Residual current circuit breakers (RCCB) switch off the power supply when dangerously high residual currents occur. In this way, they 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 B switches are universally sensitive at frequencies from 0 Hz (smooth DC residual currents) to 150 kHz. They are resistant to increased surge currents and storms. SK series residual current circuit breakers stand for residual current protection and high system availability. They are characterized by a lower response sensitivity at higher frequencies. The SK characteristic curve is optimized for systems in which no fire protection is required. Standard devices are designed for monitoring circuits with a rated voltage of 230 V, 400 V and a rated frequency of 50 Hz. With an airtight encapsulated release made of a special alloy and the stainless steel switch lock, residual current circuit breakers in HD design are particularly protected against corrosion, harmful gases, moisture and strong temperature fluctuations. Properties: high immunity to operational leakage and fault currents at frequencies from 1 kHz, universal current sensitive for fault currents with frequencies and mixed frequencies from 0 Hz (smooth direct current) to 150 kHz, mains voltage independent tripping for fault currents of type A, voltage dependent detection of smooth direct fault current and alternating fault currents with frequencies not equal to 50/60 Hz, full functionality with mains voltages from at least 50 V AC on any two active conductors, 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', connection C1 neutral conductor position on the left, mounting type: quick fastening on mounting rail, installation position as desired, feed preferably from above, areas of application: commercial and industrial installations with TN-S, TT and TN-CS systems in which power electronics equipment is used without galvanic network isolation, such as frequency converters, switching power supplies, high-frequency converters. Photovoltaic and UPS systems with transformerless inverters. Notes: suitable for use in 50 Hz AC networks, RCCB for other frequencies on request.Not intended for use in DC networks or on the output side of controlled electrical equipment such as frequency converters.