To check whether the motor is working, it is necessary to combine the three core dimensions of appearance observation, electrical inspection, and operation testing, and troubleshoot the fault points step by step (applicable to common AC asynchronous motors, DC motors, etc.).

1、 Preliminary preparation: Safety first+tool list
1. Safety precautions (must be followed first)
Disconnect the motor power supply (unplug or turn off the circuit breaker), and use a multimeter to “on/off” to confirm that there is no residual voltage and avoid electric shock. If the motor has just stopped running, wait for it to cool down (surface temperature may exceed 100 ℃) to prevent burns.
For large motors (such as industrial grade motors), it is necessary to confirm that the transmission components such as couplings and belts have been disconnected to avoid mechanical injury caused by misoperation during testing.

2、 Step 1: Appearance and mechanical inspection (eliminate visual faults)
First, check non electrical issues with the naked eye and hand feel. Most simple faults (such as jamming or loose wiring) can be detected at this step:
Observe the external state of the motor

Shell: Whether there is any damage, deformation, oil leakage (for motors with reducers) or burnt marks (if there is a burnt smell, it may be due to burnt windings).
Junction box: Open the box cover and check if the wiring terminals are loose, oxidized (blackening/rusting of the terminals can cause poor contact), and if the wires are broken.

Cooling components: Whether the fan blades are intact (without breakage or deformation), and whether the cooling holes are blocked by dust/debris (blockage can cause overheating and shutdown).

Mechanical rotation inspection
When the power is off, rotate the motor shaft (or coupling) by hand: normally, it should rotate smoothly, without any jamming or obvious looseness.
If the rotation is stuck, it may be due to bearing wear (with a “rustling” friction sensation), rotor stator friction (sweeping the bore), or load end jamming (such as pump body or gearbox failure, the load needs to be disconnected to test the motor separately).
If the shaft is significantly loose, it may be due to bearing damage or loose end cap screws, and further disassembly and inspection are required.

3、 Step 2: Electrical performance testing (core troubleshooting steps)
By using a multimeter and a shaking table to detect the winding continuity, insulation, and power input of the motor, electrical faults such as winding burnout, grounding, and phase loss can be determined.

1. Check the continuity of the winding (determine if there is an open circuit)
The motor winding (stator winding) is the core conductive component, and an open circuit can cause the motor to completely stop rotating.
Operation method (taking three-phase motor and single-phase motor as examples, the number of windings varies for different motors):
Three phase asynchronous motor (commonly found in industrial equipment, with 6 terminals in the junction box: U1/U2, V1/V2, W1/W2):
Disconnect the motor power supply and unplug the power cord from the junction box.

Adjust the multimeter to the “resistance range” (200 Ω or 2k Ω range, depending on the motor power: the winding resistance of low-power motors may range from a few Ω to tens of Ω, while high-power motors may have a resistance of<1 Ω).
Measure the resistance of three sets of windings separately: U1-U2, V1-V2, W1-W2.
Normal situation: The three sets of resistance values are basically the same (error ≤ 5%), indicating that the winding is conductive and there is no local short circuit.

Abnormal situation: If the resistance of a certain group is “infinite” (the multimeter shows “OL”), it indicates that the winding is open circuit (possibly due to wire breakage or winding burnout).

4、 Step 3: Run the test (observe the actual working status when powered on)
If the appearance and electrical inspection are normal, the motor can be powered on to test its operating sound, speed, and temperature to determine if there are any hidden faults (such as local short circuits or load mismatches).

1. Power on and start observation
Turn on the power and observe if the motor starts:
Normal: Smooth start, no severe shaking, uniform speed.
Exception:
Completely non rotating with a buzzing sound: it may be due to phase loss (three-phase motor), secondary winding open circuit (single-phase motor), or load jamming.
Immediately trip after startup: it may be due to winding short circuit (excessive current) or grounding fault (leakage protector action).

.2. Running status detection
Listen to the sound: Use a stethoscope or screwdriver (with one end attached to the motor housing and the other end attached to the ear) to listen for the running sound:
Normal: Only a uniform “buzzing” electromagnetic sound, no noise.
Abnormal: There are “rustling” sounds (bearing wear), “friction” sounds (sweeping the bore), and “crisp” sounds (winding short circuit).
Temperature measurement: Power on and run for 10-30 minutes (depending on motor power), use an infrared thermometer to measure the temperature of the casing:
Normal: The temperature of the ordinary motor casing is ≤ 60 ℃ (when the ambient temperature is 25 ℃), and the temperature of the high-temperature motor is ≤ 80 ℃.

Abnormal: If the temperature rises rapidly (over 100 ℃) or there is a burnt smell, it indicates that the winding is short circuited or overloaded.
Check speed (optional): Use a tachometer to measure the motor shaft speed and compare it with the “rated speed” indicated on the motor nameplate (such as the rated speed of three-phase motors usually being 1440r/min and 2900r/min). If the deviation is too large, it may be due to winding failure or heavy load.