FREQUENTLY ASKED QUESTIONS

HOW DOES GROUNDING FOR PERSONNEL SAFETY DIFFER FROM GROUNDING FOR EQUIPMENT PROTECTION?

The National Electric Code (NEC), written by the National Fire Protection Agency (NFPA), has been adopted in all 50 states. It is the benchmark for safe electrical design, installation, and inspection to protect people and property from electrical hazards. In order to protect people, it requires a single electrode to have a resistance of 25 ohms or less as a safety precaution. Grounding for equipment protection (frequently 5 ohms or less) is typically more in depth, including both the basic personnel safety requirements from the NEC and the grounding requirements for specific equipment, applications or industries.

CAN A VALID GROUND RESISTANCE TEST BE PERFORMED ON A GROUND SYSTEM THAT IS IN USE (I.E. ENER-GIZED)?

Yes and no. Traditionally a grounding system can only be tested properly if the grounding system is isolated. The Institute of Electrical and Electronics Engineers (IEEE) Std. 81, which covers the Fall-of-Potential Test, states that probe spacing for a valid test must be at a distance that exceeds the grounding systems sphere of influence to be tested. If the ground system is bonded to equipment (i.e. utility neutral) the sphere of influence is theoretically infinite and no spacing would be ade-quate for a proper test.

The only way an active grounding system can be tested properly is via a Clamp-on Resistance Test using a meter like the AEMC® 3711. This test is only effective if the grounding system is configured in such a way that a single pathway exists between the ground system to be tested and the utility neutral reference. The 3711 was designed to test single driven ground rods, with the rod on one side of the meter and the utility reference on the other side of the meter. Therefore, a ground system can only be properly tested if every part of the ground system being tested is on one side of the 3711 and the utility reference is on the other side. This is known as a "single point ground" and insures that no ground loops are created during testing.

WHY DO SO MANY APPLICATIONS TODAY REQUIRE A 5-OHM GROUND OR LESS?

The NEC prescribed 25 ohms is a requirement for fire and personnel safety (see above). It is meant to provide a reference to ground for the proper operation of the overcurrent protection devices. Five ohms is typically for the clearing of external power/lightning faults.

In addition, today's facilities contain computers, communications equipment, and other types of sensitive electronics that do not function properly without a 5 ohm (or less) ground for reference. Furthermore, many equipment vendors impose specific grounding requirements on end users. If these grounding requirements are not met, and there is equipment damage that can be attributed to a grounding problem, the vendors may not honor their warranties. In other situations, operators of data centers, medical facilities, utilities, telecommunication switches and related equipment find that a good ground of less than 5 ohms is needed to keep everything running "smoothly" and trouble-free (at least from grounding issues). These same operators frequently find that when a grounding system is above 5 ohms, the problem of transient voltages, loss of data, fault currents, and degradation of or damage to the facility's electrical equipment occurs more often. They also conclude the lower the ground resistance, the longer sensitive equipment will last and the better it will perform.

WHEN IS A GROUND POTENTIAL RISE (GPR) STUDY NECESSARY?

A GPR study is required when a proposed site will be located in, within or near a high voltage environment such as a substation or transmission line and can be energized in the event of a fault. One objective of a GPR study is to pro-tect equipment. Another objective of a typical GPR study is to include a "Step and Touch" analysis to determine personnel safe-ty issues if a fault occurs while personnel are at the site (construction crews, maintenance workers etc). Inadequate provisions for or execution of a GPR study (and the grounding configuration required by the study) can result in not only major equipment failure in the event of a fault but also the tragic loss of human life.

HOW DO YOU DETERMINE IF EXTERNAL LIGHTNING PROTECTION IS REQUIRED FOR A FACILITY OR OTHER IN-STALLATION (OTHER THAN SURGE PROTECTION DEVICES)?

Lightning protection is not required per se, however, in a high lightning area, lightning protection should be utilized. Even in non-lightning areas, it should be considered if the uninterrupted operation of equipment is critical. To perform a lightning risk assessment for an existing or proposed facility, one should use the Lightning Risk Assessment as per NFPA 780-2004, Annex L.

WHAT ARE SOME OF THE MOST PREVALENT STANDARDS IN THE MARKET FOR GROUNDING FACILITIES, OTHER THAN THE BASIC REQUIREMENTS OF THE NEC?

Most telecom companies have their own internal standards (typically 5 ohms or less) which are derived or related from industry-wide telecom standards such as Telcordia (formerly Bellcore) and Motorola R56. These standards are also influenced by equipment vendors such as Nortel and Lucent whose warranties typically require 5 ohms or less. In addition, telecom standards apply to data centers and any facility where communications equipment is installed. Since facilities where data centers and communications equipment are pervasive, the telecom standards frequently become the functional default standards for all facilities.

