Thank you for your question regarding lightning protection class, it is our pleasure to help.

There are a number of different and varied methods of providing protection from lightning strikes, and the selection of which methods to use is a critical one.  Clearly, a chemical factory, a facility handling flammable materials, or a computer data center with millions of dollars worth of electronics, should be very  concerned with the damage caused by a lighting strike.  A warehouse holding non-flammable items, a garage, a simple office building, etc., may not be so concerned.

The proper design of a Lightning Protection System is a detailed task, especially when protection is needed in complex 3-dimmensional environments (such as irregular shaped buildings, lattice structures, pipe systems, towers, tanks, etc.).  A lightning strike at an unprotected facility could cause catastrophic damage that could result in fire, explosions and serious risk to bodily harm for personnel.  As such, a properly designed Lightning Protection System (LPS) is needed.

There are three (3) steps to consider when designing a Lightning Protection (LP) system for critical systems:

1. Lightning Protection Planning –This tells the engineer where lightning protection systems need to be installed in order to protect the facility.
2. Lightning Protection System Construction Documents –These documents include A/E drawings and blue prints, work plans, grounding systems, and installations specifications necessary to get applicable permits and complete the physical installation of the LP system.
3. Lightning Strike Analysis – This analysis defines the anticipated lightning strike profile in electrical terms.  Details such as the Ground Potential Rise, the Time Domain, and the Frequency Spectrum of the strike are determined.  This data is used to reduce downtime in the event of a lightning strike by allowing custom designed surge suppression systems and critical data for the electrical coordination study.

The purpose of item #1, Lightning Protection Planning, is to determine where lightning protection systems should be installed at the facility, where lightning masts are needed, catenaries, and other protection systems in order to meet the required standards.  The standard that we recommend most is the Rolling Sphere Method (RSM) based on IEEE998.  Other methods, such as the Protection Angle Method (PAM), the Improved Electrogeometric Method (IEM), the Standard Collection Volume Method (CVM-S), and the Mesh Method (MM) are often considered during the design phase.  However, the best method of lightning protection is the IEEE998 RSM.  The level of protection is based on a risk percentage.  We often see either a Level 1 (99%) or a Level 3 (91%) selected.  This selection automatically determines the Angles, sphere radius, peak current, and basic impulse level.  Please see IEEE998 for more information.

The second step (#2) of the process is the development of actual work plans, and construction drawings, including A&E blue prints.  These documents will be used by the various contractors to obtain permits, purchase materials, and construct the actual system.  Specific details regarding what lightning masts to purchase, specific placement (x,y) of the masts, footing depths, maximum cantenary wire distances, etc. will be detailed out at during this process.  As such, such details such as this are not determined during step #1.

The third step (#3) of the process takes us back to the computer where more analysis is conducted.  This step can often be made concurrently with step #2.  The goal of this process is to analyze specific details regarding the electrical profile of a lightning strike at the specific facility.  When lightning strikes an object, the object itself becomes an antenna for the strike, thereby predictably changing the frequencies at which the strike will resonant.  Knowing the predicted frequency profile of the lightning strike at the facility can allow the Electrical Engineers conducting the facilities OCPD coordination study to compensate the timing of breakers so to minimize downtime.  The data can also be used to tune band-pass filters to the specific frequencies of the strike, thereby providing better surge protection.

Modeling a good lightning protection system requires computer program in order to ensure that all the variables have been covered.  We here at E&S Grounding Solutions use and recommend SES-Shield 3D which is part of the CDEGS software package www.sestech.com. We would of course be more than happy to help you with your Lightning Protection Plan, but if not us, please get someone with the proper software to help you with this critical task.  Feel free to call us at 310-318-7151 California time or email us at mesparza@esgrounding.com for more information.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: http://www.flickr.com/photos/snowpeak/3762193048/sizes/o/in/photostream/

Thank you for your question regarding omni-potential grounding, it is our pleasure to help.

