Description
Product Overview
The BENDER IRDH275-435 is an ISOMETER insulation monitoring device designed for continuous monitoring of insulation resistance in unearthed AC, AC/DC, and DC IT systems.
It is intended for electrical systems where the first insulation fault should be detected before it develops into a more serious electrical problem. The device continuously measures the insulation resistance between the live conductors and earth and provides alarm signals when the resistance falls below the configured response value.
The IRDH275 series uses BENDER’s AMP Plus measuring principle, making it suitable for modern electrical systems that may include rectifiers, converters, variable-frequency drives, switched-mode power supplies, and other power electronic equipment.
Key Features
- Continuous insulation resistance monitoring
- Designed for unearthed IT systems
- Suitable for AC, AC/DC, and DC networks
- Monitors AC systems up to 793 V
- Monitors DC systems up to 650 V
- Measuring range extendable with suitable coupling devices
- AMP Plus measuring principle
- Automatic adaptation to system leakage capacitance
- Two independently adjustable response values
- Response value range from 1 kΩ to 10 MΩ
- Digital LCD display
- Integrated TEST and RESET functions
- Two separate alarm relays
- Voltage-free SPDT relay contacts
- Backlit display
- Internal and external test/reset capability
- RS-485 interface
- Automatic self-monitoring
- Suitable for systems with high leakage capacitance
Technical Parameters
| Parameter | Specification |
|---|---|
| Brand | BENDER |
| Model | IRDH275-435 |
| Product Family | ISOMETER IRDH275 Series |
| Product Name | Insulation Monitoring Device |
| Monitoring System | Unearthed IT systems |
| Monitored Voltage AC | 0…793 V |
| Monitored Voltage DC | 0…650 V |
| System Type | AC / AC-DC / DC |
| Measuring Principle | AMP Plus |
| Response Values | 1 kΩ…10 MΩ |
| Response Value Settings | Two independent values |
| Display | Backlit LCD |
| Alarm Outputs | 2 independent alarm relays |
| Relay Contacts | Voltage-free SPDT |
| Communication | RS-485 |
| Self-Test | Integrated |
| External Test/Reset | Supported |
| Leakage Capacitance | Automatic adaptation |
| Coupling Device | Supported for extended voltage ranges |
| Mounting | DIN rail / panel installation depending on installation arrangement |
| Application | Industrial and electrical power systems |
| Product Condition | New Surplus / Open Box, depending on stock |
How It Works
The IRDH275 monitors the electrical insulation between the conductors of an unearthed system and earth.
When the insulation resistance remains above the configured response value, the system stays in its normal operating state. If insulation resistance decreases below the selected threshold, the device detects the condition and changes the corresponding alarm relay state.
Two independently adjustable response values allow the device to provide different alarm levels. This is useful when the first insulation deterioration should generate an early warning while a lower resistance value generates a more serious alarm.
The AMP Plus measuring method also allows the device to work with electrical systems containing power converters and other components that can produce significant leakage capacitance.
Installation & Configuration
Before installation, verify the exact IRDH275-435 variant, auxiliary supply requirements, monitored system voltage, and wiring configuration.
A typical installation procedure includes:
- Disconnect the electrical system according to the applicable safety procedure.
- Mount the IRDH275 in the control cabinet.
- Connect the device power supply according to the specific model rating.
- Connect the monitoring terminals to the unearthed system.
- Connect the earth/reference connection correctly.
- Wire the alarm relay contacts to the control or alarm system if required.
- Configure the response values through the front-panel controls.
- Apply power and allow the device to perform its self-test.
- Check the displayed insulation resistance.
- Perform a controlled TEST operation and verify the alarm outputs.
Correct PE/earth connection is particularly important because the device determines insulation resistance relative to earth.
Application Areas
The IRDH275-435 can be used in electrical installations where continuous insulation monitoring is required without immediately shutting down the system after the first insulation fault.
