Construction
Concrete is naturally basic (has high pH). Ufer observed this means that it had a ready supply of ions and so provides a better electrical ground than almost any type of soil. Ufer also found that the soil around the concrete became "doped", and its subsequent rise in pH caused the overall impedance of the soil itself to be reduced. The concrete enclosure also increases the surface area of the connection between the grounding conductor and the surrounding soil, which also helps to reduce the overall impedance of the connection.
Ufer's original grounding scheme used copper encased in concrete. However, the high pH of concrete often causes the copper to chip and flake. For this reason, steel is often used instead of copper.
When homes are built on concrete slabs, it is common practice to bring one end of the rebar up out of the concrete at a convenient location to make an easy connection point for the grounding electrode.
Ufer grounds, when present, are preferred over the use of grounding rods. In some areas (like Des Moines, Iowa) Ufer grounds are required for all residential and commercial buildings. The conductivity of the soil usually determines if Ufer grounds are required in any particular area.
An Ufer ground of specified minimum dimensions is recognized by the U.S. National Electrical Code as a grounding electrode. The grounding conductors must have sufficient cover by the concrete to prevent damage when dissipating high-current lightning strikes.
A disadvantage of Ufer grounds is that the moisture in the concrete can flash into steam during a lightning strike or similar high energy fault condition. This can crack the surrounding concrete and damage the building foundation.
Read more about this topic: Ufer Ground
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