Abstract: An electricity supply assembly comprises a circuit breaker comprising a housing (2) having generally flat, parallel side faces provided on the underside with a mounting recess (4), for mounting on a mounting rail of the conventional "top hat" section, comprising a base (7), spaced parallel flanges (8) extending from the base, and parallel outwardly extending flanges (9) which together provide a support surface which may be engaged by an underside of the recess (4). Extending from the underside of the circuit breaker at right angles to the plane of the base is a contact member (22). A supply assembly (28) comprises an elongate housing (30) within which an elongate bus-bar (32) is located, the bus-bar being provided with spaced intervals with spring clips (34). The housing (30) comprises a cover (36), provided at spaced intervals, corresponding to the spacing between the spring clips (34), with apertures (38).