The Impact of Power Cable Length on Electrical Performance and Ampacity

Power cables are an essential component of any electrical system that transmits high-voltage power from one location to another.

The length of the power cable can significantly affect the electrical performance of the system, including its ampacity and the performance of connected electrical equipment.

In this article, we’ll explore the effects of power cable length on electrical performance, how it affects different types of power cables, and what you can do to minimize its impact.

Understanding Power Cable Length

Power cable length refers to the distance between two points where the cable is connected to a power source or a device.

It is usually measured in feet or meters. The length of the power cable can impact the electrical performance in different ways, depending on the type of cable, its material, and the frequency of the power it carries.

Effects of Power Cable Length on Ampacity

The ampacity of a power cable refers to the maximum amount of electrical current that the cable can carry without exceeding its temperature rating. Read my comprehensive article Cable ampacity her for more information.

The longer the power cable, the higher its resistance, which can lead to an increase in temperature and a reduction in ampacity. This can affect the performance of the system, especially in applications that require a high level of current.

To prevent overheating and ensure optimal performance, it’s important to choose a cable with a suitable ampacity rating for the application and to consider the impact of cable length on ampacity.

Impact on Electrical Equipment Performance

Power cable length can also affect the performance of connected electrical equipment.

When a long power cable is used, there may be a voltage drop across the cable, which can result in reduced power output and inefficient operation of the equipment. This can lead to equipment failure, reduced lifespan, and increased maintenance costs.

Additionally, longer cables may also be more susceptible to electromagnetic interference, which can further impact equipment performance.

Read my in-depth article Impact of distance on voltage drop, for more information about how cable length impact electrical systems.

Minimizing the Impact of Power Cable Length

Minimizing the Impact of Power Cable Length on Electrical Performance To minimize the impact of power cable length on electrical performance, there are several things you can do.

One of the most effective ways is to use high-quality cables with low resistance, impedance, and capacitance. You can also use thicker cables or increase the number of cables to reduce the resistance and impedance.

Additionally, you can use cable shielding to reduce electromagnetic interference from other cables and external sources.

It’s also important to consider the ampacity rating of the cable when selecting a suitable cable for the application.

how to overcome the impact of cable length on ampacity by derating the cable

When a cable is used over a longer distance, its electrical resistance increases due to the length of the cable. This results in a voltage drop along the cable length which can lead to a decrease in the amount of current that can be carried by the cable.

This is referred to as “ampacity derating“. Derating refers to the practice of reducing the maximum current that a cable can carry to compensate for the impact of the cable length on its electrical performance.

Ampacity derating is important to ensure that the cable does not exceed its maximum temperature rating due to the increased electrical resistance caused by the cable length.

Exceeding the maximum temperature rating can lead to cable failure or other hazards. Derating is typically done in accordance with industry standards and regulations, and is an important consideration when selecting cables for use in a particular application.

The amount of ampacity derating required will depend on the length of the cable, the type of cable, the ambient temperature, and the current carrying capacity of the cable.

Want to learn more? Read my detailed article about Cable derating factors.


Power cable length can significantly impact the electrical performance of a system, including its ampacity and the performance of connected electrical equipment.

By understanding these effects and taking measures to minimize their impact, you can ensure the optimal performance of your electrical system and equipment.