Things to note when measuring DC current with a clamp ammeter
1. Things to note before measuring
The first step is to correctly select the clamp ammeter according to the type and voltage level of the current being measured. The voltage of the line being measured 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 used. Low-voltage clamp ammeters can only measure the current in low-voltage systems, but cannot measure the current in high-voltage systems.
Secondly, the appearance of the clamp ammeter must be correctly checked before use. Be sure to check whether the insulation performance of the meter is good, the shell should be undamaged, and the handle should be clean and dry. If the pointer is not at zero, mechanical zero adjustment should be performed. The jaws of the clamp-type ammeter should be tightly connected. If the pointer shakes, the jaws can be opened and closed again. If the shaking still exists, check carefully and pay attention to remove debris and dirt from the jaws, and then measure.
Because the clamp ammeter contacts the circuit being measured, the clamp ammeter cannot measure the current of bare conductors. 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 the insulating pad, and other equipment should not be touched to prevent short circuit or grounding.
2. Things to note when measuring
First, when using it, press the wrench tightly to open the jaws, put the wire under test into the center of the jaws, then loosen the wrench and 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 processed to make the reading accurate. In addition, do not clamp two wires at the same time. After reading, open the jaws, withdraw the wire under test, and set the gear to the highest current gear or OFF gear.
Secondly, the appropriate range of the clamp-type ammeter must be selected according to the size of the measured current. The selected range should be slightly larger than the measured current value. If it cannot be estimated, in order to prevent damage to the clamp ammeter, measurement should be started from the maximum range and gradually change gears until the range is appropriate. It is strictly prohibited to switch the gear of the clamp ammeter during the measurement process. When changing gears, the conductor under test should be withdrawn from the clamp before changing gears.
When measuring a current less than 5 amps, in order to make the reading more accurate, if conditions permit, the current-carrying wire to be measured can be wound several times and then put into the clamp for measurement. At this time, the actual current value of the measured wire should be equal to the meter reading divided by the number of wire coils placed in the jaws.
When measuring, attention should be paid to keeping a safe distance between all parts of the body and charged objects. The safe distance for low-voltage systems is 0.1 to 0.3 meters. When measuring the current of each phase of a high-voltage cable, the distance between the cable heads should be more than 300 mm and the insulation should be good. The measurement can only be carried out when it is deemed convenient. When observing the timing of the meter, special attention should be paid to keeping a safe distance between the head and the live parts. The distance between any part of the human body and the live body shall 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, each phase fusible fuse or busbar should be protected and isolated with insulating materials before measurement to avoid short circuit between phases. When one phase of the cable is grounded, measurement is strictly prohibited to prevent ground breakdown and explosion due to low insulation level of the cable head, which may endanger personal safety.
3. Things to note after measurement
After the measurement is completed, the switch of the clamp ammeter should be pulled to the maximum range to avoid inadvertent overcurrent during next use, and should be stored in a dry room.
