OMRON H3CT-8H Timer Relay – H3CT Series

OMRON H3CT-8H: Multi-Range On-Delay Timer Relay in Industrial Control Circuits

The OMRON H3CT-8H occupies a well-defined functional position in discrete control architectures: it provides deterministic on-delay timing between a trigger event and an output switching action, without reliance on PLC scan cycles or software task scheduling. In machine sequencing panels, motor protection circuits, and process interlocking systems, this role is non-trivial. A hardware timer operating independently of the controller eliminates the risk of timing drift caused by PLC program scan overruns, communication latency, or watchdog resets. The H3CT-8H executes its timing function in analog solid-state circuitry, making its output transition time repeatable to within ±0.5% across the full operating temperature range of −10°C to +55°C.

The H3CT-8H belongs to OMRON’s H3CT series, a product line engineered specifically for panel-mount and DIN rail socket applications where dimensional standardization and interchangeability are engineering constraints. The 8-pin octal footprint (compatible with OMRON P2CF-08 and P3G-08 sockets) allows field replacement without rewiring. The unit accepts a universal supply voltage of 100–240 VAC or 100–125 VDC, which simplifies spare-part management across facilities operating on different grid standards. A single SKU covers North American 120 VAC, European 230 VAC, and DC bus applications in the 100–125 VDC range.

The output stage is a single-pole double-throw (SPDT) electromechanical contact rated at 5 A resistive load. This contact rating is sufficient to directly switch pilot relays, solenoid valve coils (within rated VA), indicator lamps, and low-power contactor coils. For higher-load switching, the H3CT-8H output drives an interposing relay or contactor without additional signal conditioning. The time range is selectable via a front-panel rotary switch across multiple decades, covering 0.05 seconds to 300 hours in a single unit — a span that eliminates the need to stock multiple timer SKUs for different application time constants.

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Technical Parameters

Hardware Logical Analysis

The H3CT-8H timing circuit is built around an RC charge network referenced against a precision voltage comparator threshold. When supply voltage is applied, the capacitor in the timing network begins charging through a resistor network whose effective resistance is set by the front-panel potentiometer and range selector. The comparator monitors the capacitor voltage; when it crosses the threshold — calibrated to correspond to the selected time set point — the output relay is energized. This architecture produces a timing characteristic that is inherently linear within each range decade and is not subject to the quantization errors present in digital counter-based timers operating at low clock frequencies.

The universal input stage incorporates a full-wave rectifier and voltage regulation circuit that maintains stable DC rail voltage for the timing circuitry across the 100–240 VAC input range. This regulation is critical: timing accuracy is directly dependent on the stability of the reference voltage applied to the comparator. Variations in supply voltage that are not compensated at the input stage would translate directly into timing error. OMRON specifies voltage influence at ±2% maximum, which is achieved through active regulation rather than passive filtering alone.

EMC performance is addressed at the input stage with transient suppression components rated to absorb surge events consistent with IEC 61000-4-5 Level 2 (1 kV line-to-line, 2 kV line-to-earth). The output contact circuit includes an arc suppression network (RC snubber) across the contact terminals, which limits the rate of voltage rise (dV/dt) during contact opening and reduces radiated interference from inductive load switching. This is particularly relevant in panels where the timer output switches solenoid valve coils or contactor coils, which are inherently inductive loads with stored energy that must be dissipated at contact break.

The mechanical output relay is specified for a minimum electrical life of 100,000 operations at rated load, and a mechanical life of 10,000,000 operations. In applications where the timer cycles frequently — such as intermittent conveyor sequencing or periodic pump alternation — the contact life budget must be evaluated against the expected cycle rate. For high-cycle applications exceeding 10 cycles per hour over multi-year service periods, a solid-state output variant or an interposing relay with a higher contact life rating should be considered.

The front-panel potentiometer uses a conductive plastic track rather than a wirewound element, which provides smooth, continuous adjustment without discrete steps and maintains consistent contact resistance over the adjustment life. The rotary range selector is a detented switch with positive mechanical indexing, preventing intermediate positions that would produce undefined time ranges.

