Electrical Load / Cable Sizing Safety Calculator

Calculates full load current, a recommended minimum copper conductor size, and voltage drop, using NEC (National Electrical Code) Table 310.16 ampacities with ambient temperature and conductor-bundling derating.

Scope note: This tool implements NEC Table 310.16 for copper conductors, 10 AWG through 500 kcmil, in raceway/cable/earth, with standard ambient-temperature correction (310.15(B)(1)) and conductor-bundling adjustment (310.15(C)(1)). It does not cover 14/12 AWG branch circuits (subject to the NEC 240.4(D) small-conductor override rule), aluminum conductors precisely (shown only as an approximate 78% rule of thumb), parallel conductor runs, special occupancies, or IEC/BS 7671 methodology. Always verify final sizing against the complete code and a qualified electrical engineer before installation.

Load Details

Supply Phase

Load (kW)

Voltage (V) Line-to-line for 3-phase, line-to-neutral for single-phase.

Power Factor

Design & Installation Factors

Continuous Load Design Factor NEC 210.19/215.2 requires conductors sized at 125% of continuous load current.

Insulation Temperature Rating

Ambient Temperature (°C)

Current-Carrying Conductors in Raceway

Circuit Length & Voltage Drop

One-Way Circuit Length (feet) 1 metre ≈ 3.281 ft.

Full Load Current (A)

Design Current (A)

—

Min. Copper Conductor Size

Formula Reference

Full Load Current (1\u03c6) = (Load kW × 1000) ÷ (Voltage × Power Factor)
Full Load Current (3\u03c6) = (Load kW × 1000) ÷ (√3 × Voltage × Power Factor)
Design Current = Full Load Current × Design Factor
Adjusted Ampacity Required = Design Current ÷ (Ambient Correction Factor × Bundling Adjustment Factor)
Voltage Drop (1\u03c6) = (2 × I × L × R) ÷ 1000 | Voltage Drop (3\u03c6) = (√3 × I × L × R) ÷ 1000 (L in ft, R in Ω/kft)

Derating Factors Used (NEC 310.15)

Ambient 26–30°C	1.00
Ambient 31–35°C	0.94 (75/90°C) / 0.91 (60°C)
Ambient 36–40°C	0.88 (75/90°C) / 0.82 (60°C)
Ambient 41–45°C	0.82 (75/90°C) / 0.71 (60°C)
4–6 current-carrying conductors	0.80
7–9 current-carrying conductors	0.70
10–20 current-carrying conductors	0.50

Recommended maximum voltage drop is commonly cited as 3% for a branch circuit and 5% total (feeder + branch combined) — an NEC-referenced best-practice guideline, not a strict code maximum in most jurisdictions.

Based on NEC (National Electrical Code / NFPA 70) Table 310.16 and associated derating tables. This is a simplified planning calculator for a single, common installation scenario — it does not replace a full engineering calculation or IEC/BS 7671 methodology, and does not cover parallel conductors, special occupancies, or short-circuit withstand rating. Always verify final conductor and overcurrent protection sizing against the complete, current edition of the applicable electrical code, and have the design reviewed by a qualified electrical engineer before installation. For customized calculators tailored to your organization, please contact Impact Tech Solutions.