On a transformer's nameplate, how is the rated power output expressed?

The rated power output of a transformer is expressed in kVA, which stands for kilovolt-amperes. This unit measures the apparent power, which takes into account both current (in amperes) and voltage (in volts) but does not consider the power factor, which is a reflection of how effectively the power is being used.

Transformers are typically rated in kVA because they are designed to handle both inductive and resistive loads. The kVA rating provides a clear and standardized way to denote the transformer's capability to deliver power without implying any specific power factor. Since the load connected to a transformer can vary, using kVA allows for a more universal interpretation of the transformer's capacity under different operating conditions.

In contrast, measuring power in watts would imply a specific efficiency and power factor, which is not always applicable for transformers across various applications. Amperes measure current and volts measure electrical potential, but neither reflects the full capacity of a transformer to deliver power over time like kVA does. Thus, kVA is the most appropriate and widely accepted unit used on a transformer's nameplate to convey its rated power output.