Electrical Wire Size & Voltage Drop Calculator (NEC Table 310.16)
Calculate minimum AWG copper/aluminum wire gauge, continuous load derating, and voltage drop compliance per NEC codes.
Circuit Parameters & Electrical Load
NEC 2023 / 2026Mandatory for EV chargers, space heaters, solar inverters, and commercial lighting.
NEC Informational Note 210.19: Recommend ≤ 3%
3.69 V
Loss on conductors236.3 V
From 240V sourceCalculations adhere strictly to NEC Table 310.16 ampacity ratings,NEC 210.19(A) branch circuit conductor sizing, and NEC 240.4(D) small conductor overcurrent protection rules (14 AWG = 15A max, 12 AWG = 20A max, 10 AWG = 30A max).
About This Calculator & Field Methodology
Professional electrical wire sizing and voltage drop calculator based on National Electrical Code (NEC 2023/2026) Table 310.16. Analyzes single-phase and 3-phase circuits, calculates 125% continuous load requirements, checks copper vs aluminum conductors across 60°C/75°C/90°C thermal ratings, and automatically bumps wire gauge to keep voltage drop under the recommended 3% threshold over long conduit runs.
Standard formulas derived from international trade engineering standards (NEC Table 310.16, ACCA Manual J 8th Ed, ACI Concrete Mix Manual). Actual physical installations may require local authority having jurisdiction (AHJ) approval.
ToolHub Trade Engineering Team
Master Electrician & Electrical Engineer · Master Electrician License & IEEE Member
Strict compliance with NEC, ACCA, and ACI code standards.
Frequently Asked Questions
Q:What is the maximum allowable voltage drop under the NEC?
The National Electrical Code (NEC Informational Note 210.19(A) and 215.2(A)(1)(b)) recommends a maximum voltage drop of 3% for any branch circuit, and no more than 5% total drop across both the feeder and branch circuit combined. Exceeding 3% causes motor overheating, dimming lights, and reduced lifespan of sensitive electronics.
Q:When must I apply the 125% continuous load factor?
Per NEC Article 100, any electrical load where the maximum current is expected to run continuously for 3 hours or more (such as commercial lighting, EV chargers, water heaters, and electric resistance heating) is considered a continuous load. Overcurrent protection devices (circuit breakers) and conductors must be sized to at least 125% of the continuous load plus 100% of the non-continuous load.
Q:Why does Aluminum wire require a larger gauge than Copper?
Aluminum has higher electrical resistivity (K ≈ 21.2 ohms-cmil/ft) compared to Copper (K ≈ 12.9 ohms-cmil/ft). To carry the same amperage safely without overheating and with equivalent voltage drop, aluminum conductors must be roughly two AWG sizes larger than copper (for example, a 100A feeder requires #4 AWG Copper or #2 AWG Aluminum).
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