Simply stated, structures must have properly grounded electrical systems for basic reasons: to protect people from serious or fatal shock, to enable a facility’s power distribution system to function properly, and to protect electrical components from serious damage.


To correctly install and maintain a system’s grounding requires careful testing. While some multiuse testers include ground tests, sources for this report recommend using dedicated grounding testers.


“Proper grounding is of primary importance in order to provide personal safety from shock hazard and lightning protection,” said John Olobri, director of sales and marketing, AEMC. “Transient-­voltage surge suppression [TVSS] requires proper grounding. From an economic standpoint, good grounding practices provide protection from damaging electrical fault currents. From an accuracy standpoint, we live in an electronically sensitive digital world. Utility grounds are the anchor of the distribution system. Good grounds provide the zero reference point at which virtually all electrical/­electronic systems operate.


“For accuracy and repeatability, it is best to use dedicated ground testing equipment with primary design and functions centered around ground testing.


“Ground testers verify the resistance to ground of an electrical circuit. There are three types of grounding testers: fall-of-potential, clamp-on testers, and a model that performs both functions. Fall-of-potential testers are used for disconnected ground systems and large grids. Clamp-on testers are used for single bonded rods or small grids. The clamp-on also can be used to verify the connections to grids inside substations.


“Tests include resistance of unbonded rods. Soil resistivity can be used to determine upgrade requirements. Partial-grid resistances can be verified to design specs. A four-pole ground tester and a clamp-on are recommended. In the early stages of construction, a soil resistivity four-pole test should be conducted to determine conductivity of the site soil. From this data, it can be determined how deep and/or how many electrodes must be driven to achieve the desired resistance.


“For existing sites and/or upgrades, the classic fall-of-potential [three-pole] test typically is used where the utility neutral may be disconnected. In this manner, an artificially low resistance reading is avoided due to tying the vast utility grounding system in parallel with the ground under test.


“One of the most ignored features of ground-test equipment is the ability to record, store and report test results. Today’s ground testers have higher output currents, are user-programmable, and can accomplish automatic frequency variation data storage with capacity that has become larger and easier to download. Software has improved, allowing quicker report generation, or more customized reports can be generated.


“A major new innovation in the handheld ground testers is the ability to display the voltage present on a given grounding electrode. Also, smartphone and tablet apps are available for reviewing and transmitting the test results.


“It is advisable always to perform grounding tests during routine preventive maintenance as degradation is always present in a grounding system. Ground resistance can vary during the year as well as from year to year due to droughts and other environmental conditions. Soil has a tendency to be acidic, and, therefore, corrosion always is a possibility,” Olobri said.


“A properly grounded system can prevent catastrophic injuries from occurring. It all comes down to safety,” said Bob D’Amico, sales/support engineer, Hioki USA. “The National Electric Safety Code [NESC] requires a 25-ohm ground on single-point grounded systems; therefore, having a correct reading is critical. In most cases in the utility industry, 25 ohms is the target even though sometimes it may not be obtainable. Clamp-on and three- or four-point type earth-resistance meters are used at equipment locations and substations. In the utility industry, multipoint earth resistance is required, generally performed during construction.


“Multiuse testers probably could be used for ground test if they have the necessary features or accessories to capture needed readings. However, that may cause confusion with some workers who may not understand how the meter is obtaining its readings, and that may cause misinterpretation. Keeping it simple is best by using ground testing meters,” D’Amico said


Luis Silva, electrical products marketing manager, Fluke Corp., said, “Proper electrical grounding is essential for two reasons: personal safety and equipment uptime. Without an effective grounding system, workers could be exposed to the risk of electric shock. If fault currents have no path to the ground through a properly designed and maintained grounding system, they will find unintended paths that could include people. Lightning strikes with poorly maintained grounding systems destroy millions of dollars of equipment and cause lost production every year. 


“Earth-ground testers identify poorly grounded systems, helping increase uptime and reducing a host of possible intermittent dilemmas. Earth-ground testers fall in two basic categories: stake-based and clamp-based testers, also referred to as stakeless testers. Some units can perform both types of tests.


“Soil-resistivity tests, with four stakes, are performed to determine the best location to build a new site. Fall-of-potential tests, made with three or four stakes, are used to measure the ability of an earth-ground system or an individual electrode to dissipate energy from a site. However, fall-of-potential tests require the earth electrode to be disconnected from its connection to the site, making the system vulnerable and the user exposed during testing.


“For ground-loop measurements on multiple grounded systems, many electrical contractors use a stakeless testing method. This testing technique eliminates the dangerous, time-consuming activity of disconnecting parallel grounds and the process of finding suitable locations for auxiliary ground stakes.


“The biggest changes to grounding testers are the ways technicians collect and transfer data. The basics of earth-ground testing have not changed appreciably, but the need to collect and share that information has grown. Earth-ground tests have progressed from man-meter-pencil to the current standard of USB port, memory storage and data transfer. 


“Another important change is in ease of use. Most earth-ground testers require that ground stakes be placed at long distances apart from each other and from the tester itself. This means paying out wire off of spindles and winding it up when done. The new wire reels, such as those we offer, are larger and hand-cranked, which can save as much as 50 percent of setup and teardown time,” Silva said.


“The basic requirements of ground-resistance testers are fixed to the fall-of-potential test model, as defined by the IEEE in Standard 81,” said Jeffrey R. Jowett, senior applications engineer, Megger. “This standard has recently been revised and is worth reviewing, even though the fundamental method of performing a ground test has not changed. The tester is required to inject an AC test signal from the test ground to ‘remote earth’ and measure voltage drop caused by ground resistance via a second probe to select points. Information then can be plotted and graphed. 


“There are two types of ground resistance testers: traditional three- and four-terminal models and clamp-ons. Traditional models can be used anywhere. Clamp-ons have to meet three conditions for effective use: the ground cannot be isolated from the electrical system, the ground must have a lone connection from the electrical system to the electrode [there cannot be multiple connections to ‘ground’], and the measurement must be accepted as given by the tester; it cannot be ‘proofed.’


“Refinements to this fundamental procedure are in the form of convenience and reliability factors; noise suppression, accuracy and reliability of measurement; warning indicators to alert the operator to problems in the test circuit; storage and downloading of test data; graphing and calculation capability; and conformance to various relevant standards for safety and field ruggedness.


“With the clamp-on, the overriding issue is noise suppression, both extraneous from the environment, and cross-talk between the two measuring circuits which are right next to each other in the jaws. Again, the basic technology is well fixed, but convenience features can be added. Ruggedness is significant because these are strictly field testers. Physical dimensions, both to the body and the jaw shape, are critical in dealing with the testing environment, cramped quarters, recessed test wells, and the like. Features like data hold and backlight are also useful in dealing with difficult physical environments.


“Two additional refinements have been developed through the use of attachable clamps. One is the ability to perform a clamp-on test with a standard tester by utilizing two clamps in place of the jaws [two windings in jaws] of a handheld clamp-on tester. This capability makes for an all-in-one unit, with the ability to perform both rigorous traditional tests and convenient clamp-on tests. The other refinement is the ability to use the current clamp to separate test current going to ground through the test ground from that going back through the utility ground. This capability enables testing of connected grounds without having to lift the utility connection,” Jowett said.