buildings are connected to the grounding circuit.
If necessary, grounding to the counterpoise may be
permitted. In areas with low thunderstorm frequency
and good ground conductance, the counterpoise ground
rods may be spaced up to 600 meters (2000 feet)
apart but other areas may require grounding at less
than 300 meters (1000 feet) separation.
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3.14.1
Counterpoise Installation
Counterpoise wire shall be laid for entire length of circuits supplying
airfield lighting. Wire shall be in one piece, except where distance
exceeds the length usually supplied. Counterpoise shall be installed on
top of the envelope of concrete-encased duct and approximately 150 mm 6
inches above direct burial cables and duct lines. Where trenches or duct
lines intersect, counterpoise wires shall be electrically interconnected by
exothermic welding or brazing. Counterpoise to earth ground shall be
connected at every [600] [_____] m [2,000] [_____] feet of cable run, at
lighting vault, and at feeder connection to light circuit by means of
ground rods as specified. Counterpoise shall be installed in a separate
duct under roads, railroads, and paved areas above the highest duct
containing electrical or communications circuits.
3.14.2
Fixture Grounding
Each fixture or group of adjacent fixtures shall be grounded by a grounding
circuit separate from the counterpoise system unless required otherwise or
by driven ground rods if permitted. Fixtures, steel light bases or
grounding bushings on steel conduits shall be connected to an independent
ground rod by a No. 6 AWG bare stranded copper wire. Semiflush fixtures
for direct mounting in pavement need not be grounded. Copper wire shall be
connected to ground rods by exothermic weld or brazing.
3.15
MARKING AND LIGHTING OF AIRWAY OBSTRUCTIONS
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NOTE: If Section 09900 PAINTS AND COATINGS is
included, painting requirements should be
transferred to it. Local conditions may necessitate
modification to the following paragraph. Refer to
FAA AC 70/7460-1 for further information on marking
of obstructions.
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Towers, poles, smokestacks, buildings of certain shapes and sizes, and
other obstructions shall be marked and lighted in accordance with FAA AC
70/7460-1 and as indicated in or required otherwise.
3.15.1
Painting of Airway Obstructions
Patterns and colors to mark obstructions shall conform to FAA AC 70/7460-1
and shall be as indicated.
3.15.2
Obstruction Marker Lights
Obstruction marker lights shall be installed on radio towers, elevated
water tanks, smokestacks, buildings, and similar structures with 25 mm 1
inchzinc-coated rigid steel conduit stems using standard tees and elbows,
SECTION 16526A
Page 39
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