During braking, with the aid of a motor, electrical energy is fed back into the drive. This action dissipates energy from the DC bus during deceleration of the motor load. If excess energy is not dissipated, this energy is fed back into the drive and can cause an over-voltage fault. An external device like the Kollmorgen regeneration resistor, or ‘regen’ resistor, dissipates excess energy and allows the drive to function normally when braking, but correct sizing of the resistor is crucial.