Grounding System Design

In designing electrical grounding solutions, we use specialized design software to model and build an electrical grounding system design based on the soil data, design goals, and other factors. After modeling the area, we will engineer an electrical grounding system design that will meet your performance objectives.The engineers at ComSite Construction Company can help you plan and execute an electrical grounding design that will provide the best performance available within the constraints of your available area, budget, and equipment being protected.To schedule your initial consultation, please contact us or call 864-480-7680.

Some of the many reasons to ensure you have a well-designed grounding (and bonding) system:

  • A lightning protection system is pointless without it (see short discussion, below).
  • Human safety is critical during ground potential rise events in work place areas.
  • Federal law mandates mitigation of all known hazards in the workplace. Substations are always considered workplaces; step and touch potentials must be eliminated to ensure the safety of work personnel.
  • Although transmission and distribution towers or poles are not always considered work places and are often exempt from these requirements, sometimes they are. Install equipment that’s not related to the electric utility company and requires outside vendors for support, and it’s now considered a workplace.

Cellular telecommunications, environmental monitoring, and microwave relay equipment are good examples of equipment that, when installed on a high-voltage tower, turn the tower into a workplace. Federal regulation CFR 1910.269 specifically requires eliminating step and touch potentials on transmission and distribution lines that include any related communication equipment.

Let’s discuss lightning a little bit more.

A lightning strike analysis can save lives and protect property, if its recommendations are correctly implemented. Lightning is a random and unpredictable event. Globally, some 2,000 ongoing thunderstorms cause about 100 lightning strikes to the earth each second. Did you know that total equipment damage costs from lightning strikes is about 150 million dollars every year in the United States alone? A lightning strike analysis is a critical step in a comprehensive site grounding design.

The purpose of a lightning protection system for a building is to provide a preferred path for the lightning strike to follow (to the earth) without injuring people or damaging equipment in the building. The main components of a lightning protection system are:

  • Air terminals. These are mounted up high, typically directly on the roof. They provide a preferential target for the lightning.
  • Down conductors. These are special conductors along which the lightning travels to the grounding elements. Being millions of volts and high frequency, lightning travels along the skin of these conductors and can jump across bends in the conductors or leave the conductors entirely if the installer doesn’t strictly follow the installation standards.
  • Grounding elements. These are often copper-clad ground rods, but may be in some other configuration (e.g., counterpoise or mesh) depending on what will work in that location. The job of the grounding element is to diffuse the lightning into the earth. How well it can diffuse the energy is a function of soil resistivity versus the total surface area of the grounding element in contact with the soil. This is why good system designers rely so heavily on soil resistivity data (and why bad designers who “wing it” can leave the site unprotected).

Whether to install (and subsequently maintain) a lightning protection system is a critical decision. Its benefits include:

  • Safety of personnel.
  • Protection of property.
  • Reduction of insurance costs.
  • Reduction of downtime.

The engineers at ComSite Construction Company provide lightning stike analysis based on the requirements set out in NFPA 780 Risk Analysis Guidelines (National Fire Protection Association Standard for the Installation of Lightning Protection Systems). To schedule your free initial consultation, please do not hesitate to contact us or call 864-480-7680.

In the old television series, Star Trek: The Next Generation, the unrelenting Borg were known for their mantra “Resistance is futile.” But for a high performance electrical grounding system design, soil resistivity testing is far from futile. It’s critical that you get this done and done correctly.

Accurate soil resistivity data are essential for precise designs and predictable results. Absent these data, the design is really just guesswork that may cost too much or provide too little protection.

The type of soil, moisture, electrolytic content, and temperature all affect soil resistance. Frost line depth, water table level, bedrock, and available space dictate some specifics of the grounding system design. We determine soil resistivity using the Wenner 4 Point test method, or by analyzing soil samples.

As part of our electrical grounding system design, the engineers at ComSite Construction Company provide a written recommendation along with a drawing of the site illustrating the recommended grounding configuration, quantity, and location of the electrical grounding electrodes. We detail out the recommended grounding electrode spacing, and we model the recommended installation. To schedule your free initial consultation, please do not hesitate to contact us or call 864-480-7680.

To electrical people, ground testing is a matter of soil resistivity. We do that kind of testing, but also test the ground for structural properties. By utilizing the Wenner 4 Point system, along with soil resistivity results from geotechnical surveys, we’re able to map the dynamic time domain simulation of bus structures under various excitations. These include:

  • Magnetic forces.
  • Wind loading.
  • Ice loading.
  • Earthquakes.
  • User-defined forces and moments.

