GFM-100 Battery Ground Fault Monitor

Model # GFM-100

The Eagle Eye GFM-100 Ground Fault Monitor is an easy-to-use, inexpensive & real-time solution for monitoring battery ground faults. The GFM-100 works for 24V, 48V, 125V and 250V applications, and reads battery bus status, detects out-of-limit conditions, and provides alarm indications per-user settings. The monitor's status, under voltage and over voltage trip values, ground fault, time delay, and IP address settings are easily accessible on the user-friendly color touchscreen interface. Installation of the GFM-100 Ground Fault Monitor is simple - it can be installed as a wall, panel, or DIN rail unit, and includes a mounting kit for DIN rail or wall mounts.

When the GFM-100 Ground Fault Monitor is installed and power is applied to the monitor, the firmware reads the stored settings and begins battery string ground fault monitoring. Changing the stored settings, including the ground fault resistance trigger level & the monitor's IP address is done on the GFL-100 color touchscreen. The touchscreen will display both settings when powered, and a horizontal bar indicating the balance in ground fault resistance between the negative and positive battery buses will also be continuously displayed. The status and the bar indicator updates approximately twice per second. When the ground fault occurs, the bar will turn red and an alarm message will be displayed. If a ground fault is detected, a positive or negative ground fault monitor message will appear, and the GFM-100 can activate a Form C contact. The GFM-100 Ground Fault Monitor has (4) Form C contacts - (2) for positive ground faults and (2) for negative ground faults. Modbus protocol output is also available on all units.

Battery ground faults can be difficult to locate and may create catastrophic and costly damage if they remain undetected. The entire battery system will be compromised and subject itself to overheating, thermal runaway, and reduced battery capacity. Continuous battery string ground fault monitoring will eliminate those risks, and allow for immediate corrective action to happen if a ground fault is located.

The GFM-100 includes:

  • GFM-100 unit (for 24V, 48V, 125V or 250V)
  • DIN rail mounting clip
  • Backplate for wall mounting
  • User Manual

The GFM-100 is one of a family of digital monitors that read offset voltage from ground and alarms for ground faults. Eagle Eye offers the VM-100 Voltage Monitor reads DC voltage level, and alarms for voltage levels outside of the user-programmed settings. Eagle Eye also offers the VGM-100 Battery Ground Fault Monitor which combines the functions of the GFM-100 Ground Fault Monitor & the VM-100 Voltage Monitor into a single unit - allowing monitoring for battery string voltage and ground faults.

Eagle Eye Power Solutions offers battery monitoring solutions to power utilities worldwide. NERC (North American Reliability Corporation) is a not-for-profit regulatory authority that ensures the reliability of the BES by enforcing reliability standards. The GFM-100 Ground Fault Monitor will comply with NERC PRC-005-2 guidelines that require DC ground fault monitoring and alarming. When the GFM-100 is integrated with Eagle Eye's stationary battery monitoring systems full NERC PRC-005-2 compliance will be met. Eagle Eye's Battery Monitoring NERC Compliance Solutions eliminate the need for periodic testing and maintenance activities.

  • Specifications
  • FAQs
  • Benefits

Technical Specs

Measurement Range:Battery Voltage: 20-28, 38-56, 90-155, 180-320 VDC
Fault Resistance Limit Set: 1 – 100 kOhm
Fault Resistance Limit Set:1 – 100 kOhm
Output Contacts:(4) Form C
Contact Rating:125 VAC/VDC: 0.5A
30VDC: 2A
Maximum Switching Power:60 W
Power requirements:Powered by connected battery DC voltage
Noise Immunity:IEEE/ANSI Standard C 37.90a-1989 compliance
Time Delay to Alarm:Adjustable 1 – 999 seconds
Operating Environment:Temp: 0 – 55°C (32 – 131°F), Humidity: 0 – 95% RH
Dimensions / Weight:147 x 91 x 45 mm (5.77 x 3.56 x 1.77 in)
353 g (12.45 oz)


What are some common applications areas for this product?
Common applications include but are not limited to:

  • Power Utilities
  • Telecommunications
  • CATV / Broadband
  • Mission Critical Facilities
  • UPS Systems
  • Power Generation & Distribution
  • Financial Institutions
  • Oil, Gas & Fuel & Petrochemical Operations
  • Mining
  • Government/Defense
  • Transportation Operations
  • Hospitals
  • Emergency Lighting
  • Green Energy
  • Call Centers
  • Battery Suppliers and Manufacturers
  • Battery Service Groups
  • Medical/Biotechnology

How does the GFM-100 Ground Fault Monitor detect ground fault conditions?
DC ground fault detection is determined by measurement of the voltage imbalance relative to ground. These measurements are made through very high resistance divider networks. One establishes the ground reference, and the other measures the positive and negative DC voltages. These values are applied to analog-to-digital converters, and the microcontroller firmware compares the sum of these DC values to the ground reference. If the sum is 0, the DC voltage is perfectly balanced relative to ground. If the sum is positive or negative, the DC voltage is unbalanced positive or negative. User settings determine the extent of imbalance that will result in an alarm condition.

Will the GFM detect a ground fault via a leaked battery jar?
The system would detect a ground fault via a leaked battery provided the ground fault resistance setting (a user setting) was set to the proper value. Since a leaking jar would result in a path to ground of some resistance, the VGM would sense the resulting voltage imbalance and would alarm, provided the path to ground created by the leak was of a resistance lower than that setting.

What is the k ohm limit for ground detection?
Up to 300k ohm.

What is are the contact ratings for the Form C contacts?
The relays have a contact rating of 60W, with a maximum voltage rating of 220VDC, and a maximum current rating of 2A. With these ratings, this relay can switch 2A at 30VDC or less, 0.5A at 125VDC, but only 0.009A at 220 VDC. An external relay would be needed if the customer wanted to increase the rating past the limit.

Do the connections between the monitor and the batteries need to be fused?
No, the monitor has a built in fuse to protect the monitor. However, you may want to fuse the connections to protect against the possibility of a short circuit occurring in the wiring to the monitor.

Is the GFM-100 Ground Fault Monitor CSA certified?
The Ground Fault Monitor is CE certified. For Canadian customers, CSA certification is not required on DC powered units. Please contact Eagle Eye with any questions on certification requirements.


  • Color touchscreen simple interface
  • Ethernet connectivity to web interface or Modbus protocol
  • (4) Form C Contacts
  • High reliability & durability
  • Simple installation with mounting kit for DIN rail or wall mount
  • Monitors Ground Faults in 24V, 48V, 125V, & 250V batteries
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  • Model #

    Ground Fault Monitor, available for 24V, 48V, 125V, or 250V

    Determine part number for required voltage, Ex. GFM-100-XXX would be GFM-100-125 for 125V applications.

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Companies We Serve
  • Duke Energy: Ground Fault MonitorCenovus Energy: Ground Fault Monitoring System
  • SMUD: Ground Fault Monitoring American Electric Power: Ground Fault Testing
  • ATT: Ground Fault Monitor OG&E: Battery Ground Fault Testing