Abstract: The invention is a simple amplifier circuit for a current transformer to measure very small AC currents, as required for ground fault detection. The circuit presents a very low impedance to the current transformer output and provides high amplification of the current transformer signal. Concurrently and with no additional components, the inventive circuit supplies a bias current to the current transformer to improve its performance and provides output signals which can be used to detect disconnection of the current transformer or a short circuit between either of the current transformer terminals and ground.

Abstract: The invention comprises a set of methods to detect the resistance of a connection to safety ground and to detect the presence of voltage hazardous to people in systems where an unknown amount of current intermittently flows in the safety ground circuit. Samples of voltage between two points in the safety ground circuit are taken repeatedly. When the voltage caused by the unknown currents in the safety ground circuit is below a preset threshold, a known current is applied and another voltage sample is taken to detect the electrical resistance of the safety ground circuit. If an excessive resistance or voltage is detected, one or more outputs are activated or deactivated to indicate the problem and remove power from the system. The invention requires no current sensor for its operation.

Abstract: A rotary circuit breaker door safety interlock for use with a power switch actuated by a rotating shaft installed in a enclosure with a hinged door is disclosed. The door safety rotary circuit breaker interlock functions both to prevent the enclosure door from being opened unless the power switch has first been turned OFF, and to prevent the power switch from being turned ON while the enclosure door is open. The door safety rotary circuit breaker interlock can be intentionally overridden to allow the enclosure door to be opened without turning the power switch OFF, and to allow the power switch to be turned ON while the enclosure door is open. The door safety rotary circuit breaker interlock is simple mechanically, requires no springs or deformable members for its operation, and can be adapted to many mounting variations in enclosures having doors that hinge at the left, right, top, or bottom.

Abstract: A rotary circuit breaker door safety interlock for use with a power switch actuated by a rotating shaft installed in a enclosure with a hinged door is disclosed. The door safety rotary circuit breaker interlock functions both to prevent the enclosure door from being opened unless the power switch has first been turned OFF, and to prevent the power switch from being turned ON while the enclosure door is open. The door safety rotary circuit breaker interlock can be intentionally overridden to allow the enclosure door to be opened without turning the power switch OFF, and to allow the power switch to be turned ON while the enclosure door is open. The door safety rotary circuit breaker interlock is simple mechanically, requires no springs or deformable members for its operation, and can be adapted to many mounting variations in enclosures having doors that hinge at the left, right, top, or bottom.