Voltage Drop: Causes, Solutions and Calculations

Voltage drop refers to the decrease in electrical potential (voltage) in an electrical circuit as current flows through it.

This phenomenon occurs because electrical conductors, such as wires and cables, have resistance, and when current flows through them, some of the electrical energy is converted into heat due to this resistance. The result is a drop in voltage along the length of the conductor.

We face a voltage drop when transferring electrical energy through long cables or transmission lines. For this reason, electrical energy is transferred with high voltages to overcome the voltage drop.

To mitigate voltage drop, electrical engineers and designers take into account factors like the length and gauge (size) of the conductors, the current load, and the electrical code requirements.

They may use larger wire sizes or employ voltage drop calculations to ensure that the voltage at the point of use remains within acceptable limits.

Voltage drop is an important consideration in electrical system design to ensure the safe and efficient operation of electrical circuits and devices.

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Voltage drop calculator android app
Voltage drop calculator android app


Voltage drop implications in electrical systems

Voltage drop can have practical implications in electrical systems. Excessive voltage drop can lead to several issues:

  1. Diminished Performance: In electrical circuits, especially in power distribution systems, a significant voltage drop can lead to reduced performance of devices and appliances connected to the circuit. For example, lights may appear dimmer, and motors may run less efficiently.

  2. Overheating: Voltage drop causes power losses in the form of heat. When voltage drop is excessive, it can lead to overheating of conductors, connectors, and electrical components, potentially causing damage or creating a fire hazard.

  3. Inaccurate Voltage Supply: Sensitive electronic equipment, such as computers or medical devices, may require a stable and precise voltage supply. Excessive voltage drop can result in these devices not operating correctly or even failing.

why does voltage drop occur?

cable size 70mm2 power cable
cable size 70mm2 power cable

Voltage drop occurs in electrical circuits primarily due to the resistance of the conductors and other components in the circuit. Several factors contribute to voltage drop, and they include:

  1. Conductor Resistance: The primary cause of voltage drop is the resistance of the conductors (wires, cables) through which current flows. All conductors have some level of resistance, and when current flows through them, a portion of the electrical energy is converted into heat due to this resistance. Ohm’s Law (V = I * R) describes the relationship between voltage (V), current (I), and resistance (R). As the current increases or as the resistance of the conductor increases, the voltage drop across the conductor also increases.

  2. Length of Conductors: Longer conductors have more resistance than shorter ones, leading to a higher voltage drop over the length of the wire. This is why it’s important to consider the distance between the power source and the load when designing electrical circuits.

  3. Conductor Material: Different materials have different resistivity values, affecting their resistance to the flow of electrical current. Copper and aluminum are commonly used conductors in electrical wiring, with copper having lower resistance than aluminum. The choice of conductor material can impact the magnitude of voltage drop.

  4. Current Load: The amount of current flowing through the circuit has a direct impact on voltage drop. Higher current loads result in larger voltage drops because they encounter more resistance in the conductors.

  5. Conductor Size (Gauge): The cross-sectional area or gauge of the conductor also affects its resistance. Larger-gauge conductors have lower resistance and therefore less voltage drop for a given current load. Choosing an appropriate conductor size is crucial in minimizing voltage drop.

  6. Temperature: Temperature can affect the resistance of conductors. As the temperature of a conductor increases, its resistance also tends to increase. This is especially important to consider in high-temperature environments.

  7. Connections and Junctions: Poorly made connections or splices in the electrical circuit can introduce additional resistance, leading to voltage drop. Loose or corroded connections are common culprits.

  8. Voltage Source Impedance: The impedance of the voltage source itself, such as a transformer or generator, can contribute to voltage drop in a circuit, especially if the source has a significant internal impedance.

To minimize voltage drop in electrical circuits, engineers and electricians carefully consider these factors during the design and installation process.

They may use thicker conductors, minimize circuit lengths, and ensure proper connections to maintain acceptable voltage levels at the load.

Calculations and standards provided in electrical codes are often used to determine acceptable levels of voltage drop for specific applications.

I’ve written a detailed article about How does cable sizing affect voltage drop, read it for more information.

Can a loose connection cause a Voltage drop?

Yes, a loose electrical connection can cause voltage drop in an electrical circuit. When a connection is loose, it creates additional resistance in the path of the electrical current.

This additional resistance leads to an increase in voltage drop across the connection, which can have several consequences:

  1. Voltage Drop: As current flows through the loose connection, it encounters higher resistance than it should. According to Ohm’s Law (V = I * R), an increase in resistance (R) will result in a higher voltage drop (V) for the same current (I).