The ground system simulations results include:

  • Magnetic force magnitude.
  • Buss work displacements.
  • Torques and moments.
  • Tensile, compression, and shear forces.
  • Tensile, compression, and shear stresses.

We provide reports of these quantities in time plot format and in tables of maximum values.We use meter elements to select the locations for the reports of displacements, forces, and stresses.

What reports are customers typically interested in? In our many years of experience, we have found those to be the following:

  • Soil resistivity analysis
  • Low frequency grounding / earthing analysis
  • Frequency domain grounding / earthing¬†analysis
  • Line and cable constants (parameters) and induction analysis
  • Detailed fault current distribution and EMI analysis
  • Electromagnetic fields analysis
  • Automated fast fuorier transform analysis
  • Simplified fault current distribution analysis
  • Ground system resistance report
  • Ground conductor current report
  • Soil current density report
  • Enhanced touch voltage computations
  • Ground conductor voltage plots
  • Fault current contribution reports

Qualified tower installers know to where to bond and where to ground. What’s the difference between these two concepts?

When you ground, you connect something to the earth (you can read more about this distinction in the IEEE-142, the Green Book and in the National Electrical Code, Article 250 and in other sources). So when you think of grounding, you could think of it as “earthing” to keep things straight in your mind. We ground for lightning protection purposes. We do not ground to create an equipotential plane, because the resistance of the earth is far too high to facilitate that. Anyone who’s done ground resistance testing can tell you this

When you bond, you create a conductive path between metallic objects. We bond for several purposes. For example, we bond metallic objects to prevent a flashover between them. For electrical systems, we bond to create a low-impedance path for fault current to flow.

Let’s address some common misconceptions about grounding:

  • Myth: When you ground something, a person touching it is at the same potential as the ground rod and so can’t be electrocuted. The problem here is Ohm’s Law. You can stand on a ground rod and be electrocuted if your other foot is on the dirt because the earth has resistance and so does your body. Draw out the circuit on paper, and do the math.
  • Myth: Grounding eliminates differences of potential. No, this is what bonding does. When you bond, you create an extremely low impedance path between metallic objects. That’s why lightning protection standards require bonding metallic objects on a roof to prevent flashover.
  • Myth: Grounding eliminates electrical noise. This misconception arises from the misuse of the word “grounding.” We talk about signal ground, but it’s not actually ground (earth). Airplanes are not connected to the earth, yet their electronics have signal “ground.” What’s meant here is a reference plane, not an actual ground.
  • Myth: Grounding creates a return path for electricity. This is a very dangerous myth to believe in. Suppose, for example, we eliminated the neutral wiring in homes and just used ground as a return path. This would make taking a shower a rather lethal experience. Similarly, consider the common 277V lighting system in commercial and industrial buildings. The return path is the neutral, not the bonding or grounding system. In cases where the installers have used the metallic raceway instead of a neutral (a code violation), the result has been undesired circulating current. Why? That brings us to our final myth….
  • Myth: Electricity seeks the path of least resistance. This directly contradicts Kirchoff’s Law of Parallel Circuits, upon which our entire electrical infrastructure and all of our electronic devices are based. The reality is that electricity flows along all available paths, in reverse proportion to the resistances.

So, does grounding actually serve any purpose? Yes. The National Electrical Code devotes considerable space to this topic, as do the lightning protection standards. Grounding provides a path to earth for lightning and other high voltage transients. For towers, this is critically important. Lighting strikes tall structures, preferentially. So a tower, being tall, is essentially a big lightning rod. Without a lightning protection systems (which relies on grounding), the tower can suffer catastrophic damage from the million plus volts it gets hit with. But deficiencies in how that system is designed and/or installed can result in currents flowing through structural connectors, overheating those connectors, and weakening them over time. The lightning protection system diverts this energy to ground, thereby protecting the tower.

The three grounding standards in the USA are:

  • IEEE-142, The Green Book.
  • NFPA 70 (NEC), Article 250.
  • IAEI Soares Book on Grounding.

The two lightning protection standards in the USA are:

  • LPI-175, the Lightning Protection Institute’s Standard of Practice for the Design, Installation, and Inspection of Lightning Protection Systems.
  • NFPA 780, the National Fire Protection Association’s Standard for the Installation of Lightning Protection Systems Article 250.