Percent Voltage Drop
Worked example: 6.9 V lost on 230 V → 3% — press Try an example to run it live, then adjust anything.
Enter your known values, leave one input blank, and solves for the missing one. Tap a variable’s symbol to see what it means, with a typical value. Try different units for next level excitement!
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Percent Voltage Drop explained
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.
Percent Voltage Drop formula
- = Percent voltage drop (%)
- = Voltage drop (V)
- = Supply voltage (V)
Missing one of these? Work it out first, then come back
- Percent voltage drop — Available Short-Circuit Current from Percent Impedance, Transformer Percent-Impedance Voltage Drop
- Voltage drop — Voltage Drop, Single Phase, Voltage Drop, Three Phase
- Supply voltage — LED Series Resistor, RC Capacitor Charging