The surge impedance of an underground cable is significantly lower than overhead lines, usually around:
A40 to 50 ohms
B5 to 10 ohms
C1000 ohms
D400 to 500 ohms
Explanation
Underground cables have high capacitance because conductors are close together and dielectric constant is higher, reducing surge impedance Z_c = sqrt(L/C) to 40-50 ohms.

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