used]. Use a ground loop when two of any three ground rods, driven not
less than 3050 mm 10 feet into the ground, a minimum of 3050 mm 10 feet
apart, and equally spaced around the perimeter, give a combined value
exceeding 50 ohms immediately after having driven. For ground loop,
provide continuous No. 1/0 bare stranded copper cable or equivalent
material having suitable resistance to corrosion. Lay ground loop around
the perimeter of the structure in a trench not less than 765 mm 30 inches
below grade, at a distance not less than 610 mm 2 feet nor more than 3050 mm
10 feet from the nearest point of the structure. Install a ground loop in
earth undisturbed by excavation, not earth fill, and do not locate beneath
roof overhang, or wholly under paved areas or roadways where rainfall
cannot penetrate to keep soil moist in the vicinity of the cable. Make
connections between ground conductors and grounds or ground loop, and
between ground loop and grounds electrically continuous. [Where so
indicated, provide an alternate method for grounding electrodes in shallow
soil by digging trenches radially from the building. Provide 1/0 bare
copper cable arranged in a star pattern with the structure at the center
for radial systems. Bury the radials at least 765 mm 30 inches inches
below grade external to the structure. Lower ends of down conductors [or
their equivalent in the form of metal strips or wires] are buried in
trenches].
3.1.7
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NOTE: The use of grounding plates is discouraged in
Military Handbook MIL-HDBK-1004/6, paragraph 3.3.4;
however, the use of grounding plates is an
acceptable alternative to ground rods in areas where
excessive rock and surface ledge is encountered.
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Provide a grounding plate for down conductor. Set grounding plates not
less than 610 mm 2 feet nor more than 3050 mm 10 feet, from the structure.
Grounding plate is to be buried as deeply in the existing dirt as local
conditions allow, without exceeding 3050 mm 10 feetin depth.
3.2
APPLICATIONS
3.2.1
Nonmetallic Exterior Walls with Metallic Roof
Bond metal roof sections together which are insulated from each other so
that they are electrically continuous. Connect air terminals so that they
are electrically continuous with the metal roof as well as the roof
conductors and down conductors. Bond ridge cables and roof conductors to
the roof at upper and lower edges of roof and at intervals not to exceed 30
m 100 feet. Bond down conductors to roof conductors and to lower edge of
metal roof. Where metal of roof is in small sections, make connections
between air terminals and down conductors to at least four sections of the
metal roof. Make connections electrically continuous and have a surface
contact of at least 1935 square mm 3 square inches.
3.2.2
Metal Roofs with Metal Walls
Bond metal roof and metal walls so that they are electrically continuous
and considered as one unit. Connect air terminals to and make them
electrically continuous with the metal roof as well as the roof down
conductors. Bond all roof conductors and down conductors to metal roof or
metal walls at upper and lower edges at intervals not to exceed 30 m 100
SECTION 13100N
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