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Brand: Bender
Bender IRDH275BM-7 ISOMETER Medium-Voltage Insulation Monitor
Description
An ISOMETER that reaches medium-voltage IT systems through a coupling device
The Bender IRDH275BM-7 is an ISOMETER used together with the coupling device AGH675S-7 (up to 7.2 kV) or AGH675S-7MV15 (up to 15.5 kV) to monitor the insulation resistance of unearthed medium-voltage systems (IT systems). The datasheet describes universal use in 3AC, combined AC/DC and DC systems, including AC systems with extensive DC-supplied loads, because the AMPPlus measuring method (European patent EP 0 654 673 B1) copes with rectifiers, converters and thyristor-controlled DC drives. The device adapts itself to the system leakage capacitance to optimise measuring time, and it keeps a history memory with real-time clock for alarm messages.
The ISOMETER itself carries the article number B91065120 (type IRDH275BM-7, supply AC 19.2 to 55 V or DC 19.2 to 72 V). The coupling device is ordered separately: AGH675S-7-500 (B913060, 500 mm cable), AGH675S-7-2000 (B913061, 2000 mm cable) or AGH675S-7MV15-500 (B913058, up to 15.5 kV). This page describes the ISOMETER; confirm the coupling device for your voltage level before ordering.
Technical specification
| Parameter | Specification |
|---|---|
| Type / article number | IRDH275BM-7, B91065120 |
| Supply voltage Us | AC 19.2 to 55 V, 42 to 460 Hz; DC 19.2 to 72 V; power consumption max. 14 VA |
| Monitored systems | Via AGH675S-7: AC, 3(N)AC and DC 0 to 7.2 kV, 0 to 460 Hz; via AGH675S-7MV15: up to 15.5 kV; use for medium-voltage converters up to 15.5 kV |
| Response values | Ran1 and Ran2 adjustable 100 kOhm to 10 MOhm; relative error plus/minus 100 kOhm (100 to 500 kOhm), 0 to +20 % (500 kOhm to 10 MOhm); hysteresis 25 % |
| Response time | max. 5 min |
| Measuring circuit | Measuring voltage max. 50 V; measuring current max. 21 uA at RF = 0; internal DC resistance min. 2.4 MOhm; permissible Ce max. 5 uF (factory setting 2 uF) |
| Display | Illuminated two-line display, 2 x 16 characters; range 50 kOhm to 10 MOhm; error plus/minus 50 kOhm (50 to 500 kOhm) and plus/minus 10 % |
| Outputs | 2 changeover contacts K1 (Alarm 1) and K2 (Alarm 2, system fault); N/O or N/C; 12 000 operations; rated contact voltage AC 250 V / DC 300 V; making capacity 5 A |
| Analogue / serial | Current output 0(4) to 20 mA (load max. 500 Ohm, accuracy plus/minus 10 %, plus/minus 100 kOhm) for kOhm meter SKMP; RS-485 with BMS protocol, address 1 to 30 (factory 3), up to 1200 m |
| Insulation coordination | Rated voltage AC 800 V; rated impulse voltage 8 kV; pollution degree 3 |
| Environment | Operating temperature -10 C to +55 C; storage -40 C to +70 C; climatic class 3K5; shock 15 g / 11 ms; vibration 1 g at 10 to 150 Hz; EMC per EN 61326 |
| Connection | Screw terminals; rigid 0.2 to 4 mm2, flexible 0.2 to 2.5 mm2 (AWG 24 to 12); 0.5 Nm |
| Enclosure | Halogen-free (type X112), UL 94 V-0; IP30 / IP20 terminals; DIN rail IEC 60715; weight approx. 510 g |
| AGH675S-7 data | Rated insulation voltage AC 7.2 kV; AGH675S-7MV15 15.5 kV; IP64 resin-encapsulated block; operating temperature -10 C to +60 C; weight up to 5100 g |
What the coupling device does
Medium-voltage systems cannot be connected directly to a low-voltage ISOMETER. The AGH675S-7 is a resin-encapsulated coupling block with a high-voltage cable connection and an internal resistance of at least 2.39 MOhm; the MV15 version has at least 4.7 MOhm. The datasheet gives type-test values for the blocks: 40 kV impulse and 20 kV AC for AGH675S-7, and 111 kV impulse and 70 kV AC for AGH675S-7MV15, with partial-discharge tests of 14 kV and 29 kV. For converters, the high-voltage cable of the coupling device is connected to the mid-point of the DC intermediate circuit, or two MV15 devices are connected to L+ and L-.
Selection and installation notes
- Order the ISOMETER and the coupling device(s) separately; the system voltage decides between AGH675S-7 and AGH675S-7MV15.
- Supply the IRDH275 through a 6 A fuse (5 A for UL and CSA applications); terminals L1 and L2 are not connected.
