A practical guide with expert advice
Written by Schneider Electric's most talented electrical distribution experts, the Electrical Installation Guide is written for professionals who design, install, inspect, and maintain low-voltage electrical installations in compliance with the standards published by the International Electrotechnical Commission (IEC).

Our experts “do the heavy lifting” and share their industry-leading knowledge about new and updated electrical installation standards and technological evolutions so that you can have the most up-to-date and relevant information.

Herbert G. Ufer was a vice president and engineer at Underwriters Laboratories who assisted the U.S. military with ground-resistance problems at installations in Arizona. Ufer’s findings in the 1940s proved the effectiveness of concrete-­encased grounding electrodes. The military required low-resistance (5 ohms or less) ground connections for lightning protection systems installed at its ammunition and pyrotechnic storage sites at the Navajo Ordnance Depot in Flagstaff and Davis-Monthan Air Force Base in Tucson. Ufer developed the initial design for a concrete-encased grounding electrode that consisted of ½-inch, 20-foot-long reinforcing bars placed within and near the bottom of 2-foot-deep concrete footings for the ammunition storage buildings. Test readings over a 20-year period revealed steady resistance values of 2 to 5 ohms, which satisfied the specifications of the U.S. government at that time. This work eventually resulted in what we know today as the concrete-encased electrode in the NEC. More details about Ufer’s research are provided in his October 1964 IEEE paper CP-978, “Investigation and Testing of Footing-Type Grounding Electrodes for Electrical Installations.”

• What Is A 'Ufer' Ground? Concrete-Encased Grounding Electrodes

• On Solid Ground: Defining and Understanding UFER Ground
• Electrical Service Grounding Option: The Steel Rebar 'Sticking-Out' Method?

Effective, reliable grounding electrodes or grounding electrode systems are required for all electrical services and systems. This presented a problem for Herbert Ufer. During WWII, he served as an Army consultant overseeing the building of bomb storage vaults in the vicinity of Tucson and Flagstaff, Ariz. Ufer found the high-Ohm resistance of the dry, sandy Arizona desert presented a grounding challenge. Conventional ground rods were unable to meet the required low-ground resistance requirements. He addressed the challenge by developing a concrete-encased ground, which now carries his name, the Ufer ground.

Properties of concrete provide the key

The Ufer ground takes advantage of the properties of concrete. Essentially, concrete absorbs and retains moisture quickly, but loses it slowly over time. In addition, the composition and pH of concrete is such that it allows ionic transfer, which means that it has available ions to conduct electric currents. Furthermore, the soil around the concrete becomes “doped” by the presence of the concrete. As a result, the pH of the soil rises and consequently reduces what would normally be high-Ohm resistance conditions.

Ufer fond that a concrete-encased ground provides a safe, elegant and practical alternative to the exterior metal-driven rod system we all are familiar with and which we know can be subject to damage or tampering.Amendments to the 2008 NEC, National Electric Code have clarified some provisions of previous concrete encased electrode language. Although the word “Ufer” is not used in the text of the code, NEC Section 250.52(A)(3) addresses Ufer grounds.

A solidly grounded system is one in which the neutral points have been intentionally connected to earth ground with a conductor having no intentional impedance and this partially reduces the problem of transient over-voltages found on the ungrounded system.

While solidly grounded systems are an improvement over ungrounded systems, and speed the location of faults, they lack the current limiting ability of resistance grounding and the extra protection this provides. The destructive nature of arcing ground faults in solidly grounded systems is well known and documented and are caused by the energy dissipated in the fault. A measure of this energy can be obtained from the estimate of Kilowatt-cycles dissipated in the arc:

Kilowatt cycles = V x I x Time/1000.

In the same IEEE Standard as reference above, section 7.2.2 states that:

"one disadvantage of the solidly grounded 480v system involves the high magnitude of ground-fault currents that can occur, and the destructive nature of arcing ground faults."

Since the vast majority of arcing faults start their life as single-phase faults, the key to reducing their impact is to use technology that either significantly reduces the fault current level thereby reducing the magnitude of the arc hazard and/or using technology that prevents transient overvoltages that can lead to single-phase faults escalating into arcing faults.

