The premiere engineering service offered by ComSite Construction Company is the Ground Potential Rise (GPR) Study. Our electrical grounding experts will take the data and perform the calculations needed to provide you with the information you need to ensure you have a safe facility.And if there’s something that needs correction, our engineers 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.
Electrical damage from Ground Potential Rise (GPR) costs companies millions of dollars every year. Your company doesn’t have to be one that’s hemorrhaging money due to GPR issues.
Has an electrical engineer told you not to worry? The problem there is many electrical engineers are unfamiliar with what ground potential rise is. If you’ve gotten assurance there’s no problem, ask the engineer to explain GPR to you. Then ask for the data and calculations to back the assertion. Then call us and find out the real conditions at your facility.
Has a Master Electrician or electrical inspector told you there’s no GPR concern because your facility complies with the National Electrical Code (NEC)? Get a copy of the NEC and read Article 90. The NEC states it’s not a design guide. It’s the minimum required to protect people and property from such things as fire and electrocution. Yes, you should ensure your facility has no NEC violations. But optimum performance and/or lowest total cost of ownership nearly always requires going beyond NEC minimums.
To know how far to go beyond, at least when it comes to your grounding and bonding, you need a GPR Study. Maybe everything is fine, but probably it isn’t. And if it isn’t, then you have a high risk of GPR-related events.
Damage from GPR can occur when a high-voltage difference exists between a grounded site and a remote site. An example is the cellular base station transmitter that is connected to a remote central telco office. There’s actually a current path between these two places. How do we know?
You may have heard someone say “Electricity follows the path of least resistance.” That saying is absolutely not true. In fact, electricity follows all paths before it, in inverse relationship to the resistances presented by each path. That’s Kirchoff’s Law of Parallel Circuits, and it’s a foundational concept behind the design of every electrical and electronic device in existence. If that law were not true, you would not be able to read this page online because there would be no computers and no Internet.
The existence of this path is why proper cell site grounding design is of particular importance to the telecommunications industry. The amount of GPR is a function of the amount of grounding electrodes in contact with the soil, soil resistivity, the number of conductors leaving the site, and various other factors..
Equipment damage from GPR is usually located at:
- Cellular towers or cell sites.
- Power substations.
- Power generating facilities.
- Radio communication towers.
ComSite Construction Company offers two GPR evaluation services:
- Ground Potential Rise Calculation.
- Ground Potential Rise Study.
The Ground Potential Rise Calculation provides all the data required for:
- T-1 line applications, including the total fault current; site eligibility and Telco T-1 hard-line requirements in high-voltage areas.
- Ground Potential Rise GPR voltage.
- X/R factor and the 300 volt line.
- All the Ground Potential Rise (GPR) information you will need to get your T-1 lines approved. Fast!
The Ground Potential Rise Study provides you with:
- All the information in the GPR Calculation.
- A full analysis of the Step & Touch Potential Voltages present at your site.
- All the structural design recommendations needed to eliminate any potential electrical hazards.
- The GPR information needed to meet Telco T-1 requirements.
The GPR study has these major components:
- Site Review of Ground System
- Soil Resistivity Test: Wenner 4 point
- Computer Modeled Ground System Design
- Safety Calculations & Recommendations
- Ground Potential Rise GPR Calculation & Written Report
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 strike 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.
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.