If a transformer has a primary voltage of 480 volts and a secondary voltage of 240/120, where is the secondary voltage measured?

The secondary voltage of a transformer is measured on the secondary side, which is where the output of the transformer is located. In this case, the secondary voltage is specified as 240/120 volts, indicating that the transformer takes the higher primary voltage of 480 volts and steps it down to these lower voltages on the secondary side.

Measuring the secondary voltage on the secondary side ensures that the voltage reflects what is available to the loads connected to it. By measuring directly at the secondary terminals of the transformer, one can ensure accurate readings of the voltages that will be supplied to various circuits or equipment. This measurement is crucial for determining the operating voltage that equipment will receive, ensuring compatibility with electrical devices designed to operate at these voltages.

The other choices refer to locations that do not directly reflect the transformer’s secondary output voltage. The primary side measures the input voltage, the main service box might show aggregated voltages from various circuits, and the load distribution point could experience voltage drops due to line losses, making them less suitable for accurate measurement of the transformer's secondary voltage.