A motor’s full-load speed rating is related to its torque characteristics. Higher torque is achieved largely by designing the motor to have greater slip. For this reason, NEMA Designs A and B (conventional torque characteristics) have full-load slips well under 5%, while NEMA Designs C and D (high torque) may have full-load slips exceeding 5%. All other things remaining equal (which never occurs), achieving high torque requires some sacrifice of efficiency.