BEYOND THE GREEN WIRE

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

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

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

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

Where to start?

Whether in design, forensics or rehab take a line from medical ethics

“First do no harm”

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

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

Standards

IEEE Std. 80 (1986) IEEE Std. 142-2007 (Green Book for

Commercial / Industrial Facilities) IEEE Std. 1100-2007 (Emerald Book for

Electronics)

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

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

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

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

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

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

Design Considerations

Types of Grounding Systems Facility Layout Conductor & Electrode Materials Special Considerations

Types of Grounding Systems Solidly Grounded Low Resistance Grounding High Resistance Grounding Ungrounded

System Layout

Grid Counterpoise Instrumentation – Dedicated System

Conductor Materials

Copper or Tinned Copper Aluminum

Braided Concentric

Insulated Bare

Electrode Materials

Galvanized Steel Copperclad Steel Zinc or Magnesium Solid Shapes Graphite Chemically Enhanced Ground Rod Ufer

Special Considerations

Risk of Copper Theft Soil Reactivity Raw and Finished Products of Facility Depth of Conductors Cathodic Protection Systems Other Utilities

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

Why establishing a baseline is important.

We have a problem.

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.