Abstract: A master metering module is taught which utilizes a programmed microprocessor and externally operated switches to alert the module as to what kind of system is being monitored thereby. For example, is the system being monitored a .DELTA.-connected electrical system or a Y-connected electrical system. This is useful in providing output indications of line-to-line voltage or line-to-neutral voltage, for example. When measuring voltages whether line-to-line or line-to-neutral one voltage value is substituted from another. A differential amplifier is utilized to do this. In one case the differential amplifier subtracts one line voltage from another line voltage, but in another case it subtracts neutral or zero ground potential from a line voltage. A switching arrangement is provided which interconnects one terminal of the differential amplifier with the neutral input terminal and with a line input terminal through appropriate conditioning of the microprocessor.

Abstract: A solid-state load protection system whereby a poly-phase alternating current system is monitored enabling a loss of phase feature to be used. A current sensing function is utilized so as to produce an output signal which is related to the current in an electrical circuit. Attached to the current sensing function are two capacitors each having their own signal path so as to have different charging and discharging rates. During a loss of phase condition, one capacitor discharges more quickly than the remaining capacitor with the result that the voltage across the quickly discharging capacitor, which during normal conditions is greater than the remaining capacitor, now becomes less than the remaining capacitor. A loss of phase sensing function detects this difference in potential levels thereby initiating a trip signal to the output function.