You are working for Pacific Power company. An underground high voltage power sup

Question

You are working for Pacific Power company. An underground high voltage power supply cable has failed. Preliminary measurements suggest that the insulating wrap around the HV wire was faulty and the HV wire became connected to the neutral or ground wire in the cable. The high current produced enough heat to weld the two wires together. Of course, this failure happened somewhere along the wire under the ground. At the cable end you connect a 12 V car battery to the two wire ends and measure a current flow of 6 A.

1) Where do you instruct the repair crew to dig to find the problem? The wires are AWG 4 wires. (Look up the resistance/length for the AWG 4 wire size on wikipedia)

Explanation / Answer

4AWG =  2.5947 mm radius

voltage = 12 V

current = 6 A

Resistance = 12/6 = 2 ohm

R = resistivity * length / area

length = 2* pi* [(2.5947)^(-3)]^2 / Resistivity

at this length dig the groung.

put value of resistivity of the material used in wire and get the answer.

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