A stored energy-type circuit breaker includes a sensor that operates as a full open sensor, and that is used to prevent the circuit breaker from closing in response to either a closing signal or a manual operation. The full open sensor exhibits a first output condition when the moveable contact is in a fully open position and a second output condition when the moveable contact begins to leave the fully open position. An electronic trip unit (ETU) is electrically connected to the sensor and, when in a close break mode, blocks the circuit breaker from closing. The ETU does this by, upon detecting that the sensor is in the second output condition, generating a signal that will cause the breaker's opening spring to return the moveable contact to the fully open position.