Methods and precautions for measuring current with a clamp meter

A clamp meter is an instrument that combines a current transformer and an ammeter in one. 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-type magnetoelectric system with a reaction force instrument.

Instructions:

(1) Mechanical zeroing is required before measurement

(2) Select the appropriate range, first select the larger range and then the smaller range or estimate based on the nameplate value.

(3) When using the minimum range for measurement and the reading is not clear, you can wind the measured wire a few turns. The number of turns should be based on the number of turns in the center of the jaws. Then the reading = indicated value × range/full deviation × number of turns

(4) After the measurement is completed, place the conversion switch at the maximum range.

(5) When measuring, the conductor to be measured should be placed 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 meter. 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, two people should operate it. Non-duty personnel should also fill out a second work ticket. When measuring, they should wear insulating gloves and stand on insulating mats. They must not touch other equipment to prevent short circuits or grounding.

(2) When observing the timing of the clamp meter, pay special attention to maintaining a safe distance between the head and the live parts. The distance between any part of the human body and the live part must not be less than the entire length of the clamp meter.

(3) When measuring on a high-voltage circuit, it is prohibited to use a wire to connect another meter from a clamp ammeter. 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 considered convenient.

(4) When measuring the current of a low-voltage fusible fuse or a horizontally arranged low-voltage busbar, the fusible fuses or busbars of each phase should be protected and isolated with insulating materials before measurement to avoid causing a phase-to-phase short circuit.

(5) 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.

(6) After the clamp ammeter is finished measuring, pull the switch to the maximum range to avoid accidental overcurrent during the next use; and it should be stored in a dry room.