Methods and precautions for measuring current with a clamp meter
A clamp meter is an instrument that combines a current transformer and an ammeter. It is an important branch of a digital multimeter. It is a portable instrument that can directly measure the AC current of a circuit without disconnecting the circuit. The clamp meter is essentially composed of a current transformer, a clamp wrench and a rectifier magnetoelectric system with reaction force instrument.
Instructions:
(1) Mechanical zero adjustment is required before measurement.
(2) Select the appropriate range, first select the large range, then select the small range or estimate based on the nameplate value.
3) When using the minimum range measurement and the reading is not obvious, you can wind the wire under test a few turns. The number of turns should be based on the number of turns in the center of the jaw. Then the reading = indicated value × range / full deviation × number of turns.
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4) After the measurement is completed, place the transfer switch at the maximum range.
(5) When measuring, the conductor under test should be in the center of the jaws and the jaws should be closed tightly to reduce errors.
Precautions:
(1) When using a high-voltage clamp meter, pay attention to the voltage level of the clamp ammeter. It is strictly forbidden to use a low-voltage clamp meter to measure the current of a high-voltage circuit. When measuring with a high-voltage clamp meter, it should be operated by two people. Non-duty personnel should also fill in the second work ticket when measuring. They should wear insulating gloves and stand on the insulating pad when measuring. They should not touch other equipment to prevent short circuit or grounding.
(2) When observing the time 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.
(3) When measuring on a high-voltage circuit, it is prohibited to use wires from the clamp-type ammeter to another meter for measurement. When measuring the current of each phase of a high-voltage cable, the distance between the cable heads should be more than 300mm and the insulation should be good. The measurement can only be carried out when it is deemed convenient.
(4) 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.
(5) When one phase of the cable is grounded, measurement is strictly prohibited. Prevent the occurrence of ground breakdown explosion due to the low insulation level of the cable head, which may endanger personal safety.
(6) After the measurement of the clamp ammeter is completed, pull the switch to the maximum range to avoid inadvertent overcurrent the next time it is used; and it should be stored in a dry room.
