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What is Ground Potential Rise (GPR)

A cloud to ground lightning strike can introduce millions of volts of multi-frequency electricity that

flows as an Earth return fault current; AC power line faults can also result in lesser amounts of Earth

return fault current.  According to IEEE 487, Ground Potential Rise is “the product of a ground

electrode impedance, referenced to remote earth, and the current that flows through that electrode

impedance”.  GPR is governed by Ohm’s Law which states that    Voltage = Current * Impedance;

therefore, current will flow back to equilibrium through paths of least resistance.  The current flows out in all directions from the source, the cumulative current flow through all pathways equals the amount of current introduced, therefore the less resistance the pathway presents the more current will flow through it.


As current flows outward from the source, it dissipates due to the ever growing pathways transmitting the current; however, when a highly conductive multi-grounded asset is encountered a significant portion of the GPR current will flow through it.  The amount of current that flows into a grounding system is an amount equal to the potential difference of the various grounds / paths the current encounters as it radiates out from the GPR point of origin.  The resulting current flow will go through all attached site equipment as it passes from the grounding system to the AC power grid.


The potential voltage differential of GPR dissipating across multiple grounds on a site can be in the 10’s of thousands of volts.  Any attached equipment that differential passes through is damaged as the current flows from ground to AC power grid.  This continuous path to the AC grid is path of least resistance for the GPR to flow.  SensorGuard eliminates the pathway for GRP current to flow and eliminates circuit potential due to air gap isolation.

  • Threats to your Assets

  • Lightning Damage is a Real Danger

  • What is Ground Potential Rise (GPR)?

  • SensorGuard Protects your Assets

A great example of how GRP current flows is when a building’s ground rod is connected via the AC power connection neutral to a very well-grounded power substation; a potential difference will exist between the two upon a lightning strike at or near the building.  As the imbalance that exists between these two ground sources equalizes, the resulting fault current flow will often damage sensitive circuits in the path.  The figure to the right well illustrates the dispersal of lightning GPR and how tens of thousands of volts of potential difference can be generated at any given site.


A typical office or commercial facility is connected to multiple ground sources; a multi-grounded neutral from the AC Power provider, the buildings ground system, and the multiplicity of remote earth grounds from data or telephone network interface devices.  As fault currents flow between these multiple ground sources, damage easily results in delicate electronic circuits, UPS systems, servers, PC’s, printers, alarms, PABX, and phones.  These are only a few examples in an endless list of equipment that is susceptible to damage as a result of lightning induced fault currents.


Ground voltage in the vicinity of the strike can rise and fall by tens of thousands of volts, causing GPR induced surges wherever electrical paths are available.  Easily replicated experiments show that two conducting stakes at a distance of only a few yards apart can experience a potential difference of thousands of volts and the resulting energy/current flow has a wide range of frequencies from a few hertz up to megahertz.  Sites with extensive grounding still suffer damage due to the differing frequencies which cause electronic components to oscillate, heat up, and fail.


Additionally, the miniaturization of components (particularly microprocessors) dramatically increases the risk of equipment damage because components are laid out in closer proximity to each other; this promotes pathways for GPR to travel and increases equipment vulnerability.  Damage to equipment can be immediate or delayed; cumulative GPR damage will likely result in delayed cascading failures of sensitive equipment.  SensorGuard isolates equipment prior to lightning strikes; therefor it prevents both immediate and delayed GPR damage and keeps sites operational.


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