Usage Steps of a Clamp Meter
(1) Select the clamp ammeter correctly based on the type and voltage level of the measured current. For general communication lines below 500V, T301 type is selected. When measuring the current of high-voltage lines, a high-voltage clamp ammeter that matches its voltage level should be selected.
(2) Correctly inspect the appearance, clamp closure, and meter head of the clamp ammeter to ensure they are functioning properly. If the pointer is not at zero position, mechanical zeroing should be performed.
(3) Select the appropriate range of clamp type ammeter based on the magnitude of the measured current. The selected range should be slightly larger than the measured current value. If the magnitude of the measured current is unknown, the maximum range estimation should be selected first.
(4) Accurate measurement. When measuring, the wrench should be tightened to open the jaws. Place the tested wire into the center of the clamp, release the wrench and close the clamp tightly.
(5) After reading, open the jaws and exit the tested wire, and set the gear to the highest current or OFF position.
Measurement example: Measuring the working current of a cage type asynchronous motor during operation. According to the magnitude of the current, it is possible to check and determine whether the motor is working properly to ensure safe operation and extend its service life. Firstly, select the voltage level of the clamp type ammeter correctly, check whether its external insulation is good, whether there is any damage, whether the pointer swings flexibly, and whether the clamp is corroded. Estimate the rated current based on the motor power to select the range of the meter. When measuring, it can be done once for each phase or once for all three phases. At this time, the number on the meter should be zero (because the sum of three-phase current phasors is zero). When there are two phase lines in the clamp, the displayed value on the meter is the current value of the third phase. By measuring the current of each phase, it can be determined whether the motor is overloaded (the measured current exceeds the rated current value), whether there is a problem with the internal or power supply voltage of the motor, that is, whether the three-phase current imbalance exceeds the limit of 10%.
