MTA Transit Electrical Helper (Exam No. 4612) Practice Exam

The correct choice, a potential transformer, is specifically designed to step down high voltages to a lower, more manageable level, allowing for safer measurement with instruments like voltmeters. When connecting a voltmeter to a high potential AC bus, it's essential to ensure that the voltage is reduced without losing the accuracy of the measurement. A potential transformer accomplishes this by providing a secondary output that is proportional to the high voltage input, thereby enabling the voltmeter to read a lower voltage that is safe for operation.

Using a potential transformer not only ensures safety but also maintains the integrity and precision of the voltage readings, making it the preferred choice in high-voltage applications. The transformer operates on the principle of electromagnetic induction, facilitating measurements of AC voltages without direct exposure to the high potential, which could be hazardous to both the equipment and the personnel involved.

Other devices, such as a standard transformer, might be used for voltage reduction in general applications, but they are not specifically optimized for measurement purposes. Shunts are typically used for current measuring and not voltage. Resistors can be used to limit current or create voltage dividers, but they are not suitable for direct measurement of high AC voltages without risking damage to the measuring instrument or introducing inaccuracies. Therefore, the