Voltage Drop Calculation Basis

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

Single-Phase % Voltage Drop = Calculated Current in Amps * Effective Z * (Wire Length / 1,000) * 100 * 2 / Line-to-Neutral Voltage

Effective Z = R cos(theta) + X sin (theta) (NEC Table 9 Note 2)

R = Resistance set in the Wire Ampacity command.

X = Reactance set in the Wire Ampacity command.

theta = Power factor of the electrical system.

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

The wire impedance values are based upon NEC Table 9. These values can be modified by the user using the Wire Ampacities command.

Feeder Values

Calculated Current in Amps is the Total Estimated Demand Current on the electrical equipment. This load is calculated by Revit based upon the loads connected to the electrical equipment and the demand factors.

Wire Length is the Feeder Length value for the panel. Set the feeder length using the Panel Edit command.

Branch Circuit Values

Calculated Current 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 Circuit Edit 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 the Panel Edit command or Family Edit command.

The voltage drop through transformers can be included, ignored, or reset to 0. Use the Transformer voltage drop calculation method option in the Options command to control how the voltage drop is calculated.


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