How are transformers rated?

Transformers are rated in volt-amperes (VA) at the secondary side because this unit reflects the apparent power that a transformer can effectively handle. The VA rating indicates both the voltage and the current capacity of the transformer, providing a comprehensive understanding of its capability to carry electrical loads.

Using VA as the standard measurement is essential because it accounts for both voltage and current without distinguishing between the two, which is particularly important in AC systems where power factors can affect the actual power delivered. The VA rating is crucial for selecting the right transformer for specific applications where the load characteristics might vary.

This approach helps in ensuring that the transformer operates within safe limits and avoids overheating, which could lead to equipment failure. In contrast, ratings based on watts, volts, or amps alone would not provide as complete or accurate an assessment of the transformer's capabilities in real-world applications, particularly where loads may not be purely resistive.