SINOFUSE RS309-MF-S Series 700V/750V High-Speed Bolt-Connected Fuse
The SINOFUSE RS309-MF-S Series is a cylindrical bolt-connected high-speed fuse family designed for demanding electrical protection applications in electric vehicles, power conversion systems, energy storage equipment, and industrial power electronics.
According to the SINOFUSE manufacturer specification, the series is rated at AC/DC 700V under IEC specifications and DC 750V under UL specifications. It covers 16 rated-current options across two ranges: 70A–100A and 225A–800A.
RS309-MF-S fuses feature an aR utilization category, compact cylindrical construction, low I²t characteristics, high breaking capacity, and resistance to current surges, mechanical vibration, impact, temperature variation, and demanding operating environments.
RS309-MF-S Series Technical Specifications
- Manufacturer: SINOFUSE
- Series: RS309-MF-S
- Product Type: Cylindrical bolt-connected high-speed fuse
- IEC Rated Voltage: AC/DC 700V
- UL Rated Voltage: DC 750V
- Rated Current Ranges: 70A–100A and 225A–800A
- Utilization Category: aR
- AC Breaking Capacity: 100kA
- DC Breaking Capacity: 50kA
- DC Time Constant: ≤15ms
- Performance Standards: UL 248 and IEC 60269
- Safety and Application Reliability References: ISO 8820 and GB/T 31465
- Certifications: CE and UL, as specified by the manufacturer
- Environmental Compliance: RoHS
Key Features
The RS309-MF-S Series combines high breaking capacity with compact construction and current-limiting characteristics suitable for demanding electrical protection systems.
- Compact cylindrical bolt-connected construction
- Low pre-arcing and total clearing I²t characteristics
- High breaking capacity for AC and DC applications
- Resistance to current surges and mechanical impact
- Resistance to vibration and demanding temperature conditions
- Suitable for road-vehicle electrical applications
- Multiple mechanical sizes for different current ratings
RS309-MF-S Model Range
The RS309-MF-S Series includes 16 rated-current models across three mechanical size groups: 3SA, 6TA, and 7TA.
The available ratings are divided into two groups: 70A–100A and 225A–800A. The manufacturer does not list RS309-MF-S models between 101A and 224A in this specification.
Mechanical Sizes and Mounting Requirements
| Size Code | Current Ratings | Mounting Bolt | Recommended Torque |
|---|---|---|---|
| 3SA | 70A, 80A, 90A, 100A | M8 | 12 ±1 N·m |
| 6TA | 225A, 250A, 275A, 300A, 325A, 350A, 400A | M10 | 21 ±1 N·m |
| 7TA | 450A, 500A, 600A, 700A, 800A | M10 | 21 ±1 N·m |
The mounting hardware and tightening torque must be selected according to the exact fuse model and manufacturer installation requirements. Reliable terminal contact is important for maintaining proper electrical and thermal performance.
RS309-MF-S Electrical Performance Data
The following table summarizes the rated current, mechanical size, pre-arcing I²t, total clearing I²t, and power-loss values provided in the manufacturer specification.
| Model | Size | Pre-Arcing I²t (A²s) | Total Clearing I²t (A²s) | Power Loss (W) |
|---|---|---|---|---|
| RS309-MF-S70A | 3SA | 385 | 1,520 | 18 |
| RS309-MF-S80A | 3SA | 540 | 2,210 | 20 |
| RS309-MF-S90A | 3SA | 760 | 3,320 | 23.5 |
| RS309-MF-S100A | 3SA | 1,100 | 4,980 | 25 |
| RS309-MF-S225A | 6TA | 9,200 | 29,900 | 45 |
| RS309-MF-S250A | 6TA | 12,300 | 40,300 | 47.5 |
| RS309-MF-S275A | 6TA | 15,300 | 49,700 | 51 |
| RS309-MF-S300A | 6TA | 23,000 | 59,900 | 56 |
| RS309-MF-S325A | 6TA | 34,500 | 74,500 | 60 |
| RS309-MF-S350A | 6TA | 28,500 | 88,900 | 64 |
| RS309-MF-S400A | 6TA | 52,000 | 119,000 | 77 |
| RS309-MF-S450A | 7TA | 41,500 | 132,000 | 95 |
| RS309-MF-S500A | 7TA | 56,000 | 168,000 | 105 |
| RS309-MF-S600A | 7TA | 76,600 | 249,000 | 120 |
| RS309-MF-S700A | 7TA | 95,700 | 325,000 | 125 |
| RS309-MF-S800A | 7TA | 124,000 | 428,000 | 140 |
Manufacturer Data Note: The published electrical test data were obtained under DC test conditions. The manufacturer specifies test time constants and circuit arrangements with reference to IEC 60269 and UL 248. Actual protection performance should be evaluated against the applicable system operating conditions.
