Scope of Services
Soil Resistivity Testing
Grounding System Survey
VFD & Motor Shaft Current
Complete Installation and Testing
CP Corrosion System Compatibility
SCADA & Monitoring Disruptions
Ground Fault Analysis
Grounding System Design & Planning
A grounding design starts with a site analysis, collection of geological data, and soil resistivity of the area. Typically, the site engineer or equipment manufacturers specify a resistance-to-ground number. The National Electric Code (NEC) states that the resistance-to-ground shall not exceed 25 ohms for a single electrode. However, high technology manufacturers will often specify 3 or 5 ohms, depending upon the requirements of their equipment. For sensitive equipment and under extreme circumstances, a one (1) ohm specification may sometimes be required. When designing a ground system, the difficulty and costs increase exponentially as the target resistance-to-ground approaches the unobtainable goal of zero ohms.
Once a need is established, data collection begins. Soil resistivity testing, geological surveys, and test borings provide the basis for all grounding design. Proper soil resistivity testing using the Wenner 4-point method is recommended because of its accuracy. This method will be discussed later in this chapter. Additional data is always helpful and can be collected from existing ground systems located at the site. For example, driven rods at the location can be tested using the 3-point fall-of-potential method or an induced frequency test using a clamp-on ground resistance meter.
With all the available data, sophisticated computer programs can begin to provide a soil model showing the soil resistivity in ohm-meters and at various layer depths. Knowing at what depth the most conductive soil is located for the site allows the design engineer to model a system to meet the needs of the application.
Soil resistivity is the key factor that determines the resistance or performance of an electrical grounding system. It is the starting point of any electrical grounding design. As you can see in Tables 2 and 3 below, soil resistivity varies dramatically throughout the world and is heavily influenced by electrolyte content, moisture, minerals, compactness and temperature.
Mining, Oil & Gas
Power Generation & Utilities
Telecom & Data Centers
What We Offer
Our grounding systems design services help assure the installation begins with the proper foundation that follows through all the wayto the complete system installation . Our site surveys and design services exceed the industry standards and include detailed explanations with photos illustrating any issues identified along with the appropriate plan of action to solve any correction. Our engineering team provides site specific solutions providing you with Total Site and Facility Protection.
Site Audit & Surveys Include The Following:
Ground System Performance, Internal Bonding/Grounding, NEC Compliance, Electrical Safety, Lightning Protection System, & AC Surge Suppression.
A full written report with observations, recommendations, pictures and CAD of the grounding design recommendation is provided upon completion.
The grounding system must address low earth impedance as well as low resistance. A spectral study of lightning’s typical impulse reveals both a high and a low frequency content. The high frequency is associated with an extremely fast rising “front” on the order of 10 microseconds to peak current. The lower frequency component resides in the long, high energy “tail” or follow-on current in the impulse. The grounding system appears to the lightning impulse as a transmission line where wave propagation theory applies.
A single point grounding system is achieved when all equipment within the structure(s) are connected to a master bus bar which in turn is bonded to the external grounding system at one point only. Earth loops and differential rise times must be avoided. The grounding system should be designed to reduce ac impedance and dc resistance. The shape and dimension of the earth termination system is more important a specific value of the earth electrode. The use of counterpoise or “crow’s foot” radial techniques can lower impedance as they allow lightning energy to diverge as each buried conductor shares voltage gradients. Ground rings around structures are useful. They should be connected to the facility ground. Exothermic (welded) connectors are recommended in all circumstances.
Cathodic reactance should be considered during the site analysis phase. Man-made earth additives and backfills are useful in difficult soils circumstances: they should be considered on a case-by-case basis where lowering grounding impedances are difficult an/or expensive by traditional means. Regular physical inspections and testing should be a part of an established preventive maintenance program.
- Site Survey & Audit 80%
- Design Services 45%
- Certified Installation 95%
WHAT ARE SOME OF THE MOST PREVALENT STANDARDS IN THE MARKET FOR GROUNDING FACILITIES, OTHER THAN THE BASIC REQUIREMENTS OF THE NEC?
Most telecom companies have their own internal standards (typically 5 ohms or less) which are derived or related from industry-wide telecom standards such as Telcordia (formerly Bellcore) and Motorola R56. These standards are also influenced by equipment vendors such as Nortel and Lucent whose warranties typically require 5 ohms or less. In addition, telecom standards apply to data centers and any facility where communications equipment is installed. Since facilities where data centers and communications equipment are pervasive, the telecom standards frequently become the functional default standards for all facilities.
The IEEE (“Institute of Electrical and Electronic Engineers”) proposes the following as a guideline for grounding: “The maximum 25-ohm value of the NEC “should not be interpreted to mean that 25 ohms is a satisfactory level for a grounding sys-tem.” IEEE Std. 142-1991 (4.1.2) The IEEE goes on to say that: “Resistances in the 1 – 5 ohm range are generally found suitable for industrial plant substations, buildings and large commercial installations.” IEEE Std. 142-1991 (4.1.2)
The National Electrical Manufacturers Association (NEMA) gives its own general guideline that “As a rule of thumb, an effective ground for lightning and surge protection purposes should be somewhere around 10 ohms.” NEMA also makes the point that “More important than the absolute value of the ground resistance, is to ensure that all the equipment in the facility is referenced to an equi-potential ground plane through adequate bonding. By ensuring this, all separate pieces of equipment will raise to the same potential during a surge condition.” The latter is one of the objectives of a Lyncole Grounding Survey or Grounding System Compliance Testing.
What our clients expect.
SGS Grounding works with savvy clients. Our clients and partners have been a crucial part to the success of SGS. We work closely with our clients dedicating a project management team to strategically accomplish the best finished product or result our industry has to offer. Our clients are business relationships are long term and we strive to maintain the same type of integrity and trust that we seek with our own contractors. We strive to provide a win win situation to each of our clients that is truly beneficial to both us as well as the client. We are in business to implement the highest of quality standards throughout each aspect of our processes, whether it be within our estimating, design, installation or certification process.
What is your turn around time?
Our turnaround time on testing is 48 hours or less. We are setup to meet project demands and schedules and have the ability to operate under accelerated schedules with minimum surcharge.
Do you have a certification program?
Grounding certifications through Lyncole. Please see www.Lyncole.com for classes and schedules.
We have worked with SGS Grounding Systems for several years and have a strong business relationship. The people at SGS are very knowledgable and have been able to save me a lot of time and money on my projects.Gene Basco
I was in the middle of a project when we were looking for Grounding Companies. I called on SGS to give me a price and they were able to put a proposal together and get on the site in a timely manner. Thank you to the team at SGS for pulling us out of a tough situation.Aaron Coplan
We would recommend SGS for your electrical grounding and lightning protection solution. Their staff is knowledgable and the project management team was easy to work with. We got the materials and the job done on time. Thanks for keeping up with our schedule.John Browning
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