The rated current of the motor refers to the line current, measured from the mains or protection switch, or the contactor.
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 running current of the motor, which is generally smaller than the rated current. Only the current of the motor under the rated load is the rated current.
By measuring the current of each phase of the motor during operation, it can be judged whether the motor is overloaded (the measured current exceeds the rated current value), whether there is a problem with the motor or the power supply voltage, that is, whether the three-phase current imbalance exceeds the limit of 10%.
1. Correctly select the voltage level of the clamp-type ammeter, check whether the appearance of the ammeter is good, whether there is damage, whether the pointer swings flexibly, whether the jaw is rusted, etc. Estimate the rated current based on the motor power to select the range of the meter.
2. When measuring, it can be measured once for each phase, or once for three phases. Because the sum of the three-phase current phasors is zero, the number on the meter should be zero when the three-phase measurement is performed once.
3. When there are two phase wires in the jaw, the value displayed on the table is the current value of the third phase.
