Overload protection of A-C instruments

USUALLY OVERLOADED instruments sustain either mechanical damage or thermal damage or both. The application of a sudden overload develops a torque which accelerates the moving parts of the instrument. Mechanical damage may occur during such acceleration or it may occur during subsequent deceleration when the stop is reached. A slight permanent deformation of one of the parts may spoil the accuracy of the calibration and therefore should be considered as mechnaical damage even if no parts are broken.