Mitsubishi S-K Series Magnetic Contactors: S-K50 S-K65

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 within Mitsubishi's low-voltage switching apparatus lineup. Deployed extensively across global heavy industry — including petrochemical complexes, nuclear auxiliary systems, refinery motor control centers (MCCs), and steel mill drive panels — the S-K Series represents a standardized, IEC-compliant contactor family engineered for continuous-duty motor switching applications. Their compact DIN-rail and panel-mount form factors, combined with AC/DC coil options and broad auxiliary contact configurability, have made them a default specification in Asian and Southeast Asian industrial installations for over three decades. The series covers a rated current range from approximately 9 A to 150 A (AC-3 duty), addressing motor control requirements from small pump starters to large compressor drive circuits.

The Evolution of S-K Series Architecture

The S-K Series was introduced as part of Mitsubishi Electric's rationalized contactor platform, succeeding earlier S-N and S-T frame designs in specific current classes. The architecture is defined by a double-break main contact system, a laminated silicon-steel electromagnet core optimized for reduced inrush current, and a modular auxiliary contact block system (CA-series add-on blocks) that allows field reconfiguration without replacing the base unit.

Early production variants used asbestos-free silver-cadmium oxide (AgCdO) main contacts; later revisions transitioned to silver-tin oxide (AgSnO₂) contact material in compliance with RoHS directives, improving arc erosion resistance under high-cycle duty. Coil voltage options span 24 V DC, 100–110 V AC (50/60 Hz), 200–220 V AC, and 380–440 V AC, enabling integration into both legacy relay-logic panels and modern PLC-driven MCC architectures.

Compatibility note: S-K Series contactors use the same mounting footprint as selected S-N Series frames, allowing direct mechanical substitution in many panel layouts, though terminal torque specifications and auxiliary block interfaces differ between generations and must be verified before substitution.

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

The following SKUs represent the verified core catalog of the Mitsubishi Electric S-K Series. Models are classified by rated operational current (AC-3, 380 V) and primary application class.

Standard AC Motor Contactors

• S-K9: 9 A AC-3 contactor; 3-pole main contacts; suitable for 4 kW motor at 400 V.
• S-K11: 11 A AC-3 contactor; compact frame; used in conveyor and pump starters.
• S-K16: 16 A AC-3 contactor; standard auxiliary contact block interface; common in HVAC fan control.
• S-K18: 18 A AC-3 contactor; intermediate frame; used in compressor pilot circuits.
• S-K21: 21 A AC-3 contactor; 3-pole; suitable for 11 kW motor switching at 400 V.
• S-K25: 25 A AC-3 contactor; high-cycle duty rated; used in injection molding machine control.
• S-K32: 32 A AC-3 contactor; panel-mount or DIN-rail; common in water treatment MCC panels.
• S-K40: 40 A AC-3 contactor; 3-pole main + 1NO/1NC auxiliary standard; used in crane hoist circuits.
• S-K50: 50 A AC-3 contactor; reinforced main contact bridge; rated for 22 kW at 400 V; standard in refinery pump MCCs.
• S-K65: 65 A AC-3 contactor; heavy-duty frame; rated for 30 kW at 400 V; used in steel mill auxiliary drives.
• S-K80: 80 A AC-3 contactor; large frame; suitable for 37 kW motor control; common in chemical plant fan drives.
• S-K95: 95 A AC-3 contactor; high-capacity frame; used in large pump and blower starters.
• S-K115: 115 A AC-3 contactor; used in high-power motor control centers in power generation facilities.
• S-K125: 125 A AC-3 contactor; suitable for 55 kW motor at 400 V; deployed in offshore platform MCC panels.
• S-K150: 150 A AC-3 contactor; top-of-range S-K frame; used in large compressor and chiller motor starters.

Reversing & Auxiliary Configurations

• S-K50 (with CA-3DN): S-K50 base unit fitted with CA-3DN 3NO auxiliary contact block for multi-circuit interlocking.
• S-K65 (with CA-2DN): S-K65 base unit with CA-2DN 2NO/2NC auxiliary block; used in reversing starter assemblies.

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

Several lower-frame S-K Series models (S-K9 through S-K25) have entered end-of-production status in certain regional markets, with Mitsubishi Electric directing new designs toward the S-T and S-N Series successors. However, the installed base of S-K Series contactors in operational plants — particularly in Asia-Pacific petrochemical and power generation facilities — remains substantial, creating sustained demand for replacement units and spare contact kits.

DriveKNMS maintains a dedicated inventory program for S-K Series lifecycle support, covering: new-old-stock (NOS) units sourced from authorized regional distributors; tested-used units reconditioned to OEM contact gap and pressure specifications; and contact bridge/spring kits for field refurbishment of in-situ units. All sourced units are cross-referenced against Mitsubishi Electric's published supersession tables to confirm dimensional and electrical compatibility before dispatch.

For plant maintenance teams operating under long-term service agreements (LTSA) where panel redesign is not permissible, DriveKNMS provides documented substitution reports confirming S-K to S-K or S-K to S-N cross-compatibility on a per-model basis.

Quality Control for the S-K Series Range

Magnetic contactors present specific failure modes that require targeted test protocols beyond standard continuity checks. DriveKNMS applies the following procedures to all S-K Series units processed through its facility:

• Coil impedance measurement: AC coil resistance and inductance verified against OEM published values at rated voltage; DC coil pull-in and drop-out voltage thresholds tested under load.
• Main contact resistance: Four-wire milliohm measurement across each main pole at rated contact pressure; values exceeding 200 µΩ trigger contact replacement.
• Mechanical endurance check: Manual actuation cycle count and armature travel measurement to assess spring fatigue and contact wear depth.
• Auxiliary contact block verification: Each CA-series add-on block tested for NO/NC state accuracy and contact bounce duration using a digital contact analyzer.
• Dielectric withstand test: 2 kV AC applied between main circuit and control circuit for 1 minute per IEC 60947-4-1 requirements.
• Operational test under load: Units energized at rated coil voltage with resistive load applied to main contacts; switching waveform captured to confirm arc extinction within specification.

All test records are retained and available for customer review upon request. Units that fail any single test parameter are quarantined and not dispatched.

For S-K50, S-K65, and all S-K Series inquiries — including bulk orders, emergency replacement sourcing, and cross-reference requests:

• Email: [email protected]
• WhatsApp: +86 18359293191
• Web: driveknms.com