Mitsubishi S-N Series Magnetic Contactors — S-N25

Technical Dossier

Product Details And Specifications

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

The Mitsubishi Electric S-N Series magnetic contactors are among the most widely deployed switching devices in global heavy industry. Installed across petrochemical complexes, nuclear power auxiliary systems, oil refineries, steel mills, and large-scale water treatment facilities, the S-N Series has established a dominant position in motor control centers (MCCs) and distribution panels operating under IEC 60947-4-1 standards. Their compact frame-to-rating ratio, robust silver-alloy contact construction, and compatibility with Mitsubishi's NF-series circuit breakers and TH-N/TH-T overload relays make them the default specification in Asian and European industrial projects. The series covers a rated operational current range from 9 A to 800 A (AC-3 duty), accommodating applications from small pump starters to large compressor drives.

The Evolution of S-N Series Architecture

The S-N Series traces its lineage to Mitsubishi Electric's early magnetic contactor designs of the 1970s, which were engineered for Japan's expanding industrial base. The original S-N10 through S-N50 frames established the mechanical architecture: a double-break main contact system, a laminated silicon-steel electromagnet core, and a modular auxiliary contact block interface that has remained backward-compatible across multiple generations.

In the 1990s, Mitsubishi introduced the SD-N sub-series, which added surge suppression circuits and improved coil insulation for compatibility with PLC transistor outputs operating at 24 V DC. The 2000s saw the introduction of the SK-N and SN-series variants with enhanced arc chute geometry, reducing contact erosion rates by approximately 30% under AC-3 repetitive switching duty. Current production units comply with RoHS directives, substituting cadmium-free silver-tin oxide (AgSnO₂) contact materials for earlier silver-cadmium oxide (AgCdO) alloys. Older installed units using AgCdO contacts remain in service at many legacy sites; replacement contact kits are available for life extension without full contactor replacement. Coil voltage options have expanded from the original 200/220 V AC to include 24 V DC, 48 V DC, 100 V AC, 110 V AC, 200 V AC, 220 V AC, and 380 V AC variants, enabling integration with modern DCS and SCADA control architectures.

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

The following SKUs represent the core S-N Series range. Each entry identifies the frame size, rated current (AC-3), and primary application context.

S-N10: 9 A AC-3 contactor; standard motor starter for fractional-kW loads, DIN-rail mount.
S-N11: 11 A AC-3 contactor; compact frame for panel-space-constrained MCC bays.
S-N18: 18 A AC-3 contactor; 7.5 kW at 400 V; common in HVAC fan and pump circuits.
S-N20: 20 A AC-3 contactor; reversing and star-delta starter configurations.
S-N25: 25 A AC-3 contactor; 11 kW at 400 V; high-cycle-rate conveyor and compressor duty.
S-N35: 35 A AC-3 contactor; 15 kW at 400 V; process pump and agitator applications.
S-N50: 50 A AC-3 contactor; 22 kW at 400 V; medium motor control in refinery utilities.
S-N65: 65 A AC-3 contactor; 30 kW at 400 V; compressor and chiller motor control.
S-N80: 80 A AC-3 contactor; 37 kW at 400 V; heavy-duty pump and fan starters.
S-N95: 95 A AC-3 contactor; 45 kW at 400 V; large motor control center applications.
S-N125: 125 A AC-3 contactor; 55 kW at 400 V; industrial press and crane duty.
S-N150: 150 A AC-3 contactor; 75 kW at 400 V; high-inertia load starting.
S-N180: 180 A AC-3 contactor; 90 kW at 400 V; steel mill auxiliary drive control.
S-N220: 220 A AC-3 contactor; 110 kW at 400 V; large compressor and blower duty.
S-N300: 300 A AC-3 contactor; 132 kW at 400 V; power distribution switching in substations.
S-N400: 400 A AC-3 contactor; 200 kW at 400 V; main incomer switching in MCCs.
S-N600: 600 A AC-3 contactor; 315 kW at 400 V; large industrial drive bypass and transfer switching.
SD-N10: DC-coil variant of S-N10; 24 V DC coil for PLC direct output control.
SD-N25: DC-coil variant of S-N25; 24 V DC / 48 V DC coil options; DCS interface duty.
SD-N50: DC-coil variant of S-N50; surge-suppressed coil; suitable for solid-state relay interfaces.

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

Several S-N Series frames — particularly S-N10 through S-N50 units manufactured before 2005 with AgCdO contacts and non-RoHS coil assemblies — are no longer in standard production. Mitsubishi Electric's official end-of-life notifications for these variants have been issued, but installed base volumes at petrochemical and power generation sites remain substantial, creating sustained demand for verified replacement units and sub-components.

DriveKNMS maintains a dedicated inventory of new-old-stock (NOS), reconditioned, and functionally equivalent S-N Series contactors sourced through authorized distribution channels and controlled secondary markets. Each unit is individually cataloged by coil voltage, contact configuration (3NO main + auxiliary block type), and frame revision. For plant maintenance teams operating under long-term service agreements (LTSAs) that prohibit design changes, DriveKNMS can supply like-for-like replacements without requiring panel re-engineering or updated SIL assessments. Bulk procurement for scheduled turnaround maintenance is supported with lead-time commitments and certificate-of-conformance documentation.

Quality Control for the S-N Series Range

The S-N Series presents specific verification requirements due to its multi-decade production history and the prevalence of counterfeit units in secondary markets. DriveKNMS applies the following test protocol to all S-N Series stock prior to dispatch:

Coil resistance and inductance measurement: Each coil is tested at rated voltage and frequency to verify pull-in and drop-out voltage thresholds against Mitsubishi Electric factory specifications. DC-coil variants (SD-N sub-series) are tested for surge suppression diode integrity.
Main contact resistance: Four-wire milliohm measurement across each main pole at rated current. Contact resistance exceeding 1.5× the factory new value triggers contact replacement or unit rejection.
Auxiliary contact block verification: NO/NC state confirmation under simulated coil energization, including contact bounce measurement for high-speed PLC input applications.
Mechanical endurance check: Manual operation cycling to verify armature travel, return spring force, and interlock mechanism function.
Insulation resistance test: 500 V DC megohm test between poles and between poles and frame, minimum 100 MΩ acceptance criterion.
Visual and dimensional inspection: Arc chute condition, contact wear depth, coil bobbin integrity, and terminal torque verification per IEC 60947-4-1 maintenance guidelines.

All test records are retained and available for customer audit. Units supplied with third-party inspection certificates (SGS, BV, or equivalent) are available on request for critical plant applications.