SELLC Engineering Calculators

Voltage drop

Check a conductor you have already selected. See the drop in volts and per cent, the estimated voltage at the load, and how the run compares with your design target.

Circuit and conductor

The load

Voltage across the two supply wires for single-phase; line-to-line for three-phase. Up to 600 V.

Line current at the operating load, without a 125 % continuous-load sizing factor.

Enter 0 to 1; use 1 for a resistive load.

A chosen design target for this run; meeting it does not establish code compliance.

The run

Supply to load only. The single-phase return path is already included.

One conductor per phase; no parallel sets. Impedance at 75 °C and 60 Hz.

Result

Loading calculator. If this message remains, reload the page to load the calculation scripts.

Preliminary calculations only. Not for construction. This checks voltage drop only. Check ampacity, overcurrent protection, grounding, and applicable installation requirements separately.

Method & limits

The calculator uses the same generated NEC Chapter 9 Table 9 resistance and reactance data and voltage-drop function as the conductor-size calculator. The result names the edition in that data file. Verify table values against the adopted Code before using them for design.

ΔV = K × I × L × (R × PF + X × √(1 − PF²)) / 1000. K is 2 for a single-phase two-wire circuit and √3 for balanced three-phase. I is line current in amperes, L is one-way length in feet, and R and X are ohms per 1,000 feet. Metres are converted using 1 ft = 0.3048 m.

This is an approximate steady-state AC calculation using 600 V cable impedance at 75 °C and 60 Hz. Table 9 assumes three single conductors in conduit; applying its values to a two-wire circuit is an approximation. Aluminum raceway uses its own resistance column and the nonmagnetic (PVC) reactance column.

Receiving voltage is supply voltage minus the calculated drop, on the same voltage basis. The model excludes DC, leading power factor, unbalanced or shared-neutral circuits, parallel conductors, motor starting, harmonics, and source or transformer impedance. It does not model constant-power loads changing current as voltage falls.

The default 3 % target is editable and is not a universal Code requirement. This result covers only the entered run; include upstream drop when evaluating a complete feeder and branch circuit.