually increase the calculated copper size by ~56% (e.g., 16 mm² Cu → 25 mm² Al) and apply IEC 60287 derating for reduced thermal conductivity. Always consult manufacturer ampacity tables—aluminium cables require larger terminations and anti-oxidant compounds to prevent creep and corrosion at joints per IEEE 835 and BS EN 50618.

The calculator computes line current as I = P / (√3 × V × PF) for three-phase AC (default assumption), and I = P / (V × PF) for single-phase—though the UI doesn’t explicitly toggle phase count. This is critical: misapplying the formula causes ~73% current error (e.g., 5 kW at 400 V yields 7.2 A 3φ vs. 15.6 A 1φ). For accuracy, confirm your system configuration before inputting. Real-world measurements often deviate due to harmonic distortion (IEC 61000-4-30), unbalanced loading, or non-sinusoidal waveforms—so always validate with a clamp meter under actual load. The calculator provides theoretical RMS current only; derating for harmonics (e.g., IEC 60364-5-52 Annex G) is user responsibility.

Yes—but with key adjustments. For DC, remove √3 and power factor (set PF = 1.0), since I = P / V. Voltage drop becomes ΔU = 2 × ρ × L × I / A (factor of 2 for +/− conductors), unlike AC’s √3-based approximation. Also, DC lacks skin effect but suffers more from contact resistance and oxidation—especially at terminations. Standards like IEC 62548 (PV systems) mandate ≤1.5% drop for string wiring and ≤3% for DC distribution. Use XLPE-insulated, sunlight-resistant cables (e.g., PV1-F) rated for continuous DC voltage (UL 1703, EN 50618). Always verify polarity marking and arc-fault protection per NEC Article 690.71.

Voltage drop scales linearly with length (ΔU ∝ L), while current depends on P/V—so doubling distance doubles drop, but doubling power *or* halving voltage only increases current (and thus drop) proportionally. For instance, 10 kW at 400 V draws 32 A; at 230 V it draws 54 A—yet a 200 m run at 400 V may need 35 mm², whereas 100 m at 230 V might still require 25 mm² due to higher current density. Length also affects thermal dissipation: longer cables have greater total resistance (R = ρL/A), raising I²R losses and requiring larger A to stay within temperature limits (e.g., 70°C for PVC, 90°C for XLPE per IEC 60502).

Ambient temperature and installation method directly impact current-carrying capacity (Iz) via derating factors per IEC 60364-5-52 Table D.1–D.7. For example, a 16 mm² Cu/XLPE cable rated 92 A in free air at 30°C drops to 76 A at 50°C ambient (derating factor 0.83), or to 62 A when 6 cables are bundled in conduit (derating 0.67). Our calculator estimates minimum size for voltage drop only—not thermal limits. Thus, after obtaining the voltage-drop-driven size, you *must* cross-check against Iz tables, applying all relevant derating: ambient temp, grouping, enclosure type, soil thermal resistivity (for buried cables), and solar radiation. Failure risks insulation degradation, premature failure, or nuisance tripping.

Yes—rounding up is not just safe but mandatory per IEC 60228 and IEC 60364-5-52. Standard nominal cross-sectional areas for Cu cables are 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240 mm² (IEC 60228 Class 2). Never round down—even if calculation yields 12.3 mm², select 16 mm². Oversizing improves voltage regulation, reduces losses, extends lifespan, and accommodates future load growth. However, excessive oversizing wastes cost, complicates termination (larger lugs, bending radius), and may cause protective device coordination issues (e.g., too high a let-through energy for fuses). Always verify that the chosen size fits terminal chambers and complies with maximum conductor fill rules (e.g., 40% for conduits per NEC Chapter 9).