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ETTL Engineers & Consultants Inc. |
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ETTL Engineers & Consultants Inc. |
Helping to Make Sure that Grounding Systems Will Work Effectively
| As a special service, ETTL has been helping clients make sure the grounding systems they are designing (or have already installed) will be compatible with the soil in which they are placed. |
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Almost everyone recognizes the importance of earth grounding for electrical systems -- the need to provide a low-impedance path to the earth for high currents from lightning strikes and power surges, as well as a path for low currents from RFI (radio frequency interference) and static build-ups -- and also to ensure that non-current carrying metal parts are at ground potential for the sake of personnel safety. What is not as well known is that soil resistivity (electrical resistance of the subsurface itself) varies widely, often within the same site, depending on soil type and density as well as depth. Which means that a soil resistivity "profile" can be crucial to grounding system design. If soil resistance is too high, the system may fail, resulting in loss of (or damage to) highly expensive electrical equipment, such as exists in TV towers (like the one being erected at left), cellular towers, water towers, electrical billboards, elevator electrical systems and countless other types of installations. |
| In a recent project, ETTL provided soil resistivity services, as well as site assessment and geotechnical services, for the tower shown, which was completed in 2004 for a CBS affiliate. With a completed height of 1600 feet, it is the tallest TV tower in East Texas. In the photo at right, an ETTL engineer is shown taking readings of soil resistivity at the tower site with an AEMC Digital Ground Resistance Tester, generating data for the design phase of the tower's grounding system. Four electrodes were used to make a series of measurements at different locations in the site under study, in both the N-S and E-W directions, so a grid could be established, centered where the actual grounding system would be embedded. Designers were thereby provided by ETTL with resistivity readings to appropriate system depths, which were subsequently used for the design of the now completed grounding system. |  |
| A similar procedure, using three electrodes, provides soil resistivity determinations for existing grounding systems, to determine how compatible they are with the soil in which they have been embedded. In addition, knowing soil resistivity is important for control of corrosion in buried structures. |
For in-depth information about ETTL's Soil Resistivity
Testing Services, contact Robert Duke
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