Itron Inc. CCU100A Manual Do Utilizador
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TDC-0971-011 CCU 100 and Repeater 100 Installation Guide
95
Proprietary and Confidential
• temperature
• depth and spacing of the ground rods.
For more information about using a Megger to measure the resistance to ground, see
• depth and spacing of the ground rods.
For more information about using a Megger to measure the resistance to ground, see
• 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.
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.
• 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.
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%.
reduction. Three rods improve resistance by 66%.
• 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.
matched to that type of rod. This will result in an approximate 40% reduction in
ground resistance.
• 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.
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.
• 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.
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 (Megger) is preferred in installations of new equipment that cannot be
connected to an existing ground ring.
resistance measuring device is recommended for existing locations, and an earth
resistance meter (Megger) is preferred in installations of new equipment that cannot be
connected to an existing ground ring.
The earth resistance meter is less expensive, but it requires multiple ground probes and
leads from the tester with specific distance requirements between rods. Then
measurements are plotted on a monograph in order to calculate the actual resistance of the
ground.
leads from the tester with specific distance requirements between rods. Then
measurements are plotted on a monograph in order to calculate the actual resistance of the
ground.