How to measure motor running current with clamp meter

The rated current of the motor refers to the line current, measured from or at the protective switch. The rated current is not measured, it is determined by the manufacturer's design of the motor. It can operate safely for a long time under this current. The clamp meter measures the motor operating current, which is generally smaller than the rated current. Only the current of the motor under rated load is the rated current.

By measuring the current of each phase during operation, it can be determined whether the motor is overloaded (the measured current exceeds the rated current value), whether there is a problem inside the motor or the power supply voltage, that is, whether the three-phase current imbalance exceeds the 10% limit.

(1) Correctly select the voltage level of the clamp ammeter, check whether its insulation is good and whether it is damaged, whether the pointer swings flexibly, whether the jaws are rusted, etc. Estimate the rated current based on the motor power to select the range of the meter.

(2) When measuring, you can measure once for each phase or once for three phases. Since the phasor sum of the three-phase currents is zero, the number on the meter should be zero when measuring three phases.

(3) When there are two phase wires in the jaw, the value displayed on the meter is the current value of the third phase.