Mitsubishi S-K50 / S-K65 – High-Capacity Magnetic Contactor | S-K Series AC Motor Starter Platform
Engineering Background
The S-K Series magnetic contactors are engineered by Mitsubishi Electric as part of their comprehensive motor control and protection lineup. Designed to IEC 60947-4-1 standards, the S-K50 and S-K65 are heavy-duty AC contactors built for demanding industrial environments where reliable motor switching, long electrical life, and compact panel integration are non-negotiable requirements.
Product Positioning
The S-K50 (50A rated) and S-K65 (65A rated) serve as the workhorses of medium-to-large motor control centers (MCCs), conveyor systems, compressor panels, and pump stations. Their robust silver-alloy contact construction and arc-quenching chamber design make them the preferred choice for procurement engineers specifying IEC-compliant motor starters across Asia-Pacific and global OEM projects.
Complete Technical Specifications
| Parameter | S-K50 | S-K65 |
|---|---|---|
| Rated Current (AC-3) | 50 A | 65 A |
| Motor Rating (400V, AC-3) | 22 kW | 30 kW |
| Motor Rating (200V, AC-3) | 11 kW | 15 kW |
| Rated Insulation Voltage | 690 V AC | |
| Rated Impulse Withstand Voltage | 6 kV | |
| Coil Voltage Options | AC 100V / 110V / 200V / 220V / 380V / 440V; DC 24V / 48V / 110V / 220V | |
| Frequency | 50 / 60 Hz | |
| Auxiliary Contacts (Standard) | 1NO + 1NC | |
| Mechanical Life | 10,000,000 operations | |
| Electrical Life (AC-3) | 1,000,000 operations | |
| Operating Temperature | -10°C to +60°C | |
| Storage Temperature | -40°C to +70°C | |
| Degree of Protection | IP20 (open type) | |
| Standards | IEC 60947-4-1, JIS C 8201-4-1, GB 14048.4 | |
| Mounting | 35mm DIN rail / screw mount | |
| Weight | approx. 1,140 g | |
| Country of Origin | Japan | |
Proven Application Environments
- Motor Control Centers (MCC): Direct-on-line (DOL) and star-delta starter panels for pumps, fans, and compressors up to 30 kW
- Conveyor & Material Handling: Reversing contactor pairs for bi-directional belt and roller conveyor drives
- HVAC Systems: Chiller compressor and air-handling unit (AHU) motor switching in commercial buildings
- Water Treatment Plants: Submersible pump and blower motor control with high cycle frequency
- OEM Machine Builders: Integrated into Mitsubishi FREQROL-A700 / FR-A800 VFD bypass circuits and soft-starter bypass panels
- PLC-Controlled Systems: Output-relay-driven coil activation from Mitsubishi MELSEC Q/L/iQ-R series PLCs
Engineering Advantages
- Silver-Cadmium Oxide (AgCdO) Contacts: Superior arc resistance and low contact resistance for extended electrical life under AC-3 duty
- Double-Break Main Contacts: Reduces arc energy per contact gap, enabling compact enclosure design without sacrificing interrupting capacity
- Integrated Arc Chute: Rapid arc extinction minimizes contact erosion and EMI generation in sensitive control environments
- Wide Coil Voltage Tolerance (±15%): Reliable pick-up and drop-out across fluctuating industrial supply voltages
- Modular Auxiliary Contact Blocks: Field-attachable side-mount auxiliary blocks (e.g., S-N11, S-N20) for expanded interlocking and feedback circuits
- DIN Rail & Screw Mount Compatibility: Flexible panel installation without additional adapters
- IEC / JIS / GB Triple Certification: Accepted by international inspection bodies for export projects
System Architecture & Signal Flow
In a typical PLC-driven motor control loop, the Mitsubishi MELSEC iQ-R series PLC outputs a 24V DC signal to a relay or SSR, which energizes the S-K50/S-K65 coil. The main contacts close, connecting the 3-phase supply (up to 690V AC) to the motor terminals. The 1NC auxiliary contact feeds back a “contactor closed” status signal to the PLC digital input, enabling closed-loop confirmation. An overload relay (e.g., Mitsubishi TH-N series) is wired in series with the main circuit to provide thermal protection, with its NC contact in the control circuit for automatic trip-out.
For reversing applications, two S-K50/S-K65 units are mechanically and electrically interlocked using the S-N11 auxiliary block’s NC contact cross-wired to the opposing contactor coil circuit, preventing simultaneous energization.
Sourcing & Quality Verification
- All units sourced through authorized Mitsubishi Electric distribution channels or verified OEM surplus with full traceability documentation
- Pre-shipment inspection includes: coil resistance measurement, contact resistance check (<1 mΩ), insulation resistance test (>100 MΩ at 500V DC), and mechanical operation verification
- Original manufacturer packaging, labels, and date codes preserved where available
- Certificate of Conformity (CoC) and test reports available upon request for project documentation
- Counterfeit screening performed against Mitsubishi Electric genuine part identification guidelines
Procurement Process
- Step 1 – Inquiry: Submit your BOM or part number to support@konmask.com with required quantity and delivery timeline
- Step 2 – Quotation: Receive a formal quotation with unit price, lead time, and shipping options within 24 business hours
- Step 3 – Order Confirmation: Confirm PO; payment via T/T, PayPal, or credit card accepted
- Step 4 – Inspection & Dispatch: Pre-shipment QC completed; tracking number issued within 2 business days of payment clearance
- Step 5 – After-Sales Support: 12-month warranty on genuine parts; technical support available via email or WhatsApp
Technical FAQ
Q: What is the difference between S-K50 and S-K65?
A: The S-K50 is rated for 50A / 22kW (400V AC-3) while the S-K65 handles 65A / 30kW. Both share the same frame size and mounting footprint, making them interchangeable in panel designs where future capacity upgrades are anticipated.
Q: Can the S-K50/S-K65 be used with a Mitsubishi FR-A800 VFD?
A: Yes. They are commonly used as bypass contactors or input-side isolation contactors in VFD installations. Ensure the coil voltage matches the control circuit supply and that the contactor is not switching the VFD output under load (use AC-1 duty rating for output-side applications).
Q: Are replacement coils and contact kits available?
A: Yes. Mitsubishi Electric offers replacement coil assemblies and contact kits for the S-K series. Contact us with your specific coil voltage requirement for availability.
Q: What overload relay is recommended for pairing?
A: Mitsubishi TH-N60KP (for S-K50) and TH-N120KP (for S-K65) are the factory-recommended thermal overload relays, providing direct mounting without additional adapters.
Q: Is CE marking available?
A: The S-K series complies with IEC 60947-4-1 which is the basis for CE marking under the Low Voltage Directive (LVD) 2014/35/EU. Declaration of Conformity documentation is available upon request.
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