  2. Heat Generation: Loose connections not only increase resistance but can also create localized hot spots due to the increased resistance. This can lead to overheating of the connection and nearby components, potentially causing damage or fire hazards.

  3. Intermittent Operation: Loose connections can sometimes cause intermittent electrical operation. The connection may momentarily disconnect when the resistance becomes too high, causing a loss of power or signal.

  4. Voltage Fluctuations: In some cases, loose connections may lead to voltage fluctuations, especially if they are in a critical part of the electrical system. These fluctuations can affect the proper operation of connected devices and equipment.

  5. Reduced Efficiency: In electrical circuits, efficiency is critical. Loose connections waste electrical energy as heat due to the increased resistance. This inefficiency can result in higher energy costs and may negatively impact the performance of electrical systems.

To prevent voltage drop and other issues caused by loose connections, it’s important to regularly inspect and maintain electrical connections.

Proper installation techniques, including tightening bolts, screws, or connectors to the manufacturer’s specifications, can help ensure secure and reliable connections.

Periodic inspections and preventive maintenance can detect and address loose connections before they lead to more significant problems in an electrical system.

How can we overcome Voltage Drop?

To address voltage drop issues in electrical circuits, there are several solutions and strategies that can be employed:

  1. Increase Conductor Size: Using larger-gauge conductors with lower resistance can reduce voltage drop. This is especially effective when dealing with long circuit runs or high-current loads.

  2. Reduce Circuit Length: Minimizing the distance between the power source and the load can significantly reduce voltage drop. This can involve rearranging the layout of the electrical system or placing the power source closer to the load.

  3. Higher Voltage Supply: Increasing the supply voltage can mitigate voltage drop. However, this approach is often used in larger electrical distribution systems, and it may not be practical or safe for all applications.

  4. Balanced Phases: In three-phase AC systems, ensuring that loads are evenly distributed among the phases can help reduce voltage drop. Balanced loads result in less voltage imbalance and drop.

  5. Voltage Regulators: For critical applications where a stable voltage supply is essential, voltage regulators can be employed to maintain the voltage at the desired level, compensating for voltage drop.

  6. Power Factor Correction: Improving the power factor of the electrical system can help reduce voltage drop. Power factor correction devices, such as capacitors, are used to offset inductive loads and improve the efficiency of power distribution.

  7. Minimize Connections and Junctions: Ensure that all connections and junctions in the electrical circuit are properly made and secure. Loose or corroded connections can introduce additional resistance and increase voltage drop.

  8. Use Low-Resistance Materials: Choose conductors and components with lower resistance. For example, copper conductors have lower resistance than aluminum, and high-conductivity materials can be used in connectors.

  9. Temperature Management: In environments where temperature can affect conductor resistance, consider temperature management solutions like proper insulation or cooling systems.

  10. Optimize Circuit Design: Work with an experienced electrical engineer or designer to optimize the circuit layout and design. This may involve rearranging loads, selecting the right conductor sizes, and minimizing unnecessary circuit extensions.

  11. Voltage Drop Calculations: Perform voltage drop calculations to determine the expected voltage drop in a circuit. This helps in making informed decisions about conductor size and circuit layout.

  12. Regular Maintenance: Conduct regular inspections and maintenance of electrical systems to identify and address any issues that may contribute to voltage drop over time.

  13. Voltage Stabilizers: In situations where voltage fluctuations are common, voltage stabilizers or surge protectors can help maintain a stable voltage supply to sensitive equipment.

  14. Smart Load Management: Implement smart load management systems that can adjust power distribution in real time to minimize voltage drop during peak demand periods.

  15. Consult Electrical Codes: Refer to local electrical codes and standards for guidance on acceptable levels of voltage drop for specific applications. Compliance with codes ensures safety and reliability.

The specific solution(s) chosen will depend on the nature of the electrical system, the extent of the voltage drop, and the criticality of the application.

It’s often advisable to consult with a qualified electrical engineer or electrician when dealing with voltage drop issues to ensure that the most appropriate and safe solutions are implemented.

Why Does Voltage drop with the increase of the load?

Voltage drop occurs with an increase in load in an electrical circuit due to the fundamental relationship described by Ohm’s Law, which states:

V = I * R


  • V: represents voltage (in volts)
  • I: represents current (in amperes)
  • R: represents resistance (in ohms)

When you increase the load on an electrical circuit, the current flowing through the circuit increases. Since the resistance of the conductors and components in the circuit remains relatively constant, an increase in current (I) will result in a corresponding increase in voltage drop (V).

In other words, as more current flows through the same conductors and components, they experience greater resistance, leading to a higher voltage drop.

