Littelfuse LLSRK.400 - RK1 fuses are extremely current-limiting fuses meaning they greatly reduce or eliminate damage to circuits and equipment under short-circuit conditions. Replacing existing Class H, K and RK5 fuses with RK1 fuses is one of the easiest ways to immediately improve the protection of plant workers and equipment.
Littelfuse

LLSRK.400

Alternate Item Number: LSRK.400T

UPC: 079458350234

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Overview

Littelfuse RK1 fuses (SKU: LLSRK.400) are high-performance current-limiting fuses engineered to deliver unparalleled protection for industrial electrical systems. Designed as a direct replacement for Class H, K, and RK5 fuses, these fuses significantly reduce or eliminate damage to circuits and critical equipment during short-circuit conditions, ensuring operational continuity and worker safety. With Littelfuse’s decades of expertise in circuit protection, the RK1 series stands as a trusted solution for facilities seeking to upgrade their electrical infrastructure with minimal downtime and maximum reliability. The RK1 fuses are specifically formulated to meet the rigorous demands of industrial environments, where electrical faults can lead to catastrophic failures, costly repairs, and extended outages. By integrating Littelfuse RK1 fuses into your system, you benefit from their exceptional current-limiting capabilities, which restrict fault currents to safe levels before they escalate. This proactive protection not only safeguards sensitive equipment such as motors, transformers, and control panels but also enhances overall system stability. Unlike conventional fuses, RK1 models provide a higher degree of precision in fault interruption, reducing the risk of arc flash and associated hazards, which is critical for compliance with OSHA and NFPA 70E safety standards. Typical applications for Littelfuse RK1 fuses span a wide range of industries, including manufacturing plants, data centers, utilities, and commercial buildings. They are particularly well-suited for protecting branch circuits, panelboards, and motor control centers where reliable fault interruption is paramount. Professionals in electrical engineering and maintenance teams favor RK1 fuses for their ease of installation and compatibility with existing Class H, K, and RK5 fuse holders, eliminating the need for costly retrofits. Additionally, these fuses are available in a variety of ampere ratings to accommodate diverse system requirements, from low-voltage distribution to high-fault current scenarios. Selecting the right fuse for an industrial application involves evaluating factors such as interrupting rating, voltage rating, and coordination with upstream protective devices. Littelfuse RK1 fuses are rated for high interrupting capacities, often exceeding 200,000 amperes, making them ideal for systems with substantial fault current potential. Their time-current characteristics are optimized for fast response, ensuring rapid clearing of faults while maintaining coordination with downstream protective devices. This balance of speed and selectivity is essential for minimizing nuisance tripping and maintaining system reliability. Beyond their technical performance, Littelfuse RK1 fuses are backed by the manufacturer’s global reputation for innovation and quality in circuit protection. Littelfuse, a leader in the industry since 1927, is known for its commitment to rigorous testing and adherence to international standards such as UL, CSA, and IEC. The RK1 series is no exception, having undergone extensive validation to ensure consistent performance in the most demanding conditions. For facilities prioritizing safety, efficiency, and long-term cost savings, upgrading to Littelfuse RK1 fuses represents a strategic investment in electrical system resilience. In summary, Littelfuse RK1 fuses (SKU: LLSRK.400) provide a robust solution for industrial current-limiting protection, combining advanced engineering with practical installation benefits. Whether you are replacing outdated fuses or designing a new system, RK1 fuses deliver the reliability and performance required to protect personnel, equipment, and operations in today’s high-stakes industrial landscape.
  • High-performance current-limiting protection for industrial circuits
  • Direct replacement for Class H, K, and RK5 fuses
  • Reduces or eliminates damage during short-circuit conditions
  • High interrupting capacity (200,000+ amperes)
  • Fast response time for rapid fault clearing

Specifications

Amperage Rating
0.4 Amp
Application
All general purpose circuits
Brand Name
Littelfuse
Series
RK1
Special Features
Time-Delay
Standard
Standard 248-12 UL Listed/CSA
Sub Brand
LLSRK Series
Type
Class RK1
Fuse Block 600VAC 600VDC Class CC 30A 1/4in Quick Connect / Solder 90 angle screw Knob Panel Mount

GPM-SRR90

Fuse Block 600VAC 600VDC Class CC 30A 1/4in Quick Connect / Solder 90 angle screw Knob Panel Mount
Fuse Holder Modulostar® Size 10x38 IEC 690VAC 690VDC 3-Pole IP20

E1062696

Fuse Holder Modulostar® Size 10x38 IEC 690VAC 690VDC 3-Pole IP20
Fuse Holder UltraSafe™ 800VAC 1000VDC UL Fuse size 14x51 1-Pole Visual Indicator Microswitch Pressure Plate IP20

C331156

Fuse Holder UltraSafe™ 800VAC 1000VDC UL Fuse size 14x51 1-Pole Visual Indicator Microswitch Pressure Plate IP20
Fuse Block 1500VAC 1500VDC 400A 1-Pole Stud M8

1SCM8

Fuse Block 1500VAC 1500VDC 400A 1-Pole Stud M8
9F61 Size B Clips 1.6in

9F61BWW460

9F61 Size B Clips 1.6in
POWR-JAW clamps improve the contact between fuse and clip. The unnecessary heat from poor contact due to the loss of spring force in the clips can cause nuisance fuse opening and premature aging of surrounding components. High temperature phenolic resin knob designed for the most severe environments 7 sizes to provide effective coverage. Simple design makes installation easy.