We have actually never seen that term in use before. “Omni-” means all or everywhere, so perhaps “omni-potential” means all-voltages?  We suspect it just means that the ground system is at the same potential everywhere on your site, which is pretty much the goal of all grounding systems. 

E&S Grounding Solutions uses an in-house guideline of a maximum 0.1 ohms resistance from any point on the grounding system back to the first service disconnect.  We would more accurately use the term “equipotential” to describe a grounding system with an effective low-resistance path from any point within the system.  “Equipotential” is also the term used by the National Electrical Code (NEC).

The NEC describes an “equipotential grounding plane” or “equipotential bonding” in Article 547.2, 682.2 and 680.26 in similar, but slightly different ways.  In summary that definition is: Where wire mesh, rebar in concrete, other conductive elements, all metal structures, and fixed nonelectrical equipment that may become energized, are connected to the electrical grounding system to prevent voltage gradients from developing within the plane [E&S Grounding Solutions summarized definition].

In essence, a properly constructed equipotential grounding system would have virtually every piece of metal bonded to the grounding system.  This would include things such as the rebar inside concrete foundations, building steel, columns, motor chassis, tanks, piping systems, water pipes, gas pipes, lightning protection systems, lighting poles, telecommunication & data grounding systems, conduit, cable trays, support stands, electrical cabinets, doors, gates, fence posts, fences, barbed wire, hand rails, fixtures or all types, etc.

We hope you find this answer useful.  If you should have any further questions, please do not hesitate to email us again or call us at 310-318-7151, and someone will be happy to discuss your project, free of charge.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: http://www.flickr.com/photos/kecko/6309581194/sizes/o/in/photostream/

Thank you for your question regarding resistance-to-ground calculations, it is our pleasure to help.

It sounds like you are trying to conduct hand calculations which is indeed a very limited and frustrating process.  It is also highly inaccurate.  In particular, hand calculations cannot take into account  three (3) key factors: Complex ground designs, multi-layer soil, and frequency. 

As you point out in your email, there are no readily available formulas to hand calculate for ground rings with ground rods.  This is because such a formula would be a multi-staged process and would require a white paper just to explain how to conduct the formula.  But that really isn’t the issue with hand calculations you should be worried about.  Your concern for hand calculations is that the formulas found in the Green Book assume a uniform soil resistivity, which simply does not exist in nature.  Therefore, you can never accurately calculate even the most simple of electrode structures using these formulas, let alone trying to hand calculate a complex grounding system.

Let’s consider the calculation for a single (1) 10-ft ground rod.  Hand calculations almost never get the actual resistance right because the formulas don’t account for changes in soil resistivity with depth.  There have been several studies conducted that show that the typical soil is best modeled using 3 to 5 layers, with the top 3 layers generally occurring within 10-ft of the surface.  We often see 3 to 4 layer models, so as to leave the 5^th layer available for changes in soil resistivity due to frost line issues during winter conditions (when soil freezes, the resistivity of the soil increases by a factor of at least 10x).  This means that your 10-ft ground rod will often have 3 to 4 different soil resistivities along its length, and will have a higher resistance-to-ground during winter.  That said, you would need to calculate the change in resistance of the electrode as the soil resistivity changes along its length at depth.  This means that you really need to account for leakage current rates and voltage drops across the length of the electrode.

Of course, keep in mind that you are probably not even dealing with Direct-Current (0 Hz), your ground system is probably being used for a 60 Hz system, which means that you actually should be concerned with impedance-to-ground.  Of course frequency based calculations are not discussed in the Green Book at all.  And yes, impedance makes a huge difference in the final calculations.  You also need to account for the material properties of your grounding system.  The horizontal conductors of the ring will almost certainly be made of copper, while the ground rods will be made of a low-grade steel.  Copper is 12 to 17 times (based on the steel) more conductive than steel, and is at least 250 times less magnetic.  Proper calculations will take into account these two dissimilar materials and the change that the conductivity and magnetism will have on the ground system.

