Abstract: This paper shows a systematic approach to optimize the mechanical characteristic of a medium voltage (MV) circuit-breakers (CB) for a wide range a operating temperatures. The mechanical damper is the critical element which strongly determines the travel curve behavior of the CB when opening. Most dampers used in MV-CB contain oil as one of the damping elements. The viscosity of the oil is varying with temperature. Therefore also the damping characteristic of oil damper is temperature depending. To make sure the CB works correctly under all ambient conditions encountered in service measures have to be taken to make sure the CB is able to operate correctly and reliably and fulfills the switching duties required. An existing MV-CB was tested under different ambient temperatures and showed unsatisfactory results. The design of the CB was analyzed and the damper identified as the main root cause. A special test setup for the complete CB and a test jig for the damper only was developed. Based on the findings obtained with this new setups the damper was optimized only by modifying some internal parts of the damper, keeping the outside dimensions and the oil filling the same. Thus eliminating the need of any changes on the CB design. The tests on the CB with the optimized damper showed excellent results at all requested ambient temperature levels. The newly developed damper test rig can be used to quickly and efficiently derive damper parameters or for performance testing of dampers during development or final testing in damper production.