Motor Electrical Protection

 
INTRODUCTION 
Electrical supply, while generally very reliable, is subject to influences that can result in inadequately protected motors being damaged.
As the heart of the motor is the windings, we need to protect the windings from failure.
During normal operation, thermal, mechanical and electrical stresses can be encountered by motors. 
 
POSSIBLE PROBLEMS 
Refer to page P-1 in the Fan Trouble Shooting section for a list of possible problems and solutions. 
 
PROTECTION DEVICES 
There are motor protective devices available which detect a range of abnormal conditions and automatically switch off the motor.
Different protective devices and the conditions they protect are:-
Fuses
- short circuit between phases or earth
- high current overload
Thermal Overload Relays
- current overload
- start-up problems
- stalling
- phase imbalance (three-phase motors)
- over-temperature
- phase loss (single-phasing of three-phase motors)
- under-voltage
- incorrect phase sequences (three-phase motors)
Thermistors and Thermal Contacts
l over-temperature of the windings 
 
WARRANTY 
Note that warranty is void if the thermal contacts are not used.
SABS wiring rules state that motors required to run unattended shall be fitted with over-temperature devices such as thermal overload relays. If this is not complied with,warranty will be void.A licensed electrical contractor or engineer, experienced in motor protection, should beengaged to assess the motors and specific requirements of the installation.An encumbend in possession of a wireman certificate shall do the final electricalconnection to the fan.On all motors above 5,5 KW soft starting or star delta starter to be utilized.
 
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