Percent Voltage Drop

Volts lost only mean something relative to volts supplied: 6.9 V is a trivial loss on 4160 V and a serious one on 230 V, where it is 3%. The familiar limits — the NEC's informational 3% on a branch circuit and 5% overall, and similar figures in IEC and CEC practice — are recommendations aimed at equipment performance, not safety minimums, but designers treat them as hard rules because the consequences are real.

Undervoltage is unkind to motors in particular: torque falls with the square of voltage, so a motor at 90% voltage makes only 81% of its torque and pulls extra current to compensate, running hotter for it. Incandescent lamps dim visibly at a few percent, and electronic supplies simply draw more amps as voltage sags, deepening the drop. Note this solver's percent fields also accept a plain fraction.