ABB CT-APS.21S (Industrial-Grade OFF-Delay Timer Relay)

The ABB CT-APS.21S represents a precision-engineered timing solution designed for industrial automation environments demanding reliable delayed de-energization control. Manufactured in Sweden to ABB's exacting quality standards, this compact DIN rail timer combines universal voltage compatibility with an exceptionally wide timing range—from milliseconds to days—making it the versatile choice for applications spanning HVAC sequencing, motor protection, and process automation.

Built for professionals who require dependable timing control without compromise, the CT-APS.21S eliminates the complexity of managing multiple relay types. Its 24-240V AC/DC universal input accepts virtually any control voltage, while dual SPDT outputs deliver the flexibility to control multiple circuits simultaneously. Whether you're designing new control panels or retrofitting existing systems, this timer relay integrates seamlessly into diverse electrical architectures.

What sets the CT-APS.21S apart is its OFF-delay timing characteristic: outputs energize instantly when voltage is applied, then maintain their state for a preset duration after the control signal drops. This behavior proves essential for applications requiring controlled run-on periods—ventilation systems that must purge air after occupancy ends, coolant pumps protecting machinery during thermal shutdown, or conveyor systems ensuring complete material clearance before stopping.

Core Features & Benefits

→ Ultra-Wide Timing Spectrum (0.05 seconds to 300 hours)
Configure delays from 50 milliseconds for rapid sequencing to 12.5 days for extended run-on applications. Single device replaces multiple fixed-delay relays, reducing inventory costs and panel complexity. Logarithmic adjustment dial enables precise setting across the entire range without requiring external programming tools.

✓ Universal Voltage Architecture (24-240V AC/DC)
Eliminates voltage-specific relay selection in mixed control systems. Accepts AC or DC control signals without modification, simplifying spare parts management and reducing procurement complexity. Wide voltage tolerance maintains operation during supply fluctuations common in industrial environments.

✓ Dual SPDT Contact Configuration
Two independent changeover contacts (6A @ 250V AC each) provide simultaneous NO and NC outputs. Control multiple loads, create redundant circuits, or implement fail-safe logic without additional components. Gold-plated contacts ensure low contact resistance and extended mechanical life exceeding 10 million operations.

→ Space-Efficient DIN Rail Design (17.5mm Width)
Occupies minimal panel real estate—equivalent to one standard circuit breaker position. Front-accessible time adjustment allows setting changes without relay removal or circuit de-energization. Snap-mount installation on 35mm DIN rail enables tool-free installation and rapid replacement during maintenance.

✓ Industrial Temperature Range (-25°C to +55°C)
Maintains timing accuracy across extreme ambient conditions found in outdoor enclosures, unheated facilities, and high-temperature process areas. Conformal-coated PCB resists moisture, dust, and chemical vapors, ensuring reliable operation in harsh industrial atmospheres.

→ Swedish Precision Engineering
Manufactured by ABB in Sweden using automotive-grade components and rigorous quality control protocols. Each relay undergoes 100% functional testing before shipment, guaranteeing out-of-box reliability. Backed by ABB's global support network and comprehensive technical documentation.

Typical Application Scenarios

HVAC Ventilation Sequencing
Maintain exhaust fan operation for 15-30 minutes after restroom occupancy sensors deactivate, ensuring complete odor removal and meeting building code ventilation requirements. Adjustable timing accommodates different room volumes without rewiring. Reduces energy waste compared to continuous-run systems while maintaining air quality standards.

Machine Tool Coolant Protection
Extend coolant pump run time 2-5 minutes after CNC machining centers complete their cycles, preventing thermal shock to cutting tools and spindle bearings. Programmable delays match specific coolant system capacities and machine thermal mass. Extends tool life by 20-40% compared to immediate shutdown, reducing tooling costs and unplanned downtime.

Parking Structure Lighting Control
Keep LED fixtures illuminated for 5-10 minutes after motion detection ceases, providing safe egress time for pedestrians and vehicles. Eliminates nuisance switching that reduces LED driver lifespan. Single relay controls multiple lighting zones through contactor interfaces, simplifying control panel design.

Conveyor Material Clearance
Delay downstream conveyor shutdown 30-90 seconds after upstream sections stop, allowing in-transit materials to reach collection points. Prevents product accumulation and jamming that causes production delays. Timing adjustments accommodate different belt speeds and transfer distances without PLC reprogramming.

