The IRDH275B-427 is a high-performance insulation monitoring device from Bender, designed for unearthed AC, AC/DC, and DC power systems (IT systems). It continuously monitors the insulation resistance of the main circuit and is suitable for modern power supply systems that contain rectifiers, frequency converters, thyristor-controlled DC drives, and directly connected DC components. The device complies with IEC 61557‑8 and also meets or exceeds the requirements of NEC 250.21(B), CEC 10‑106(2) for ground detectors in ungrounded AC systems, as well as NEC 250.167(A) for ungrounded DC systems.
Model Number Explanation
· IRDH275 – Product family designation
· B – Enhanced version
· 427 – Hardware variant configured for low-voltage AC/DC supply (AC 19.2…55 V / DC 19.2…72 V)
Enhanced Features (B Version)
· History memory with real-time clock – Stores up to 300 alarm messages with precise date and time stamps
· Electrically isolated RS‑485 interface (BMS protocol) – For data exchange with other Bender devices and integration into central monitoring systems and PLCs
· ISOMETER® disconnecting relay – Can temporarily disconnect the device from the monitored IT system via an external control signal, suitable for coupled IT systems
· Isolated 0(4)…20 mA analog current output – Provides a signal proportional to the measured insulation value for connection to PLCs or SCADA systems
Key Features
· AMPPlus Measuring Principle – Uses Bender‘s patented AMPPlus measuring technology, delivering accurate insulation monitoring even in systems with extensive DC components and high leakage capacitances – including pure DC systems, systems with rectifiers, and those with variable-frequency drives (VFDs). In systems with high leakage capacitance, the device automatically adjusts to maintain reading accuracy.
· Automatic Adaptation to System Leakage Capacitance – 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 Response Values – Features two separately adjustable alarm relays (Alarm 1 and Alarm 2), each configurable 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, system leakage capacitance, and other parameters. Front-panel keys (INFO, TEST, RESET, MENU, ESC, Arrow keys, Enter) enable easy operation.
· Alarm Indicators – Front panel equipped with three LED indicators: AL1 LED (pre-warning), AL2 LED (critical alarm), and System Fault LED (lights on connection or device error).
· Built‑In Self‑Test and Connection Monitoring – Automatic self-test continuously verifies internal measuring circuits and system components. Connection monitoring supervises the integrity of the measuring leads. The TEST button can manually trigger a test.
· External Test and Reset Functions – Supports connection of external test push-button (normally open) and external reset push-button (normally closed). When the reset button terminals are open, fault messages will not be stored.
· Standby Contact – Includes a standby contact. When the contact is closed, insulation measurements stop.
· Fault Memory (Selectable) – Fault memory function can be activated as needed to help identify intermittent faults.
· De‑Energised System Monitoring – Powered by an independent external supply, the device can monitor the system even when the main circuit is de‑energised.
· Voltage Extension via Coupling Devices – Using 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.
Technical Specifications
· Nominal system voltage (Uₙ): 3(N)AC 0…793 V; AC 0…793 V; DC 0…650 V
· Frequency range (fₙ): DC, 0.1…460 Hz
· Supply voltage (Uₛ): AC 19.2…55 V (42…460 Hz); DC 19.2…72 V
· Response value range (Rₐₙ₁ / Rₐₙ₂): 1 kΩ … 10 MΩ, two thresholds independently adjustable
· Maximum permissible system leakage capacitance: ≤ 500 μF
· Measuring principle: AMPPlus
· Response time: ≤ 5 s (at R_F = 0.5 × R_an and C_e = 1 μF)
· Measurement accuracy: 1 kΩ … 1 MΩ: ±15% ±1 kΩ; 1 kΩ … 10 MΩ: ±15% ±0.1 MΩ
· Measuring voltage: ≤ 50 V
· Measuring current: ≤ 280 μA
· Alarm relays: Two independent changeover contacts, AC 250 V / 5 A
· Analog current output: 0(4)…20 mA, isolated
· Communication interface: RS‑485, electrically isolated, supporting BMS protocol
· Fault memory: 300 records with real-time clock
· Disconnecting relay: Yes
· Standby contact: Yes
· Operating temperature: –10 °C … +55 °C
· Storage temperature: –40 °C … +85 °C
· Protection class: Terminals IP30, enclosure IP20
· Mounting: DIN rail (35 mm standard rail)
· Weight: Approx. 0.55 kg
· Standards compliance: IEC 61557‑8, DIN EN 61557‑8
· Order number: B91065105
Typical Applications
· Industrial IT systems
· Medical locations (operating theatres, ICUs)
· Marine and offshore applications
· UPS and battery systems
· Photovoltaic and renewable energy systems
· Coupled IT systems
· Extended voltage applications (with AGH coupling devices)
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