Ground absence detector and protective device

Claim 1

A GROUND-ABSENCE DETECTION AND PROTECTIVE DEVICE COMPRISING A THREE-PRONG PLUG ENGAGEABLE IN A THREE-TERMINAL CURRENT SUPPLY SOCKET OF THE TYPE HAVING A FEMALE GROUND TERMINAL INTENDED TO BE INTERNALLY CONNECTED TO ONE OF THE SOCKET CURRENT SUPPLY CONDUCTORS, SAID PLUG HAVING A PAIR OF LINE PRONGS AND A GROUND PRONG, BALANCED CIRCUIT MEANS INCLUDING A RELAY, MEANS CONNECTING SAID BALANCED CIRCUIT MEANS ACROSS SAID PAIR OF LINE PRONGS, SAID BALANCED CIRCUIT MEANS HAVING A CENTER JUNCTION DIVIDING THE BALANCED CIRCUIT MEANS INTO TWO SUBSTANTIALLY SYMMETRICAL CIRCUIT SECTIONS, MEANS CONNECTING SAID CENTER JUNCTION TO SAID GROUND PRONG, WHEREBY ONE OF SAID CIRCUIT SECTIONS IS SHUNTED WHEN THERE IS AN INTERNAL CONNECTION BETWEEN THE SOCKET FEMALE GROUND TERMINAL AND ONE OF THE SOCKET CURRENT SUPPLY TERMINALS WHEN THE PLUG IS INSERTED IN THE SOCKET, MEANS TO ENERGIZE SAID RELAY FROM THE LINE PRONGS RESPONSIVE TO THE SHUNTING OF SAID ONE OF THE CIRCUIT SECTIONS, SAID RELAY HAVING A PAIR OF CONTACTS CLOSED WHEN THE RELAY IS DEENERGIZED AND OPEN WHEN THE RELAY IS ENERGIZED, AN ELECTRICAL INDICATOR, AND CIRCUIT MEANS CONNECTING SAID INDICATOR TO SAID LINE PRONGS THROUGH SAID CONTACTS, WHEREBY THE INDICATOR WILL BE ENERGIZED WHEN THE PLUG IS INSERTED IN A THREE-TERMINAL SUPPLY SOCKET WHOSE FEMALE GROUND TERMINAL IS NOT INTERNALLY CONNECTED TO ONE OF ITS CURRENT SUPPLY CONDUCTORS.