<p>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 producing 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 producing circuit simulates the overcurrent signal on the basis of the test voltage. <IMAGE></p>
