When checking the voltage at an AC motor's terminals, which instrument should be used?

Using a voltmeter is the appropriate method for checking the voltage at an AC motor's terminals. A voltmeter is specifically designed to measure electrical potential difference (voltage) across two points in an electrical circuit. In the case of an AC motor, it allows you to determine if the motor is receiving the proper voltage as required by its specifications. This is critical for ensuring optimal performance and preventing damage due to under-voltage or over-voltage conditions.

A voltage meter, while similar in function to a voltmeter, is a more general term and may not refer specifically to the kind of device used for AC voltage measurements. An ammeter measures current, not voltage, which makes it unsuitable for this particular task. Similarly, a frequency meter is used to measure the frequency of the electrical current rather than its voltage. Therefore, the most effective and specialized tool for measuring the voltage at an AC motor's terminals is, indeed, the voltmeter.