The IRDH275B-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 particularly 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 and also meets or exceeds the requirements of NEC 250.21(B) and CEC 10‑106(2) for ground detectors in ungrounded AC systems.
The “B” in the type designation indicates that this device is the enhanced version of the IRDH275 series, featuring the following additional functions compared to the standard IRDH275-435:
· History memory with real-time clock – Stores all alarm messages with precise date and time stamps
· BMS interface (RS‑485) – For data exchange and integration with other Bender devices
· ISOMETER® disconnecting relay – Can temporarily disconnect the device from the monitored IT system via an external control signal, suitable for coupled IT systems (where multiple IT subsystems are interconnected)
· 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 & Functions
· Patented AMPPlus Measuring Principle – The IRDH275B-435 employs Bender‘s patented AMPPlus measuring technology (European Patent EP 0 654 673 B1), which automatically adapts to complex modern power system conditions including directly connected DC components and system leakage capacitance. This technology is particularly effective in systems with variable-frequency drives (VFDs), rectifiers, and other power electronic equipment.
· Automatic Adaptation to System Leakage Capacitance – Modern power systems often generate high leakage capacitances to earth due to interference suppression measures. The IRDH275B-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, offering flexible configuration to meet different system safety requirements.
· Two-Line LC Display – Equipped with a clear two-line LC display, the device shows measured insulation resistance values and other parameters in real time. Front-panel keys enable easy on-site status checks and parameter adjustments.
· Connection Monitoring – Continuously monitors the connections of the measuring leads (L1/+, L2, L3/–) 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.
· History Memory with Real-Time Clock – Built-in fault memory with a real-time clock stores all alarm messages with precise date and time stamps, facilitating fault tracing, maintenance planning and event analysis.
· RS‑485 Communication Interface (BMS Protocol) – An electrically isolated RS‑485 interface supports the BMS (Bender Measuring Device Interface) protocol, enabling seamless data exchange with other Bender devices and integration into central monitoring systems and PLCs.
· Isolated 0(4)…20 mA Analog Current Output – Provides an isolated analog current output (configurable to 0…20 mA or 4…20 mA) that is proportional to the measured insulation resistance, allowing connection to external instruments, PLCs or SCADA systems for remote monitoring.
· ISOMETER® Disconnecting Relay – An integrated disconnecting relay, controlled via external terminals (F1/F2), allows the ISOMETER® to be temporarily disconnected from the monitored IT system. This is a key function for coordinated operation of multiple devices in coupled IT systems, ensuring that only one ISOMETER® remains active at any given time when multiple IT subsystems are interconnected.
· External Test and Reset Functions – External push-buttons can be connected to perform device self-test and to reset stored fault messages, enhancing convenience and safety for remote or cabinet-mounted installations.
· Selectable Fault Memory – The fault memory function can be activated or deactivated as required. When activated (latching mode), alarm relays remain in the alarm condition until manually reset, helping to identify intermittent faults.
· 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.
· Wide Operating Temperature Range – The device is designed for harsh environments, with an operating temperature range of –40 °C … +70 °C and a storage temperature range of –40 °C … +85 °C.
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)
· 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
· Analog current output: 0(4)…20 mA, galvanically isolated
· Communication interface: RS‑485, electrically isolated, supporting BMS protocol (Bender Measuring Device Interface)
· Fault memory: Built-in storage with real-time clock; stores date- and time-stamped alarm messages
· Disconnecting relay: Internal ISOMETER® disconnecting relay for coupled IT system operation
· Connection monitoring: Yes
· Self-test: Automatic device self-test
· External functions: Supports connection of external test and reset push-buttons
· Operating temperature: –40 °C … +70 °C
· Storage temperature: –40 °C … +85 °C
· Protection class: Terminals IP30, enclosure IP20
· Mounting: DIN rail (35 mm standard rail) or panel mounting
· Standards compliance: IEC 61557‑8, DIN EN 61557‑8; meets or exceeds NEC 250.21(B), CEC 10‑106(2) for ground detectors in ungrounded AC systems
· Order number: B91065004
Model Number Explanation
· IRDH275 – Product family designation for Bender 275 series insulation monitoring devices
· B – Enhanced version with the following additional features: history memory with real-time clock, electrically isolated RS‑485 interface (BMS protocol), ISOMETER® disconnecting relay for coupled IT systems, and isolated 0(4)…20 mA analog current output
· 435 – Supply voltage variant indicating 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, variable-frequency drives (VFDs), and other power electronic loads.
· Medical locations – Insulation monitoring for IT systems (isolated power systems) in operating theatres, intensive care units, and other group 2 medical locations, complying with IEC 60364‑7‑710.
· UPS systems and battery systems – Continuous monitoring of insulation integrity in uninterruptible power supplies and battery backup installations.
· Marine and offshore applications – For shipboard electrical systems where a single ground fault must not cause a power outage.
· Data centres and telecommunications – Insulation monitoring for critical server and UPS power systems.
· Photovoltaic and renewable energy systems – IT systems with high leakage capacitance in solar PV arrays and wind power systems.
· Coupled IT systems – Installations where multiple IT subsystems are interconnected via coupling switches, utilising the ISOMETER® disconnecting relay to ensure coordinated operation of multiple devices.
· De‑energised / offline system monitoring – Applications where continuous insulation monitoring is required even when the main circuit is de‑energised, such as during maintenance periods.
· 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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