The answer in both cases is high resistance grounding, as recognized in the Canadian Electrical Code section 10-1100, and the National Electrical Code section 250-36.

High resistance grounding of the neutral limits the ground fault current to a very low level (typically from 1 to10 amps) and this is achieved by connecting a current limiting resistor between the neutral of the transformer secondary and the earth ground and is used on low voltage systems of 600 volts or less, under 3000 amp. By limiting the ground fault current, the fault can be tolerated on the system until it can be located, and then isolated or removed at a convenient time.

In tests, damaging voltage transients measured on a 480 volt ungrounded system were eliminated once the circuit was converted to high resistance grounded.

With respect o the magnitude of fault current, the energy or I 2 t value for a 1 amp fault is 1/ 1,000,000 of a 1000 amp fault assuming an equal amount of time.

The National Electric Code allows a fault level of 1200 amps for one second on a solidly grounded system before a circuit must trip, however in practice fault levels in excess of 20,000 amps are common for a short period of time.

The term "Ufer" grounding is named after a consultant working for the US Army during World War II. The technique Mr. Ufer came up with was necessary because the site needing grounding had no underground water table and little rainfall. The desert site was a series of bomb storage vaults in the area of Flagstaff, Arizona.

The principle of the Ufer ground is simple, it is very effective and inexpensive to install during new construction. The Ufer ground takes advantage of concrete’s properties to good advantage. Concrete absorbs moisture quickly and looses moisture very slowly. The mineral properties of concrete (lime and others) and their inherent pH means concrete has a supply of ions to conduct current. The soil around concrete becomes "doped" by the concrete, as a result, the pH of the soil rises and reduces what would normally be 1000 ohm meter soil conditions (hard to get a good ground). The moisture present, (concrete gives up moisture very slowly), in combination with the "doped" soil, make a good conductor for electrical energy or lightning currents.

Ufer techniques are used in building footers, concrete floors, radio and television towers, tower guy wire anchors, light poles, etc. Copper wire does not function well as a "Ufer" ground due to the pH factor of concrete (+7pH is common). The use of steel reinforcement as a "Ufer" ground works well and concrete does not chip or flake as has been found with copper. The use of copper wire tied to the reinforcement rods outside the concrete shows none of these problems. ///

http://web.archive.org/web/20190613223847/http://www.psihq.com/iread/ufergrnd.htm

Electrodes were next bonded to a 10,000-ft (3,000-m) length of AWG 2/0 copper extending along the length of the lift. For protection, the cable was buried in a 3-ft deep trench (Figure 6). Now, all towers would be at very nearly the same ground potential, and the probability that ground loop currents could arise between towers was sharply reduced.

At all sites, there is either or both a main service disconnect and a fused disconnect. A main service disconnect may be located at a meter location away from the building. A main disconnect located within the shelter, equipment room or area may be fed by a feeder circuit originating at a main service disconnect located in an electrical room in a different location in the building or even a separate building. Typically, the neutral and ground conductors are bonded in the main service disconnect.

When the main service disconnect is located remotely from the equipment room or area, a separately derived system should be installed in the equipment room. (See NFPA 70-2005, Article 250.30 and 250.32 for additional information.)

One of the reasons for the separately derived system is to reestablish the neutral/ground bond, thereby improving the effectiveness of normal mode suppression.

-- Motorola R56-2005, p 6-2

The primary focus of this presentation will be wiring and grounding techniques and practices that are recommended to be part of the design of new or renovated structures. These practices will help prevent power quality problems from occurring in the first place, or diminish their effect to the point that they are not significant.

This webinar will review the elements of a building’s wiring and grounding systems (including lightning protection) that pertain to power quality at communications facilities and improve up-time. Proper wiring and grounding, beyond those minimal requirements of the NEC, can greatly alleviate power quality problems in broadcast and public service communications facilities. These improvements can be very cost-effective, usually simple in description, and help prevent costly downtime and equipment damage. The presentation concentrates on actual experiences at broadcast facilities where grounding and lightning protection were of paramount importance in maintaining system availability.

About Your Instructor - David Brender, P.E., National Program Manager Copper Development Association, Inc.

