Handbook of Electric Power Calculations, Third Edition
A powerful calculations tool for electric power engineers and technicians, this book offers essential, step-by-step procedures and examples for solving a wide array of electric power problems.
TABLE OF CONTENTS Handbook of Electric Power Calculations, Third Edition
CONDUCTOR RESISTANCE
CONDUCTOR RESISTANCE
Calculate the resistance of 1000 ft (304.8 m) of solid round aluminum conductor, type EC-H19 (AWG No.1) at 20 and 50 C. The diameter=0.2893 in. (7.35 mm).
Calculation Procedure
1. Calculate Resistance at 20 C
Use R= ? l/ A, where R is the resistance in ohms, ? is the resistivity in ohm-circular mils per foot ( ? cmil/ft), l is the length of conductor in feet, and A is the area in circular mils (cmil), which is equal to the square of the conductor diameter given in mils. From Table 9.1, the percentage of conductivity for EC-H19 is 61 percent that of copper. For IACS copper, ?=10.4 ? cmil/ft. Therefore, for aluminum, the resistivity is 10.4/0.61=17.05 ? cmil/ft. The resistance of the conductor at 20 C is R=(17.05)(1000)/289.3 2=0.204 ?.
2. Calculate Resistance at 50 C
Use R T= R 20 [1+ ?( T 20 )], where R T is the resistance at the new temperature, R 20 is the resistance at 20 C, and ? is the temperature coefficient of resistance. From Table 9.1, ?=0.00403. Hence, R 50 =0.204[1+0.00403(50 20)]=0.229 ?.
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