BENDER IRDH275B-425 Insulation Monitoring Device – IRDH275 Series

BENDER IRDH275B-425: Insulation Monitoring Architecture for Unearthed IT Power Networks

In unearthed IT systems, the first ground fault does not interrupt supply — it creates a latent hazard. The second fault, occurring anywhere on the network, completes the circuit and produces a fault current that can damage equipment, trigger arc flash events, or endanger personnel. The BENDER IRDH275B-425 is the instrument that closes this detection gap. It continuously measures the total insulation resistance between the active conductors of an IT network and earth, issuing an alarm the moment that resistance falls below a configurable threshold — before the second fault can occur.

This is not a passive monitoring function. The IRDH275B-425 applies a low-level DC measuring voltage (≤12 V) superimposed on the monitored network, independent of system frequency and voltage waveform. This method, standardized under IEC 61557-8, allows the device to monitor AC systems, DC systems, and mixed-frequency networks — including those with significant harmonic content from variable-frequency drives — without generating interference or requiring system shutdown. The measurement is continuous, real-time, and unaffected by normal load switching events.

For procurement engineers and system integrators specifying safety instrumentation for hospitals, offshore platforms, industrial drive systems, or renewable energy installations, the IRDH275B-425 represents a mature, field-proven implementation of IT system insulation monitoring with a communication architecture that integrates directly into modern SCADA and building management environments.

Real-time Stock & RFQ: [email protected] | WhatsApp: +86 18359268345

Technical Parameters

Hardware Logical Analysis

Superimposed DC Measurement Principle: The IRDH275B-425 injects a low-amplitude DC test signal (≤12 V) onto the monitored IT network via internal coupling capacitors. This signal is galvanically isolated from the device’s own supply circuit and rides on top of the network’s AC or DC operating voltage without disturbing load operation. The device measures the return current through the earth reference path and calculates the total insulation resistance using Ohm’s law. Because the measurement signal is DC, it is inherently immune to the capacitive leakage currents generated by long cable runs and EMC filter capacitors — a known source of false alarms in AC-injection IMD designs.

EMC Design and Interference Rejection: Industrial IT networks in drive-intensive environments carry significant common-mode noise from PWM switching transients. The IRDH275B-425 incorporates digital filtering algorithms that distinguish the device’s own DC measurement signal from superimposed high-frequency noise, preventing nuisance alarms triggered by EMC events rather than genuine insulation degradation. The internal signal processing applies adaptive averaging over the measurement cycle, ensuring that transient disturbances — such as motor start inrush or capacitor bank switching — do not produce false threshold crossings.

Dual-Relay Output Architecture: The device provides two independent changeover relay outputs. The primary alarm relay activates when the measured insulation resistance falls below the configured Ran threshold. The second relay can be configured for pre-alarm, device fault indication, or system-level interlock functions. Both relays are fail-safe by design: the alarm relay is energized in the healthy state and de-energizes on fault or supply loss, ensuring that a device power failure does not suppress an active insulation alarm.

RS-485 Communication with BCOM and Modbus RTU: The integrated RS-485 port supports BENDER’s proprietary BCOM protocol for native integration with BENDER BMS, COM465 gateways, and BENDER EDS earth fault location systems. Modbus RTU mode allows direct integration with third-party SCADA platforms, PLCs, and building management systems from Siemens, Schneider Electric, ABB, and Rockwell Automation. The communication interface transmits live insulation resistance values, alarm status, device diagnostics, and configuration parameters — enabling remote monitoring without physical access to the switchgear panel.

Universal Supply Input: The AC/DC 24–240 V universal supply input eliminates the need for a dedicated 24 V DC power supply in installations where only AC distribution is available, and equally supports DC-bus-powered control cabinets. This single-SKU supply range simplifies global procurement and reduces the risk of specification errors when deploying across multiple sites with different control voltage standards.

System Integration Benefits

• Continuous Monitoring Without System Interruption: The IRDH275B-425 operates without requiring the monitored IT network to be de-energized or load-disconnected. Insulation resistance is measured in real time during normal operation, eliminating the periodic test windows required by older point-in-time measurement methods.
• Configurable Alarm Threshold Across Eight Decades: The 1 kΩ – 10 MΩ response range spans eight decades of resistance, accommodating both low-impedance industrial networks with significant capacitive leakage and high-impedance medical IT systems where IEC 60364-7-710 mandates alarm at ≥50 kΩ. A single device covers both application classes without hardware modification.
• Real-Time Resistance Readout for Trend Analysis: The backlit LCD displays the live insulation resistance value in engineering units (kΩ or MΩ), not merely an alarm/no-alarm binary state. Maintenance engineers can observe gradual insulation degradation trends over time — identifying aging cable insulation or moisture ingress before the alarm threshold is reached.
• SCADA Integration via Modbus RTU: Insulation resistance values and alarm states are available as Modbus registers, enabling integration into plant-level SCADA historians. This supports predictive maintenance workflows where insulation resistance trending is correlated with environmental conditions, load cycles, and maintenance intervals.
• Fail-Safe Relay Logic: The energize-to-healthy relay design ensures that a loss of supply to the IRDH275B-425 itself — whether from a blown fuse, wiring fault, or power interruption — produces the same relay state as an insulation alarm. This prevents the monitoring gap that would otherwise occur if the IMD lost power silently.
• Compatibility with BENDER EDS Fault Location: When used alongside BENDER’s EDS earth fault location system, the IRDH275B-425 provides the alarm trigger that initiates active fault location. The EDS system then identifies the specific branch or load where insulation degradation has occurred, reducing fault isolation time from hours to minutes in complex multi-branch IT networks.
• Diagnostic Transparency via BCOM Protocol: BCOM communication exposes device self-diagnostic data — including internal reference resistance verification, relay test results, and communication health — to the BENDER BMS. This allows the monitoring system itself to be monitored, satisfying the functional safety requirement that the IMD’s own integrity be verifiable without manual intervention.
• Wide Operating Temperature Range for Harsh Environments: The −25 °C to +70 °C operating range covers outdoor switchgear installations in cold climates, engine room environments in marine applications, and high-ambient industrial enclosures without requiring additional thermal management. The device does not require warm-up time and begins monitoring immediately on power application.

Quality Assurance & Global Logistics

Every BENDER IRDH275B-425 unit supplied by siemensplc.com is sourced from verified OEM channels with documented chain of custody. BENDER’s factory calibration to IEC 61557-8 is performed at the point of manufacture and is not repeatable in the field — sourcing from unverified channels introduces the risk of receiving units with compromised calibration records or undisclosed repair history. siemensplc.com’s procurement process requires batch traceability documentation for every unit, and pre-shipment inspection confirms physical integrity, connector condition, and label authenticity before dispatch.

All international shipments originate from Xiamen, China — a Tier-1 container port with direct sea freight routes to Southeast Asia, the Middle East, Northern Europe, and the Americas. For time-critical orders, Xiamen Gaoqi International Airport provides air freight access with door-to-door transit times of 3–5 business days to most major industrial centers. Export documentation — commercial invoice, packing list, certificate of origin, and HS code classification — is prepared in compliance with Xiamen Customs requirements, eliminating the risk of customs holds at destination ports that commonly extend lead times when sourcing from non-compliant exporters.

ESD-safe anti-static packaging and moisture barrier protection are applied as standard for all electronic component shipments. Shipment tracking is provided from dispatch to delivery, with carrier-diversified routing to maintain delivery reliability across multiple destination regions.

Contact Information

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