What You Don’t Know About Grounding Can Hurt You ...

May 3, 2006
... and not only hurt you, but cost you lost data and equipment

Thirty years ago, Hank Aaron was still playing baseball, the first programmable pocket calculator became available, and the word “Internet” appeared for the first time in print. Unless your plant still uses the identical technology it did 30, 20, even 10 years ago (when Google didn’t yet exist), then trusting your plant’s operation to a grounding system installed decades ago - or testing it with a technology developed 80 years ago - isn’t perhaps the wisest choice.

What you don’t know about your industrial plant’s grounding could not only hurt you, resulting in loss of life, but can cost you lost data and equipment as well as slowing processes or halted production. No industrial facility manager would consider violating fire code for fear of the consequences. Yet, in too many plants, the foundation for all things electric - the grounding system - is allowed to go out of spec due to aging, corrosion, or facility and soil changes, as well as infrequent/inadequate grounding test evaluation. But out of sight does not mean out of danger when it comes to grounding.

“Failing to properly evaluate and fix grounding problems can not only result in unnecessary lightning and transient damage, but also data/equipment loss, process anomalies, plant shutdown, as well as increased fire and personnel risk,” explains Joe Lanzoni, a manager with Boulder, CO-based Lightning Eliminators & Consultants Inc. (LEC), a firm specializing in electrical grounding, surge suppression, and lightning protection. “Particularly susceptible to these disruptions are plants with sensitive computer, communication, and process control equipment, requiring low grounding impedance from 1 to 10 ohms to work properly.”

Proper grounding is the first line of defense against the $1 billion spent annually on damage around the globe due to lightning and 60 percent of system outages due to lightning on the East Coast alone. Power surge protection equipment also depends on good grounding to defend against power surges and spikes, as well as diverting lightning discharges of up to 400,000 amps to ground. Many U.S. industrial grounding systems are in poor repair, and the limitations of traditional grounding system testing are hindering efforts to resolve the problem.

Fortunately, there are technologies being designed to keep up with technical advances in the manufacturing and process control industries. Improved ground system testing methods, such as Smart Ground Testing, are now offered by consulting firms such as LEC. Any facility experiencing equipment, process, or production anomalies could benefit from a grounding evaluation to determine if it is a possible source of the problem. In fact, any facility without a recent grounding evaluation could benefit, especially those involved in manufacturing, process control, or with sensitive electronic equipment or data centers.

Industrial Grounding Systems Deteriorating
In many cases, the grounding rods in U.S. industrial plants have exceeded their usable lifespan of 30 years because they haven’t been properly tested or maintained since installation decades earlier (some pre-date WWII). Out of sight unless dug up, the grounding rods and connectors of these buried grounding grids typically suffer corrosion and undetected electrical discontinuities - causing dangerous faults, processing errors, or shutdowns. The problem is especially pronounced in the low-resistivity soils near coasts and waterways, which accelerate corrosion.

“Existing grounding capacity is often compromised when contractors dig up or sever grounding wires when burying pipe or telecom cables,” adds Lanzoni. “Plant changes and expansions just aggravate the problem when grounding isn’t tested and upgraded to meet facility or equipment demands.”

These grounding problems often continue for years, causing electrical problems, equipment failure, and even risking personnel electrocution from ground faults that are not safely conducted into the earth through the grounding system. Until recently, even when facilities managers tried to resolve grounding problems, the drawbacks of traditional ground system testing have stood in the way.

The Limitations of Traditional Ground System Testing
Clamp-on ground resistance testers, although convenient, should be limited to testing power distribution poles and residential grounds. Their primary weakness is that their accuracy suffers - to the point of displaying nothing or a meaningless number - if resistance is low or a ground loop is present. The grounding electrode being tested must also be parallel with a large number of other electrodes, which is not always practical.

Three-point Fall-of-Potential (FOP) ground resistance testing, which has been used for over 80 years without much advancement, also has significant limitations. Using the FOP test, the grounding system being tested must be disconnected from the equipment being grounded, de-energized, and isolated - but this can be impossible to do in an operating industrial facility where output and processes must be maintained. Because FOP testing doesn’t detect grounding discontinuities, the actual grounding rods and connectors to be examined must be physically dug up. Given how expensive and time-consuming this is, checking for grounding discontinuities simply isn’t done on a routine basis.

Another drawback of FOP ground testing is that the recommended distance between the grounding grid and current test probe can be excessive - more than 5 times the diagonal distance of the grounding grid. In a large industrial plant, such as a refinery, this can require extending the current probe several miles onto neighboring property or roadways, an impractical or perhaps impossible task.

The FOP test, which has difficulty measuring low-resistance grounds, also has no assurance of accuracy. “Because of the distance between test probes, weak injected signal strength, and background noise, the FOP test has a poor signal to noise ratio,” explains Dr. Sakis Meliopoulos, an IEEE Fellow and Field Award Winner, and professor of electrical engineering at Georgia Tech, Atlanta. “Accuracy suffers when trying to measure low voltage on long leads between test probes, with interference from potentially stronger sources - such as stray current or electromagnetic interference/EMI from nearby power circuits.”

Safer, More Effective Plant Production with Smart Ground Testing
Unsatisfied with the limitations of FOP and clamp-on ground test methods for industrial use, Dr. Meliopoulos developed a new type of ground multimeter with sponsorship from the Electric Power Research Institute (EPRI). Output from the Smart Ground Multimeter feeds into EPRI-approved advanced software.

Unlike the FOP and clamp-on methods, the Smart Ground Testing equipment has been designed to operate on energized substations and industrial grounds, minimizing downtime and protecting production capacity. This can be done even when real estate is limited or the surrounding area saturated with roads or buildings because the leads between test probes are relatively short - just twice the length of the grounding system, instead of the FOP method’s 5 to 10 times the distance.

For greater accuracy in discovering the root cause of industrial grounding problems and for safer, improved plant production, Smart Ground Testing combines several testing functions not available in previous FOP and clamp-on methods. Because of the increased test accuracy, grounding grid continuity can be verified and diagnosed without the expensive, time-consuming digging up of grounding rods and connectors that other approaches may require.

“Not only does the software reduce interference by compensating for stray current, background noise and EMI, but also it is capable of injecting a signal that is many hundreds of times greater than other equipment,” explains Dr. Meliopoulos. “Together, this dramatically improves the signal-to-noise ratio for more accurate grounding measurement.”

While FOP ground tests typically employ a test signal with a frequency indicating transient response at less than 420 Hertz, Smart Ground Testing, for instance, raises this up to 2,500 Hertz. And where low-impedance locations require higher currents for confident results, the best FOP ground tests do so with just 0.05 amps, compared to Smart Ground Testing’s up to 100 amps (a 2,000-fold difference).

“To give facilities managers the statistical validity they need to verify or upgrade grounding status, Smart Ground Testing also generates thousands of test data points, compared to FOP’s typical 100 or less,” adds Lanzoni.

To generate these added data points, each of Smart Ground Testing’s 6-voltage probes makes 10 computer-controlled current injections in contrast to an FOP probe’s single current injection - a 60:1 difference.

“The added data and higher signal-to-noise ratio of Smart Ground Testing provide quantified confidence test levels that FOP and clamp-on tests have never been able to make,” says Lanzoni. “The result is unprecedented ground test accuracy and analysis. This allows facilities managers to either verify their plant meets safe grounding specs or take corrective action to protect plant safety and production.”

Del Williams is a technical writer based in Torrance, CA.

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