Custom Search
|
|
|
||
 3.1.6
Joint Test. After assembly, each joint shall be tested at the site
and shall be measured by a digital ohmmeter with a 0.01-ohm resolution and an
accuracy of 5 percent of the reading, plus one digit. Tests shall consist of
comparative measurements across slip joints, with equal spacing of meter
probes at least 4 ft (1.22 m) apart. An acceptable joint is one yielding a
measurement equal to or less than a similar measurement of the parent metal in
a given section of the mast, with the same spacing of the meter probes. The
lowest meter range providing an indication in the scale region of greatest
accuracy should be used. If the meter reads zero or infinity, an incorrect
scale has been chosen or the meter is broken.
3.1.7
Metal Mast Foundation. Foundations for setting metal masts shall be
in accordance with the following:
a) Steel or aluminum, mounted by anchor bolts set in a concrete
foundation poured in place. Follow manufacturer's recommendations for
foundation design and type and for setting of anchor bolts.
b) Steel, mounted by means of a stub set directly into a concrete
foundation. Corrosion-resistant steel masts may be set directly into earth
where soil conditions permit.
3.2
Grounded Aerial Conductors. Overhead conductors shall be spanned
between masts and connected to a ground counterpoise to suit the type of
installation. (Refer to Appendix A.)
3.3
Earthed Energy Dissipation Systems
3.3.1
Electrodes. Made electrodes, as defined in the NEC, shall consist
of ground rods not less than 3/4 in. (19 mm) diameter and 10 ft (3.05 m)
long. Ground rods shall be copper clad steel or solid copper. Connections to
ground rods shall be made by bolted clamp type devices.
3.3.2
Ground Counterpoise. Each ground counterpoise shall consist of a
No. 1/0 AWG (53.5 mm2) bare copper cable completely surrounding the
facility, with its ends connected together to form a closed loop. The size of
any strand of the cable shall be not less than No. 17 AWG (1.04 mm2). The
counterpoise shall be buried at least 30 in. (762 mm) below grade, external to
the structure and away from structural foundations or footings (see Figures 1
and 3). Each counterpoise shall be fixed by driven ground rods. Connection
at each ground rod shall be made with a bolted clamp type device to facilitate
disconnection of the counterpoise from the ground rod for periodic testing.
3.3.3
Radials. Radial systems shall consist of No. 1/0 AWG (53.5 mm2)
bare copper cables arranged in a star pattern with the structure at the
center. The size of any strand shall be not less than No. 17 AWG (1.04
mm2). The radials shall be buried at least 30 in. (762 mm) below grade,
external to the structure. Each radial shall be fixed by ground rods.
Connection at each ground rod shall be made with a bolted device to facilitate
disconnection of the radials from the ground rods for periodic testing.
Quantity and length of radials shall be as required to provide the required
ground resistance. Refer to IEEE 142, Recommended Practice for Grounding,
Industrial and Commercial Power Systems, for resistance calculations.
|
 
|
|
|
||
