A residuel current circuit breaker (1) has a partition wall (3) which separates an over-current protection device (4) from a residual current detection circuit (5). A plunger rod (24) extends through a bore (23) in the armature (21) of a coil (20) and is moved independently through the coil (20) to trip the breaker if a residual current is detected by the circuit (5). The plunger rod (24) is moved by a drive rod (31), the operation of which is controlled by a permanent magnet (35) which retains the drive rod (31) retracted and an electromagnet (30) which allows the drive rod (31) to drive forwardly under the action of a spring (32) in the event of a residual current being detected. The plunger rod (30) is reset by a reset lever (40) which is moved when an operating handle (18) of the breaker moves from a non-tripped to a tripped position on tripping of the breaker.
