The ABB S201-K4 (order number 2CDS251001R0337) is a high-performance miniature circuit breaker from the System Pro M Compact S200 series. Designed for DIN rail mounting according to EN 60715 standard (35mm rail), this 1-pole MCB provides reliable overcurrent and short-circuit protection for motor control circuits, transformers, lighting systems, and other inductive loads with high start-up currents.

Protection Mechanism: The S201-K4 features two independent tripping mechanisms that work in tandem to ensure comprehensive circuit protection. The thermal tripping mechanism provides delayed overload protection using a bimetallic strip that responds to sustained overcurrent conditions. The electromagnetic tripping mechanism delivers instantaneous short-circuit protection through a solenoid coil that triggers when current exceeds the magnetic threshold. This dual-mechanism design ensures fast and accurate fault response, minimizing equipment damage and enhancing electrical safety.

Tripping Characteristic K: The K-curve characteristic is specifically designed for the protection of motor control circuits and associated equipment. It features a very sensitive thermal curve for overload protection, combined with a magnetic tripping threshold of 8 times the rated current (In). For the S201-K4 rated at 4A, this means electromagnetic tripping occurs when current reaches 32A. This high magnetic threshold is specifically engineered to avoid nuisance tripping caused by inrush currents and surge peaks that commonly occur during motor starting and transformer energization, while still providing reliable protection against sustained overcurrent conditions. The K characteristic is defined according to DIN VDE 0660 for power circuits, motors, transformers, lamps, and line protection.

Electrical Specifications: The device is rated for 230/400V AC operation with a maximum operating voltage of 253V for single-pole configuration and 440V for multi-pole configurations. For DC applications, it supports up to 72V DC for single-pole operation. The short-circuit breaking capacity is 6kA in accordance with IEC/EN 60898-1 for household and similar installations, and 10kA in accordance with IEC/EN 60947-2 for industrial applications. The rated impulse withstand voltage is 4kV at 2000m altitude, with a rated insulation voltage of 440V. The device operates at 50-60 Hz and achieves current limiting class 3, significantly reducing let-through energy during short-circuit events. Dielectric test voltage is 2kV at 50/60 Hz for 1 minute. Power loss is approximately 1.4W to 1.7W per pole under rated operating conditions.

Mechanical Design: The S201-K4 occupies a single modular width of 17.5mm, conforming to the standard DIN rail module size (1 modular spacing). Overall dimensions are approximately 17.5mm in width, 88-100mm in height, and 68-76mm in depth (mounting depth 68-69mm). The device features IP20 finger-safe protection on the terminal side and IP40 protection on the housing side, preventing accidental contact with live parts during installation and maintenance. The compact form factor enables space-efficient panel design, accommodating up to 12 devices per standard 210mm DIN rail section. Housing material is insulation group II (RAL 7035 light grey).

Termination and Wiring: The circuit breaker is equipped with patented twin cage terminals (failsafe bi-directional cylinder-lift terminals) with captive screws, designed to accommodate solid or stranded copper conductors across a wide range of cross-sections. Solid conductors from 0.75mm² to 35mm² are supported, while fine-stranded conductors from 0.75mm² to 25mm² can be terminated. Wire stripping length is 12.5mm with a recommended tightening torque of 2.8 Nm using a Pozidriv 2 screwdriver. The terminals feature finger-safe design, allowing safe installation without special tools. Both top and bottom terminals can be used as line or load side, providing flexible installation options. The terminals also support simultaneous connection to busbars and cables.

Visual Indication and Operation: A clear red-green contact position indicator (CPI) provides immediate visual confirmation of the switching state. Red indicates closed position (circuit ON), while green indicates open position (circuit OFF). The large toggle lever is ergonomically designed for comfortable manual operation with distinct I/ON and O/OFF position markings. The actuator is made of insulation group II material in black, sealable for tamper-proof applications. A busbar slot on the back of the housing ensures optimal visibility during installation when used with comb-type busbars. The device can be mounted in any orientation without affecting performance.

Environmental and Compliance: The S201-K4 operates reliably across a wide temperature range from -25°C to +55°C, with storage capability from -40°C to +70°C. The device complies with RoHS regulations (RoHS conform, date of RoHS guidelines 3/31/15) and is SVHC-free (Substances of Very High Concern) with REACH compliance. It meets IEC/EN 60898-1 for household and similar installations, as well as IEC/EN 60947-2 for low-voltage switchgear and controlgear. UL1077 and CSA 22.2 No. 235 certifications are also available for North American applications, expanding its suitability for global use in residential, commercial, and industrial contexts. Country of origin is Germany, with customs tariff number 85362010. WEEE category is 5 (Small Equipment).

Durability and Reliability: The S201-K4 is rated for 20,000 electrical operating cycles and 20,000 mechanical operating cycles, ensuring long service life in demanding applications. The current-limiting design significantly reduces the let-through energy during short-circuit conditions, protecting downstream equipment from thermal and mechanical stress. The robust construction incorporates high-quality materials and precision manufacturing processes characteristic of ABB's System Pro M Compact series, delivering dependable long-term performance in diverse operating environments.

Application Scenarios: This miniature circuit breaker is ideally suited for a wide range of applications including motor control circuits and motor protection, transformer primary and secondary protection, lighting circuits with high inrush currents (HID, fluorescent, LED drivers), industrial control panels and machine controls, commercial building electrical systems, auxiliary circuits in industrial environments, power circuits with high start-up currents, and equipment where surge peaks are present. The K characteristic makes it particularly suitable for applications where functional peak currents can reach up to 10 times the rated current without causing nuisance tripping, while still providing excellent protection to cables, lines, and damageable elements in the overcurrent range.

Accessories and Compatibility: The S201-K4 is compatible with the full range of S200 series accessories, including auxiliary contacts (S2C-H6R, S2C-H11L) for remote status indication, shunt trips for remote tripping, undervoltage releases for voltage monitoring, alarm contacts for fault signaling, and comb-type busbars for efficient multi-pole power distribution. Bottom-fitting auxiliary contacts can be mounted on S200 to save 50% of panel space compared to side-mounted alternatives. All accessories mount directly to the device without requiring additional space, maintaining the compact 17.5mm module width.