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Causes of blown fuses or circuit breakers tripping on the line side of a PCS or PF Softstarter

The softstarter typically is not the cause of the fuses blowing or a breaker tripping. Excess current demand that can result in fuses blowing or breakers tripping are: Short circuits: Check for loose, disconnected or damaged wires Megger the motor to see if there is a short in the windings - keep rotating the motor in about 10º increments and check around the entire motor. Make sure that the proper lugs are being used - over sized lugs may result in arcing between the phases Check for moisture in the conduit Fuse or breaker sizing and type: What type of fuses or breaker is being used and is it the proper one for the application. High inertia load with long start times and PFD Smart Motor Breaking may result in high current demand Line Power: Is the line power "solid" Are there transients and spikes on the line or was there a known occurrence on the line at the time of a fuse blowing or breaker tripping. Was there a storm that resulted in lightning strikes in the area?