AQ: Motor fuses
Mainly Fuses are used for protection against short Circuits due its high rupurting capacity (breaking capacity) and fast response (less than 10ms).
As far the electrical drives are concerned, Fuses can be used to protect the feeders, while the Electrical Motors will be protected by Thermomagnetic CB to achieve Short Circuit as well as overload protection. At least thermal overload has to be provided for the Electrical Motors.
Accordingly, Plow of fuses depend on the type of Short Circuit, Single phase or 3 Phase fault (ie location of the fault) and the let through energy. In case one phase blown (say earth fault) -ve sequence and Zero sequence will be generated and subsequently the motor thermal overload will operate to protect the Motor.
It is worth to mention that, now a day proper protections for Electrical motors are commonly used, MCCB/MCB for overcurrent (short Circuit & overload), Single Phasing, Under voltage, Phase sequence relays… etc.
Thermal Protection can be achieved by many technique (ie Bi-metal, thermostat, resistance (NTC or PTC),,,etc.
The Fuse for Electrical Motor is efficient for O/C (Short Circuit, either L-G or L-L) or/and internal fault in the Motor windings. Taking into consideration the fuse rating considering the Starting current of the Motor. Therefore the fuse will not be effective for overload protection on the similar case.
However, I believe the motor was either subjected to an internal fault due to insulation failure (Humidity, water, bearing damages, high temperature rise, Stator/rotor gap,,etc) , subsequently the fuse blown or in prior the fuse blown due to an external factor and the thermal overload device associated with Motor Control panel not operated / out of order in the proper time -The heat rise impaired the winding accordingly or the Motor was subjected to stall current and prolong starting period.
