ABB HESH447449R11/70LR01A Relay Module – HESH Series

ABB HESH447449R11/70LR01A – Plug-In Relay Module for Industrial Switching and Signal Isolation

The ABB HESH447449R11/70LR01A is a 24 V DC coil, SPDT (1 Form C) plug-in relay module engineered for high-cycle industrial switching applications. Mounted on the ABB 70LR01A relay socket, this assembly forms a mechanically and electrically matched pair that eliminates field wiring disturbance during relay replacement — a design attribute that directly reduces mean time to repair (MTTR) in production-critical panels. The module is rated at 8 A / 250 V AC contact load, making it suitable for direct actuation of motor starters, solenoid valves, and pilot devices without interposing contactors in the majority of low-power field circuits.

Within a control loop architecture, this relay occupies the output isolation boundary between the logic solver — whether a PLC digital output card, DCS I/O module, or safety logic controller — and the field load. Its galvanic isolation prevents ground loops and transient voltage spikes generated by inductive loads from propagating back into the control system backplane. This boundary function is not incidental; it is the primary reason relay modules of this class remain specified in new panel designs despite the proliferation of solid-state output alternatives.

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Technical Parameters

Hardware Logical Analysis

The HESH447449R11/70LR01A is built around a bifurcated gold-alloy contact system. Gold plating on the contact surfaces maintains a stable, low-resistance interface — typically below 100 mΩ — across the full mechanical life cycle. This is not merely a material choice for corrosion resistance; it is a functional requirement for reliable switching of dry-contact signals in the 5–24 V DC range where silver-alloy contacts would exhibit intermittent resistance due to oxide layer formation under low-energy arcing conditions.

The coil circuit incorporates a built-in freewheeling diode across the coil terminals. When the drive transistor on a PLC output card switches off, the collapsing magnetic field in the relay coil generates a back-EMF spike that can reach several hundred volts in an unprotected circuit. The integrated suppression diode clamps this transient to approximately 0.7 V above the supply rail, protecting the output transistor from avalanche breakdown — a failure mode that is cumulative and often manifests as intermittent output card faults before catastrophic failure.

The 70LR01A socket provides a positive-locking retention mechanism. A spring-loaded retaining clip engages a groove on the relay body, requiring deliberate lateral pressure to release. This prevents relay ejection under vibration conditions per IEC 60068-2-6 (sinusoidal vibration, 10–150 Hz). The socket’s screw-clamp terminals accept conductors from 0.5 mm² to 2.5 mm² without ferrules, accommodating both control cable and instrument cable cross-sections within a single terminal block standard.

EMC performance is addressed at the socket level through the optional RC snubber accessory, which suppresses contact arc energy on inductive AC loads. The relay body itself is housed in a flame-retardant polycarbonate enclosure rated UL 94 V-0, which limits flame propagation in the event of an internal fault — a requirement for UL 508A panel certification in North American markets.

The manual actuator on the relay body allows forced mechanical operation of the armature without coil energization. This is a commissioning and maintenance tool: it allows a technician to verify field wiring continuity and actuator response before the control system is powered, eliminating the need to temporarily energize the coil from an external 24 V source during panel pre-commissioning checks.

System Integration Benefits

• Zero-rewire replacement: The plug-in architecture of the HESH relay into the 70LR01A socket allows relay substitution in under 30 seconds without disturbing any field wiring terminations, reducing scheduled maintenance windows and unplanned downtime duration.
• PLC output card protection: Galvanic isolation between the coil circuit and contact circuit prevents inductive load transients from reaching PLC digital output transistors, extending output card service life and reducing unplanned card replacements.
• Visual state confirmation: The integrated coil-energization LED provides a direct, real-time indication of relay state without requiring a multimeter or SCADA screen access — accelerating fault localization during live troubleshooting.
• Low-signal contact reliability: Gold-alloy bifurcated contacts maintain reliable switching of signals as low as 5 V / 1 mA, making this relay suitable for PLC input feedback circuits and position switch monitoring without signal conditioning.
• Deterministic switching timing: Operate and release times ≤ 20 ms each provide predictable switching latency for time-critical interlock sequences, allowing PLC programmers to set accurate timer presets without empirical calibration.
• High-density panel layout: The 70LR01A socket’s compact 6.2 mm pitch allows relay density of up to 16 relays per 100 mm of DIN rail, supporting high I/O count marshalling panels without requiring additional enclosure width.
• Standardized accessory ecosystem: Compatibility with ABB marker strips, test plugs, and retaining clips means panel builders can maintain a single accessory inventory across all HESH-series relay positions, simplifying spare parts management.
• Wide operating temperature range: The -20 °C to +55 °C operating envelope covers outdoor enclosure installations in temperate and subtropical climates without requiring panel heating or cooling, reducing auxiliary equipment cost.
• Dual-standard compliance: Simultaneous CE and UL 508 certification allows a single relay model to be specified in both European and North American panel designs, eliminating the need for region-specific relay variants in global machine builder programs.
• Integrated back-EMF suppression: The built-in freewheeling diode eliminates the need for external suppression components on each relay position, reducing BOM complexity and panel wiring labor.

Quality Assurance & Global Logistics

Every ABB HESH447449R11/70LR01A unit supplied through siemensplc.com is sourced from verified industrial distribution channels with full traceability to ABB’s manufacturing batch records. Pre-shipment inspection covers coil resistance measurement (tolerance ±10% of nominal), contact continuity verification on both NO and NC paths, and visual authentication against ABB OEM packaging and holographic label standards.

Units are dispatched from our warehouse in Xiamen, China — a major export hub with direct access to DHL Express, FedEx International Priority, and UPS Worldwide Express services. Standard in-stock orders are processed and handed to the carrier within 1–3 business days. Export documentation — including commercial invoice, packing list, and Certificate of Origin — is prepared for all international shipments. A Certificate of Conformance (CoC) is available upon request at no additional charge.

All supplied units carry a 12-month warranty from the date of shipment, covering manufacturing defects under normal operating conditions as defined by ABB’s published application guidelines. Anti-static packaging with moisture barrier bags and desiccant is used for all relay module shipments to prevent contact oxidation during transit.

Contact Information

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