A circuit breaker module , comprising - a circuit breaker housing having a first housing part and a second housing part ; - a switching device ; and - at least one first connection module and one second connection module with a connection contact for a connection line; - wherein, in a joined or assembled state, said first and second housing parts form a front side and a rear side located opposite said front side and at least one connection side and end faces located opposite one another; - wherein a holding chamber for on of the connection modules is formed on the front side and/or on at least one of the connection sides ; - wherein the first and second connection module has a module housing that is formed with a connection opening for a connection line, said connection opening leading to the connection contact , and a contact opening ; - wherein the connection opening is arranged at that housing side of the module housing that faces toward the front side or the connection side , is flush therewith or forms same when the connection module is inserted into the holding chamber ; - wherein the contact opening is arranged at that housing side of the module housing that faces toward a chamber base of the holding chamber when the connection module is inserted into the holding chamber ; - wherein the first connection module or the second connection module has a screw terminal as connection contact or is configured as a screw terminal or has a screwless spring terminal as connection contact or is configured as a screwless spring terminal; - wherein the connection contact has a contact element for electrical connection to a coupling contact held by said housing parts in the joined or assembled state; and - wherein the coupling contact is accessible via a housing slot , which is formed on the connection side . - a circuit breaker housing having a first housing part and a second housing part ; - a switching device ; and - at least one first connection module and one second connection module with a connection contact for a connection line; - wherein, in a joined or assembled state, said first and second housing parts form a front side and a rear side located opposite said front side and at least one connection side and end faces located opposite one another; - wherein a holding chamber for on of the connection modules is formed on the front side and/or on at least one of the connection sides ; - wherein the first and second connection module has a module housing that is formed with a connection opening for a connection line, said connection opening leading to the connection contact , and a contact opening ; - wherein the connection opening is arranged at that housing side of the module housing that faces toward the front side or the connection side , is flush therewith or forms same when the connection module is inserted into the holding chamber ; - wherein the contact opening is arranged at that housing side of the module housing that faces toward a chamber base of the holding chamber when the connection module is inserted into the holding chamber ; - wherein the first connection module or the second connection module has a screw terminal as connection contact or is configured as a screw terminal or has a screwless spring terminal as connection contact or is configured as a screwless spring terminal; - wherein the connection contact has a contact element for electrical connection to a coupling contact held by said housing parts in the joined or assembled state; and - wherein the coupling contact is accessible via a housing slot , which is formed on the connection side . <EOS>