Current sensing relay circuit with adjustable sensitivity and tracking test circuit

摘要

Ground fault interrupting circuit breaker (10) includes a sensing coil (20) which is the secondary winding of a current transformer having a core (18) and includes a test coil (22) also wound about the core with load conductors passing through the core. A current sensing circuit (30) compares the output from the sensing coil to a reference voltage which is adjustable to set the sensitivity of the breaker. A test circuit (42) generates in the test coil a test current whch has its magnitude determined by the same reference voltage which determines the sensitivity of the breaker, thus causing the test current to automatically track the sensitivity of the breaker without separate adjustment.