3 Phase Motor Cable Size Calculator

Quickly and accurately determine the correct cable size for your 3-phase motor installation. This tool calculates the full load current and recommends a cable that safely handles the current while limiting voltage drop, ensuring efficient and reliable motor operation. Essential for engineers, electricians, and maintenance professionals.

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Calculator

Cable Size Recommendation

Recommended Cable Size

2.5 mm² Copper

Full Load Current (FLC)

15.3 A

Calculated Voltage Drop

2.1%

Input Summary

  • Motor Power: 7.5 kW
  • Voltage: 415 V
  • Power Factor: 0.85
  • Efficiency: 88%
  • Cable Length: 50 m
  • Conductor: Copper
  • Installation: In Conduit
  • Max VD: 3%

Calculation Method

Based on IEC 60364-5-52 for current-carrying capacity and standard voltage drop formulas.

°C
The calculator will apply a standard temperature derating factor based on this input.

This calculator uses simplified tables based on IEC 60364. For other standards like NEC (National Electrical Code), consult the appropriate codebook.

How it works

The calculator follows two critical principles of electrical design. First, it ensures the chosen cable can carry the motor's full load current without overheating, accounting for installation conditions. Second, it verifies that the voltage drop over the cable length does not exceed a safe limit (typically 3-5%), which is crucial for motor performance and lifespan.

Inputs explained

  • Motor Power & Voltage: The basic electrical ratings of your motor.
  • Power Factor & Efficiency: These values, usually found on the motor's nameplate, are needed to accurately calculate the current draw.
  • Cable Length & Installation: Longer cables and poor heat dissipation (e.g., in a conduit) require larger cables to manage heat and voltage drop.

Example

For a 15 kW motor with a 415V supply, 50 meters away, installed in conduit, the calculator first determines the FLC is ~28A. It then checks a standard cable table and might initially suggest a 4 mm² copper cable. After calculating the voltage drop, it might find it's too high and recommend a 6 mm² cable instead to meet the 3% VD limit.

Tips & notes

  • Always round up to the next standard cable size if your calculation falls between sizes.
  • Aluminum conductors have a lower current-carrying capacity than copper of the same size.
  • This tool is a guide. Always cross-reference with official electrical codebooks and consult a licensed electrician for final design and installation.

FAQs

Full Load Current (FLC) is the current drawn by a motor when it is operating at its rated power, voltage, and frequency under full load conditions. It's a critical parameter for sizing cables and protective devices.

Excessive voltage drop can cause motors to overheat, operate inefficiently, or fail to start. It can also reduce the torque and speed of the motor, leading to performance issues and shortened lifespan.

A derating factor is a multiplier applied to a cable's current-carrying capacity to account for installation conditions that reduce its ability to dissipate heat, such as high ambient temperature, grouping of cables, or installation method.

Copper has better conductivity and smaller voltage drop than aluminum for the same size. However, aluminum is lighter and less expensive. For most applications, copper is preferred for its reliability and smaller size requirements.

No, this calculator is for educational and preliminary design purposes only. All electrical work must comply with local and national electrical codes and should be performed by a qualified and licensed professional.

Disclaimer

This calculator provides an estimate for educational and preliminary design purposes. It is based on simplified standards and does not account for all possible installation variables. All electrical work must comply with local and national electrical codes and should be performed by a qualified and licensed professional. CalculatorBolt is not liable for any damages or injury resulting from the use of this tool.

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About This Tool

The 3 Phase Motor Cable Size Calculator helps electrical engineers and electricians determine the correct cable size for motor installations. Reviewed by Electrical Engineer.