Voltage Drop Limits by Standard — A Cheatsheet for Multi-Standard Projects

Voltage drop limits vary significantly between standards, and getting them wrong means failed compliance checks or oversized cables that blow the budget. This A4 portrait cheatsheet puts all four major standards side by side in a clear comparison table: NEC limits voltage drop to 3% for branch circuits and 5% total (feeder + branch), IEC 60364 allows 4% from the origin of the installation, AS/NZS 3008 permits up to 5% from the point of supply, and BS 7671 splits the allowance into 3% for lighting and 5% for other circuits from the origin. The cheatsheet clarifies where each standard measures from — the point of supply, the origin of the installation, or the service entrance — because this measurement origin is one of the most common sources of confusion on international projects. Below the comparison table you get the universal single-phase and three-phase voltage drop formulas (ΔV = I × L × (R cosφ + X sinφ) × 2 / 1000 for single-phase), maximum cable length tables for common sizes at unity power factor, and a quick-check method for estimating whether a cable run will pass before running the full calculation. A QR code links to our online voltage drop calculator.