and remains de-energized until the work is completed.
The same precautions apply to new lines when
construction has progressed to the point where they
can be energized from any source.
The installation of protective grounds and short-
circuiting leads at the work site protects against the
hazards of static charges on the line, induced voltage,
and accidental energizing of the line.
When a de-energized line and an energized line
parallel each other, the de-energized line may pick up a
static charge from the energized line because of
proximity of the lines. The amount of this static voltage
picked up on the de-energized line depends on the
length of the parallel, weather conditions, and many
other variable factors. However, it could be hazardous;
and precautions must be taken to protect against it by
grounding the line at the location where the work is to
be completed. Grounding will drain any static voltage
and protect the workman from this potential hazard.
When a de-energized line parallels an energized
line-carrying load. the de-energized line may have a
voltage induced on it in the same manner as the
secondary of a transformer. If the de-energized line is
grounded at a location remote from where the work is
being done, this induced voltage will be present at the
work location. Grounding the line at the work location
will eliminate danger from induced voltage.
Grounding and short circuiting protect against the
hazard of the line becoming energized from either
accidental closing ofthe line or accidental contact with
an energized line that crosses or is adjacent to the de-
The procedures established to control the
operation of equipment in an electrical system
practically prevent the accidental energizing of a
transmission or distribution line. Hold-off tagging
procedures have proven to be very effective. If a
circuit should be inadvertently energized, the
grounds and short circuits on the line will cause the
protective relays to initiate tripping of the circuit
breaker at the source end of the energized line in a
fraction of a second and de-energize the hot line.
During this short interval of time, the grounds and
short circuits on the line being worked on will protect
the workmen (fig. 4-38). If it is not grounded, it is not
Figure 4-38.Grounding cluster installation.
Electric distribution circuits have been installed
underground for many years. The conventional
underground systems employ the use of some, if not
all, of the following: conduits encased in concrete,
manholes, ducts and trenches, direct burial cable and
riser/potheads, underground power cables, and
underground communication cables. After it has been
determined that the load density is high enough to
justify the expenses associated with an underground
system, the system must be designed; and then
construction may begin.
Manholes, handholes, and vaults will be designed
to sustain all expected loads that may be imposed on
the structure. The horizontal or vertical design loads
will consist of dead load, live load, equipment load,
impact, load due to water table or frost, and any other
load expected to be imposed on or occur adjacent to the