1. A dc power distribution cable has two #6 copper wires. The copper wire table
ID: 1846469 • Letter: 1
Question
1. A dc power distribution cable has two #6 copper wires. The copper wire table in the textbook lists each wire as having resistance of Ro=.4028 ohms per thousand feet at temperature of 25C. The temperature coefficient of copper is alpha=.004 per C. IF the cable is expected to operate at 75C, then the resistance would be R = Ro +Ro(alpha)(delta*T), where delta*T=50C is the temperature rise above 25C. If the cable is 455 feet long, calculate the resistance of each wire at 75C. Calculate the total cable resistance due to both wires.
2. A DC source of 48V is connected to one end of the cable. The other end of the cable supplies a DC load. If the load current is 12.5 A, calculate the voltage drop due to the cable resistance and the laod voltage. Assume the cable temerature is 75%C. Sketch the circuit and label all the voltages on the sketch.
Explanation / Answer
A) Resistance of each wire =(.4028/1000)*455=0.183274 ohm at 25 centigrade
Resistance of wire at 75 C=0.183274*(1+.004 *(75-25))=0.219928 ohms
Resistance of cable is =r/2 as two wires are in parallel =0.1099644 ohms
b)Voltage drop in cable is R*I =0.109964*12.5 =1.374555 VOLTS
Voltage across load =48-1.374555=46.625445 volts
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