The experimental results showing the relation between rate of rise of recovery voltage (RRRV) and percentage of N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> - SF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> mixture, by pressure, are reported. A description of the test vehicle and the test procedure is also included. For a constant di/dt the optimum interrupter performance, judged in terms of its voltage recovery capability, is observed to occur when the SF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> mixed with N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> is in the range of 40 to 50 percent. In the limited range of pressures tested, the voltage recovery capability showed to be proportional to the upstream pressure raised to the 1.5 power.