Comsite Construction Inc., utilizes the latest software modeling tools available, such as CDEGS and WinIGS, to provide our clients the results you deserve. For more information, or to schedule a site specific analysis, feel free to contact us or call 877-202-3963. We look forward to working with you.
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:
User-defined forces and moments.
The ground system simulations results include:
Magnetic force magnitude.
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 fourier transform analysis
Simplified fault current distribution analysis
Ground system resistance report
Ground conductor current report
Soil current density report
Enhanced touch voltage vomputations
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 facilitiate 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 elecricity 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 Installatoin of Lightning Protection Systems.