The original HRG system developed in the 1950’s and 1960’s provided process continuity, however, they were unable to solve potential safety issues, such as a second ground fault, leaving the ground on the system too long and monitoring of the neutral path.

There is a concern that the first ground will be left on the system and ignored. Since the zero-sequence current transformers identify the faulted feeder, the relay has the ability to begin a (user programmable, usually in hours) timer when the ground fault first occurs. Unless the ground fault is removed or the timer is reset, the faulted feeder is shunt-tripped offline. The purpose is to continually remind maintenance personnel to either remove the ground fault or to reset the timer every so many hours.

In the event that a second ground fault occurs prior to removing the first ground fault, a phase-to-ground-to-phase or phase-to-phase fault can occur. When this occurs on the original HRG, it would cause both feeder circuit breakers and possibly the main circuit breaker to trip.

However, the modern relay can be programmed to prevent this and only shunt-trip the lesser priority feeder, leaving the more important feeder on-line.

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Sleuth is a neutral grounding device that limits ground fault currents to non-damaging levels under a single line-to-ground fault condition. Sleuth is the ideal tool for sensing and locating ground faults quickly and easily. When a ground fault occurs, Sleuth controls and limits the fault current, provides an alarm that indicates an active fault, enabling electrical personnel to follow a simple sequence to locate and isolate the fault without interrupting the circuit or opening circuit breakers.

Sleuth Benefits

  • NEMA 3R enclosure containing current limiting resistor and ground fault relay
  • Available with artificial neutral for use on delta systems
  • Visual indication of system normal, active ground fault and pulsing active
  • Available for 480V, 600V and 4160V distribution systems
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Voltage Alarm Indicator

The VIA has been designed specifically for Ground Fault Indication on Wye or Delta-connected, three-phase, three-wire, resistance grounded or ungrounded power systems. It may be used on systems between 120 volts or 600 volts (up to 690 without CSA approval) or up to any voltage with the use of 120 volts or 240 volts potential transformers (PT’s). Additionally, the VIA can detect DC ground faults on Variable Frequency Drives that are on AC fed systems. One or more optional flush mounted external displays (VIA -R) can be mounted on panel doors or other locations. Isolation inside the VIA protects the external displays from high voltages.More Information >


Arc flash hazard is the energy released in an arc flash and is proportional to the duration of the arcing fault; hence arc flash hazard can be reduced by lowering time delay settings of the ground fault overcurrent protective devices.

Continuity of service is very important, and is maximized by time-current coordination of the ground fault devices. The drawback of time-current coordination is that an extra time delay is required on upstream protection devices.

Zone Selective Instantaneous Protection (ZSIP), improves arc flash safety upstream in the distribution system without affecting service continuity.

With ZSIP, the Sentri relay senses a fault and trips with no intentional delay unless it receives a restraint signal from the Sentri relay immediately downstream; if so restrained, the Sentri relay waits to time out before tripping allowing the downstream Sentri to clear the fault.


The I-Gard mGARD is a microprocessor based ground fault relay designed and built to be used on solidly grounded or resistance grounded systems. This innovative digital electronic relay measures ground fault current using built-in zero sequence current sensor (ZSCS). The mGARD operates on any control voltage from 40-240 volts direct current (DC) or alternating current (AC), and contains an isolated power supply. Options are available for operation at 5 VDC, 12 VDC and 24 VDC.

The mGARD reacts to alternating current only and will reject direct current signals. With the harmonic filtering feature enabled, the mGARD rejects all higher frequencies than fundamental. This can be used to eliminate false tripping when the relay is used on systems with variable frequency drives. With the harmonic filter disabled, the relay will respond to AC currents between 25 and 400Hz. The relay can be connected to the mGARD-SYM remote indicator (with Modbus connectivity) for remote test/reset and monitoring. The mGARD-SYM provides detailed device status information.

mGARD Benefits

  • Due to its very low sensitivity (down to 10ma) the mGARD is ideal for people safety in areas wherever the public is exposed to water and electricity such as water parks and fountains.
  • Ideal for Motor Control Centers
  • Suitable for solidly grounded or resistance grounded systems, three phase or single phase loads
  • Wide range of trip levels and delays
  • Wide range AC and/or DC control voltage

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Operator safety from electrical shock depends to a large extent on the integrity of the grounding of the equipment when it is energized. It is vital, therefore to know if this grounding has been compromised; to do this a second auxiliary ground conductor is incorporated in the trailing cable to the mobile equipment.

