Voltage Drop Calculation Method

$$Three-Phase\>\%\>Voltage\>Drop = {{Load\>in\>Amps \times Effective\>Z \times {Wire\>Length \over 1,000}} \over Line-to-Neutral\>Voltage} \times 100$$ $$Single-Phase\>\%\>Voltage\>Drop = {{Load\>in\>Amps \times Effective\>Z \times {Wire\>Length \over 1,000} \times 2} \over Voltage} \times 100$$

$Load\>in\>Amps$ 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.

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

(Visit NEC Table 9 Note 2)

$Resistance$ and $Reactance$ are set in the Wire Sizing command.

$Power\>Factor = 0.85$

$Line-to-Neutral\>Voltage$ 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."

$Voltage$ 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.