Why use a clamp meter to measure current when installing a motor
The actual current of one phase line is measured using a clamp type ammeter, because the clamp type ammeter is equivalent to a CT with an opening in the primary winding. The current detected in one test will be reflected in the second test, which is not related to the connection method of the three-phase motor.
Step 1: Measure the phase separately, which can directly measure the phase voltage on the secondary side of the voltage transformer (the same method as above), The phase voltage can be directly measured at the input end of a clamp meter. However, it requires the insertion of a probe and the selection of a suitable range. Its "bayonet" can only measure AC current with a specialized clamp meter. Keep the pointer on the right and use it in the same way as a regular multimeter, gradually shifting from high to low gear under unknown voltage levels;
Step 2: Measure the voltage through parallel connection of the probes. The clamp meter measures the voltage through its accompanying multimeter. The clamp meter cannot directly "clamp" the voltage and modulate the conversion switch to an appropriate range.
Usage of digital clamp watch
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 the nameplate value
3. When using the minimum range measurement and the reading is not yet obvious, the measured wire can be wound several turns, and the number of turns should be based on the number of turns in the center of the clamp, then the reading=the indicated value × Range/full deviation × Number of turns
4. After the measurement is completed, the transfer switch should be placed at the maximum range
5. When measuring, the measured wire should be placed in the center of the clamp and the clamp should be tightly closed to reduce errors
Precautions for digital clamp watches
1. The voltage of the tested circuit should be lower than the rated voltage of the clamp meter
2. When measuring the current of high-voltage lines, it is necessary to wear insulating gloves, shoes, and stand on an insulating mat
3. The jaws must be tightly closed and cannot be changed with power
Using a clamp ammeter to measure the current of a single winding of a motor is phase current, but it may cause trouble in actual measurement. Either connect all three pairs of winding wires to the outside; The current on the power line is always the line current; It is difficult and impractical to calculate the power of a certain motor. The power factor is an uncertain factor, unless a power factor meter is also connected, but it should be noted that due to load reasons, the power factor is changing.
