ERICO Practical Guide to Electrical Grounding - Manual (Page 25)

CONCRETE ENCASED ELECTRODES,
“UFER GROUNDING”
Herb Ufer reported on probably the first use of concrete-
encased electrodes at a bomb storage facility at Davis-
Monthan AFB in Tucson, Arizona which he inspected early
in World War II. The grounding system was to protect
against both static electricity and lightning. He later
reinspected the installation and made further tests, proving
that concrete-encased electrodes provide a lower and more
consistent resistance than driven ground rods, especially in
arid regions. Due to this early usage, the use of a wire or rod
in the concrete foundation of a structure is often referred to
as a “Ufer ground.”
The concrete electrode, however, was never tested under
high fault conditions until 1977 when Dick and Holliday of
the Blackburn Corp. published an IEEE paper discussing
high-current tests on concrete-encased electrodes. They
concurred with the previous tests that concrete-encased
electrodes do provide a low resistance ground, both before
and after high current faults. But they also found that a high
current fault (500 to 2600 amperes) usually caused damage
to the concrete - from minor damage to complete
destruction.
In a 1975 survey of 1414 transmission towers, a large
electrical utility found 90 fractured foundations that were
grounded using the Ufer method. They believed the
fractures were the result of lightning strikes on the static
wires. Verbal reports have discussed leakage currents
causing disintegration of the concrete (which turns to
powder) if a break in the metallic path occurs within the
current path in the concrete. This could also be the case if
the anchor bolts were not connected to the rebar cage in
the foundation.
Based on the above and other reports, the latest edition
(1986) of IEEE Std 80 (substation grounding guide)
discusses both the merits and problems of the Ufer ground.
The document also points out that it is practically
impossible to isolate the rebar from the grounding system.
The lower resistance of the Ufer grounding system can be
explained by both the large diameter or cross section of the
concrete as compared to a ground rod and the lower
resistivity of the concrete as compared to the earth.
Concrete is hygroscopic (absorbs moisture from the
surrounding earth). This aids in lowering the resistance,
even in arid regions.
17 Chapter 1: Building and Service Entrance Grounding
3-1/2"
3-1/2"
3-1/2"
CADWELD
1" Min.
Repair Splices Without Current Derating With Cadweld
Only 1 Inch of Conductor Need Be Exposed From Concrete
3-1/2"
Typical Horizontal Repair Splice
Spliced Cable
Weld Collar
Broken Cable Stub
Horizontal Splice Vertical Splice
Conductor Mold Weld Mold Weld Weld
Size P/N Metal P/N Metal Collar*
1/0 SSR2C001 #45 SVR2C001 #90 B3452C
2/0 SSR2G001 65 SVR2G001 90 B3452G
4/0 SSR2Q005 90 SVR2Q001 115 B3452Q
250 SSR2V002 115 SVR2V001 150 B3452V
350 SSR3D002 150 SVR3D001 200 B3453D
500 SSR3Q003 200 SVR3Q001 250 B3453Q
*One required per weld, horizontal or vertical splice.
L160 handle clamp required for above molds.
Contact factory for other sizes.
Fig. 1-41
Grounding Book 4/14/99 10/5/99 6:01 PM Page 17 (Black plate)