Voltage Drop Calculator - NEC

NEC voltage drop calculator. Copper & aluminum, 1-phase/3-phase, Tables 8 & 9.

NEC voltage drop calculator for electricians, apprentices, and electrical engineers. Calculate voltage drop instantly using official NEC Chapter 9 data — Tables 8 and 9. Supports single-phase and three-phase circuits with copper or aluminum conductors. Works 100% offline on the job site.

Whether you're running a long feeder to a sub-panel or checking branch circuit voltage drop for a commercial project, this voltage drop calculator gives you accurate NEC-compliant results in seconds. Enter your wire length and circuit distance to check voltage loss — use it as your feeder sizing tool for any run length.

VOLTAGE DROP CALCULATOR FEATURES:
• Single-phase and three-phase voltage drop calculations
• 5 voltage presets: 120V, 208V, 240V, 277V, 480V
• Copper and aluminum conductors: 14 AWG through 1000 kcmil
• 3 conduit types: PVC, Aluminum, Steel
• NEC Chapter 9 Table 9 effective impedance (Z) at power factor
• Custom power factor support (default 0.85)
• Voltage drop in volts and percentage
• PASS/FAIL indicator based on NEC 3% recommendation
• Recommends minimum wire size to meet 3% voltage drop threshold
• Shows voltage at load end

NEC VOLTAGE DROP REFERENCES:
• NEC 210.19(A) Info Note 4 — Branch circuit: max 3% voltage drop
• NEC 215.2(A) Info Note 2 — Feeder: max 3% voltage drop
• Combined feeder + branch: max 5% voltage drop
• Chapter 9 Table 8 — DC resistance at 75°C
• Chapter 9 Table 9 — AC resistance, reactance, effective Z

PRO FEATURES (one-time purchase):
• No ads — clean interface for professionals
• Save voltage drop calculation history
• Export calculations as PDF reports for permits and records
• Dark theme support

BUILT FOR ELECTRICIANS ON THE JOB SITE:
This voltage drop calculator is designed by electricians, for electricians. Enter your circuit parameters, see voltage drop instantly, and get a recommended wire size — no complicated menus or unnecessary features.

ACCURATE NEC VOLTAGE DROP DATA:
All resistance and reactance values are sourced from NEC Chapter 9. Effective impedance is calculated using Z = R·cos(θ) + XL·sin(θ) per the NEC method. Always verify voltage drop calculations against the official NEC code book before installation.

PERFECT FOR:
• Licensed electricians checking voltage drop daily
• Electrical apprentices studying for journeyman exams
• Electrical engineers and designers
• Electrical contractors bidding commercial and residential jobs
• Long feeder runs and sub-panel installations
• NEC code exam preparation

OFFLINE & PRIVACY:
• Works 100% offline — no internet needed on the job site
• No account required
• No data collection — your voltage drop calculations stay on your device

Simplify your voltage drop calculations on the job site.