System Integration Benefits

• PLC-independent timing redundancy: The H3CT-8H operates entirely in hardware, providing a timing function that remains active even during PLC program faults, communication interruptions, or watchdog-triggered CPU restarts. This makes it suitable as a backup timing element in safety-adjacent sequences where software timer failure must not result in uncontrolled machine states.
• Zero-configuration socket replacement: The 8-pin octal socket interface allows field replacement of a failed unit in under two minutes without rewiring. The socket retains all field wiring; the timer plugs in and is secured by the locking clip. This reduces mean time to repair (MTTR) in production environments where downtime cost is significant.
• Single-SKU multi-range coverage: Nine selectable time ranges from 0.05 s to 300 h eliminate the need to stock separate timer models for different application time constants. A single H3CT-8H in the spare-parts cabinet covers motor start delay (seconds), HVAC compressor restart delay (minutes), and batch process timing (hours).
• Universal voltage input simplifies global deployment: The 100–240 VAC / 100–125 VDC input range means the same part number is valid for facilities in North America (120 VAC), Europe (230 VAC), and industrial DC bus systems. Procurement teams maintain one part number across global sites.
• High repeat accuracy supports process consistency: At ±0.5% repeat accuracy, a 60-second set point will trigger within ±0.3 seconds across repeated cycles under stable temperature conditions. This level of consistency is adequate for motor sequencing, valve actuation delays, and most process interlocking applications without requiring closed-loop timing verification.
• Certified for international machine safety standards: UL, CSA, CE, and TÜV certifications allow the H3CT-8H to be incorporated into machine control panels destined for North American, European, and Asian markets without requiring component-level re-certification. This reduces compliance engineering effort for OEM panel builders.
• Diagnostic transparency via LED indication: The power-on LED and output-state LED provide immediate visual confirmation of timer state without requiring a multimeter or PLC diagnostic screen. Maintenance personnel can verify timer operation during commissioning and troubleshooting by direct observation of the front panel.
• Broad ecosystem compatibility: The H3CT-8H integrates with Siemens S7-300/400/1200/1500, Mitsubishi MELSEC Q/L/iQ-R, Allen-Bradley MicroLogix/CompactLogix, and OMRON CJ/CS/NX series PLCs as an auxiliary hardware timer. It also fits standard 35 mm DIN rail (EN 60715) and is dimensionally compatible with Rittal, Schneider PrismaSeT, and ABB ArTu enclosure systems.
• Low power consumption reduces panel thermal load: At ≤2 VA (AC) or ≤1.5 W (DC), the H3CT-8H contributes negligible heat to the control panel thermal budget. In densely populated panels where thermal management is a design constraint, this is a meaningful advantage over older electromechanical timer designs with higher coil power consumption.

Quality Assurance & Global Logistics

Every OMRON H3CT-8H unit supplied by siemensplc.com is sourced through verified distribution channels with full supply chain traceability. Label authenticity, date code consistency, and original OMRON packaging integrity are inspected prior to dispatch. Batch records and certificates of conformity are available on request for OEM procurement and MRO audits. A 12-month warranty against manufacturing defects applies to all units.

Logistics operations are based in Xiamen, China — a major export hub with direct access to international freight carriers including DHL Express, FedEx International Priority, UPS Worldwide Express, and SF International. In-stock orders are processed and dispatched within 1–2 business days. Standard international transit times are 3–7 business days to most destinations in Europe, North America, Southeast Asia, and the Middle East. Export documentation including commercial invoice, packing list, and certificate of origin is prepared for all international shipments. For time-critical procurement, air freight with tracking is the default dispatch method.

For bulk orders, OEM supply agreements, or project-based procurement requiring scheduled delivery, contact the sales team directly to discuss lead times, volume pricing, and logistics arrangements tailored to your project schedule.

Contact Information

Email: [email protected]
WhatsApp: +86 18359268345
Web: siemensplc.com
Location: Xiamen, China
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