The point of the above information is to demonstrate the futility of hand calculations.  The formulas in the green book are for theoretical use only; they assume direct-current electrical systems in imaginary uniform soil conditions.    The only accurate way to calculate even a simple ground electrode, is by using a computer program designed for this task.  We recommend and use the CDEGS computer program from Safe Engineering Services www.sestech.com

Now, if you are simply insistent on hand calculations, you would need to calculate the ground ring by hand, then calculate the ground rods separately, and then combine the two by adding resistances in parallel.  That is the best you can do.  The problem with adding resistances in parallel is that it does not take into account resistance loss due to overlapping spheres of influence, so we wouldn’t recommend that you show the results to your customer.  But then again, we wouldn’t show any calculation from the Green Book to a customer.

There is really a lot to know about this subject.  If you have further questions, please feel free to call us at 310-318-7151 and someone will be happy to speak with you about your project, free of charge.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: http://www.flickr.com/photos/mamchenkov/373592682/sizes/o/in/photostream/

Thank you for your question regarding probe depths while conducting a Wenner 4-point soil resistivity test, it is our pleasure to help.

Here is some information on Wenner 4-Pin Soil Resistivity Testing:  http://www.esgroundingsolutions.com/about-electrical-grounding/what-is-soil-resistivity-testing.php

When conducting a Wenner 4-point soil resistivity test, we need to consider the effects that the “Sphere-of-Influence” will have on our test, in two (2) ways:

1. The distance our test is being conducted from any buried metallic objects, railroad tracks, fence lines, etc.  This distance should be equal or greater than the maximum (“a”) spacing of our test.  In other words, if you are conducting a Wenner 4-point test with a maximum probe spacing of 60-meters (a 180-meter traverse), there should be no interfering objects (fence, buried metal pipes, etc.) within 60-meters of any part of our test.

2. The probes we use to conduct the test, will have their own sphere-of-influence that they will generate based on the depth they are driven in to the earth.  For hand calculations, the probe depth may not exceed 1/20 of the spacing of the Wenner test.  Advanced computer algorithms can adjust for these differences, but the 1/20th rule is a good one.

Here is some more information on the sphere-of-influence:  http://www.esgroundingsolutions.com/about-electrical-grounding/grounding-electrode-sphere-of-influence.php

The bottom line is that deeper depth probes are not better, they are worse.  In fact, some people actually use a heavy weight or a pile of heavy chain with a little salt water, and don’t drive any probes in to the earth at all!  We try not to go much deeper than 6-9 inches for probe depth, and when we conduct the short range readings we actually only go 2-inches into the earth.

Keep in mind that arguably the second most important spacing’s for the Wenner soil resistivity test, are the very short spaced readings.  You should be taking measurements starting at a 6-inch (0.15 meters) spacing and incrementing in interval size by a ratio no greater than 1.5, with a 1.33 ratio preferred.  The probe depth for a 6-inch spaced Wenner measurement should be no greater than 2-inches for the Potential probes, and 4-inches for the Current probes.  This arrangement clearly violates the 1/20 rule.  However, good computer modeling software can adjust for this and still provide good data.

See the following blog for more information: http://www.esgroundingsolutions.com/blog/893/893

You of course should be using true DC test meters, with test lead cables.  We recommend meters that provide 800 Volt p-p signals with at least 500 mA DC.  See www.agiusa.com for more information.

The last component is of course computer software.  Your raw data and hand calculation are nearly worthless.  In fact, hand calculations will only provide you with what is called “apparent resistivity”, not the actual soil resistivity.  This requires a computer to do properly, and is so complex that it can actually take a high-end processor several minutes of computing time to provide an analysis!  Why even take the test if you are not going to process the data correctly?

The raw data you collect during the Wenner test, must be analyzed and processed in order to develop a soil model (or soil profile).  This soil model will tell you what the resistivities of the soil are at various depths down through the earth at your site.  We recommend the RESAP module from the CDEGS computer program for proper analysis.  See www.sestech.com for more information.

