Abstract: An electronic circuit breaker is provided with a plurality of air coils, each of which is coupled to a main circuit and an overcurrent signal integrating circuit which receives the output of the air coil to output an overcurrent signal when the current through the main circuit exceeds a predetermined value. A current signal simulating an overcurrent in the main circuit is fed from an external testing device into a current signal receiving terminal (CST). A test voltage generating resistor (TVGR) is connected between the CST and ground. The current signal flows through the TVGR to develop a test voltage across the TVGR. Thus, the overcurrent signal integrating circuit simulates the overcurrent signal on the basis of the test voltage.

Abstract: In a multicircuit control apparatus (10) including a mechanical main contact (125) and plural semiconductor switching devices such as triacs (13a, --, 13d) each connected in series to the main contact, the main contact is closed by a control circuit 15 prior turning-on of any of the semiconductor switching devices and is also opened by the control circuit 15 after completion of turning-off of all the semiconductor devices.

Abstract: A novel and improved control and supervisory system for power distribution equipment including a plurality of terminal control and/or supervisory devices each capable of controlling and/or supervising a plurality of power distribution devices in an extremely simple, high-speed and efficient manner without requiring any central control and/or supervisory unit. To such control and/or supervisory operation, no vast and full knowledge of permitted and inhibited operations of varying kinds of power distribution devices connected therewith, as well as of the control and supervisory procedures therefor, is required.

Abstract: In a four-pole circuit breaker having U, V, W and N poles for protection of corresponding phases, only an N phase signal, which is reproduced by a current signal reproducing circuit in response to a current flowing through an N phase line, is amplified by a rated current reducing circuit and supplied to a maximum phase signal selection circuit together with other phase signals.

Abstract: In a prealarm circuit breaker which can issue a prealarm signal before occurrence of trip, a pair-transistor is employed in a charging circuit of a pair of capacitors, one of which serves to make a time delay after pickup of an overcurrent and the other of which serves to make a time delay pickup of a current of prealarm level.

Abstract: A tripping device with burning prevention switch has a electromagnet 10 and a burning prevention switch 14 both of which are cased in each separate insulating bodies. The electromagnet 10 and the burning prevention switch 14 are combined by engagement of projections 15, 16, provided on the burning prevention switch 14 and a hollow 12 and a hole 13, respectively, that are provided on the electromagnet 10.