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

Technical Dossier

Product Details And Specifications

Mitsubishi Electric S-K Series Technical Notes

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.

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.