Feeder voltage drop percentage calculator

It is useful after a conductor, circuit, or feeder calculation has already produced the absolute voltage loss and you need the normalized figure used in design reviews, schedules, and reports. Enter both values in volts, and the calculator applies the standard ratio, returns a clearly labeled percentage, and preserves the original inputs for an easy audit trail.

Turn an absolute voltage loss into a comparable percentage

A voltage drop stated only in volts does not tell the whole story. A loss of six volts has a very different meaning on a 120-volt system than it does on a 480-volt system. The percentage puts the calculated loss in context by comparing it with the nominal system voltage. Supply the previously calculated feeder drop in volts as calculated_voltage_drop_v, then provide the system rating in volts as nominal_system_voltage_v. The calculator divides the first value by the second and multiplies the ratio by 100. For example, a drop of 7.2 volts on a 240-volt system is 3 percent. This capability does not estimate the drop from conductor size, material, current, power factor, or length. Those values belong in an upstream feeder or conductor calculation. Its deliberately narrow job is to normalize an existing voltage-drop result, making results from systems with different nominal voltages easier to compare consistently in a worksheet, design note, or automated engineering workflow.

Choose inputs that describe the same feeder condition

Both inputs must refer to the same operating case. If the absolute voltage drop was calculated at a particular load, conductor temperature, route length, phase arrangement, and power factor, the percentage represents that same case; changing only the nominal voltage does not create a new electrical calculation. Use volts for both fields and use the nominal voltage that forms the intended comparison basis in your project documentation. Do not enter a percentage in the voltage-drop field, and do not substitute the measured receiving-end voltage for nominal system voltage unless that is explicitly the basis required by your method. The voltage drop may be zero, which correctly returns zero percent. The nominal system voltage must be greater than zero because division by zero has no physical or mathematical meaning. Negative drops are rejected because this tool expresses loss magnitude rather than voltage rise. A result over 100 percent is not hidden or clipped; it usually signals an unsuitable, extreme, or incorrectly assembled input case that deserves review.

Interpret and document the result responsibly

The returned voltage_drop_percent is rounded to six decimal places for stable reporting and repeatable automation. The response also includes the two accepted voltage values, so a saved result remains understandable without reconstructing the request. Compare the percentage with the design criterion, specification, or rule that actually governs your installation. The calculator does not declare pass or fail because allowable voltage drop depends on jurisdiction, equipment, circuit purpose, design stage, and the standard or client requirement being applied. It also does not determine whether the nominal voltage should be phase-to-phase or phase-to-neutral; use the same basis that was used for the absolute drop calculation. In automated workflows, store the upstream assumptions with this result and avoid treating the rounded percentage as a substitute for the underlying electrical model. The browser version performs the same deterministic arithmetic as the API. Interactive use is free on the page, while programmatic API execution is available for $0.002 per request when you need repeatable calculations in schedules, checks, or report generation.