Patent ID: 7595644

Claim:
An apparatus for measuring electrical isolation between a plurality of POE (Power-Over-Ethernet) conductors in a POE system and earth ground, the apparatus comprising: an alternating current (AC) generator having a first terminal and a second terminal; a capacitor having a first terminal coupled to at least one of the POE conductors which normally has high isolation from earth ground and having a second terminal coupled to the first terminal the AC generator; a current-to-voltage converter having a first terminal coupled to the second terminal of the AC generator having a second terminal coupled to earth ground, and having a third terminal for providing an AC voltage representative of the AC current flowing in the series connected AC generator, capacitor, and current-to-voltage converter; an AC detector having a first terminal coupled to the third terminal of the current-to-voltage converter and having a second terminal for providing a direct current (DC) voltage representative of the AC current flowing in the series connected AC generator, capacitor, and current-to-voltage converter; and a comparator having a first terminal coupled to the second terminal of the AC detector, having a second terminal coupled to a reference voltage source, and having a third terminal, wherein the comparator is adapted to change a voltage state of the third terminal as the voltage at the first terminal of the comparator goes above and below the reference voltage at the second terminal of the comparator, and wherein, in a condition of high isolation between the POE conductors and earth ground, the AC current flow in the series connected AC generator, capacitor, and current-to-voltage converter is below the comparison threshold set by the reference voltage such that the comparator output is indicative of high isolation and wherein, in a condition of reduced isolation between the POE conductor and earth ground, the AC current flow in the series connected AC generator, capacitor, and current-to-voltage converter is above the comparison threshold set by the reference voltage such that the comparator output is indicative of isolation loss.