Low-voltage circuit breaker (1) exhibiting live levers (24) operatively connected to a control device (10) for opening and closing the circuit breaker (1), fixed live terminals (25, 26) and electric arc extinction chambers (75), there being provision for the levers (24), the terminals (25, 26) and an extinction chamber (75) to be enclosed in half-shells (20, 21) constituting a pole (2), for the half-shells (20, 21) to be made from insulating material and for several poles (2) to be clamped in a supporting frame (3, 4, 5, 6, 7, 8, 9).