The description of the electromagnetic retarder or eddy current retarder. Electromagnetic Retarders serve to slow vehicles down, or maintain a steady speed on inclines. They are usually not capable of bringing vehicles to a standstill, as their effectiveness diminishes at low speeds. They are usually used to slow vehicles down, with the final braking being carried out by a friction brake. As the friction brake does not then need to be used so much, particularly at higher speeds, the service lifetime of friction brakes is enhanced. The technical data ofthe air cooled electromagnetic retarder or air cooled eddy current retarder.