A braking resistor is used in motion systems where a motor in controlled by a drive. Typically, these are high-speed servomotors controlled by a servodrive. When accelerating, electrical energy is converted to a mechanical force to move a mass. When decelerating, that kinetic energy is converted (via the motor) back into electrical energy, and must go somewhere. To brake quick enough, the energy must be dumped into a power resistor, to be dissipated as heat.