A circuit breaker like the ones found on a railway switchboard. Circuit breakers are used to switch the circuit of in a magnetic field on and off. The main current enters through rear post A; B is the heavy tripping coil that of wire that the main current passes through, thus operating the breaker; C contact block; the main current passes from C to D, which is a copper bridge; E is a heavy block where the current goes through after D. To set the breaker, the handle L is pulled. This causes a reaction that stops the flow of the electrical current through the system.
International Correspondence Schools A Textbook on Electric Lighting and Railways (Scranton, PA: International Textbook Company, 1901)