Patent ID: 6707652
Filing Date: 2004-03-16
Classification: H02H

Abstract:
An electrical switching device comprising:a line circuit having a first temperature; a neutral circuit having a second temperature; a load terminal; separable contacts adapted to electrically connect said line circuit and said load terminal; an operating mechanism for opening said separable contacts in response to a trip signal; a first temperature sensor outputting a first signal representative of the first temperature of said line circuit; a second temperature sensor outputting a second signal representative of the second temperature of said neutral circuit; means for determining a difference between the first and second signals; means for providing said trip signal as a function of said difference, and wherein said means for determining a difference comprises a first resistor, a second resistor, a third resistor, a fourth resistor, and a differential amplifier having a first input, a second input and an output, said first resistor being electrically connected between said first temperature sensor and the first input of said differential amplifier, said second resistor being electrically connected between said second temperature sensor and the second input of said differential amplifier, said third resistor being electrically connected between the output of said differential amplifier and one of the first and second inputs of said differential amplifier; wherein said first and second temperature sensors have a common reference; and wherein said fourth resistor is electrically connected between the other of the first and second inputs of said differential amplifier and said common reference.