Grounding Cable
Grounding
cables should be flexible and be of Type I or Type II per clause 32.3 of ASTM
F855-97e1. Cable size should be capable of sustaining maximum fault current,
with full asymmetry, when part of portable
grounding
assembly, as demonstrated by tests per clause 12.3 of ASTM F855-97e1 or per
clause 6.6 of IEC 61230 (1993-09).
Master Ground
A master
ground is a portable device designed to short circuit and connect (bond) a
de-energized circuit or piece of equipment, or both, to a ground electrode. It
is normally located remote from, and on both sides of, the immediate work site,
and primarily used to provide safety for personnel during construction, reconstruction,
or maintenance operations.
Personal Ground
A personal
ground is a portable device designed to connect (bond) a de-energized conductor
or piece of equipment, or both, to a ground electrode. It is distinguished from
a master ground in that it is utilized at the immediate site when work is to be
performed on a conductor or piece of equipment that could accidentally become
energized.
Structure Base Ground
A structure
base ground is a portable device designed and used to connect (bond) equipment
to a metal structure. It is primarily used to provide safety for personnel
during construction, reconstruction, or maintenance operations.
Running Ground
A running
ground is a portable device designed to connect a moving conductor or wire
rope, or both, to a ground electrode. This device is normally placed on the
conductor or wire rope adjacent to the pulling and tensioning equipment located
at either end of a sag section. It is primarily used to provide safety for
personnel during construction or reconstruction operations.
Traveler Ground
A traveler
ground is a portable device designed to connect a moving conductor or wire
rope,
or both, to
a ground electrode. It is primarily used to provide safety for personnel during
construction or
reconstruction
operations. This device is placed on the traveler (sheave, block, etc.) at
strategic locations
where
electrical grounds are required.
A traveler
with a ground is usually sensitive to direction pull. Care shall be exercised
in hanging the traveler. Usually the ground is to the pulling end. It shall be
connected with temporary grounding, or to some conductive medium that is at
ground potential.
Care shall be taken in regard to the length of the grounding
cable and the anchor point. Too short of a cable may pull with block movement,
and too long of a cable may become entangled with the sheaves and rollers, thus
destroying the cable and conductor.
The traveler
ground should have a suitable grounding stud located in an accessible position
to enable placing and removing the ground clamps, with a ground stick when necessary.
The traveler ground will also help protect the sheave linings.
Ground Grids
A ground
grid is a system of interconnected bare
conductors, metallic surface mats, and/or grating, arranged in a pattern over a
specified area. Normally, it is bonded to ground rods driven around and within
its perimeter to increase its grounding capabilities and provide convenient
connection points for grounding devices.
The primary purpose of the grid is to
provide safety for workers by limiting
potential
differences within its perimeter to safe levels in case of high currents that
could flow if the circuit being worked became energized for any reason or if an
adjacent energized circuit faulted. When used, these grids are employed at
pull, tension, and splice sites.
Ground rod
A ground rod
is a rod that is driven into the ground to serve as a ground terminal, such as
a copper-clad rod, solid copper rod, galvanized iron rod, or galvanized iron pipe.
The ground rod is commonly used during conductor stringing operations to
provide a means of obtaining a ground electrode using portable grounding
devices.
If a ground
rod is free of paint, grease, and oil, the contact resistance between the rod
and the earth is negligible. Therefore, the main resistance is contained in the
body of earth immediately surrounding the ground rod.
When a
current flows from a ground rod into the earth, it flows outward in all
directions. It can be assumed that the current flows through a series of
concentric spherical-like shells, surrounding the ground rod
The shell
immediately surrounding the electrode has the smallest cross sectional area
(highest resistance); as the distance from the electrode is increased, each
shell is correspondingly larger in cross section (lower resistance). Therefore,
when a current flows, the voltage drop next to the ground rod is very high and decreases
as it moves out from the rod.
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