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DOE Handbook Electrical Safety
- Work in Excess of 600 Volts -
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7.0 WORK IN EXCESS OF 600 VOLTS
Qualified and competent electrical workers are required to perform a variety of tasks with and
around higher voltage electricity, electrical equipment, and apparatus. The nature of such work necessitates an
understanding of applicable safety policies and rules.
Many electrical hazards and work practices are the
same regardless of the voltage involved. However, due to the nature of high voltage work, there are many
hazards and work practices that are specifically related to high voltage. Refer to chapter 2 of this document
for more details.
7.1 RESPONSIBILITIES FOR SAFETY
This section provides safety guidelines and
requirements for carrying out assigned job tasks. It is essential that each employee exercise sound judgment to
perform assigned tasks safely. Safety is the responsibility of each employee.
7.1.1 WORKERS
The
greatest responsibility for a worker's safety lies directly with the worker. This means that all workers are
responsible for performing their work in a manner that does not endanger themselves, their co-workers, or
others in the area and for complying with safety rules and requirements. Workers should not rely solely on the
care exercised by another for their protection. Workers are encouraged to contribute to the safety program and
bring to the attention of their supervisors or safety representative any condition they believe is unsafe.
Other safety responsibilities of workers include the following:
1. The worker should examine the work area
for existing hazards and proceed in a safe manner.
2. When seen in a dangerous situation, fellow workers
should be warned in such a manner as to avoid confusing, startling, or suddenly alarming them.
3. Before climbing poles, ladders, or other such structures or before working on scaffolds,
workers shall make a careful inspection to determine whether the structures are safe and are properly
supported. Workers should not carry anything in their hands while ascending or descending ladders. Small
objects or tools may be carried in pockets or pouches. Larger objects, however, should be raised or lowered by
use of hand lines or ropes and blocks. Others working nearby or below should remain out of line of the work
area in case anything should accidentally be dropped.
4. It is the responsibility of each worker to attend safety meetings. Workers should also make a practice of
learning safety information made available to them that will help them perform
their work more safely.
5. The worker shall report to the supervisor any personal injury as defined by the
facility as soon as possible.
6. The worker should exercise care and good judgment when lifting heavy
material, obtaining help if the object is too heavy or awkward for one person to handle.
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7.1.2 SUPERVISORS
Supervisors are responsible for knowing and implementing applicable safety policies and
directives and taking action as required to provide for the safety of the personnel and operations they
supervise. This includes; taking positive action to determine and reduce, as necessary, the hazards associated
with their operations; instructing employees in safe work methods and associated safety requirements; allowing
only those employees that are qualified for the work to perform the work; and ensuring that employees perform
their work safely.
Supervisors shall be responsible for the safety of all employees under their supervision. They
shall enforce the rules that apply to the hazards involved.
Supervisors shall make certain that each new or
transferred employee is instructed in the safe practices pertaining to his or her work.
Supervisors
shall ensure that the appropriate employees receive instruction in appropriate emergency techniques, such as
CPR, first aid, pole top, and confined space rescue, warranted by the employee's duties.
Other duties of
supervisors include the following:
1. Provide instructions on safe practices for the crew and see that they are followed.
2. Periodically examine supervised employees on their knowledge of the safety rules and approved emergency
techniques.
3. Not allow a worker to perform any task that cannot be performed safely or for which the
worker is not qualified.
4. Report every injury in the established manner prescribed for the facility.
5. Be responsible for the care and proper use of all protective devices.
6. Be responsible for proper
posting of hazardous work areas as a safeguard to those supervised. Under no circumstances shall the supervisor
allow work to continue if safety
precautions are ignored.
7. Designate a qualified worker to be in charge of work during the supervisor's
absence. The supervisor should not leave the job while dangerous work is in progress.
8. Coach and
direct employees who are working near exposed, energized wires, equipment, or apparatus.
9. Prescribe,
along with employees, the appropriate PPE when establishing safety related work practices.
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7.2 TRAINING
7.2.1 EMPLOYEE TRAINING
Employees shall be trained in and familiar with the
safety-related work practices, safety procedures, and other safety requirements in this section that pertain to
their respective job assignments.
Employees shall also be trained in and familiar with any other safety
practices, including applicable emergency procedures that are not specifically addressed in this section but
are related to their work and necessary for their safety.
7.2.2 QUALIFIED EMPLOYEE TRAINING
Qualified employees shall be trained and competent in:
1. The skills and techniques necessary to
distinguish exposed live parts from other parts of electrical equipment.
2. The skills and techniques
necessary to determine the nominal voltage of exposed live parts.
3. The skills and techniques necessary to
determine the minimum approach distances corresponding to the voltages to which they are exposed.
