The IR425-D4-1 is an insulation monitoring device from Bender, designed for unearthed AC and DC control circuits (IT systems). It continuously monitors the insulation resistance of systems with voltages from 0 to 300 V AC/DC and triggers an alarm when the insulation resistance falls below a preset threshold. The device complies with IEC 61557‑8.
The IR425-D4-1 uses the AMP measuring principle, which ensures that DC components present in AC/DC systems do not influence the operating characteristics. An external supply voltage allows de‑energised systems to be monitored as well. The device features a compact 36 mm width (2 standard modules), making it suitable for control cabinet installations where space is limited.
Technical Specifications
· Rated system voltage (Uₙ): AC/DC 0…300 V, 15…460 Hz
· Supply voltage (Uₛ): AC 16…72 V; DC 9.6…94 V
· Frequency range: 15…460 Hz
· Response value range (Rₐₙ): 1 kΩ … 200 kΩ, two independently adjustable thresholds
· Maximum permissible system leakage capacitance (Cₑ): ≤ 20 μF
· Measuring principle: AMP (Adaptive Measuring Principle) – superimposes a pulsating measuring voltage onto the monitored IT system; ohmic insulation faults close the measuring circuit between the IT system and earth
· Power consumption: ≤ 4 VA
· Alarm relays: Two independent changeover contacts (Alarm 1 and Alarm 2), AC 250 V / 5 A
· Display: Multi‑function LC display showing current insulation resistance values
· LED indicators: Power On, Alarm 1 (pre‑warning), Alarm 2 (critical alarm)
· Connection type: Screw‑type terminals (each connection point with dual terminals)
· Mounting: DIN rail (35 mm standard rail)
· Width: 36 mm (2 standard modules)
· Dimensions (W × H × D): Approx. 36 × 71 × 90 mm
· Weight: Approx. 0.15 kg
· Operating temperature: –25 °C … +55 °C
· Protection class: Terminals IP20, internal components IP30
· Housing material: Polycarbonate
· Standards compliance: IEC 61557‑8, DIN EN 61557‑8
Key Features
· AMP Measuring Principle – Uses the Bender AMP measuring principle. The device superimposes a pulsating measuring voltage onto the monitored IT system; ohmic insulation faults close the measuring circuit between the IT system and earth, and the currently measured insulation resistance value is shown on the display. DC components present in AC/DC systems do not influence the operating characteristics.
· Two Independently Adjustable Response Values – Equipped with two independently adjustable alarm relays (Alarm 1 and Alarm 2), with a response value range of 1 kΩ to 200 kΩ. Two‑stage alarm levels (pre‑warning and critical alarm) can be configured.
· Preset Function – When the device is first powered on, the preset function automatically measures the rated system voltage and sets basic parameters. When Uₙ ≤ 72 V, the response values are preset to 20 kΩ and 10 kΩ; when Uₙ > 72 V, they are preset to 46 kΩ and 23 kΩ.
· Multi‑Function LC Display – Equipped with a multi‑function LC display showing real‑time insulation resistance values, alarm information, and device parameters.
· LED Status Indicators – Front panel includes LED indicators: Power On, Alarm 1 (pre‑warning), Alarm 2 (critical alarm).
· Connection Monitoring – Continuously monitors the connection status of measuring leads (system/earth) to ensure measuring circuit integrity.
· Built‑In Self‑Test with Automatic Alarm – Features an automatic self‑test function that continuously verifies internal measuring circuits and system control components. A fault triggers an automatic alarm.
· Internal/External Test and Reset – Self‑test and reset can be triggered via front‑panel keys, or by connecting external test and reset push‑buttons.
· Selectable Fault Memory – The fault memory function can be activated as needed. When activated, alarm relays remain in the alarm condition until manually reset, helping to identify intermittent faults.
· Adjustable Response Delay – Response delay time can be configured (0…99 seconds) to prevent nuisance alarms caused by system transients.
· Password Protection – Integrated password protection prevents unauthorised changes to critical alarm threshold parameters.
· De‑Energised System Monitoring – Powered by an independent external supply, the device can monitor the system even when the main circuit is de‑energised.
· Screw‑Type Terminals – Features screw‑type terminals with dual terminals at each connection point for secure wiring.
· Compact Design – 36 mm width (2 standard modules) for space‑saving DIN rail mounting in control cabinets.
Model Number Explanation
· IR425 – Product family designation for Bender 425 series insulation monitoring devices
· D4 – Supply voltage variant: AC 16…72 V / DC 9.6…94 V
· 1 – Terminal type: screw‑type terminals (Version 2 uses push‑wire terminals)
Typical Applications
· Industrial control circuits – Monitoring auxiliary and control circuits in machine electrical equipment according to IEC 60204‑1
· Power plant automation – Ensuring insulation integrity of unearthed control systems in power generation facilities
· Elevator systems – Monitoring insulation of DC control panels and safety chains in elevators
· Small AC/DC IT systems – Such as lighting systems
· AC/DC auxiliary circuits – Complying with DIN VDE 0100‑725
· Automation systems – Control circuit insulation monitoring in mechanical engineering and automation equipment
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