Which instrument is best used to measure the current in a motor operating on three-phase power?

A clamp-on ammeter is the most suitable instrument for measuring current in a three-phase power motor due to its ability to easily measure the current without requiring direct contact with the electrical conductors, which improves safety and ease of use. This type of ammeter utilizes a magnetic field generated by the flow of current in the wires, allowing it to clip around one of the conductors of the motor.

In contrast, a digital multimeter, while versatile, generally requires the circuit to be interrupted to connect its leads, which is not always practical or safe in a three-phase system. An oscilloscope primarily measures voltage over time and is less suited for simple current measurement tasks in this scenario, while a wattmeter is designed to measure power (the product of voltage and current), and it does not directly indicate the current flowing in the conductors. Therefore, the clamp-on ammeter stands out as the best option for efficiently and safely monitoring current in three-phase power applications.