Transformer Secondary Wire Size Calculator

Introduction: The Transformer Secondary Wire Size Calculator is a valuable tool for electricians and individuals involved in transformer installations. This calculator simplifies the process of determining the appropriate wire size for the secondary winding of a transformer based on the secondary voltage, transformer VA rating, and the maximum allowable wire length. Ensuring the correct wire size is crucial for minimizing voltage drop and optimizing performance.

Formula: The recommended secondary wire size is calculated using the formula: (Transformer VA Rating * 2) / (Secondary Voltage * Max Wire Length * 0.866). The result is rounded up to the nearest whole number to provide a practical wire size in American Wire Gauge (AWG).

How to Use:

  1. Enter the secondary voltage of the transformer in volts.
  2. Input the VA rating of the transformer.
  3. Enter the maximum allowable wire length in feet.
  4. Click the “Calculate” button to obtain the recommended secondary wire size in AWG.

Example: If the secondary voltage is 120 volts, the transformer has a VA rating of 1000, and the maximum wire length is 50 feet, enter these values into the calculator, click “Calculate,” and the result will provide the recommended secondary wire size in AWG.


  1. Q: Why is it important to choose the correct secondary wire size for a transformer? A: Choosing the correct wire size ensures minimal voltage drop, efficient power transfer, and compliance with safety standards.
  2. Q: Can I use this calculator for different types of transformers? A: This calculator is suitable for general use with transformers. Ensure that the specific transformer characteristics are considered for accurate results.
  3. Q: What is the significance of the 0.866 factor in the formula? A: The factor accounts for the root mean square value of a sine wave and is used to adjust for AC resistance in the wire.
  4. Q: Why is wire length a factor in determining the wire size? A: Longer wire lengths result in higher resistance, and choosing the right wire size helps compensate for this resistance and minimize voltage drop.
  5. Q: Can I use a wire size smaller than the recommended value? A: It’s essential to follow the recommended wire size to ensure safe and efficient operation. Using a smaller size may lead to excessive voltage drop and overheating.

Conclusion: The Transformer Secondary Wire Size Calculator is a valuable resource for professionals involved in electrical installations. Use this calculator to determine the recommended secondary wire size, promoting safe and efficient operation of transformers in various applications.

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