U=I*R. First, we will need to calculate the resistance value of the line, which is calculated by r=PL/S. “P” represents the resistivity of the line material. For example, the resistivity of the copper line is normally 0.0175 per meter. “L” is the length of the line (m), and “S” is the cross-sectional area of the line (mm2). Then we will use i=P/u to calculate the current. P is the power of the light, and u is the voltage of the line. After we know the current and the resistance value, we can use U=I*R to calculate the voltage drop.
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