10These mechanisms are similar in principle to the trigger, spring, and hammer of a firearm: the mechanical energy necessary to ignite the primer of a cartridge comes from a spring that has been “charged” either by manual operation of by the action of the gun during the last firing cycle. This spring energy is released by a sensitive sear mechanism driven by the finger-operated trigger, requiring very little energy to operate. In a similar manner, the operating springs of large circuit breakers are “charged” by an electric motor whenever a relaxed state is detected. That mechanical energy is then released by a relatively sensitive mechanism driven by an electric solenoid, allowing a small electrical signal to rapidly operate the large contact mechanism.