Here’s a more detailed explanation:

  1. Resistance: Conductors, such as wires and cables, have resistance to the flow of electrical current. Resistance is an inherent property of materials, and it remains relatively constant for a given conductor under normal operating conditions.

  2. Ohm’s Law: Ohm’s Law describes the relationship between voltage (V), current (I), and resistance (R). According to Ohm’s Law, the voltage drop (V) across a conductor is directly proportional to the current (I) passing through it and the resistance (R) of the conductor. Therefore, if you increase the current while keeping the resistance constant, the voltage drop will increase proportionally.

  3. Increased Load: When you add more electrical devices or loads to a circuit, these devices draw additional current from the power source. This increased current flows through the same conductors, encountering the same resistance, resulting in a higher voltage drop along the circuit.

To address voltage drop issues caused by increased load, you may need to take steps to reduce the resistance or increase the conductor size (lower resistance) to ensure that the voltage at the load remains within acceptable limits.

This is especially important in situations where maintaining a stable voltage supply is critical for the proper operation of electrical equipment and devices.

voltage drop formula for cable

To calculate the voltage drop specifically for a cable in an electrical circuit, you can use the following formula:

Vd = (I * L * R * 2) / (1000 * K)


  • Vd is the voltage drop (in volts).
  • I: is the current in amperes (A) flowing through the cable.
  • L is the length of the cable in feet (ft).
  • R is the resistance of the cable material in ohms per 1000 feet (Ω/1000 ft).
  • K is the circular mils (CM) or circular mil area (CMA) of the cable’s cross-sectional area.

This formula is commonly used to calculate voltage drop in cables. Here’s how you can use it:

  1. Determine the current (I) flowing through the cable, which is the load current or the current drawn by the connected devices.
  2. Measure the length of the cable (L) in feet. If you’re working with meters, you can convert them to feet (1 meter ≈ 3.28084 feet).
  3. Find the resistance of the cable material (R) in ohms per 1000 feet. This value is typically provided in cable specifications or reference materials. It depends on the type and size of the cable.
  4. Calculate the circular mils (CM) or circular mil area (CMA) of the cable’s cross-sectional area. This involves knowing the cable’s diameter and the specific cross-sectional shape (e.g., round, flat).
  5. Plug the values into the formula to calculate the voltage drop (Vd).

Remember to consider the units consistently. The formula assumes that the length is in feet, the resistance is in ohms per 1000 feet, and the current is in amperes. The result will be in volts.

Please note that cable voltage drop calculations are important for ensuring that the voltage at the load remains within acceptable limits, especially in long cable runs or when dealing with high-current loads. Accurate voltage drop calculations are critical for proper electrical system design and performance.

Calculations of Voltage Drop Formula for Cable :

Let’s go through an example of how to calculate the voltage drop for a cable using the formula I provided earlier:

Suppose you have a 120-volt electrical circuit, and you want to calculate the voltage drop for a 100-foot length of 12-gauge copper wire (which has a resistance of approximately 1.588 ohms per 1000 feet) carrying a current of 10 amperes.

  1. Current (I): The current flowing through the cable is 10 amperes (I = 10 A).
  2. Length of Cable (L): The cable length is 100 feet (L = 100 ft).
  3. Resistance of the Cable (R): For 12-gauge copper wire, the resistance is approximately 1.588 ohms per 1000 feet. So, for 100 feet, the resistance is (1.588 Ω / 1000 ft) * 100 ft = 0.1588 ohms.
  4. Circular Mil Area (CMA): The circular mil area depends on the cable’s specific cross-sectional shape and size. Let’s assume a round cable with a CMA of 6530 circular mils.

Now, we can calculate the voltage drop (Vd):

Vd = (I * L * R * 2) / (1000 * K) Vd = (10 A * 100 ft * 0.1588 ohms * 2) / (1000 * 6530 circular mils)

Let’s calculate this step by step:

  1. 10 A * 100 ft = 1000 A*ft
  2. 0.1588 ohms * 2 = 0.3176 ohms
  3. (1000 A*ft * 0.3176 ohms) / (1000 * 6530 circular mils) = 0.0486 volts

So, the voltage drop for this 100-foot length of 12-gauge copper wire carrying a 10-ampere current is approximately 0.0486 volts or about 48.6 millivolts.

Keep in mind that this is a simplified example, and actual cable calculations may involve more complex factors, such as temperature, insulation, and frequency (for AC circuits). However, this calculation gives you a basic idea of how to estimate voltage drop in a cable for DC circuits. For more precise and detailed calculations, consult cable specification sheets and relevant electrical codes.

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