Abstract: The monitor includes a pair of circuits; each circuit includes a resistor and an SCR in series and each circuit is connected to a respective end of a center-tapped primary of a current transformer. Means are provided to alternately and cyclically operate the SCR's from an OFF to an ON state. A current path is provided between the center tap of said primary and ground. Current through the pair of circuits and the current path is monitored to determine leakage to ground for controlling alarm means.The novel alarm structure accomplishes the foregoing with a means that derives a DC voltage representative of the condition and combines that voltage in subtractive relationship with the voltage of a reference source and applies the sum to the gate of a Silicon Controlled Rectifier.