Voltage Drop Calculation Basis
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Three-Phase % Voltage Drop = Calculated Load in Amps * Effective Z * (Wire Length / 1,000) * 100 / Line-to-Neutral Voltage
Single-Phase % Voltage Drop = Calculated Load in Amps * Effective Z * (Wire Length / 1,000) * 100 * 2 / Voltage
Effective Z = R cos(theta) + X sin (theta) (See NEC Table 9 Note 2)
R = Resistance set in the command.
X = Reactance set in the command.
theta = Power factor of the electrical system. This value is based upon the Voltage drop power factor option in the command.
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 using the command.
Calculated Load in Amps is the Total Estimated Demand Current on the distribution equipment. This load is calculated by Revit based upon the loads connected to the distribution equipment and the demand factors.
Wire Length is the Feeder Length value for the panel. Set the feeder length using the command.
Branch Circuit Values
Calculated Load in Amps is the the Apparent Current on the circuit. This load is calculated by Revit based upon the devices connected to the circuit.
Wire Length is the Circuit Length value for the circuit. Set the circuit length using the command. The voltage drop calculation assumes the entire circuit load is located this distance from the panel.
Transformer Voltage Drop Basis
The transformer impedance values are for dry-type indoor transformers. These values can be modified by the user using thecommand or command.
The voltage drop through transformers can be included, ignored, or reset to 0%. Use the Transformer voltage drop calculation method option in the command to control how the voltage drop is calculated.
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