A New Look at the Ufer Ground System

Originally published December 13, 1989, Radio World.

© Copyright 1989 Chris Scott

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.

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Construction

I designed a cheap, convenient version of the Ufer ground system for WHHT, a new class A FM station I was working with in Glasgow, Kentucky. The transmitter was located on a three- hundred foot knoll where just one-hundred feet of tower would provide four-hundred feet above average terrain. A two-bay ERI antenna would be mounted at the top. This location was great for signal propagation and... lightning. One seventy-foot tower was already on site for two-way radio service. The land owner warned us that this tower was frequently struck, and equipment had been repeatedly damaged despite increased precautions. Indeed, during July construction, the masonry workers left the site after "a bolt sent fireballs rolling down the [existing] tower". With a sensitive CMOS controlled transmitter and a talking remote control selected for the installation, I knew that any transient overvoltage protection devices I would specify would need a very conductive path to ground to divert strike energy away from the equipment.

I asked the concrete contractor to use additional wire ties to connect the re-bar together, to double-wrap them, and tighten them more than usual. Tack-welding them together was preferable, but the equipment was not readily available at the time. I later made the ground connection to several bars that were intentionally left protruding from the foundation.

Standard copper strap connections were used along with Metal Oxide Varistor / L-C filter transient protection.

Testimonial

In sixteen months, the site has maintained twenty-four hour per day operation with ZERO downtime except due to AC power failure. With equipment so susceptible to transients, this kind of performance is unusual in this region, especially on this hill. I am convinced that the low cost, combined with the proven performance of the Ufer ground is the ideal system for new installations.

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