Power lines have a limit on the maximum size of the electric field they produce. In most states a maximum of 4 kN/C at about 21 m from the wires is allowed. This is quite large compared to the Earth's fair-weather electric field of about 100 N/C. Assume that the charge on the wire is static (not true, but a simplification here) and use the formula for the electric field for a wire (E = 2k/r) to determine how much charge per unit length is on the wire.