Precautions for Measuring DC Current with Clamp Ammeter
1. Precautions before measurement
The first is to correctly select the clamp ammeter according to the type and voltage level of the measured current, and the voltage of the measured line should be lower than the rated voltage of the clamp meter. When measuring the current of a high-voltage line, a high-voltage clamp ammeter that matches its voltage level should be selected. The clamp ammeter of low voltage level can only measure the current in the low voltage system, and cannot measure the current in the high voltage system.
The second is to correctly check the appearance of the clamp ammeter before use. Be sure to check whether the insulation performance of the meter is good, the shell should not be damaged, and the handle should be clean and dry. If the pointer is not at zero, perform mechanical zero adjustment. The jaws of the clamp ammeter should be tightly connected. If the pointer shakes, you can open and close the jaws again. If the shaking still exists, check carefully, pay attention to remove the sundries and dirt on the jaws, and then measure.
Since the clamp ammeter is in contact with the line under test, the clamp ammeter cannot measure the current of a bare conductor. When measuring with a high-voltage clamp meter, it should be operated by two people. During the measurement, insulating gloves should be worn, standing on an insulating mat, and not touching other equipment to prevent short circuit or grounding.
2. Matters needing attention during measurement
The first is to press the wrench tightly to open the jaws, put the wire to be tested into the center of the jaws, and then loosen the wrench to close the jaws tightly. If there is noise on the joint surface of the jaws, it should be opened and closed again. If there is still noise, the joint surface should be treated to make the reading accurate. Also, do not clamp two wires at the same time. After reading, open the jaws, withdraw the measured wire, and set the gear to the highest current gear or OFF gear.
Secondly, it is necessary to select the appropriate range of the clamp ammeter according to the magnitude of the measured current. The selected range should be slightly larger than the value of the measured current. If it cannot be estimated, in order to prevent damage to the clamp ammeter, start measuring from the maximum range, and gradually change gears until the range is suitable. It is strictly forbidden to switch the gear position of the clamp ammeter during the measurement process. When changing gears, the measured wire should be withdrawn from the jaws before changing the gear position.
When measuring the current of less than 5 amps, in order to make the reading more accurate, when conditions permit, the measured current-carrying wire can be wound several times and then put into the jaw for measurement. At this time, the actual current value of the wire under test should be equal to the reading value of the meter divided by the number of wire coils put into the jaws.
When measuring, pay attention to keep a safe distance between each part of the body and the charged body. The safe distance of the low-voltage system is 0.1 to 0.3 meters. When measuring the current of each phase of the high-voltage cable, the distance between the cable ends should be more than 300mm, and the insulation should be good, and the measurement can only be carried out when it is considered convenient. When observing the timing of the watch, special attention should be paid to maintaining a safe distance between the head and the live part. The distance between any part of the human body and the live body should not be less than the entire length of the clamp meter.
When measuring the current of low-voltage fusible fuses or horizontally arranged low-voltage busbars, the fusible fuses or busbars of each phase should be protected and isolated with insulating materials before measurement to avoid interphase short circuits. When one phase of the cable is grounded, it is strictly forbidden to measure to prevent the occurrence of ground breakdown explosion due to the low insulation level of the cable head and endanger personal safety.
3. Matters needing attention after measurement
After the measurement, the switch of the clamp ammeter should be pulled to the maximum range, so as to avoid accidental overcurrent in the next use, and should be stored in a dry room.
