Residual-current device

A residual-current device comprises a sum current transformer (3) which detects a fault current in a multi-phase alternating current circuit (1), a residual current detection circuit (4), a triggering device (5) which contacts in the AC circuit (1) opens, supplying a test circuit (6) according to one serving for the simulation of a fault current test current by switching on a test switch (6a), and a filter and amplifier unit (10) (between the sum current transformer (3) and the residual current detection circuit 4 ) is provided. Here, an operational amplifier (10a) is provided as the amplifier element, so that a secondary-side output current Is of the sum current transformer (3) is amplified by a gain corresponding to the set one at a sensitivity setting (11) value. In the Fl-switch, an active filter circuit including the operational amplifier (10a) in the filter and amplifier unit (10) is installed. When a test is run, the active filter circuit is switched from a low-pass filter circuit to a band-pass filter circuit, so that a noise and an offset component is eliminated, which could cause a malfunction of the test.