Portable ground fault interrupter which can be plugged into a conventional outlet to provide ground fault protection at any desired location. The interrupter includes a relay having contacts for controlling the flow of current between the outlet and a load connected to the interrupter and an operating coil for holding the contacts in their closed position when energized. The coil receives its holding current through the contacts, and in the event of a ground fault, the coil is bypassed to open the contacts. A reset switch applies current to the relay coil to reenergize it, and means is included for interrupting the current applied to the operating coil following the initial reenergization whereby the coil is reenergized and the contacts are closed only briefly in the event that the ground fault is still present when the reset switch is actuated.

A ground fault detector having an indicator which indicates the presence of a ground or similar fault in an electrical line to be protected where the fault current is not of sufficient magnitude to cause the ground fault indicator to trip a circuit breaker to thereby interrupt the circuit in which the ground fault current is flowing. The indicating circuit provides a recognizable warning that a ground fault has begun or is in progress so that appropriate steps may be taken to cure the fault to locate the fault, or to indicate the relative magnitude of the fault current before it worsens.

A MEM's reed switch array is provided having a first switch having a sensitivity causing the first switch to open or close due to a magnetic flux, and a second switch of lesser sensitivity than the first switch causing the second switch to open or close due to a magnetic flux. The first switch can be parallel to the second switch, or the first switch can be proximate to the second switch so that a center line of the first switch is coaxial to a center line of the second switch. Further, a security device for residential and/or commercial use is provided, having a magnet housing having a magnet, a switch housing having a MEM's reed switch array with a first switch and a second switch, and a gap between the magnet housing and the switch housing.

A ground fault interruptor comprising a reed relay connected to the secondary of a differential transformer, a load connected to the primary windings of said transformer through the contacts of a relay or circuit breaker, a power supply circuit for said relay or circuit breaker, a biasing circuit connected to said reed relay and a signal processing circuit for processing the signal from the secondary of said transformer to said reed relay.

A system senses alternating current in a conductor, such as a main line supplying electrical power to a home, and responds to the sensed current as by providing a warning signal when the sensed current exceeds or is less than a preset value for a predetermined short period of time. The current sensor itself is a simple coil of wire, either with an air core or a partial ferromagnetic core, which can be easily operatively associated with the current carrying conductor without the need for disconnecting the conductor from its terminals and which when installed does not present the hazards associated with current transformers.