Compressed Air System Optimization
Allow air compressors to run 3-5 minutes after demand drops below threshold, stabilizing receiver tank pressure and preventing rapid cycling. Reduces compressor motor starts by 40-60%, extending motor and valve life while lowering electrical demand charges. Adjustable timing matches different tank volumes and leakage rates.

Technical Parameters & Selection Guide

Selection Criteria: Choose the CT-APS.21S when your application requires outputs to remain energized for a specific duration after the control signal is removed. For applications requiring delayed energization (ON-delay), consider the CT-APS.22S model. If your timing needs fall outside the 0.05s-300h range, consult our technical team for alternative ABB timer relay solutions with extended ranges or multi-function capabilities.

Extended Functions

Parallel Contact Operation: Both SPDT outputs switch synchronously, allowing parallel connection for higher current capacity (up to 12A total when properly derated). Useful for controlling larger contactors or multiple parallel loads without external relay multiplication.

Series Timing Cascades: Connect multiple CT-APS.21S relays in series to create extended timing sequences or cumulative delays exceeding 300 hours. Each relay's output triggers the next stage, enabling complex multi-step shutdown sequences without PLC programming.

Fail-Safe Integration: Utilize NC (normally closed) contacts for fail-safe circuits that require de-energization upon timer failure or power loss. Meets safety requirements for emergency stop circuits and machine guarding applications when properly integrated with safety-rated components.

Delivery & Service Assurance

Lead Time: Standard stock items ship within 2-3 business days. Bulk orders (50+ units) typically ship within 5-7 business days. Express shipping available for urgent requirements—contact our sales team for expedited processing.

Warranty Coverage: Every CT-APS.21S includes a comprehensive 12-month manufacturer's warranty covering defects in materials and workmanship. Warranty includes free replacement and return shipping for confirmed manufacturing defects.

Technical Support: Our application engineers provide pre-sales consultation, wiring diagram assistance, and troubleshooting support via email and phone. Average response time: 4 hours during business hours (GMT+8).

Documentation Package: Each relay ships with installation instructions, wiring diagrams, and dimensional drawings. Complete technical manuals, CAD files, and certification documents available for download from our product support portal.

Frequently Asked Questions

What is the difference between OFF-delay and ON-delay timing functions?
OFF-delay relays (like the CT-APS.21S) energize outputs immediately when control voltage is applied, then maintain output state for the preset time after control voltage is removed. ON-delay relays wait for the preset time after control voltage is applied before energizing outputs. Choose based on whether you need delayed startup or delayed shutdown.

Can this timer relay operate on 12V DC control systems?
No, the CT-APS.21S minimum control voltage is 24V (±20% tolerance, so approximately 19.2V minimum). For 12V applications, consider ABB's CT-MVS series or contact our team for suitable alternatives compatible with low-voltage control circuits.

How do I achieve precise timing settings for critical applications?
The front rotary dial provides approximate settings via the logarithmic scale. For precision requirements, apply control voltage and use a calibrated timer or stopwatch to measure actual delay, then fine-tune the dial position. Timing accuracy is ±5% under normal conditions. For applications requiring tighter tolerances, consider digital timer relays with programmable settings.

What is the maximum switching frequency for the output contacts?
Mechanical relay contacts are optimized for timing applications, not high-speed switching. Maximum recommended switching frequency is 10 operations per minute for resistive loads. For higher-frequency applications, consider solid-state timer relays that eliminate mechanical contact wear.

Are the output contacts suitable for controlling inductive loads like motors or solenoids?
Yes, but contact life will be reduced compared to resistive loads. For inductive loads, derate contact capacity to 50% of rated current and use suppression devices (RC snubbers for AC, flyback diodes for DC) across the load. For frequent inductive switching, consider upgrading to ABB contactors controlled by the timer relay.

Can I mount this relay in any orientation?
Yes, the CT-APS.21S can be mounted in any orientation on DIN rail without affecting performance or timing accuracy. Ensure adequate ventilation around the relay and maintain specified ambient temperature limits for optimal contact life.

Ready to Optimize Your Timing Control?

The ABB CT-APS.21S delivers the reliability and flexibility your industrial automation projects demand. Whether you're designing new control systems or upgrading existing installations, this timer relay provides proven performance backed by ABB's century of electrical engineering excellence.

Contact our technical sales team today: Share your application requirements and receive expert guidance on relay selection, wiring configurations, and integration strategies. Volume pricing available for OEMs and system integrators.

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