My 3HP 3 PH planer motor hums but doesn't rotate. Someone had suggested that perhaps it had "dropped a leg". Would this be a reference to a fault in the motor or in the line between motor and sub panel? Should this be left to an electrician to figure out, or can a bumbler do it? If it's the motor, would replacing it be enuff or did something else cause it to go wonky?...none of the breakers had tripped.