Abstract: Apparatus for use with an environmentally controlled electronic system to prevent damage by supply line voltage reduction in which an air conditioning motor is connected across the supply line to the electronic system, a device is connected in the supply line upstream of the motor connection for sensing power flow in a direction away from the electronic system when the supply line voltage is reduced and the motor operates as a generator, and a switch is interposed in the supply line between the motor connection and power supply which opens in response to reversed power flow to direct power from the motor operating as a generator to the electronic system.