The GCHK-100 monitors the loop resistance of the two grounds and trips when it exceeds a preset value.

Additionally, the relay will detect if the ground loop has become shorted or has opened. In the event of a ground connection failure and internal leakage within the mobile equipment, it is possible for the frame of the equipment to become live and present a shock hazard.

For added protection, the GCHK-100 detects high equipment frame voltages and quickly trips the relay. This feature will cause a trip twice as fast as the ground check and five times quicker for frame voltages exceeding 100V.

To service the special needs of the mining industry I-Gard has developed the GCHK-100 ground fault relay to improve safety for personnel and equipment in underground or above ground applications. Detection of ground faults is important where safety from electric shock and fire risk can occur and cause serious equipment and personnel hazards.

The relay is designed for use with resistance grounded systems up to 4160V but could be used with grounded systems in branch circuit applications where Load current is limited to 800A.

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A major safety concern is the loss of neutral path, i.e. broken wire from source neutral to resistor or between resistor and ground or even a bad or loose connection.

The result is changing from a high-resistive grounded system to either an ungrounded or solidly grounded system without anyone knowing it! This would cause severe safety hazards, such as transient over-voltages, unlimited fault current, escalating arcing faults etc. With the Sigma monitoring relay the neutral path from neutral to ground (including resistor) is continuously monitored for integrity. If an open or short circuit occurs, the relay will alarm.

The I-Gard SIGMA monitoring relay is a combination neutral grounding resistor (NGR) monitor and ground fault relay. In distribution systems employing resistance grounding the SIGMA monitoring relay protects against ground faults and abnormal conditions in the path between system neutral and ground possibly caused by loose or improper connections, corrosion, foreign objects or missing or compromised ground wires.

​The SIGMA monitoring relay measures the current through the NFR, the transformer neutral-to-ground voltage and the NGR resistance. The relay compares the measured values against the field settings of the relay and provides relay outputs and LED indications when an abnormal condition is detected.

I-Gard’s neutral grounding resistors have unique properties that make them better. It starts with the element. A better grade of stainless steel with a lower coefficient of resistivity ensures that the over-current relay works – it responds when it should. Not all stainless steel does that. Read more about “The Element Difference”

Add the optional SIGMA Monitoring Relay – a combination neutral grounding resistor (NGR) monitor and ground fault relay, and you have a complete system of protection – a better NGR.

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Dynamic Braking Resistors

These are used with AC variable frequency drives to produce a braking torque in the motor during overhauling load conditions. In addition the dynamic braking resistor prevents the flow of current from reaching the current inverter and causing equipment damage. They are double insulated and rated at 1200 volts. The resistance value in ohms determines the amount of braking torque produced, and thus the rate at which the motor will stop. The resistor wattage is sized to prevent overheating during normal braking cycles.

Dynamic braking resistors are often added to prevent over-voltage trips on the drive when stopping the motor.

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Motor Control

These resistors are used to control motor starting and stopping anywhere from reduced voltage motors of low horsepower up to large motor applications such as materials handling, mine hoists, cranes etc.

The most common applications are:

  • AC wound rotor induction motors – where the resistor is wired into the motor secondary slip rings and provides a soft start as resistance is removed in steps.
  • AC squirrel cage motors – where the resistor is used as a ballast for soft starting also known as reduced voltage starting.
  • DC series wound motors – where the current limiting resistor is wired to the field to control motor current, since torque is directly proportional to current, for starting and stopping.

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Resistive Load Banks

I-Gard’s range of resistive load banks have three main applications:

  • Testing AC and DC systems, including batteries, uninterruptible power supplies and standby generators.
  • Load stabilization – acting as a load source to minimize power swings.
  • Load simulation – used in aerospace and other applications to simulate load requirements on a system.

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Harmonic Filtering

We offer a wide range from single, low wattage, high resistance elements, to large, multi-element, 150kW banks.

Our in-house, skilled engineering allows precision designs, including challenging or special requirements such as low inductance designs, and impulse withstand and testing.

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