A circuit interrupter responsive to abnormal currents in conductors of an electrical distribution system characterized by a circuit breaker mechanism for opening and closing separable contacts and which mechanism comprises a releasable member operable between latched and unlatched positions, trip means comprising a bimetal element and a trip bar movable to unlatch the circuit breaker mechanism and biased in the latched position, the trip bar having a surface facing and spaced from the bimetal element which surface is slanted at an oblique angle to the longitudinal axis of the trip bar, and manually adjustable knob connected to the trip bar for sliding the trip bar longitudinally to vary the space between the bimetal element and the trip bar surface in accordance with a desired thermal rating.