Electrical fault protection system

Claim 1

Ground fault protective circuitry and apparatus for an electrical distribution system supplied from a source of alternating current having a grounded neutral terminal, said circuitry and apparatus comprising circuit-interrupting means interposed in the system and capable of interrupting the system when relatively large fault currents are flowing, said circuitinterrupting means being responsive to relatively large fault currents for interrupting the system, disconnect switch means interposed in the system and capable, upon opening thereof, of interrupting the system when normal load or relatively small fault currents are flowing but incapable, upon opening thereof, of inteRrupting the system when relatively large fault currents are flowing, means providing a signal voltage directly related in magnitude to the magnitude of a fault current in the system, a first relay having a normally open conductive path, a second relay having a normally closed conductive path, means for impressing the signal voltage on the relays for causing operation of the respective relays in response to the signal voltage, the first relay being operative to close its conductive path at a relatively low value of the signal voltage indicative of a fault current within the interrupting ability of the disconnect switch means and the second relay being operative to open its conductive path at a relatively large value of the signal voltage indicative of a fault current greater than the interrupting capability of the disconnect switch means, electroresponsive means operative when energized to open the disconnect switch means, and an energizing circuit for the electroresponsive means including the electroresponsive means and the conductive paths of the relays connected in series.