The circuit breaker is formed by two adjoined standard multipole molded cases, resin being cold-cast between the opposite side walls, comprising reliefs, of the two cases in order to provide fixing. A spacer, secured by bolts to the side walls of the two cases, defines their distance apart and can be used to cooperate with a racking cam when the circuit breaker is drawn into a fixed frame. The circuit breaker comprises an electronic trip device, an operating mechanism and an operating bar of the poles common to all the poles. At least two adjacent poles are twinned, that is to say eletrically connected in parallel.