Abstract: An arc quenching apparatus for circuit breakers includes a quenching space (10) in which each phase has a stationary contact (11) and a knife contact (12) pivotable in relation thereto, and which has a quenching chamber (13) in whose body member (15), made of an insulating material, quenching plates (14) are disposed in a spaced-apart relation so as to be located successively in relation to the path (P) of the opening movement of the knife contact (12). To overcome the problem of soot depositing in the quenching plate support structure made of an insulating material, which makes the support structure conductive between the quenching plates and adversely affecting the breaking capacity of the circuit breaker. Stop elements (20, 21a, 21b, 31, 42) are disposed between the ends of the quenching plates (14) on the knife contact (12) side and the body member (15).