Residual current circuit breakers (RCCB) 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. Type A switches are sensitive to pulse and alternating current. This function is independent of the mains voltage. Residual current circuit breakers in W version are optimized for switch heating systems. They have a rated frequency of 16 2/3 Hz for railway systems up to 500 V. Properties: two-pole version (4 TE) with two integrated auxiliary switches (2 S) three-pole version (4 TE) with one integrated auxiliary switch (1 S) tripping independent of the mains and auxiliary voltage, sensitive for 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 labeling labels, multi-function switch toggle with three positions: 'on', 'off', 'tripped', connection C1 neutral conductor position as desired, mounting type: quick fastening on mounting rail, installation position as desired, feed direction as desired, areas of application: preferably in earthed power grids for railways to protect point heating systems, use in TN-C networks and to protect systems is excluded. in which electronic equipment can cause smooth DC fault currents.