E&S Grounding Solutions can of course help you with the data processing and soil model development.  But if not us, please get someone with the expertise to properly analyze your data.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: E&S Grounding Solutions

Thank you for your question regarding soil resistivity calculations, it is our pleasure to help.

It is important to understand that there are two (2) types of resistivity that people use today.  The first one is called Apparent Resistivity, and the second one is Actual Resistivity. 

Apparent Resistivity is a simple formula that only provides an average resistivity reading from the surface of the earth to the probe spacing distance.  It is NOT a real soil resistivity number.  For example, let’s say you have a Wenner test with a probe spacing of 5, and the apparent resistivity is 100 ohm meters.  You also have a Wenner test with a probe spacing of 10 that tells you the apparent resistivity is 75 ohm meters.  What is the resistivity between 5 and 10?  The answer is 50 ohm meters.  If the 0-5 ft layer is 100 ohm meters, and the 5-10 ft layer is 50 ohm meters, then the 0-10 ft apparent resistivity would read 75 ohm meters.  Please see the link below, because it is very important to understand the difference between apparent resistivity and actual resistivity.  You will also find the formula for apparent resistivity in this link:

http://www.esgroundingsolutions.com/about-electrical-grounding/what-is-soil-resistivity-testing.php

What you really need however, is actual resistivity values.  Unfortunately, there is really no way to properly hand-calculate actual soil resistivity, the formulas are simply to complex and numerous to do without the aid of a computer.  We recommend and use the RESAP module from the CDEGS engineering software program.   http://www.sestech.com/default.htm

The computer algorithms require a lot of data, and the data must be collected so that there are not to many “gaps” between the spacing’s.  The maximum interval between spacing’s is a 1.5 ratio, with a 1.33 ratio preferred.  So a measurement taken at a 20-ft spacing, would need to be followed up by a maximum 30-ft spacing, and preceded by at least a 14-ft spacing, in order to keep the 1.5 rule.  In other words, if you have data for a 40-ft spacing, and then jump to an 80-ft spacing, the distance between spacing’s is a factor of two (2) which is to great and will cause errors in the math.   You would need a 60-ft spacing between the 40-ft and 80-ft readings.

We recommend the following spacings for ground grids out to 240-ft maximum diagonal distances: 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7.5, 8, 9, 10, 12, 15, 20, 22.5, 30, 40, 45, 60, 80, 90, 120, 160, 180, and 240 feet.  That’s a total of 26 measurements for a single test traverse.  You should conduct several traverses depending on the project (substation, chemical factory, simple 5-ohm electrode, etc.).

E&S Grounding Solutions would be happy to help you with your project, but if not us, please get someone to assist you in this critical process.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: E&S Grounding Solutions

Thank you for your question regarding solar station grounding systems, it is our pleasure to help.

Solar stations are power generators that deal with electrical energies every bit as dangerous as that of any other power plant or electrical substation.  In fact they have certain additional dangers that many power plants don’t have.  Specifically the solar arrays can’t be turned off, and the DC arc-flash hazards are worse than AC arc-flashes and are more difficult to calculate.  That said, it is unlikely that you will have much choice in what grounding regulations you will be required to meet.  While every country will have its own specific standards, the EU, America, Canada, etc., all have requirements for ensuring human safety inside your facility, specifically Step & Touch Voltages. 

Fortunately, grounding systems that are safe for people are also safe for the equipment.  A properly designed grounding system for a power generator site is quite a complex task.  There are many critically important factors that must be taken into account and be properly engineered; public access to the exterior fence, worker safety when inside the compound, ability to handle fault currents without thermal overload, surface coverings, ground grids, deep ground wells, X/R ratios, clearing times, lighting protections and many more.  Ultimately, your grounding system will involve an extensive equipotential bonding system and will be one of the single biggest components of your solar plants design.  You will want to ensure that it is properly designed.

