Power Calc Toolsv0.1 · beta

Voltage Drop Calculator — NEC 2023

AC voltage drop for feeders and branch circuits, 14 AWG to 1000 MCM, copper or aluminum. Pass-fail against the NEC 3 % and 5 % Informational Notes with minimum-size recommendation.

AssumptionsPVC conduit·75 °C conductor temp·stranded, single circuit·no temperature derating
Circuit
Live · updates with inputs
SOURCE480 V150 A3/0 AWG Cu · 200 ft−4.88 V (1.02%)LOAD475.12 V200 ft (one-way)
Inputs
Voltage drop
1.02%4.88 V
0 %95 %97 %100 %
3 % branchPass
5 % feederPass
Receiving-end voltage475.12 V
Power lost in wire1,034 W
Min size for 3 %3 AWG
Min size for 5 %6 AWG

NEC 210.19 / 215.2 voltage-drop limits are Informational Notes — recommendations, not code-mandatory. Check your AHJ.

Disclaimer. This tool is provided for preliminary sizing and engineering reference only. Results depend on assumptions about temperature, installation method, and harmonic content that may not match your installation. Always verify with a licensed professional engineer and the applicable national wiring standard (NEC, IEC, CEC, AS/NZS, etc.) and local Authority Having Jurisdiction before construction.

Frequently asked questions

What is a voltage drop calculation?

Voltage drop is the loss of voltage along a conductor due to its impedance. For NEC the formula isVd = b × I × L × Z / 1000 / setswith Z in ohms per 1000 ft. For IEC,Vd = b × (R cosφ + X sinφ) × I × L / 1000 / setswith R, X in mΩ/m and L in metres. b = 2 for single-phase and √3 (≈1.732) for three-phase.

Should I use NEC or IEC mode?

Use NEC for installations in the United States and jurisdictions that adopt NFPA 70 (typical voltages 120 / 208 / 240 / 277 / 480 / 600 V, conductors sized in AWG and MCM). Use IEC for projects that follow IEC 60364 or a national standard derived from it — most of Europe, the UK (BS 7671), Australia / New Zealand (AS/NZS 3000), and many parts of Asia and the Middle East. The typical IEC voltages are 230 V single-phase and 400 V three-phase, with conductors sized in mm².

Is the NEC 3 % / 5 % voltage drop limit mandatory?

No. The 3 % branch-circuit limit (NEC 210.19) and the 5 % combined feeder-plus-branch limit (NEC 215.2) are Informational Notes — recommendations, not code-mandatory rules. Check with your Authority Having Jurisdiction (AHJ) for local requirements.

What are the IEC voltage drop limits?

IEC 60364-5-52 Annex G suggests a maximum voltage drop of 3 % for lighting circuits and 5 % for other uses (appliances, motors, general purpose), measured from the origin of the installation to any point of utilisation. These are guidance values; national wiring regulations (for example BS 7671 in the UK) may impose stricter limits.

Which impedance data does this calculator use?

NEC mode uses NEC 2023 Chapter 9 Table 9 AC effective impedance, linearly interpolating between the 1.0 and 0.85 power-factor columns. IEC mode uses IEC 60364-5-52 reference values for R (at 70 °C) and X for PVC-insulated single-core cables under reference method C, combined as R cosφ + X sinφ.

Does the calculator account for temperature and installation method?

Only implicitly. Table 9 (NEC) and the IEC reference values assume typical operating temperatures (≈75 °C for NEC, 70 °C for IEC PVC) and representative cable geometries. Resistance rises roughly 0.4 % per °C above these baselines, and reactance can shift by 10 – 30 % for very different installations (for example widely-spaced single cores in free air vs. a tightly bundled multi-core cable). For high-stakes designs, apply the temperature and geometry corrections from the full tables rather than the simplified values used here.