The Extension Cord Is the Circuit: Cord Gauge, Explained

A 100 ft, 16 AWG cord powering a 13 A circular saw drops about 8 V — 6.7% — before the saw's inrush even starts. Add the building wiring's own drop and the saw sees 105 V on a good day. That is why it bogs in the cut and why the cord end is warm.

Cords are wire-sizing problems

Same physics, same formula, no conduit: Vd = 2 × I × L × R / 1000. The drop lives rent-free on top of whatever the branch circuit already loses, so a "passing" outlet plus a long skinny cord routinely totals 8–10% at the tool.

What each gauge actually delivers (13 A load)

• 16 AWG, 50 ft: ~4 V (3.4%) — light duty only.
• 14 AWG, 50 ft: ~2.5 V (2.1%) — fine for most tools.
• 12 AWG, 100 ft: ~3.9 V (3.3%) — the long-cord workhorse.
• 10 AWG, 100 ft: ~2.4 V (2.0%) — compressors and heaters at distance.

Motors take it personally

Universal-motor tools lose torque roughly with V²; induction motors compensate by drawing more current, which deepens the drop in a feedback loop and cooks start windings. Heaters merely run weaker — a 1500 W heater on that 16 AWG cord delivers about 1310 W.

Rule of thumb: 12 AWG for any cord past 50 ft, 10 AWG past 100 ft or for anything with a compressor. Verify any combination in seconds with the calculator — enter the cord length as the one-way distance.