The article presents methodology for testing the electric strength of vacuum chambers designed for modern medium voltage switchgear developed by the authors, using two innovative test stands designed and constructed by the research team above. Verification of the correctness of operation of the test stands, as well as the validity of the developed methodology was carried out by performing a series of tests. It was determined that below certain pressure values in the tested chamber (from about 5.0×10 ⁰ Pa for station 1 and for about 4.0×10 ^-1 Pa for station 2), the electric strength maintains a constant value, which guarantees stable operation of the vacuum chamber. The values of the total measurement uncertainty for the electric strength tests were also estimated.