Typical applications include:
- Industrial power distribution
- Control cabinets
- UPS systems
- Battery systems
- Variable-frequency drive systems
- Rectifier systems
- Converter-based power systems
- Industrial machinery
- Process control installations
- Marine and shipboard electrical systems
- Utility and auxiliary power systems
The device is especially useful in IT systems where maintaining power availability after the first insulation fault is important.
Maintenance & Testing
Regular testing should be included in the maintenance plan of the electrical system.
Recommended checks include:
- Inspect the housing and terminal connections.
- Verify the earth/reference connection.
- Check the displayed insulation resistance.
- Test both alarm thresholds.
- Verify relay switching.
- Check the RS-485 connection when communication is used.
- Confirm that no unwanted external leakage paths affect measurement.
- Review system leakage capacitance when troubleshooting unstable readings.
- Check the device response after modifications to the monitored network.
If the monitored installation has been significantly modified, the insulation monitoring settings should be reviewed rather than simply restoring the previous configuration.
Troubleshooting Tips
Low insulation resistance is displayed continuously
Check the monitored cables, motors, drives, filters, heating elements, and other connected loads for insulation leakage. Disconnecting sections of the installation can help identify the affected circuit.
The alarm relay changes unexpectedly
Check the configured response thresholds and determine whether the monitored system has high leakage capacitance or transient disturbances.
Insulation values fluctuate
Variable-frequency drives, converters, EMC filters, and large distributed cable systems can influence the measurement. Check the installation and system capacitance before assuming the monitor itself is defective.
No insulation measurement is available
Check the auxiliary supply, system connection, earth/reference connection, and coupling device configuration where applicable.
Frequently Asked Questions
Q: What does the IRDH275-435 monitor?
A: It continuously monitors insulation resistance between an unearthed electrical system and earth.
Q: Can it monitor DC systems?
A: Yes. The IRDH275 series is designed for AC, AC/DC, and DC IT systems.
Q: What is the maximum direct monitoring voltage?
A: The standard IRDH275 range covers up to 793 V AC and 650 V DC. Higher system voltages can be accommodated using appropriate BENDER coupling devices.
Q: Does it work with variable-frequency drives?
A: Yes. The IRDH275 series is designed to handle modern systems containing converters, rectifiers, and variable-frequency drives.
Q: Does the device have alarm relays?
A: Yes. It provides two separate alarm outputs using voltage-free SPDT contacts.
Q: Can the response values be adjusted?
A: Yes. Two independently adjustable response values are available, with a setting range of approximately 1 kΩ to 10 MΩ.
Q: Does it have a display?
A: Yes. The device includes a backlit LCD for displaying insulation and system information.
Q: Does it support RS-485?
A: Yes. An RS-485 interface is provided for compatible communication applications.
Q: Is IRDH275-435 a replacement for every IRDH275 model?
A: Not necessarily. The suffix identifies a specific electrical variant. Always compare the complete model number, auxiliary supply, monitored voltage, and required functions before replacement.
Related BENDER Models
- IRDH275-435 – Insulation Monitoring Device
- IRDH275B – Insulation Monitoring Device
- IRDH275B-R – Insulation Monitoring Device
- IRDH375 – Panel-Mount Insulation Monitoring Device
- IRDH275BM-7 – Medium-Voltage Insulation Monitoring Device
- iso685-D – Insulation Monitoring Device
- iso685-S – Insulation Monitoring Device
- iso685-P – Insulation Fault Monitoring Device
- IR425-D4 – Insulation Monitoring Device
- IR420-D4 – Insulation Monitoring Device
Product Summary
The BENDER IRDH275-435 is an industrial insulation monitoring device for unearthed IT power systems. It provides continuous insulation resistance measurement, adjustable alarm thresholds, two alarm relays, self-test functions, LCD indication, and RS-485 communication.
Its ability to operate with AC, DC, mixed AC/DC systems, converters, rectifiers, and variable-frequency drives makes it suitable for a wide range of industrial electrical installations.
For replacement projects, always verify the complete suffix and electrical ratings of the existing unit before ordering.
