Voltage Drop Calculation Method

Three-Phase % Voltage Drop = Load in Amps * Effective Z * (Wire Length / 1,000) * 100 / Line-to-Neutral Voltage

Single-Phase % Voltage Drop = Load in Amps * Effective Z * (Wire Length / 1,000) * 100 * 2 / Voltage

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 = R * Power Factor + X sin (acos(Power Factor)) (See NEC Table 9 Note 2)

R = Resistance set in the Wire Sizing command.

X = Reactance 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 by the user.

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


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