Voltage Drop

Definition – Voltage drop is defined as the amount of voltage loss that occurs through all or part of a circuit due to impedance.

(Note: –   Impedance is the property of material that opposes the flow of current in the circuit. Impedance in the circuit includes resistance, inductance & capacitance).

In other words, same supply voltage will not appear across load as voltage drop occurs in the circuit due to impedance. Impedance is the net effect of resistance, inductance & capacitance offered by circuit.

Supply Voltage (Vs) = Voltage drop in line (Vd) + Voltage across the Load (VL ), or

Vs = Vd + VL


Voltage drop in the circuit can be measured by following equations –

So, for single phase system –     Vd  = 2 d l r t

for three phase system-    Vd = Г3 dlrt

Where – d = distance of one side of wire in ft,        I = Current in the circuit in Amp,

r= resistance of wire /1000 ft                 t = temperature in deg C