Mitsubishi S-K Series Contactors

Technical Dossier

Product Details And Specifications

Mitsubishi Electric S-K Series: Comprehensive Module Range and Technical Overview

The Mitsubishi Electric S-K Series magnetic contactors are a foundational component class deployed across global heavy industry, including petrochemical complexes, nuclear auxiliary systems, steel rolling mills, and offshore platform motor control centers (MCCs). Rated for AC-3 and AC-4 duty cycles per IEC 60947-4-1, the S-K Series covers a thermal current range from 9 A to 800 A, making it the standard selection for motor branch circuits from 2.2 kW to 400 kW at 400 V. The series is engineered for panel-mount and DIN-rail installation, with coil voltage options spanning 24 VDC, 110 VAC, 200 VAC, and 380 VAC to accommodate regional grid standards across Asia-Pacific, Europe, and the Americas. Auxiliary contact blocks, surge suppressors, and mechanical interlocks are available as factory-certified accessories, enabling direct integration into Mitsubishi MELSEC PLC-controlled motor management architectures.

The Evolution of S-K Series Architecture

The S-K Series traces its lineage to Mitsubishi Electric's early-generation SK contactors introduced in the 1970s for industrial motor switching. The original SK line used asbestos-free silver-alloy contacts and electromagnetic coils wound for single-voltage operation. By the mid-1980s, Mitsubishi transitioned to the S-K designation, introducing double-break main contacts, improved arc chutes, and modular auxiliary contact blocks (CA-series add-ons). The 1990s generation introduced wide-range coil technology (±15% voltage tolerance) and UL 508 / CSA C22.2 dual certification, enabling export to North American markets. The 2000s saw the introduction of the S-K Series with integrated surge absorbers and coil economy circuits for reduced heat dissipation in enclosed panels. Current production units comply with RoHS 2 and REACH directives. Legacy S-K models (pre-2005) are no longer manufactured but remain in active service across installed base equipment; cross-compatibility with current auxiliary blocks is maintained for most frame sizes up to S-K95. For frame sizes S-K150 and above, coil interface and mounting footprint differences require engineering review before substitution.

S-K Series Full Catalog & Functionalities (SKU List)

The following SKUs represent verified, commonly stocked models within the Mitsubishi Electric S-K Series. Each entry reflects the standard catalog designation. Coil voltage suffix (e.g., /AC200, /DC24) is specified at order time.

S-K9: 9 A AC-3 rated 3-pole contactor; 2.2–4 kW motor switching at 400 V; compact frame for space-constrained panels.
S-K11: 11 A AC-3 duty; suitable for 5.5 kW motors; standard DIN-rail mount; auxiliary contact block compatible.
S-K18: 18 A AC-3 rated; 7.5 kW motor control; double-break silver-alloy contacts; wide-range coil option available.
S-K20: 20 A AC-3 duty; 11 kW at 400 V; IEC 60947-4-1 compliant; coil options 24VDC–380VAC; CA-series aux block compatible.
S-K25: 25 A AC-3; 15 kW motor branch circuit; mechanical interlock accessory available for reversing contactor pairs.
S-K35: 35 A AC-3; 18.5 kW; reinforced arc chute; suitable for frequent-start duty cycles in compressor control.
S-K50: 50 A AC-3; 22–30 kW; panel-mount or busbar-mount configuration; integrated surge suppressor option.
S-K65: 65 A AC-3; 37 kW; heavy-duty frame; used in pump and fan motor control in water treatment facilities.
S-K80: 80 A AC-3; 45 kW; reinforced contact pressure spring; rated for 1,000,000 mechanical operations.
S-K95: 95 A AC-3; 55 kW; last frame size with full backward compatibility to pre-2005 auxiliary block accessories.
S-K120: 120 A AC-3; 75 kW; requires dedicated mounting rail; used in MCC bucket assemblies in chemical plants.
S-K150: 150 A AC-3; 90 kW; revised coil interface vs. legacy SK150; engineering review required for direct substitution.
S-K180: 180 A AC-3; 110 kW; three-phase motor control for large HVAC and industrial refrigeration compressors.
S-K220: 220 A AC-3; 132 kW; used in steel mill auxiliary drives and large pump stations; busbar connection standard.
S-K300: 300 A AC-3; 160–185 kW; high-capacity frame; deployed in offshore platform power distribution switchgear.
S-K400: 400 A AC-3; 220–250 kW; large-frame contactor for main incomer switching in industrial substations.
S-K600: 600 A AC-3; 315–355 kW; heavy industrial frame; used in primary motor feeders in mining and mineral processing.
S-K800: 800 A AC-3; 400 kW; top-of-range frame; deployed in high-power motor control centers in LNG terminals.

Sourcing Hard-to-Find & Obsolete S-K Series Parts

Quality Control for the S-K Series Range

Each S-K Series contactor processed by DriveKNMS undergoes a structured inspection protocol specific to electromagnetic switching devices. The procedure includes: (1) coil resistance measurement and insulation resistance test at 500 VDC between coil and frame; (2) main contact resistance measurement using a micro-ohmmeter at rated current to verify contact integrity below 100 µΩ per pole; (3) mechanical operation test — minimum 50 open/close cycles under no-load to verify spring return and armature seating; (4) auxiliary contact continuity and isolation verification per IEC 60947-1 Annex Q; (5) arc chute inspection for carbon tracking, erosion, and delamination; (6) coil energization test at 85% and 110% of rated voltage to confirm pull-in and drop-out thresholds. Units failing any parameter are quarantined and not offered for sale. Test records are retained for a minimum of five years and are available to customers on request.