This is a back EMF shunt module. It will limit the over voltage coming back from the servo motor when it’s stopping. If you have a heavy axis stopping from high speeds, the motor will generate high voltage energy back to the driver and power supply. This EM-xx unit will dump this energy to a 50W resistor to become heat and save the driver from getting damaged or being faulted. Furthermore, motor breaking will be controlled easily or smoothly.
The unit takes about few mA in standby and can take up to 7A when active. Normally, factory clamping voltage setting is 10% above the power supply voltage. However, you can set the clamping voltage to your specification.