4. The proper use of the special precautionary techniques, personal protective equipment,
insulating and shielding materials, and insulated tools for working on or near exposed energized parts of
electrical equipment.
Training may consist of a combination of classroom and on-the-job type.
7.3
JOB BRIEFINGS
The employee in charge shall conduct a job briefing with the employees involved before the
start of each job. The job briefing will at least cover the following subjects: hazards associated with the
job, work instructions involved, special precautions, energy source controls, and personal protective equipment
requirements.
If the work or operations to be performed during the work day are repetitive and similar, at
least one job briefing shall be conducted before the start of the first job of each day or shift. Additional
job briefings shall be held if significant changes, which might affect the safety of the employees, occur
during the course of the work.
A brief discussion is satisfactory if the work involved is routine and if
the employee, by virtue of training and experience, can reasonably be expected to recognize and avoid the
hazards involved in the job. A more extensive discussion shall be conducted if the work is complicated or
extremely hazardous, or the employee cannot be expected to recognize and avoid the hazards involved in the job.
An employee working alone need not conduct a job briefing. However, the employee shall ensure that the tasks to
be performed are planned as if a briefing were required.
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7.4 PERSONAL PROTECTIVE EQUIPMENT AND PROTECTIVE CLOTHING
Employees shall wear appropriate personal
protective equipment (PPE) and protective clothing (see Section 7.4.8) to protect them from hazards of
high-voltage apparatus. Employees authorized or required to work on high-voltage systems shall be completely
familiar with the PPE and protective clothing they need for adequate protection while working on such systems.
(Refer to Appendix C for suggested types of PPE and protective clothing.) (See Figure 7-1)
Figure 7-1. Appropriate personal protective equipment and protective clothing shall be worn by electrical
workers to protect them from electrical hazards.
7.4.1 SHOES
Employees should wear shoes or boots that comply with the requirements of ANSI Z41. No metal
parts shall be present in the sole or heel of the shoes where nonconductive shoes are required.
7.4.2
HARDHATS
Workers should wear approved hardhats when working aboveground on poles, structures, or
buildings or in trees.
Workers shall wear hardhats when working on the ground near poles, structures,
buildings, or trees in which work is being done. Workers shall wear hardhats when visiting or observing in
areas where overhead work is being done.
Figure 7-1. Appropriate personal protective equipment and
protective clothing shall be worn by electrical workers to protect them from electrical hazards.
7-4
7.4.3 EYE PROTECTORS
Whenever eyes are in danger of being injured, workers shall wear safety
goggles or other eye protectors meeting ANSI standards. When the work being performed dictates, workers should
wear nonmetallic and nonconductive eye protection. Appropriate PPE is needed to protect workers from arc flash
hazards.
7.4.5 METAL FASTENERS
Workers shall not wear articles such as loose chains, keys, watches, or rings if such articles
increase the hazards associated with inadvertent contact with energized parts or can become
caught under or snagged while climbing off or on structures, equipment or vehicles.
7.4.6 WORK GLOVES
When insulated gloves suitable for high-voltage are not required, otherwise suitable work gloves should be worn
while handling materials and equipment to prevent the possibility of slivers, cuts, and skin irritation.
7.4.7 WORK CLOTHES
Work clothes should be made of natural materials, such as cotton or wool, or fire
resistant materials and should have full length sleeves. Sleeves should be rolled down for greatest
protection.
7.4.8 FIRE-RESISTANT (FR) CLOTHING
FR materials, such as flame-retardant treated cotton,
meta-aramid, para-aramid, and polybenzimidazole (PBI) fibers provide thermal protection. These materials can
ignite but will not continue to burn after the ignition source is removed. FR fabrics can reduce burn injuries
during an arc flash blends, para-aramid adds strength to a fabric to prevent the fabric from breaking open
due to the blast shock wave and high thermal energy of the arc.
7.4.8.1 GENERAL
All fire resistant fabrics comply with 29 CFR 1910.269(1)(6)(iii). Untreated cotton and
wool comply if the fabric will not ignite and continue to burn under the conditions to which the employee
could be exposed. ASTM F1506-94 and 2 new ASTM provisional standards, outline the testing procedures to
determine how various fabrics react in the presence of an electric arc on an instrumented manikin or panel. The
new ASTM provisional standards provide testing procedures that expose untreated and fire resistant fabrics to
electric arcs. F1506-94 provides testing procedures that expose these same fabrics to a vertical flame test.
Also see NFPA 70E, 110.7(A) for details on flash hazard analysis.