- Connect the AK terminal to terminal 5 of the coupling device with standard low-voltage cable (maximum 200 V at terminal 5).
- Use the BMS interface (RS-485) to send data to other Bender devices and a 120 Ohm terminating resistor at the end of the bus.
- This datasheet dates from 08.2019; ask us to confirm the current revision of the device before ordering.
Typical GCC uses
Medium-voltage drives for pumps and compressors in oil and gas, water and power plants use IT systems or DC intermediate circuits that need insulation monitoring. The dual relay output lets one alarm act as prewarning. See the relays category for other Bender products on this site.
Selection and installation notes
Insulation and residual current monitoring devices are selected from the system type (IT, TN or TT), the system voltage, the leakage capacitance and the alarm levels needed. Connect the device to the system and to earth as the manual shows, set the response values from the system design, check the coupling or measuring current transformer and its wiring, and test the alarm and relay outputs after commissioning. Do not do an insulation test of the plant with the monitor connected unless the manual allows it.
Information needed for a quotation
Send the full model code, the quantity, the delivery location in Oman or the GCC, the intended use and any accessories needed, so that the complete package can be quoted together.
Documents and supply information
The manufacturer data sheet is attached to this page and should be read together with the project specification and the site risk assessment before a purchase is confirmed. Ratings, standards and dimensions are quoted as printed on that sheet. Lead time, stock position and certificates available with the shipment are confirmed in the quotation, and we supply to Oman and the wider GCC region for industrial, utility and building services projects.
Related Bender products: Bender IR425-D4-2 ISOMETER Insulation Monitor 0-300 V and Bender iso685-D-P ISOMETER Insulation Monitor 690 V AC.
Datasheets & Documents
- Datasheet Bender IRDH275BM datasheet (08.2019) Download
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About brand
Bender is a German family company specialising in electrical safety monitoring, based in Grünberg, Hesse. Walther Bender patented the insulation monitoring device he called the ISOMETER in 1942 and registered the company in Grünberg in 1946. Bender employs about 1,100 people across subsidiaries on four continents.
Seven Star LLC is an independent supplier in Muscat. We list Bender monitoring devices for power, oil and gas, marine, hospital and industrial installations in Oman and the GCC.
Bender company profile
| Founded | 1946, Grünberg, Germany |
|---|---|
| Founder | Walther Bender |
| Ownership | Bender family |
| Key invention | ISOMETER insulation monitor, patented 1942 |
| Product families | ISOMETER insulation monitors such as iso685 and IR425, EDS insulation fault locators, RCMS residual current monitors, NGRM neutral grounding resistor monitors |
Milestones
- 1942: The ISOMETER is patented.
- 1946: The company is registered in Grünberg.
- 2021: Bender marks 75 years.
Bender product series
Insulation monitors include the IR425-D4-2 for systems up to 300 V, the iso685-D-P for 690 V AC systems, the isoUG425-D4-4 earth fault monitor for 12-120 V DC and the IRDH275BM-7 for medium voltage networks. The EDS440-L-4 ISOSCAN locates the faulty feeder once an insulation fault is detected.
Residual current monitors include the RCMS460-D-2 twelve-channel monitor and the RCMA420-D-2 AC/DC monitor for 10 to 500 mA. The NGRM700 supervises neutral grounding resistors, the VMD460-NA-D-2 is a network and system protection relay, and the MK2430-11 COMTRAXX is a remote alarm indicator with twelve inputs.
Where Bender devices are used
IT power systems in plants, ships, hospitals and data centres, DC supplies and battery systems, generator and solar connections to the grid, and earthing systems with neutral grounding resistors.
Bender products we list
Ordering Bender devices: what we need
Send the Bender type and article number, system type (IT, TN or TT), nominal voltage and frequency, the supply voltage of the device and the alarm and communication outputs needed.
Facts checked against Bender's own history and 75th anniversary release, October 2026.
Browse Bender products by category: Switchgear, Enclosures & Distribution.
FAQ
Questions about the Bender IRDH275BM-7 ISOMETER Medium-Voltage
Answers from our engineering team on installation, compatibility and integration.
01Can the IRDH275BM-7 be connected directly to a medium-voltage system?
No. It is used with an AGH675S-7 or AGH675S-7MV15 coupling device that couples it to the system.
02What voltages can it monitor?
Up to 7.2 kV with AGH675S-7 and up to 15.5 kV with AGH675S-7MV15, in AC, DC and AC/DC IT systems.
03What is the article number of the ISOMETER?
B91065120; the coupling devices have their own numbers (B913060, B913061, B913058).
04What is AMPPlus?
A measuring method patented by Bender that suits systems with rectifiers, converters and thyristor-controlled DC drives.
05Does Seven Star LLC manufacture the IRDH275BM-7?
No, Seven Star LLC is an independent supplier in Muscat; send us the system voltage for the coupling-device selection.
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