Here is a link you may want to look at:

http://www.esgroundingsolutions.com/blog/category/step-touch-voltage-hazards

The design process will start with excellent soil resistivity data, predicted electrical fault data, and a site plan.  E&S Grounding Solutions would be happy to help you with your project, but if not us, please get someone to assist you in this critical process.  If you would like our assistance, please feel free to contact Michael at mesparza@esgrounding.com or feel free to call us at 310-318-7151 California time.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: E&S Grounding Solutions

Thank you for your question regarding the use of back-fill materials to reduce the resistance-to-ground of an earthing electrode, it is our pleasure to help.

The two types of back-fill material you mentioned are excellent examples of the disparity between the current available ground enhancement back-fills.

The first material you mentioned was GEM, while we have no specific knowledge of this particular brand of back-fill, it does fall into the category of carbon-based back-fills. Carbon-based ground enhancement back-fills have both a good and a bad side to them. The good side is that they are relatively inexpensive and they do have very low resistivities. Typically, these materials have resistivities that are well below 1-ohm meters, sometimes as low as 0.1 ohm meters. The bad side is that the metallurgical nobility of carbon is such that it destroys copper over time. Typically, after 5 years copper electrodes have been corroded and destroyed by the carbon. There are also potential environmental concerns with the use of carbon-based back-fills. As such, E&S Grounding Solutions does not currently recommend the use of carbon-based ground enhancement materials.

The other back-fill material you mentioned is bentonite clay. Bentonite clay is a natural earth soil (clay) that is simply mined from areas like Wyoming. It has almost no environmental concerns and will not corrode the copper. In fact, bentonite clay is protective of the copper. The down-side of bentonite clay is that it is has a resistivity of around 2-ohm meters, and needs water to stay conductive. Very dry soils may require the use of watering devices when using bentonite clay. However, the upsides of bentonite clay far out way its downsides, and as such it is the only back-fill material that E&S Grounding Solutions currently recommends for grounding systems.

Now in regards to your question about reducing the earth resistance of your electrode from 18 to under 5 ohms, it is highly unlikely that any ground enhancement material will achieve such a result. Ground enhancement materials will typically only improve your electrodes resistance-to-ground by a few percentage points, maybe 10% to 20% at best.

Generally speaking, if your electrode is currently measuring 18-ohms, than an additional electrode of the same specifications will also measure 18-ohms. Assuming you install the second 18-ohm electrode at least 2x the diagonal length away from the first electrode, you should have an electrode system that will measure 9 ohms. If you install a total of three (3) more of these 18-ohms electrodes, each at least 2x the diagonal length away from each other, for a total of four (4) electrodes, you should have a system that is just under 5-ohms.

Obviously, four (4) electrode systems can be very expensive and you may not have the physical room to install them at the spacing you need. We would recommend that you get an electrode system designed. E&S Grounding Solutions would be happy to help you with this process. All it takes is for you to email us your soil resistivity data and a site plan, and we can take care of the rest. If this is something you would like us to do for you, please email Michael and mesparza@esgrounding.com

But if not us, please get someone to help you with this important design process.

We hope you found this information useful, if you should have any questions, please do not hesitate to contact us again in the future.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: E&S Grounding Solutions

Thank you for your question regarding the calculation of step and touch voltages in a substation, it is our pleasure to help.

Properly calculating step and touch voltages is quite difficult.  Here are a few links you should review:

http://www.esgroundingsolutions.com/about-electrical-grounding/what-is-step-and-touch-potential-and-resistance-to-ground.php

http://www.esgroundingsolutions.com/blog/761/our-reading-of-earth-resistivity-is-coming-avarage-2800-ohm-meter-we-are-designing-1133-kv-co-generation-substation-what-are-the-next-steps-required-for-designing-earth-mat-for-70-x-33-meter-area

http://www.esgroundingsolutions.com/blog/657/what-about-for-separate-earthing-1-power-electric-and-2-communication-grounding-in-substations

http://www.esgroundingsolutions.com/blog/632/we-are-developing-computer-program-to-analyze-substation-grounding-system-performance-we-have-referred-to-cdegs-as-recommended-by-you-also-we-have-gone-through-etap-ggs-module-and-cymgrd-in-ieee-80

It sounds like your substation is in real need of a properly designed ground safety grid.  We recommend the CDEGS grounding software package for design, however it is quite expensive and is rarely worth your time to purchase the software and then learn how to use it.  We would be glad to help you with the design for only a fraction of the cost.