David Brender is National Program Manager for the Copper Development Association (CDA) in New York City. His duties involve directing and managing the electrical programs at CDA, including their power quality, building wire program, telecommunications wire, research and National Electrical Code activities, among others. He has presented several times before to broadcasting technical audiences.He is a principal member of Panel 5 of the National Electrical Code, a Senior Member of the IEEE, and a life member of the Association of Energy Engineers.

Brender holds a Bachelor’s degree from New York University and an MBA degree from Fairleigh Dickinson University in addition to being a licensed Professional Engineer in three states.

Power Quality
Case Studies (organized by topic)
Broadcasting
Emergency Communications
Data Centers
Other Sensitive Loads

By Jon Shea
Protection For Computers, Modems and Telephone Equipment

250.52(A) Electrodes Permitted for Grounding

The rule explaining when a structural metal frame can serve as a grounding electrode has been changed again, and the requirements for concrete encased electrodes, ground rods, and ground plates have been clarified.

(3) Concrete-Encased Electrode. At least 20 ft of either (1) or (2):

(1) One or more of bare, zinc-galvanized, or otherwise electrically conductive steel reinforcing bars of not less than ½ in. diameter, mechanically connected together by steel tie wires, welding, or other effective means, to create a 20 ft or greater length.

(2) Bare copper conductor not smaller than 4 AWG.

The reinforcing bars or bare copper conductor must be encased by at least 2 in. of concrete located horizontally near the bottom of a concrete footing or vertically within a concrete foundation that’s in direct contact with the earth.

If multiple concrete-encased electrodes are present at a building/structure, only one is required to serve as a grounding electrode

Note: Concrete containing insulation, vapor barriers, films or similar items separating it from the earth isn’t considered to be in “direct contact” with the earth.

(4) Ground Ring Electrode. A ground ring consisting of at least 20 ft of bare copper conductor not smaller than 2 AWG buried in the earth encircling a building/structure can serve as a grounding electrode.

It seems to be the lost art. None of the contractors, architects and very few of the engineers I've had contact with have ever heard of it... a cheap earthing system that consistently outperforms typical ground rod installations. This is a proven concept, but before I describe it, let me make it clear that I take no credit for its design.

During World War II, a retired Vice President of Underwriters Laboratories, Herbert G. Ufer, developed it for the U.S. Army. Igloo shaped bomb storage vaults were being built, and possible static and lightning induced detonation problems were of concern. Ground conductivity was poor, and to be effective enough, ground rods would have to be driven several hundred feet. After much research and testing Mr. Ufer advised the Army to make connection to the steel bar that would internally reinforce the concrete foundation. He had determined that concrete was more conductive than all but the best soil, and that this improved semiconducting characteristic would enhance surface area contact with the surrounding soil. The wire ties normally used would be extra secure, and attention would be given to bonding or welding the lattice- type network together. The Army adopted the idea, and built the vaults as

specified. After construction ground resistance tests were made. No measurement exceeded five ohms. This value was considered extremely low for the local soil conductivity. Later tests confirmed stability. Mr. Ufer went on to develop the concept of concrete encased grounding electrodes. Many of his findings are detailed in IEEE Transactions paper # 63-1505. His system has since been used by the military, utility companies, Lake Tahoe lifts, and industry throughout the country. Why not broadcast stations? After reading an obscure 1967 paper citing actual tests and comparisons to conventional systems written by Wismer & Becker Engineers, I decided to give it a try.

Low resistance earth grounding is essential for safety and protection of sensitive electronic equipment. It is the basis for any facility's power quality assurance program.

This paper presents the advantages of deep driven electrodes over shallow (10 foot or less) electrodes. This paper will demonstrate that deep driven electrodes provide low earth resistance, are economical to install, maintain low resistance over time, are maintenance free, and do not have environmental concerns. This paper utilizes field data taken from over 140 deep driven electrodes installed over a 5 year period in several states. A discussion includes the development of the equipment, materials, and process used to install and test deep driven made electrodes. The process includes a new technique of injecting bentonite into the coupler void to maintain full rod contact of the total length. Several site reports are presented and discussed. This paper would be of value to anyone responsible for specifying, installing, or testing low resistance ground systems.