Voltage Drop
Affiliate link — we may earn a commissionVoltage drop is the loss of electrical pressure (voltage) that occurs as current flows through a wire over distance. Every wire has resistance, and that resistance converts some voltage into heat. The longer the wire and the thinner the gauge, the greater the drop. On a 100-foot 16-gauge extension cord carrying 12 amps, the voltage at the tool end drops from 120V to about 108V. The motor receives 10% less voltage, which reduces its power output and causes it to draw more current to compensate. This is why corded tool manuals specify maximum extension cord lengths by gauge.
Why It Matters
A table saw running at 108V instead of 120V bogs down on hardwood, the motor runs hotter, and the blade slows under load. Over time, low voltage damages the motor windings. For any tool over 10 amps, use the heaviest gauge cord you can, keep runs as short as possible, and avoid daisy-chaining multiple cords.