QL-1-13-DM-9-15 is a series of mechanical and electrical components that come together to form the functional unit of a circuit breaker. This particular model includes an insulated case, a metal contact plate, a nonmetallic insert, an operating arm and a trip lever. The metal contact plate, or contact bridge, carries the electrical current and is meant to be shielded from accidental contact by the nonmetallic insert. Generally, the metal contact plate is connected to other components of the circuit, such as the main power source, and the trip lever is attached to the operating arm. The trip lever interacts with the operating arm to open and close the circuit, protecting it from excessive current.