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Voltage Drop Calculations in Electrical System

Apr, 12,2024
Posted by: Admin

What is Voltage Drop in Electrical Conductor-

One of the basic principles of Electrical engineering is Ohm’s law, which states that the voltage drop across a conductor or load is equivalent to the product of current and resistance (V = I x R). The electric current is determined by the load on a circuit, while resistance is determined by the physical properties of the conductor.



A. Type of Conducting Material

Some materials are better electrical conductors than others. For example, copper is more conductive than aluminum.

B. Carrying Current material diameter

A wider conductor has improved conductivity, because there is more material to carry electric current.

C. Conductor size

Longer conductors have a higher resistance because current must travel a longer distance between the source and the load.

D. Conductor temperature

Temperature influences the conductivity of materials. Depending on the material and the actual temperature, conductivity may increase or decrease with further increases in temperature.

E. Current carried by the conductor

Current is directly proportional to voltage drop. If current is doubled while resistance is kept the same, voltage drop also doubles.

F. Connections in the circuit

A connection represents an interruption in the conductor material, and there is a contact resistance associated with it. Deficient connections are associated with an increased voltage drop.

The concept of voltage drop is used to describe the difference between the voltage supplied at the source and the voltage measured at the load.

How we can control voltage Drop In Electrical Systems-

  1. Improving Electrical System Out put
    Assuming load stays the same, increasing the efficiency of electrical equipment reduces power consumption. Since the supply voltage is constant, improved efficiency results in less current and a reduced voltage drop.

  2. Troubleshooting
    Some electrical issues cause an unnecessary increase in current or resistance, which leads to a higher voltage drop.  Once these issues are solved, voltage drop returns to normal.

  3. Correcting conductor sizes
    If the conductors in a circuit were not selected properly, they can experience a significant voltage drop. When selecting conductors, it is important to account for factors such as full-load current, ambient temperature, and the number of conductors in a raceway.

  4. Centralized electrical distribution
    If the main electrical distribution boards are located close to the centre of a building, Length of the wiring must be smaller distances to reach the different loads. This type of layout minimizes voltage drop. On the other hand, when the electrical shaft and panels are located at one end of the building, circuits must cross the entire construction to reach loads at the opposite side.

  5. Balanced load distribution
    Large Industrial buildings typically use three-phase circuits, which have three live conductors as implied by their name. If one phase is too highly loaded, it will also experience a larger current and increased voltage drop compared with the other phases.

These are specific measures that can be deployed to reduce voltage drop. Increasing conductor diameter

  • Decreasing load Current
  • Increasing the number of parallel conductors
  • Decreasing conductor length
  • Decreasing conductor temperature

How we can Calculate Voltage Drop-

It is important to note that the voltage drop formula changes depending on the number of phases in the circuit (single-phase or three-phase). In the following equations, the variables used are:

  • Z = Impedance of the conductor (ohms per 1,000 feet, or ohms
  • I = Load current (amperes)
  • L = Length (feet)



Single-phase system

Three-phase system

V Drop = 2 x Z x I x L / 1000

V Drop = 1.73 x Z x I X L / 1000

The formulas are divided by 1,000 because standard impedance values are provided for every 1,000 feet. This way, they are converted to ohms per feet. Conductor properties, based on a 75°C temperature rating.



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