A regenerative resistor is used to discharge the regenerative power returned from the motor to the servo drive which is generated when the servo motor runs and stops a load with a large amount of inertia frequently. This regenerative power is transmitted into the capacitance of DC bus, resulting in the rise of voltage. When the voltage rises to a certain high level, the servo drive will need to dissipate the extra energy by using a regenerative resistor. In general, when the capacity of the regenerative power is small, there is no need to install a regenerative resistor. Use the regenerative resistor when: 1.A regeneration error (ALE05) is detected on the servo drive during the operation. 2.The DC bus voltage exceeds 370V or the output torque of the servo motor exceeds 100% constantly.