The IRDH275W-435 is a high-performance insulation monitoring device from Bender, part of the A-ISOMETER® series. It is designed for unearthed AC, AC/DC, and DC main circuits (IT systems) and continuously monitors the insulation resistance of the system. The device is suitable for modern power supply systems that contain rectifiers, frequency converters, thyristor-controlled DC drives, and directly connected DC components. It complies with IEC 61557‑8.
The “W” in the type designation indicates the ruggedised version, specifically designed for harsh environmental conditions. The “W” suffix represents enhanced shock and vibration resistance, with a conformal coating applied to the electronic components to protect against moisture, salt spray, and mould. 435 is the supply voltage identifier, representing a supply voltage of AC 88…264 V / DC 77…286 V.
Key Features
· AMPPlus Measuring Principle – Uses Bender‘s patented AMPPlus measuring technology (European Patent EP 0 654 673 B1), automatically adapting to complex modern power system conditions including directly connected DC components and system leakage capacitance, reliably distinguishing between actual insulation faults and inherent system leakage capacitance.
· Automatic Adaptation to System Leakage Capacitance – Modern power systems often generate high leakage capacitances to earth due to interference suppression measures. The IRDH275W-435 automatically adapts to the existing system leakage capacitance (maximum permissible ≤ 500 μF), optimising measurement time and ensuring dependable operation without manual adjustments.
· Two Independently Adjustable Alarm Response Values – The device features two separately adjustable alarm relays (Alarm 1 and Alarm 2), allowing users to distinguish between pre-warning and critical alarm. Each response value can be independently set from 1 kΩ to 10 MΩ.
· Two-Line LC Display – Equipped with a clear two-line LC display with backlight, showing real-time insulation resistance values. Front-panel keys enable easy on-site status checks and parameter adjustments.
· Connection Monitoring – Continuously monitors the connections of the measuring leads and earth (PE), ensuring the integrity of the measuring circuit.
· Automatic Device Self-Test – The device features an automatic self-test function that continuously verifies the internal measuring circuits and system control components.
· External Test and Reset Functions – External push-buttons can be connected to perform device self-test and to reset stored fault messages.
· De-Energised System Monitoring – The device is powered by an independent external supply, allowing it to monitor the system even when the main circuit is de-energised, ensuring continuous safety oversight during maintenance or system shutdown periods.
· Voltage Extension via Coupling Devices – Using appropriate Bender AGH series coupling devices, the nominal system voltage range can be extended to higher levels, such as DC 0…1760 V or 3(N)/AC 0…7200 V.
· “W” Ruggedised Features – Compared to the standard IRDH275-435, the “W” version offers enhanced shock and vibration resistance, a conformal coating on electronic components, and an extended operating temperature range, making it particularly suitable for ships, offshore platforms, rolling stock, and seismic regions.
Technical Specifications
· Nominal system voltage (Uₙ): 3(N)AC 0…793 V; AC 0…793 V; DC 0…650 V
· Frequency range (fₙ): DC, 0.2…460 Hz
· Supply voltage (Uₛ): AC 88…264 V (47…63 Hz); DC 77…286 V
· Response value range (Rₐₙ₁ / Rₐₙ₂): 1 kΩ … 10 MΩ, two thresholds independently adjustable
· Maximum permissible system leakage capacitance: ≤ 500 μF
· Measuring principle: AMPPlus (patented adaptive measuring pulse method, European Patent EP 0 654 673 B1)
· Display: Two-line LC display with backlight
· Alarm relays: Two independent changeover contacts (Alarm 1 and Alarm 2), configurable for N/O or N/C operation
· Operating temperature: –40 °C … +70 °C (“W” version enhanced range)
· Storage temperature: –40 °C … +85 °C
· Protection class: Terminals IP30, enclosure IP20
· Mounting: DIN rail (35 mm standard rail)
· Weight: Approx. 0.5 kg
· Country of origin: Germany
· Standards compliance: IEC 61557‑8, DIN EN 61557‑8
· Order number: B91065100W
Model Number Explanation
· IRDH275 – Product family designation for Bender 275 series insulation monitoring devices
· W – Ruggedised version indicator. Represents enhanced shock and vibration resistance, conformal coating on electronic components, and extended operating temperature range of -40°C to +70°C. Suitable for harsh environments such as ships, offshore platforms, rolling stock, and seismic regions
· 435 – Supply voltage identifier, representing a supply voltage of AC 88…264 V / DC 77…286 V
Typical Applications
· Industrial IT systems – Insulation monitoring for AC, DC, and combined AC/DC unearthed systems containing rectifiers, frequency converters, thyristor-controlled DC drives, and other power electronic loads
· Marine and offshore applications – For shipboard electrical systems and offshore platforms where a single ground fault must not cause a power outage; the “W” version provides enhanced shock, vibration, and moisture resistance
· Rolling stock – Suitable for railway vehicle electrical systems, capable of withstanding vibration and temperature variations during operation
· UPS systems and battery systems – Continuous monitoring of insulation integrity in uninterruptible power supplies and battery backup installations
· Photovoltaic and renewable energy systems – IT systems with high leakage capacitance in solar PV arrays and wind power systems
· Medical locations – Insulation monitoring for IT systems (isolated power systems) in operating theatres, intensive care units, and other group 2 medical locations
· Extended voltage applications – Through AGH series coupling devices, the monitoring range can be extended to higher voltages for medium‑voltage IT systems
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