What unit are transformers rated in?

Transformers are rated in Volt-Amperes (VA) because this unit reflects the apparent power that a transformer can handle regardless of the power factor. The VA rating indicates the maximum amount of current the transformer can supply at a given voltage without exceeding its thermal limits.

It's important to note that while transformers can transfer power in terms of watts when considering resistive loads, the VA rating accounts for both resistive and reactive power components in an AC circuit. This is crucial since the performance of transformers is influenced by the phase difference between voltage and current in an AC system, particularly when inductive or capacitive loads are involved.

Using watts to rate a transformer would limit the understanding of its capabilities in all types of AC scenarios, which is why Volt-Amperes (VA) is the preferred and standardized measurement in electrical engineering for transformers.