3.5 Critical SpeedsThe motor of a VSDS shall have a rigid, under critical rotor bearing system with the first critical speed over 125% of the maximum operational speed of the VSDS. The motor of a VSDS with flexible, overcritical rotor bearing system shall have the first critical speed below 80% of the minimum operational speed of the VSDS and the second critical speed over 125% of the maximum operational speed of the VSDS.