Installation Guide

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Measure the resistance to ground at the service entrance meter’s electrical ground, or of the
soil itself. Soil resistance can be affected by the following:
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moisture content
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quality and type of electrolytes
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conductive objects
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temperature
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depth and spacing of the ground rods.
For more information about using a Megger to measure the resistance to ground, see Using
a Megger on page 95.
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Drive a new service entrance ground rod. You cannot know the exact length or current
condition of the original ground rod, so it is best to install a new rod of suitable length and
composition at the service entrance. Solid copper is the preferred material; however,
galvanized or copper clad may also be suitable if acceptable resistance levels are met.
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Bond a new rod and the existing rod together. If the target ground resistance is not achieved
by a new rod, drive a second rod and bond the two rods together by exothermic welding a
piece of the grounding conductor between the two. The new rod should be approximately
one rod length or more from the first rod. Multiple rods can be connected this way.
Note: One additional rod lowers ground resistance by 40%. Two rods result in a 60%
reduction. Three rods improve resistance by 66%.
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Drive the rod deeper. Couple a new rod of equal length on top of the existing rod to
effectively double the depth of the rod. Be sure to use rods of like type and a coupler matched
to that type of rod. This will result in an approximate 40% reduction in ground resistance.
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Create a Trench Ground or Ground Ring. If your region provides a solid substrate such as
bedrock immediately below a shallow layer of soil, it is possible to create a circular trench
around the building (minimum 20 feet long) at least 30 inches deep utilizing a minimum of
#2AWG bare copper conductor, lay in the grounding conductor, bond the two ends together
to the ground rod, and then backfill the trench with soil. This allows maximum contact with
the ground, without being excessively deep to do the job.
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Create a Ground Grid. This procedure involves creating a grid of grounding electrodes, or
rods, in close proximity (10 to 20 feet, or at least one rod length apart,) and welding or
bonding the grounding conductor between the rods together. The entire grid is then
backfilled with soil and compacted to complete the grid. Also, review NEC section 250-32(b)
for more information.
Using a Megger
Measure the resistance to ground one of two ways: A special "clamp-on" ground resistance
measuring device is recommended for existing locations, and an earth resistance meter
23 June 2020 TDC-0971-012 Itron, Inc. Page 106 of 134
CCU 100 and Repeater 100 Installation Guide F Grounding Specifications