The IEEE (“Institute of Electrical and Electronic Engineers”) proposes the following as a guideline for grounding: "The maximum 25-ohm value of the NEC “should not be interpreted to mean that 25 ohms is a satisfactory level for a grounding sys-tem.” IEEE Std. 142-1991 (4.1.2) The IEEE goes on to say that: “Resistances in the 1 – 5 ohm range are generally found suitable for industrial plant substations, buildings and large commercial installations.” IEEE Std. 142-1991 (4.1.2)

The National Electrical Manufacturers Association (NEMA) gives its own general guideline that "As a rule of thumb, an effective ground for lightning and surge protection purposes should be somewhere around 10 ohms." NEMA also makes the point that "More important than the absolute value of the ground resistance, is to ensure that all the equipment in the facility is referenced to an equi-potential ground plane through adequate bonding. By ensuring this, all separate pieces of equipment will raise to the same potential during a surge condition.” The latter is one of the objectives of a Lyncole Grounding Survey or Grounding System Compliance Testing.

WHAT IS THE DIFFERENCE BETWEEN THE XIT SYSTEM AND A CONVENTIONAL DRIVEN ROD?

A study has shown that the XIT Grounding System outperforms and outlasts the conventional driven rod in almost every application. In one study, the 10 and 20-ft XIT systems provided a nearly 300% improvement over the results of a conventional 5/8-inch copper clad steel ground rod.

In conventional installations, significant deterioration may be caused by the driving process. This deterioration can commence very soon after installation if the rods are installed in soil which is corrosive. The XIT Grounding System, on the other hand, has been designed to provide a long life with a 30-year maintenance-free warranty when installed as required by Lyncole. The XIT Grounding System is also protected from corrosion by the near neutral pH of the Lynconite II® Backfill material supplied with the system.

In addition, conventional ground rods are hard to install in some conditions (rocky terrain) and may not yield the best results in some difficult soil conditions. In comparison, the XIT Grounding System offers results in difficult and high resistivity soil conditions and can be installed using either vertical electrodes or the "L" shaped horizontal model.

WHAT IS LYNCONITE II® & WHY DOES LYNCOLE USE IT?

Lynconite II backfill is a natural volcanic clay, processed to Lyncole's requirements, which has a natural resistivity of 60 ohms-cm and a high percentage of solids to retain moisture. Lynconite II has a near neutral pH and helps protect copper from corrosion. It also helps to create a perfect bond between the grounding electrode and the soil, improving the performance of a XIT Grounding System using Lynconite II as a backfill.

A test of Lynconite II yielded the following conclusion: "The useful (working) life span of properly prepared and placed Lynconite II [slurry] should significantly exceed the life span of the grounding rod or cables that are placed in it. Results from recent corrosion testing of copper grounding system elements in Lynconite II indicate that the half life (loss of 1/2 of original weight) of these elements is in excess of 115 years."

WHAT IS LYNCOLE GROUNDING GRAVEL & WHEN DOES LYNCOLE RECOMMEND THAT YOU USE IT?

Lyncole Grounding Gravel is made of small chunks of backfill and has similar properties to Lynconite II. Lyncole engineers find that Lyncole Grounding Gravel is useful when water for mixing backfill is not plentiful on the site or the water table is high. It may be applied by hand and does not require mixing equipment. Lyncole Grounding Gravel is also useful in applications where you are dealing with porous soil or for use in a trench where you are installing an XIT L-Shaped electrode or coating buried conductor with Lyncole Grounding Gravel to improve a grounding system's performance.

WHY DOESN'T LYNCOLE USE A CARBON-BASED GROUNDING BACKFILL LIKE MOST OF THE OTHER "CHEM ROD" MANUFACTURERS IN THE MARKET?

Lynconite II and Lyncole Grounding Gravel have near-neutral pH and protect the grounding rod or cables that are placed in them from corrosion. In comparison, the carbon in carbon-based backfills is a metal that will promote corrosion of the copper elements of a grounding system due to galvanic corrosion. As a consequence, any copper wire or copper clad steel ground rod installed in a carbon-enhanced backfill will corrode. The driving force for this corrosion is the potential difference between carbon (graphite) and copper in the “Galvanic Series”. The higher metal on the scale (in this case copper) will act as the anode and corrode with the carbon or graphite acting as the cathode. Some carbon sources will also produce acid that accelerates the copper corrosion, particularly if the carbon comes from a petroleum source having sulfur impurities which produce a weak (sulfuric) acid. Even the grounding system acting normally may generate weak carbonic acid, providing a weak electrolyte that will speed the corrosion of copper in the presence of carbon.

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