Abstract: A control system for protecting a computer system against external fault conditions, including, in combination, circuits for monitoring and reacting to a plurality of power supply fault conditions, circuits for monitoring and reacting to a plurality of environmental fault conditions, circuits for monitoring and reacting to unauthorized access fault conditions, and circuits for driving off the supply of 3-phase power to the computer system in response to any one or more of these fault conditions. The invention also includes the various monitoring and reacting circuits in specific subcombinations.