Calculate Voltage Drop – Understanding Voltage Drop

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How to calculate voltage drop? Because of the nearness of the impedance or inactive components, there will be some loss in voltage as the current moves through the circuit. That is, the energy provided from the voltage source will get diminished as the current flows through the circuit. Too much voltage drop may result in damage and inappropriate capacity of the electrical and electronics apparatus. Basically, the voltage drop calculation is done by Ohm’s law.

In direct current circuits, the reason for voltage drop is the resistance. For understanding the voltage drop in DC circuit, we can take an example. Assume a circuit which consist of DC source, 2 resistors which are connected in series and a load.

Calculate Voltage Drop – Understanding Voltage Drop

Here; each component of the circuit will have a specific resistance, they get and lose energy to some value. But the main factor of the estimation of energy is the physical highlights of the components.

When we measure the voltage across the DC supply and first resistor, we can see that it will be not exactly the supply voltage. We can calculate, the energy devoured by every resistance by estimating the voltage crosswise over individual resistors.

While the current flows through the wire starting from the DC supply to the first resistor, some energy that is given by the source gets dissipated owing to the conductor resistance. To verify the voltage drop, Ohm’s law and Kirchhoff’s circuit law utilized which are advised beneath. Ohm’s law is spoken to by:


V → Voltage Drop (V)

R → Electrical Resistance (Ω)

I → Electrical Current (A)

For DC closed circuits, we also use Kirchhoff’s circuit law for voltage drop calculation. It is as follows: Supply Voltage = Sum of the voltage drop across each component of the circuit.

See Also: Self Inductance: Definition and Explanation

Voltage Drop Calculation of a DC Power Line

Here, we are taking an example of 100 ft power line. So; for 2 lines, 2 × 100 ft. Let Electrical resistance be 1.02Ω/1000 ft and current be 10 A.

Voltage Drop in Alternating Current Circuits

In AC circuits; in addition to Resistance (R), there will be a second opposition for the flow of current – Reactance (X) which includes of XC and XL. Both X and R will contradict the current flow also the sum of the two is named as Impedance (Z).


XC → Capacitive reactance

XL → Inductive reactance

The amount of Z relies upon the elements, for example, attractive porousness, electrical separating components and the recurrence of AC. Like Ohm’s law in DC circuits, here it is given as:


E → Voltage Drop (V)

Z → Electrical Impedance (Ω)

I → Electrical Current (A)

See Also: Inductor: Definition, Theory and Types

Circular Mils and Voltage Drop Calculation

Circular mil is really a unit of area. It is utilized for alluding the round cross sectional region of the wire or conveyor. The voltage drop utilizing mils is given by:


L → Wire length (ft)

K → Specific Resistivity (Ω-circular mils/foot).

P → Phase constant = 2 meant for single phase = 1.732 meant for three phase

I → Area of the wire (circular mils)

See Also: Variable Resistor: Definition, Function and Types

Voltage Drop Calculation Conclusion

After going through the above portion of voltage drop calculation, now we know how to calculate voltage drop, is it easy, right? I hope you enjoy when reading this article, thank you.

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