US Patent 7944364 Protected power cord

Shielded power and power extension cords are protected from fire and other hazards caused by deterioration which may be due to age and/or excessive heat, or to physical damage which may be caused by kinking or crushing. At least one shield, which may surround multiple conductors or a single conductor is grounded through a fuse and made to function as a sensor in a fault detection circuit that opens the fuse and causes a relay to discontinue cord power transmission when a fault current passes from an ungrounded conductor to the shield. The relay circuit also refuses to fully close its contacts that transfer power to the cable in the event of receptacle wiring error and functions as a buzzer to indicate such an error.