Understanding I²t Characteristics
The I²t characteristic is an important consideration when selecting high-speed fuses for power-electronic protection.
Pre-arcing I²t represents the current-squared integral accumulated before the fuse element melts. Total clearing I²t includes the energy accumulated throughout the complete interruption process.
These characteristics can be relevant when coordinating fuse protection with semiconductor devices, power converters, and other equipment sensitive to fault energy.
Engineers should compare the fuse characteristics with the protection requirements of the equipment and verify the complete circuit conditions rather than selecting a fuse based only on rated current.
RS309-MF-S Typical Applications
According to the SINOFUSE manufacturer specification, the RS309-MF-S Series is suitable for electrical protection applications involving road vehicles, power conversion equipment, energy storage systems, and related industrial electrical equipment.
- Electric vehicle drive power systems
- Power conversion equipment
- Battery energy storage and power systems
- Variable frequency controllers
- Charging equipment
- Automotive electrical systems
- Industrial power electronics
- Electrical conductor protection
- Short-circuit protection
- Backup protection
Protection Category and Fuse Coordination
The RS309-MF-S Series uses the aR utilization category.
The aR category is associated with partial-range high-speed fuse protection. These fuses are commonly considered for applications requiring rapid interruption of high fault currents and protection of power-electronic equipment.
Because aR protection is not full-range protection, the complete electrical system may require additional overload protection or appropriate coordination with other protective devices.
For replacement or new equipment applications, the correct RS309-MF-S model should be verified against the required current rating, voltage rating, breaking capacity, time-current characteristics, I²t performance, and mechanical installation requirements.
Continuous Current Recommendation
The manufacturer recommends that long-term continuous operating current should not exceed 80% of the fuse rated current under normal operating conditions.
This recommendation should be considered together with ambient temperature, enclosure conditions, ventilation, terminal connections, and other application-specific factors.
Operating Conditions
The RS309-MF-S Series is designed for demanding operating environments. The manufacturer provides the following normal and permitted environmental conditions.
- Normal Ambient Temperature: -5°C to 40°C
- Permitted Ambient Temperature: -40°C to 120°C
- Product Storage Temperature: -40°C to 120°C
- Packaged Storage Temperature: -40°C to 70°C
- Normal Operating Altitude: Up to 2000m
- Permitted Operating Altitude: Up to 4500m
- Pollution Degree: Class III
Operating conditions outside the normal range may require parameter correction or additional application evaluation. For ambient temperatures above 40°C, the manufacturer specifies that rated-current correction may be necessary.
High-Altitude Application Considerations
High-altitude operation can affect fuse thermal performance, air pressure, and electrical insulation strength.
For certain enclosed installations where internal operating temperature does not decrease sufficiently with increasing altitude, the manufacturer specifies a current-derating guideline of approximately 2% to 5% per 1000m.
The manufacturer also notes that air insulation strength decreases at higher altitudes. Electrical clearances between live parts, adjacent components, and grounded structures should therefore be evaluated for installations above normal operating altitude.
Vibration and Mechanical Reliability
The RS309-MF-S Series is designed to withstand mechanical vibration and impact encountered in demanding electrical environments.
The manufacturer references GB2423.10-2008 4.1.2.6 and QC/T 413-2002 for vibration and impact resistance.
The series is also described as suitable for road-vehicle body mounting and rail-transport vibration Class II operating environments.
Applications involving unusually severe vibration or mechanical stress may require additional evaluation and testing.
Mounting and Installation Considerations
The manufacturer specifies that the fuse connection terminals must maintain stable and reliable electrical contact.
Depending on the installation arrangement, RS309-MF-S fuses may be mounted vertically, horizontally, or at an inclined angle, provided that electrical contact integrity is maintained.
Engineers should verify the mounting dimensions, bolt size, tightening torque, electrical clearance, and thermal operating conditions before installation.
Periodic inspection should include checking for contamination, oxidation, mechanical damage, and deterioration of electrical contacts. Mechanically damaged fuses must be replaced.
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Related SINOFUSE Technical Resources
Explore additional SINOFUSE fuse families, technical information, and related electrical protection products.
- SINOFUSE Fuse Solutions – Brand & Technical Overview
- SINOFUSE RS309-MF Series 700V/750V High-Speed Bolt-Mounted Fuse
- SINOFUSE RS309-MF-EV Series AC/DC 750V gR Cylindrical Bolt-Connected Fuse
Series Selection Note: RS309-MF-S, RS309-MF, and RS309-MF-EV are separate fuse families. Similar rated voltages or current ratings do not establish mechanical or electrical interchangeability. Exact replacement suitability must be verified using the applicable manufacturer specifications.
Industrial Sourcing and Technical Support
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For RS309-MF-S availability, technical information, or quotation requests, please provide the exact model number, rated current, required quantity, and relevant equipment or application information.