# How To Select Cable Size For Three Phase Motor

By | November 2, 2020

The selection of cable size for three phase motors is a critical step in the setup of any electrical system. It determines the amount of current that can flow through the motor, and it can be the difference between an efficient system and an unreliable one. With the right cable size selection, you can ensure your motor will operate at peak efficiency and reliability, while the wrong selection can lead to poor performance, failure, and even equipment damage.

Knowing how to select the correct cable size for a three-phase motor is essential for any electrical system. The motor’s power rating and the length of the cable run must both be taken into account when making this vital decision. This article will help explain the process of selecting the right cable size for a three phase motor, as well as provide tips for effectively inspecting existing installations and troubleshooting any issues that may arise.

When selecting a cable size for a three phase motor, the first step is to calculate the full load current of the motor. This can be done by multiplying the rated motor power (in kW) by 1000, then dividing the result by the supply voltage. For example, if the motor has a power rating of 7.5kW and its supply voltage is 400V, the calculation would be: 7.5 x 1000/400 = 18.75A. This means that the full load current of the motor is 18.75A.

Once the full load current of the motor has been calculated, the next step is to choose the appropriate cable size based on the cable's impedance, insulation type, and temperature rating. Generally speaking, cables should have an impedance that is no greater than 0.08Ω/m for single core cables, and 0.13Ω/m for multi-core cables. Additionally, the insulation used should be rated for at least 90°C.

In order to determine the exact cable size for a three phase motor, a voltage drop calculator should be used. This tool allows users to input the distance of the cable run, the full load current of the motor, and the voltage of the power supply. The calculator will then give the recommended cable size needed to achieve the desired voltage drop. It is important to note that the actual cable size used must be larger than the recommended value in order to account for circuit breakers, splicing, and other components in the system.

In addition to using a voltage drop calculator, it is important to inspect existing installations and make sure they are up to code. Cables should be properly labeled, and any splices or connections should be made securely. The insulation and jacketing of cables should also be inspected to ensure they are in good condition. If any issues are found, they should be addressed immediately to prevent any safety or operational hazards.

By following these guidelines, you can ensure the proper selection of cable size for three phase motors in your electrical system. With the right sizing, you can have an efficient and reliable system that will operate at peak performance for years to come.

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