(1) Observation method. Visually inspect the ends of the windings and the insulation in the wire trough to see if there are any signs of damage or burnt black, if any, the grounding point.
(2) Multimeter inspection method. Check with a multimeter low-resistance file. If the reading is small, it is grounded.
(3) Megohm method. According to different grades, different megohmmeters are used to measure the insulation resistance of each group of resistors. If the reading is zero, it means that the winding is grounded, but the motor insulation is damp or breakdown due to accidents, it is judged according to experience, generally speaking The pointer oscillates at "0" and can be considered to have a certain resistance value.
(4) Test light method. If the test light is on, the winding is grounded. If a spark or smoke is found somewhere, it is the grounding fault point of the winding. If the lamp is slightly bright, the insulation has a ground penetrating. If the light does not illuminate, but the test rod is grounded, sparks also appear, indicating that the winding has not broken down, only severely damp. Hardwood can also be tapped on the edge of the outer edge of the outer casing. When it is knocked to a certain place, it will be turned off, indicating that the current is on and off, then it is the grounding point.
(5) Current through burning method. With a voltage regulating transformer, after the power is connected, the grounding point will heat up quickly, and the place where the insulator smokes is the grounding point. Special attention should be paid to the fact that the small motor must not exceed twice the rated current for less than half a minute; the large motor is 20%-50% of the rated current or gradually increase the current, and immediately turn off the power when the grounding point has just smoked.
(6) Group elimination method. The grounding point is inside the core and the burning is more severe. The burnt copper wire is fused with the iron core. The method used is to divide the grounded one-phase winding into two halves, and so on, and finally find the grounding point.