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Brand: Bender
Bender NGRM700 Neutral Grounding Resistor Monitor
Description
Monitoring the neutral grounding resistor itself
The Bender NGRM700 is a neutral grounding resistor (NGR) monitor for high-resistance grounded (HRG) systems. In a resistance-grounded star point, a broken or degraded resistor makes the system unsafe without anyone noticing, because a first earth fault does not trip the plant. The NGRM700 monitors the current through the NGR, the voltage between the transformer star point and earth, and the condition of the resistor itself, including while the installation is de-energised. The datasheet states that it also measures line-to-line and line-to-earth voltages and provides a faulted phase indication.
The NGRM700 covers system voltages from 400 V to 25 kV line-to-line, neutral current up to 100 A and resistors from 15 Ohm to 5 kOhm. The NGRM750 is the variant for low-resistance grounded (LRG) systems with 10 to 2000 A and 0.1 to 200 Ohm. The NGRM700 article number is B94013700.
Technical specification
| Parameter | Specification |
|---|---|
| Type / article number | NGRM700 (HRG), B94013700; NGRM750 (LRG), B94013750 |
| System voltage | 400 V to 25 kV line-to-line; NGRM700 intended only for high-resistance grounded systems |
| Supply voltage Us | AC 24 to 240 V, 40 to 70 Hz / DC 24 to 240 V (UL: 48 to 240 V); above 2000 m up to 5000 m: 24 to 120 V; power consumption typ. max. 6.5 W / 13 VA |
| Resistor monitoring RNGR | Active measuring range 0 to 10 kOhm; uncertainty plus/minus 20 Ohm (0 to 40 C) with RS = 20 kOhm; HRG setting range 15 Ohm to 5 kOhm; response below 10 to 90 % and above 110 to 200 % of RNGR nom |
| Current monitoring INGR | 5 A and 50 mA measuring circuits, DC, 50/60 Hz and 10 to 3200 Hz, accuracy plus/minus 2 % of In; response 10 to 90 % INGR nom; ground-fault relay delay max. 40 ms; trip delay 100 ms to 48 h or infinite |
| Voltage monitoring UNGR | DC, 50/60 Hz, 10 to 3200 Hz; 400/sqrt3 to 4300/sqrt3 V with RS 20 kOhm, above 4.3/sqrt3 to 25/sqrt3 kV with RS 100 kOhm; accuracy 2 % of UNGR nom |
| Phase monitoring | 3AC 100 to 690 V, CAT III, accuracy plus/minus 1 % of Un; with potential transformers up to 25 kV |
| Coupling devices | CD1000, CD1000-2, CD5000 (RS 20 kOhm, system up to 4.3 kV); CD14400, CD25000 (RS 100 kOhm, above 4.3 kV) |
| Outputs | Ground-fault, NGR-fault and trip relays (changeover, configurable fail-safe); AC-13/AC-14 5 A / 3 A; analogue output 0/4 to 20 mA, 0 to 400 uA, 0 to 10 V, 2 to 10 V; digital inputs and outputs |
| Communication | Ethernet and web server; graphical user interface; fault and history memory; password protection; detachable HMI for door mounting |
| Features | FFT analysis of neutral current and voltage; pulser control for manual ground-fault location; tripping on RMS, fundamental or harmonics; detection of AC and DC ground faults |
| Environment | Operating temperature -40 C to +70 C (UL -40 C to +60 C); humidity up to 98 %; altitude up to 5000 m AMSL; mechanical class 3M12 |
| Protection and approvals | IP30 internal parts; UL 94 V-0; protective coating SL1307 (UL file E80315); UL file numbers E493737 and E173157 printed |
| Weight | 1050 g |
Why HRG systems need an NGR monitor
In a high-resistance grounded plant the neutral resistor limits an earth-fault current to typically a few amperes so that production continues on the first fault. The price is that the resistor becomes a safety-critical component: if it opens, the star point floats and the next earth fault may cause overvoltages; if it is shorted, the fault current rises. The NGRM700 therefore combines a continuous active measurement of the resistor value with measurement of voltage and current, and gives separate relays for ground fault, NGR fault and delayed trip. The trip relay can be combined with RCMS monitors for automatic shutdown of faulted feeders, and the pulser control assists manual ground-fault location.
Selection and installation notes
- Choose NGRM700 for HRG and NGRM750 for LRG; the two devices are not interchangeable.
- Pick the coupling device by system voltage: CD1000 (400 to 690 V), CD1000-2 (400 to 1000 V), CD5000 (1000 to 4200 V), CD14400 (4300 to 14550 V), CD25000 (14551 to 25000 V).
- Measure neutral current with a transformer: CTAC35 or CTAC60 for AC up to 30 A, or CTUB103 series for AC/DC.
- For CTUB103 transformers use STEP-PS power supplies (B94053110, B94053111 or B94053112).
- Observe the measuring-circuit separation and the 10 m cable limits for digital I/O.
Typical GCC uses
Neutral-grounded medium-voltage systems on oil and gas plants, power stations and large industrial sites commonly use resistance grounding; the NGR is exposed to heat and vibration. See the relays category for other Bender monitors 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.
Frequently asked questions
What does the NGRM700 monitor?
The neutral grounding resistor in a high-resistance grounded system: its resistance, the current through it and the voltage across it.
Can it monitor the resistor when the plant is switched off?
Yes, the datasheet states continuous monitoring of RNGR even if the installation is de-energised.
What is the difference between NGRM700 and NGRM750?
The NGRM700 is for high-resistance grounded (HRG) systems, the NGRM750 for low-resistance grounded (LRG) systems.
What is the article number?
B94013700 for the NGRM700 and B94013750 for the NGRM750.
Does Seven Star LLC manufacture the NGRM700?
No, Seven Star LLC is an independent supplier in Muscat; send us the system voltage and resistor data for a quotation.
Datasheets & Documents
- Datasheet Bender NGRM700 datasheet (07.2023) Download
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About brand
Bender is a German manufacturer of electrical safety monitoring devices, founded in 1946 and based in Grünberg. It is known for ISOMETER insulation monitoring devices for unearthed (IT) systems and for residual current monitoring, insulation fault location and grid protection relays.
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 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.
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.
Browse Bender products by category: Switchgear, Enclosures & Distribution.
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Frequently Asked Questions
What does the NGRM700 monitor?
The neutral grounding resistor in a high-resistance grounded system: its resistance, the current through it and the voltage across it.
Can it monitor the resistor when the plant is switched off?
Yes, the datasheet states continuous monitoring of RNGR even if the installation is de-energised.
What is the difference between NGRM700 and NGRM750?
The NGRM700 is for high-resistance grounded (HRG) systems, the NGRM750 for low-resistance grounded (LRG) systems.
What is the article number?
B94013700 for the NGRM700 and B94013750 for the NGRM750.
Does Seven Star LLC manufacture the NGRM700?
No, Seven Star LLC is an independent supplier in Muscat; send us the system voltage and resistor data for a quotation.
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