Abstract: A status indicating and current limiting circuit includes a pair of lamp filaments connected in parallel to provide a high reliability for status indication of a monitored switch. The circuit indicates the status of the lamps as well as the open or closed status of the switch. In one embodiment, the pair of lamp filaments are serially connected in parallel between a source of current and the switch so that both the lamp filaments emit bright light when the switch is closed. The lamps are also connected to ground potential through a resistive element to maintain current flow through the lamp filaments when the switch is open, the current being at a level just below the current flow necessary to dimly light the filaments. In the event of a failure of one of the filaments, the other filament will begin to emit a dim but visible light even though the monitored switch is open indicating the failure of the one lamp filament.

Abstract: A current limiting and fault indicating circuit for connection between a load and a source of electrical current including a pair of tungsten lamp filaments connected in parallel. The lamp filaments are chosen so that the current drawn by the load during the normal operation of the load produces only a small voltage drop. In the event of an overload or a short circuit, however, the increased current flow through the lamp filaments will heat the filaments to incandescence and the non-linear increase in impedence will absorb the source voltage and indicate the circuit to malfunction by the emission of bright light. The current flowing as a result of the fault will be limited to the rated current of the lamps.