Littelfuse THDB421A - The THDB Series combines accurate timing circuitry with high power, solid-state switching. It can switch motors, lamps, and heaters directly without a contactor. You can reduce labor, component cost, and increase reliability with these small, easy-to-use, THDB Series timers. Operation (Delay-on-Break): Input voltage must be applied before and during timing. Upon closure of the initiate switch, the output energizes. The time delay begins when the initiate switch is opened. The output remains energized during timing. At the end of the time delay, the output de-energizes. The output energizes if the initiate switch is closed when input voltage is applied. Reset: Reclosing the initiate switch during timing resets the time delay. Loss of input voltage resets the time delay and output.
Littelfuse

THDB421A

Alternate Item Number: THDB421A

UPC: 079458007848

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Overview

The Littelfuse THDB421A from the THDB Series represents a significant advancement in industrial timing control, offering a robust and reliable solution for demanding applications. This dedicated Delay-on-Break timer seamlessly integrates accurate microcontroller-based timing circuitry with high-power, solid-state switching capabilities. Designed to directly control motors, lamps, and heaters, the THDB421A eliminates the need for external contactors, leading to substantial reductions in labor, component costs, and overall system complexity. Its compact and user-friendly design makes it an ideal choice for OEMs and system integrators seeking to enhance efficiency and reliability. The THDB421A operates on a Delay-on-Break principle, ensuring precise control sequences. Input voltage must be applied before and during the timing cycle. Upon closure of the initiate switch, the output immediately energizes. The time delay sequence commences only when the initiate switch is subsequently opened. Throughout this delay period, the output remains energized, providing continuous operation. At the conclusion of the programmed time delay, the output de-energizes. Importantly, if the initiate switch is closed when input voltage is initially applied, the output will energize, providing immediate functionality where required. Resetting the THDB421A is straightforward and flexible. Reclosing the initiate switch during the timing delay will reset the timer and restart the delay sequence. Alternatively, a loss of input voltage will effectively reset both the time delay and the output state, ensuring a safe and predictable return to a default condition. This dual reset capability offers adaptability for various operational scenarios and safety protocols. Key features and benefits of the Littelfuse THDB421A include: * **Microcontroller-Based Accuracy:** Offers exceptional repeat accuracy of +/- 0.5% and factory calibration of +/- 1%, ensuring consistent and precise timing performance critical for industrial processes. * **High Power Switching:** Capable of handling high load currents up to 20A, with an impressive 200A inrush capability, allowing direct control of demanding loads like motors, lamps, and heaters without the need for additional contactors. * **Solid-State Encapsulation:** The totally solid-state design, encapsulated to protect against shock, vibration, and humidity, ensures longevity and eliminates the wear and arcing associated with mechanical relays. * **Efficient Heat Transfer:** Features a metalized mounting surface designed to facilitate efficient heat transfer, crucial for maintaining optimal performance in high-current applications. * **Compact and Cost-Effective:** Its small footprint and low-cost design provide flexibility for OEM applications, reducing both physical space requirements and overall system expenses. This timer is well-suited for a wide array of industrial applications, including automation systems, HVAC controls, process monitoring, and motor control circuits where precise timing and high-power switching are paramount. The THDB421A is compatible with optional accessories such as the P1004-95 Versa-Pot for remote time delay adjustment and P1015-64 female quick connect terminals for secure and reliable connections. Trust Littelfuse, a recognized leader in circuit protection and control, for your critical timing needs with the THDB421A.
  • Microcontroller-based for precise timing accuracy (+/- 0.5% repeat accuracy)
  • High power solid-state switching up to 20A continuous, 200A inrush
  • Directly controls motors, lamps, and heaters without a contactor
  • Delay-on-Break operation with flexible reset options
  • Solid-state encapsulated design for durability and protection

Specifications

Brand Name
Littelfuse
Connection Type
Screw Terminal / Quick Connect
Current Rating
20 A
Material
Solid-state
Mounting
Surface mount with one #10 (M5 x 0.8) screw Mount
Number Of Poles
Surface mount with one #10 (M5 x 0.8) screw
Operating Temperature
-40 to 60 F
Operating Temperature, Maximum
60 F
Operating Temperature, Minimum
-40 F
Series
THDB
Special Features
10Y WARR
Standard
CE/UR/CSA
Sub Brand
SSAC
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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.