GROUNDING: PRACTICES AND ISSUES

1. BEYOND THE GREEN WIRE GROUNDING: PRACTICES AND ISSUES

2. Is grounding science, art or black magic? • Science – having the data and knowledge to competently design a system • Art – always possible to manipulate a design for a more elegant solution based on factors such as budget or the environment • Black magic – the perception created with gaps in knowledge / understanding

3. We must choose a perspective • BYNUM’S 5 LAWS OF ENGINEERS • An engineer is empirically oriented • An engineer is data driven • An engineer in one way or another sells his/her time and expertise • Liability concerns • Due diligence issues

4. Grounding, bonding, surge, lightning • Cannot be treated discretely • Each is an element of a coherent whole • All may not be necessary but none can be manipulated separately

5. Why grounding / earthing? • References a structure to the environment – potentials rise and fall together • Set points for circuit breakers • Fuse selection • Defines and identifies ground reference for ground fault and arc flash relays • Coordination of the system

6. Where to start? • Whether in design, forensics or rehab take a line from medical ethics • “First do no harm”

7. Using the first two points of Bynum’s Law • Engineers are compelled by training and discipline to design TO something • Anything else may be an educated guess, informed guess or lucky guess… but still a guess • With grounding we design between what we want or need and what the environment allows

8. Point #2 of Bynum’s Law • When the required data is not available the tendency becomes using a formerly successful “boilerplate” design or to “overdesign” effectively becoming a guess

9. Standards • IEEE Std. 80 (1986) • IEEE Std. 142-2007 (Green Book for Commercial / Industrial Facilities) • IEEE Std. 1100-2007 (Emerald Book for Electronics)

10. The perfect world • The engineer will have a certified “start point” in the form of results from a soil resistivity test • Fairly reliable predictor of grounding electrode performance

11. Soil Resistivity Tests • 4 Point Wenner Method Test developed in 1915 by Dr. Frank Wenner of NIST for U.S. Bureau of Land Management • Most accurate test • Used by civil engineers to locate water table but CE test protocol may be problematic for the electrical engineer

12. Soil Resistivity Tests • Schlumberger Array developed by Conrad Schlumberger of France in the 2nd decade of the 20th century • These are typically “green field” tests

13. Factors affecting resistivity • Moisture • Temperature (Sandy loam with a 15.2% moisture content @ 32 deg. F [ice] has almost 3 times the resistivity of the same sample @ 32 deg. F [water]) • Soil type – it has been reported the Metroplex has over 250 separately identifiable soil types

14. Factors affecting resistivity • Depth – varies with soil type, moisture content and freeze line • NOTE! There is a very real correspondence between resistivity and corrosion issues • Electrolytes in the soil (active, pH issues) • Pollution issues

15. Rules of thumb • Most useful when talking about thumbs • Designs generally specify 18” deep and 18”-24” outside of slab (drip line) • At 18” the conductor merely connects the electrodes • 30” and below (due to moisture content and freeze line) the conductor begins to act as an electrode in and of itself

16. Design Considerations • Types of Grounding Systems • Facility Layout • Conductor & Electrode Materials • Special Considerations

17. Types of Grounding Systems • Solidly Grounded • Low Resistance Grounding • High Resistance Grounding • Ungrounded

18. System Layout • Grid • Counterpoise • Instrumentation – Dedicated System

19. Conductor Materials • Copper or Tinned Copper • Aluminum • Braided • Concentric • Insulated • Bare

20. Electrode Materials • Galvanized Steel • Copperclad Steel • Zinc or Magnesium Solid Shapes • Graphite • Chemically Enhanced Ground Rod • Ufer

21. Special Considerations • Risk of Copper Theft • Soil Reactivity • Raw and Finished Products of Facility • Depth of Conductors • Cathodic Protection Systems • Other Utilities

22. Acceptance & Maintenance • Grounding is not an “Install & Forget” • Acceptance Testing & Documentation • Scheduled Testing & Maintenance

23. Why establishing a baseline is important.

24. We have a problem.

25. Summary • Grounding is a fundamental Infrastructure system • Yes, it can be expensive to get right. • It is more expensive to correct problems after construction. • It is most expensive when a ground system failure causes injury, equipment damage or loss of product.