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Voltage Drop: Chapter 9, Table 9 Method

Effective Impedance = Ze = [R x COS(θ)] + [XL x SIN(θ)]

θ = Phase Angle, e.g. 31.79 degrees
COS(θ) = COS(31.79) = 0.85 (Which is PF, or Power Factor)
SIN(θ) = SIN(31.79) = 0.527
R = AC Resistance value from Table 9, e.g. 0.054 (See the 250 kcmil line for Steel Conduit)
XL = Reactance value from Table 9, e.g. 0.052 (See the 250 kcmil line for Steel Conduit)
Ze = [0.054 x 0.85] + [0.052 x 0.527] = 0.073 = Effective Impedance

3Ø Phase Voltage Drop, VD = (1.732 x Ze x I x L) / 1000
1Ø Phase Voltage Drop, VD = (2 x Ze x I x L) / 1000

Choose Length Measurement:
Choose Conduit Type:

Power Factor, "PF"
Length in Feet, "L"
Amperes, "I"
Source Voltage, "E"
Choose Wire Size, "CM"
Copper Wires

0.85 = Power Factor
31.799 = Phase Angle in Degrees = COS-1(0.85)
0.527 = SIN(Phase Angle) = SIN(31.799)
0.054 = XL for Wires in Steel Conduit
0.1 = R for Uncoated Copper Wires in Steel conduit
0.1135 = [0.1 x 0.85] + [0.054 x 0.527] = Ze at 0.85 PF for Uncoated Copper Wires

14.755 = (2 x 0.1135 x 65 x 1000) / 1000 = 1Ø VD, Copper Wires
3.1% = (14.755 / 480) x 1000 = 1Ø, Percent Voltage Drop, Copper Wires
465.245 = 480 - 14.755 = 1Ø Voltage at the Load, Copper Wires

12.778 = (1.732 x 0.1135 x 65 x 1000) / 1000 = 3Ø VD, Copper Wires
2.7% = (12.778 / 480) x 100 = 3Ø, Percent Voltage Drop, Copper Wires
467.222 = 480 - 12.778 = 3Ø Voltage at the Load, Copper Wires
Aluminum Wires

0.85 = Power Factor
31.799 = Phase Angle in Degrees = COS-1(0.85)
0.527 = SIN(Phase Angle) = SIN(31.799)
0.054 = XL for Wires in Steel Conduit
0.16 = R for Aluminum Wires in Steel conduit
0.1645 = [0.16 x 0.85] + [0.054 x 0.527] = Ze at 0.85 PF for Aluminum Wires

21.385 = (2 x 0.1645 x 65 x 1000) / 1000 = 1Ø VD, Aluminum Wires
4.5% = (21.385 / 480) x 100 = 1Ø, Percent Voltage Drop, Aluminum Wires
458.615 = 480 - 21.385 = 1Ø Voltage at the Load, Aluminum Wires

18.52 = (1.732 x 0.1645 x 65 x 1000) / 1000 = 3Ø VD, Aluminum Wires
3.9% = (18.52 / 480) x 1000 = 3Ø, Percent Voltage Drop, Aluminum Wires
461.48 = 480 - 18.52 = 3Ø Voltage at the Load, Aluminum Wires

Try the Chapter 9, Table 8 Voltage Drop Calculator and the Easy Voltage Drop Calculator.