There is also leakage. For this fault, we need to use a shaking table. The shaking table has two wires. We connect one to any group of coils and the other to the iron sheet, and then turn the handle of the shaking table to see the direction in which the screen pointer swings. If the pointer swings to 500, it means that the coil does not leak electricity, which is normal. If you swing to the zero side, it means that the coil is leaking, and it needs maintenance.

To check the insulation of the motor, a low-voltage shaking table with insulation class of 500 volts is needed. Connect one end of the shaking table to the shell of the water pump and the other end to the three windings of the motor (the three windings need to be shorted together in advance). Then, shake the handle of the shaking table at a speed of 120 revolutions per minute. If the measured value is less than the normal value, it means that the motor insulation of the water pump has been damaged and cannot be used any more.