Residual current circuit breakers (RCCBs) switch off the power supply when dangerously high residual currents occur. They thus protect people, animals and systems. DFS 4 are two- or four-pole residual current circuit breakers for single- or three-phase networks. In the standard version, the compact devices are four division units wide. They are available with many different residual current types and versions with rated currents of up to 125 A. The large double-deck terminals can also accommodate large conductor cross-sections. The tripped position of the multi-function switch toggle makes troubleshooting easier. The free label software helps with labeling. The twin version enables the residual current circuit breaker to be tested for functionality without switching off the circuit. In this version, two complete RCCBs are combined: If both devices are switched on, one switch can be triggered using the test button. The second FI takes over the current flow and the protective function. Type A switches are sensitive to pulse and alternating current. This function is independent of the mains voltage. Standard devices are designed for monitoring circuits with a rated voltage of 230 V, 400 V and a rated frequency of 50 Hz. Properties: Functional test of the residual current circuit breaker without interrupting the power supply, standard-compliant residual current protection even during the test procedure, no costs due to system downtime, high system availability, tripping independent of mains and auxiliary voltage, sensitive to alternating and pulsating direct residual currents (type A), small size for all rated currents, high short-circuit strength, double-sided double-deck terminals for large conductor cross-sections and rail connection, switch position indicator, viewing window for labels, multi-function switch toggle with three positions: 'on', 'off', 'tripped', mounting type: quick attachment to mounting rail, installation position as desired, feed direction as desired, areas of application: power supplies for residential and commercial buildings as well as industrial plants with TN-S, TT and TN-CS networks. In IT networks, residual current circuit breakers from this series can be designed to switch off in the event of a second fault. The twin version enables the regularly required functional test to be carried out without interrupting the power supply, making it ideal for laboratory or IT areas. It cannot be used in TN-C networks or to protect systems in which electronic equipment can cause smooth DC residual currents or residual currents with frequencies other than 50 Hz. Notes: WES 2 restart lock installed at the factory.