Multi-pole circuit breaker with interchangeable magneto-thermal tripping unit

A multi-pole circuit breaker comprising a breaker unit having a molded insulating box and a plurality of pole units supported within said box, and a magneto-thermal tripping unit interchangeable according to the selected rating and including a molded insulating box which is mounted on the box of the breaker unit in a mounted position and which is removed from the box of the breaker unit in a removed position, each pole unit of the breaker unit comprising a stationary contact and a movable contact, an upstream connection terminal of the circuit breaker connected to the stationary contact and a connecting lug connected by means of a conductor to the movable contact, said tripping unit comprising, for each of said pole units, thermal and electromagnetic trip means to operate upon the occurrence of certain current conditions for effecting tripping of the circuit breaker, a downstream connection terminal of the circuit breaker and a connecting lug, said trip means being connected in series between the downstream connection terminal and the connecting lug, wherein the connecting lug of the breaker unit comprises a nut and is positioned with play within the box of the breaker unit, said conductor between the movable contact and the connecting lug being flexible to allow shifting of the connecting lug relative to the box, the connecting lug of the breaker unit and the connecting lug of the tripping unit being superimposed in the mounted position of the tripping unit box on the box of the breaker unit, said circuit breaker including, for each pole unit, a connecting screw threaded in said nut for shifting the connecting lug of the breaker unit to bear on the tripping unit connecting lug irrespective of any defects in the positioning of the boxes.