Please email us over a site plan so that we may quote you the work.  Once the paperwork is taken care of, we will only need some soil resistivity data from you and we can handle the entire process via email.

We look forward to working with you.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: http://www.flickr.com/photos/vax-o-matic/3808126381/sizes/o/in/photostream/

Thank you for your question regarding ground systems for different voltage transformers, it is our pleasure to help.

Yes, the grounding systems not only should be bonded together, but they must be bonded together under the National Electrical Code (NEC) and many other standards and regulations.

It may seem counter-intuitive, but even when you have isolation transformers, isolated grounding, DC and AC systems, multiple voltages, Delta, Wye, solidly grounded, resistive grounded, and other non-current carrying equipotential planes, they must all be bonded back together to form a common grounding system. The trick is in how you do the bonding. Series vs parallel connections and other bonding techniques are needed to properly ensure that the above-grade grounding systems are bonded to the below-grade earthing systems.

Frankly, it can get quite complex. Feel free to give us a call at 310-318-7151 California time and someone will be happy to discuss your project with you free of charge.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: http://www.flickr.com/photos/cowlet/36528536/sizes/o/in/photostream/

Thank you for your question regarding Neutral Ground Resistors, it is our pleasure to help.

The selection of a Neutral Ground Resistor is one of the main choices in deciding what type of electrical system your facility will have.  There are four (4) types of electrical systems:

1. Ungrounded Delta Systems
2. Solidly Grounded Neutral Systems (this is the most common by far)
3. Low Resistance Grounded Neutral Systems
4. High Resistance Grounded Neutral Systems

The first system is a Delta power system, and the last three are Wye power systems.  The choice of which system to use is extremely important and a fundamental decision that will impact your entire electrical system.  Generally, only power companies deal with #1 (Ungrounded Delta Systems) for their power distribution from substation to substation.  For most businesses and homes today use item #2 (Solidly Grounded Neutral Systems), as this system is the best for ensuring that any ground faults will maximize current flow enabling Over Current Protection Devices (OCPD) such as circuit breakers and fuses to function properly.  Until recently, items # 3 and #4 were considered to be dangerous options as circuit protection technology was not sufficient to ensure that OCPD would protect personnel and equipment.  In other words, resistive grounded neutral systems (#3 and #4) require advanced technology in their OCPD’s that simply wasn’t available until recently.

Today, resistive grounded systems (#3 and #4) are becoming more and more popular, as the technology to provide proper circuit protection becomes more and more available.  The advantages/disadvantages between the four (4) systems above would require a chart and graphs in order to keep track of them all.  But needless to say, the decision impacts a variety of engineering factors that will affect your entire electrical system, including:  transient over-voltages, voltage stress, arc-fault, safety to personnel, equipment reliability, ability to detect ground faults, equipment costs, multiple voltages on the same system, frequency faults, ground fault current flows, training requirements, downtime, and compliance with local electrical codes.

The selection of when and where to use a neutral ground resistor is a very important decision (possibly the single biggest decision you can make), that actually has very little to do with grounding per se.  It certainly impacts grounding, but the reasons for making the selection often have nothing to do with earthing or grounding.  As such, E&S Grounding Solutions is probably not the right company to help you with this important process.  We recommend you contact Electro Industry at 714-776-5599 (California time) right away.  They will be happy to help you.

Best regards,

The Engineering Team at E&S Grounding Solutions

Photo credit: http://www.flickr.com/photos/oskay/437342078/sizes/o/in/photostream/