an electromagnetic circuit breaker has a housing that includes a separately defined arc chamber in which the moving contact travels as the breaker is tripped , and the chamber has a divergent shape to facilitate exhausting the hot gases from the arc chamber through a metal screen and through vent openings in the end wall of the breaker housing . the housing is made in two half sections that are held together by rivets and the location of one of these rivets is isolated from the fixed contact at the lower end of the arc chamber by the unique arc chamber configuration . the lower wall of the circuit breaker housing is adapted to receive either a molded switch subassembly or to receive a terminal strip that is held in place by the primary terminals of the breaker and is adapted also to support auxiliary terminals that operate a shunt coil . the shunt coil itself is fitted on a bobbin that is selectively mounted on the bobbin that contains the primary electromagnetic coil for the breaker . thus , a single circuit breaker housing design configuration is adapted for use in assembling a number of differently configured electromagnetic circuit breakers .