Abstract: An Electric Distribution system for hospital use includes a plurality of ungrounded remote Power Supplies. Each remote Power Supply is provided with a Line Isolation Monitor. A Master Annunciator and Central Control Unit is connected to the several Line Isolation Monitors. The Master Unit, located at a central point, emits an alarm signal whenever the ground leakage current of any Power Supply exceeds a preselected value. The Master Unit also identifies the faulty Supply. Means are provided to measure the magnitude of the ground leakage. In a check mode, the Master Unit will sequentially read the leakage current of each remote Power Supply. In a test mode, the Master Unit will sequentially place artificial ground faults in each remote Supply so as to check the operation of each remote Monitor. Further circuitry may be provided to give an alarm at the Master Unit in the event that any one of the Monitors becomes inoperative due to power failure or loss of ground connection.

Abstract: A line isolation monitor which monitors ground faults on a normally ungrounded AC power line. The monitor uses a low voltage sensing current having a frequency greater than the frequency of the power line. The monitor tests each side of the power line independently. Provision can be made to indicate a double fault to ground. Further refinements include a means to monitor the connection between the monitor device and ground as well as a means for confirming continuity of annunciator lines associated with the line isolation monitor.