What separates the multimeter resistance file from the buzzer file for testing on-off
The multimeter resistance file can measure the specific size of the line resistance, and then we can analyze and judge whether the line is normal or has any faults according to the resistance.
The buzzer can only judge whether the line resistance is large or small (generally around 30-50Ω is the cut-off point, and different multimeters are slightly different).
Assuming that the critical resistance value of the beeping sound of the multimeter’s beeping gear is 50Ω, the beeping gear will only sound when the resistance of the line or load is less than 50Ω, and the smaller the resistance, the louder the beeping sound. But when the line or load resistance is more than 50Ω, the buzzer will not sound. So when the line resistance is greater than 50Ω or ∞, we can't tell it with the buzzer.
Good or bad judgment of single-phase motor
Knowing from the topic that the motor has 4 wires in total, we can infer that the motor should be a single-phase motor (the specific type of single-phase motor can only be concluded by seeing the real thing).
A single phase motor has two coil windings, one is the start winding and the other is the run winding. Since the coil of the running winding is thicker and the coil of the starting winding is thinner, the resistance of the starting winding is larger than that of the running winding. The specific resistance value is related to the motor model and power, and it is possible from more than ten ohms to one or two hundred ohms. (The larger the motor power, the smaller the resistance; the smaller the power, the larger the resistance)
If the power of the motor is small, then its resistance will be very large. If the resistance is greater than 50Ω, the result we measured with the buzzer file is that there is no sound. Similarly, if the motor winding is blown, it will not sound when we use the buzzer to test.
If the power of the motor is large, its resistance value will be very small. If the resistance value is less than 50Ω, the result we measured with the buzzer file is a buzzing sound. Similarly, if there is a short circuit in the middle of the motor winding, then we will also have a buzzing sound when we use the buzzer file to measure the result.
Therefore, for the situation you mentioned, there is really no way to judge whether the motor is good or bad. To judge whether the motor is good or bad, it is necessary to analyze it according to the resistance value and power of the motor.
For electricians who are new to the multimeter, I suggest that you use the multimeter to measure the line or load, try to use the resistance file instead of the buzzer file, which is very helpful for maintenance and mastering the multimeter. Only after you have mastered the application of the multimeter to measure resistance, use the buzzer file to increase the speed of maintenance.