LCC5

POWR-JAW clamps improve the contact between fuse and clip. The unnecessary heat from poor contact due to the loss of spring force in the clips can cause nuisance fuse opening and premature aging of surrounding components. High temperature phenolic resin knob designed for the most severe environments 7 sizes to provide effective coverage. Simple design makes installation easy.

Frequently Asked Questions about Littelfuse

What certifications and standards do Littelfuse products comply with?

Littelfuse products are certified to multiple international standards, including UL (Underwriters Laboratories), CSA (Canadian Standards Association), CCC (China Compulsory Certification), and EAC (Eurasian Conformity). Customers can verify specific product certifications by consulting individual product datasheets on Littelfuse.com, which provide comprehensive details about standards compliance for each component.

What industries and applications are Littelfuse products used for?

Littelfuse products are critical for electrical protection and safety across multiple industrial sectors, including manufacturing, automation, power distribution, and electrical control systems. Their comprehensive product portfolio serves industries that require robust electrical protection, including motor and pump applications, solar installations, programmable logic controllers (PLCs), electrical switch panels, and critical infrastructure environments. Key product lines protect against overcurrent, voltage transients, ground faults, and temperature-related electrical risks, ensuring equipment safety and operational reliability.

What technical support does Littelfuse offer?

Littelfuse offers comprehensive technical support through multiple channels. Their Technical Hotline (800-TEC-FUSE) provides direct access to engineers who can help identify issues and recommend solutions. Additionally, Littelfuse offers extensive online Technical Resources at Littelfuse.com, including datasheets, product manuals, whitepapers, application guides, and online design tools. Their experienced product and application engineers also provide step-by-step support from design to installation.

What are the main product lines offered by Littelfuse?

Littelfuse offers comprehensive industrial protection and control product lines, including fuses, fuse holders, protection relays, temperature sensors, and electrical safety components. Their key product categories span surge protective devices, custom OEM products, electrical switch panels, medium voltage fuses, ground-fault protection relays, motor and pump protection devices, and temperature sensors. These products are designed to minimize electrical safety hazards, limit equipment damage, improve productivity, and safeguard personnel from electrical faults.

What are the key features of Littelfuse products?

Littelfuse products feature exceptional circuit protection technologies with key characteristics including UL/IEC safety standard compliance, low internal resistance, and advanced protective capabilities across multiple product lines. Their components provide critical protection for industrial systems, offering features like overcurrent protection, voltage transient suppression, and resettable protection devices with ultra-low resistance and compact designs. Key product lines include fuses, metal oxide varistors (MOVs), TVS diodes, PolySwitch devices, and specialized electronic protection components that enhance system reliability and safety.

What environmental ratings do Littelfuse products have?

Littelfuse products feature comprehensive environmental ratings, including NEMA Type 1, 2, 3, 3R, 4/4X, 12, and 13 certifications, as well as IP65 protection. These ratings ensure superior protection in diverse industrial environments, with an operating temperature range of -40°F to +131°F (-40°C to +55°C). Many products also include UV-stabilized materials and neoprene gaskets for enhanced durability in outdoor and challenging conditions.

What accessories are available for Littelfuse products?

Littelfuse offers several key accessories across their product lines, including fuse holders, voltage monitoring modules, and terminal connectors. Specific accessories include the LPSM003ZXID (indicating) and LPSM003Z (non-indicating) POWR-SAFE Dead Front fuse holders for Class CC and Midget-Style fuses, the VRM6048 voltage monitor accessory module, and female quick connect terminals (P1015 series) in various wire gauge sizes. These accessories are designed to enhance protection, monitoring, and connectivity for Littelfuse electrical components.

What is Littelfuse's warranty policy?

Littelfuse provides comprehensive warranty details on their official website at www.littelfuse.com/warranty. Customers should visit this page to review the specific warranty terms and conditions for their specific product lines. For direct warranty support or questions, customers can contact Littelfuse Technical Support at 1-800-TEC-FUSE or email [email protected].

What communication protocols do Littelfuse products support?

Littelfuse supports a comprehensive range of industrial communication protocols, including PROFIBUS, PROFINET, EtherNet/IP, DeviceNet, Modbus RTU, and CANopen. Our products provide flexible connectivity solutions across multiple industrial automation platforms, enabling seamless integration with various control systems and network architectures.

How are Littelfuse products typically installed?

Littelfuse products are typically installed using specialized mounting hardware like fuse holders, blocks, and panels designed for specific industrial applications. The POWR-SAFE Dead Front holders, for example, provide optimum protection for Class CC and Midget-Style fuses, supporting installations up to 600 VAC/DC. Installation often involves using precision terminals with strain relief, such as 0.25 in. female quick connect terminals, to ensure secure and safe electrical connections in industrial control systems.