Electric Motor TroubleShooting

Electric motor troubleshooting and testing should be done very cautiously. If tested regularly the repair can be neglected. The testing is required when the smell of the burnt windings is felt.

Precautious safety glasses are to be worn whenever any electric device is tested or repaired. Power should be disabled by removing the fuses or by turning off a circuit breaker.

The wiring cover is opened by unscrewing and the screws are set aside. The motors name plate is read and the type of the motors is kept in the mind. Usually it would be a low voltage motor of 115 volts or 230 volts. It could also be a 230 volt three stage motor or a 430 volt high voltage motor. This determines the number of power leads the motor has. Two power leads motor are single phased motor of 115 volt or 230 volt whereas all the three phase motors will such as 230 volt and 430 volt have three wire leads.

The plastic wire connectors are removed that is connected to the power supply. Volt ohm meter set to the ohm condition.   In order to ensure the rotation now identify the power leads with the volt ohm meter the lead should read as Open lead (OL) or zero ohms. So when the motor is re-terminated the rotation would be correct.

Touch any one lead to the volt ohm meter to the case of the motor. It should read zero or open lead. If it shows any voltage then it could be a short in the motor windings. This shows a bad motor. If the resistance of the volt meter reads 20 mega ohms or larger in the case of a three phase motor then it is fine. Some three phase motors are designed to have high resistances. This could also be the symbol of bearing being weird and windings may be spoilt due to the excessive heat created.

In case of a single phase motor the capacitor should be removed from its housing. Do not touch the leads of the capacitor. It is similar to the battery and might have stored high voltage charge. Now turn the ohm meter to voltage and touch the leads of the exploded capacitor. If the voltage is read then the capacitor is charged. Hold the lead until the capacitor fully discharges and read zero. In case of a single phase motors only the capacitor needs to be changed most of the time.