3.1.1.5
Ground Connections
Ground connections comprising continuations of down conductors from the
structure to the grounding electrode shall securely connect the down
conductor and ground in a manner to ensure electrical continuity between
the two. All connections shall be of the clamp type. There shall be a
ground connection for each down conductor. Metal water pipes and other
large underground metallic objects shall be bonded together with all
grounding mediums. Ground connections shall be protected from mechanical
injury. In making ground connections, advantage shall be taken of all
permanently moist places where practicable, although such places shall be
avoided if the area is wet with waste water that contains chemical
substances, especially those corrosive to metal.
3.1.1.6
Grounding Electrodes
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NOTE: Where soil conditions indicate definitely
that a counterpoise will not be required, all
references to counterpoise should be deleted from
the specifications. Using the soil resistance
calculate the resistance of the ground rods. When
these calculations indicate a combination of two
ground rods will exceed 50 ohms or the system ground
resistance will exceed [_____] ohms, provide a
counterpoise.
For Air Force projects the words in the fourth
sentence, "if a counterpoise is not used" should be
deleted.
Ten ohms should be used for all installations
covered by DARCOM-R 385-100, Safety Manual.
Twenty-five ohms is acceptable at most other
installations.
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A grounding electrode shall be provided for each down conductor located as
shown. A driven ground shall extend into the earth for a distance of not
less than 3.0 meters 10 feet. Ground rods shall be set not less than 900
mm 3 feet, nor more than 2.5 m 8 feet, from the structures foundation. The
complete installation shall have a total resistance to ground of not more
than [_____] ohms if a counterpoise is not used. Ground rods shall be
tested individually prior to connection to the system and the system as a
whole shall be tested not less than [24] [48] hours after rainfall. When
the resistance of the complete installation exceeds the specified value or
two ground rods individually exceed [_____] ohms, the Contracting Officer
shall be notified immediately. A counterpoise, where required, shall be of
No. 1/0 copper cable or equivalent material having suitable resistance to
corrosion and shall be laid around the perimeter of the structure in a
trench not less than 600 mm 2 feet deep at a distance not less than 900 mm
3 feet nor more than 2.5 m 8 feet from the nearest point of the structure.
All connections between ground connectors and grounds or counterpoise, and
between counterpoise and grounds shall be electrically continuous. Where
so indicated on the drawings, an alternate method for grounding electrodes
in shallow soil shall be provided by digging trenches radially from the
building. The lower ends of the down conductors [or their equivalent in
the form of metal strips or wires] are then buried in the trenches.
SECTION 13100A
Page 10
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