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Voltage Drop Calculation Method

ThreePhase%VoltageDrop=LoadinAmps×EffectiveZ×WireLength1,000LinetoNeutralVoltage×100Three-Phase\>\%\>Voltage\>Drop = {{Load\>in\>Amps \times Effective\>Z \times {Wire\>Length \over 1,000}} \over Line-to-Neutral\>Voltage} \times 100 SinglePhase%VoltageDrop=LoadinAmps×EffectiveZ×WireLength1,000×2Voltage×100Single-Phase\>\%\>Voltage\>Drop = {{Load\>in\>Amps \times Effective\>Z \times {Wire\>Length \over 1,000} \times 2} \over Voltage} \times 100

LoadinAmpsLoad\>in\>Amps is different for feeders and branch circuits. For feeders, it is the calculated load on the panel assuming a balanced load. For branch circuits, it is based upon the connected load.

EffectiveZ=(Resistance×PowerFactor)+(Reactance×sin(arccos(PowerFactor)))Effective\>Z = \Big(Resistance \times Power\>Factor\Big) + \Big(Reactance \times \sin\big(\arccos(Power\>Factor)\big)\Big)

(See NEC Table 9 Note 2)

ResistanceResistance and ReactanceReactance are set in the Wire Sizing command.

PowerFactor=0.85Power\>Factor = 0.85

LinetoNeutralVoltageLine-to-Neutral\>Voltage is used for three-phase calculations based upon NEC Table 9 Note 2: "Multiplying current by effective impedance gives a good approximation for line-to-neutral voltage drop."

VoltageVoltage is the line-to-neutral voltage for single-pole circuits and line-to-line voltage for two-pole circuits.

The feeder impedance values are based upon NEC Table 9. These values can be modified.

The transformer impedance values are for dry-type indoor transformers. These values can be modified.