ERICO Practical Guide to Electrical Grounding - Manual (Page 23)

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Also fitting into this category are chemical type ground
electrodes consisting of a copper tube filled with salts.
Moisture entering the tube slowly dissolves the salts, which
then leach into the surrounding earth thru holes in the tube.
(Fig. 1-38) This lowers the earth resistivity in the area
around the electrode, which reduces the electrode
resistance.
For maximum efficiency, we recommend back-filling the
electrode with bentonite for the lower 1 to 2 feet and then
ERICO GEM to the level marked on the electrode.
Alternatively, the electrode can be back-filled only with
bentonite for a less efficient installation or only with earth
for an even lower efficient installation. Long term (over five
years) tests comparing 10-foot chemical type electrodes
back-filled with bentonite to 8-foot copper bonded rods
back-filled with ERICO GEM indicated that the two are
nearly equal with the GEM back-filled rod slightly better.
The chemical ground electrode system is available from
ERICO. Chemical electrodes are available in both vertical
and horizontal configurations. All ERICO chemical
electrodes are provided with a pigtail welded to the electrode
using the CADWELD process. Standard pigtail sizes include
4/0 AWG and #2 AWG tinned solid copper conductors.
The NEC requires that the ground rods be installed such
that at least 8 feet (2.5 m) of length is in contact with the
earth. If rock is encountered, the ground rod can be driven
at an angle, not to exceed 45° from vertical, or buried in a
trench which is at least 2 1/2 feet (0.75 m) below the earth.
The point of connection of the grounding electrode
conductor shall be below or flush with grade unless it is
suitably protected against physical damage.
The remaining type of “made” electrode permitted by the
NEC is the plate electrode. Section 250-83 (d) permits plate
electrodes that offer at least 2 square feet (0.19 sq. m) of
surface area which is in contact with the earth to be used.
The plates may be constructed of iron or steel of at least 1/4
inch (6.4 mm) in thickness or other nonferrous materials of
at least 0.06 inch (1.5 mm) in thickness. ERICO provides
copper plate electrodes with CADWELD pigtails that meet
the requirements of the NEC. CADWELD horizontal and
vertical steel surface connections can be used to connect the
grounding electrode conductor to the plate electrodes.
Wherever possible, the plates should be installed below the
permanent moisture or frost line. As with all electrode
connections, any nonconductive coatings shall be removed
before making the connection. Recent testing indicates that
plate electrodes are the least-efficient type of grounding
electrode for power system grounding. Plate electrodes do,
however, provide large surface area for capacitive coupling
(high frequency) required in lightning protection.
No matter which grounding electrode or electrodes are used
the NEC requires that the grounding electrode conductor,
which connects to these electrodes, be suitably protected.
Section 250-92 (a) of the Code permits the grounding
electrode conductor (GEC) to be securely fastened directly
to the surface of a building or structure. A No. 4 AWG or
smaller copper or aluminum GEC, which is exposed to
severe physical damage must be protected. While there is
no definition provided for “severe”, it is safe to assume that
locations subject to vehicular traffic, forklifts or lawn
mowers would be such locations. A No. 6 AWG GEC that
is free from exposure to physical damage can be installed
on the surface of a building or structure without any
mechanical protection. Smaller conductors shall be
installed in rigid metal conduit, intermediate metal conduit,
rigid nonmetallic conduit, electrical metallic tubing or
cable armor.
Installers of electrical systems should be aware that Section
250-92 (b) of the NEC requires that any metal enclosures or
raceways for the grounding electrode conductor shall be
electrically continuous from the electrical equipment to the
grounding electrode. If the metal enclosures are not
electrically continuous they shall be made so by bonding
Chapter 1: Building and Service Entrance Grounding
GEM Ground
Enhancement
Material
Chemical
Rod
Ground
Well
Downconductor
Bentonite
CADWELD
Connection
Fig. 1-38
Grounding Book 4/14/99 10/5/99 6:01 PM Page 15 (Black plate)