7.4.8.2 ELECTRIC ARC HAZARDS
Electric shock is a widely recognized hazard and involves current flow through or on the body. Burns from
electric arcs are not as well recognized. There is no contact required and the burns can be severe if the
clothing ignites or melts. The hazards to which the employee is exposed also include the clothing breaking open
due to the arc pressure blast, the heat from the electric arc and subsequent secondary fires or explosions.
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The extent of the employee's injury is dependent on the length of the arc gap, available fault current,
duration of the arc, the distance of the employee from the arc, percentage of the body burned, the employees
age, medical condition, and number of layers of the clothing system. The proper clothing system will minimize
or reduce the burn injury.
7.4.8.3 TYPES OF FIRE RESISTANT FABRICS
Chemically dependent fire
resistant fabrics are treated with flame retardant chemicals added to the fiber or treatments applied to the
fabric. These treatments are activated by heat and produce gases that smother the flame. Typically, these
fabrics have a definite life as defined by the manufacturer. This is usually defined by the number of home or
commercial washings the garment is exposed.
Inherently fire resistant fabrics, by their composition, do
not burn in air. The fire resistance of this fabric is not affected by washing.
7.4.8.4 CLOTHING SYSTEMS
All clothing worn by affected workers should be considered part of the employees protective clothing system.
This includes rainwear, cold weather wear and underclothing. Protective clothing should provide a good
functional fit to increase the protection and comfort of the clothing. When required, protection can be
increased by wearing single or multiple layers of flame-resistant outer garments over nonmelting clothing.
Sleeves and shirts should be fully buttoned and appropriate neck, head, and hand coverings provided.
7.4.9 RUBBER GLOVES
The following requirements apply:
1. Rubber gloves shall be of appropriate
voltage rating for the work being performed. All rubber gloves shall meet the standards set forth by ANSI/ASTM.
2. Rubber gloves issued for service shall be tested at appropriate voltage levels at intervals not exceeding 6
months.
3. Leather glove protectors shall be worn over rubber gloves except where leather protectors are
not required by 29 CFR 1910.137 or the appropriate ASTM standard.
4. Rubber gloves should be carried cuff
down in a bag, box, or container that is designed for this purpose. Rubber gloves may be kept inside of leather
protectors.
5. Rubber gloves shall be visually inspected and field air-tested before use each day and at
other times if there is cause to suspect damage.
6. Rubber gloves should be uniquely identified (i.e., serial number or other marking). The
results of dielectric tests should be documented.
7. Rubber gloves shall be wiped clean of any oil, grease,
or other damaging substances as soon as possible.
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7.4.10 RUBBER LINE HOSE, HOODS, COVERS, SLEEVES, AND BLANKETS
Linemen's rubber insulating sleeves
are worn to provide protection from electric shock and burn to the arm and shoulder areas. They are available
in several different thicknesses, lengths, and designs, depending on the maximum voltage they are designed to
protect against.
Insulating line hose (flexible hose) is used as an insulating cover for electric
conductors to protect against accidental contacts. A lengthwise slit with overlapping sides permits the hose to
be placed on conductors easily. It is available in various diameters, lengths, and compositions. Insulating
covers are used in conjunction with line hose to cover an insulator and the conductor attached to it for
protection against accidental contact.
Rubber insulating blankets are molded sheets of insulating rubber or
synthetic elastomer, usually square or rectangular in shape, designed to cover energized electrical equipment
to prevent direct accidental contact by electrical workers.
7.4.11 LIVE LINE TOOLS
A careful
periodic inspection shall be made of equipment used for handling or testing energized lines or equipment. Such
tools shall be examined before each use to make certain they are in good condition.
Particular attention
shall be given to preserving the surfaces of wooden and fiberglass tools used around electrical equipment,
including ladders, pike poles, switch sticks, live-line tools, and insulating platforms. Only colorless varnish
or other appropriate transparent insulating preservative shall be used.
Insulated tools shall be stored in a dry location. Suitable containers or racks shall be provided to
protect the tools from mechanical damage and warping.
7.4.12 STOREROOM STORAGE
Since heat, light, oil, and distortion are natural enemies of rubber, rubber protective equipment
should be guarded from these as much as possible. Rubber equipment shall not be stored near
boiler rooms, steam pipes, or radiators and should be protected from exposure to direct sunlight.
Gloves should be stored in their natural shape in the leather protector. Keep sleeves flat with the inserts
left in. Blankets should be stored flat, hung on pegs by the eyelet or rolled up. Line hose should be stored in
its natural shape.
7.4.13 TRUCK STORAGE
The storing of rubber protective equipment on the truck
should be planned. If possible, separate
compartments should be provided for each class of equipment, and each compartment should be of sufficient size
to allow the articles to lie in a natural position. Rubber gloves should be
stored in glove bags and hung up. If stored in tool bags or inside boxes, nothing should be piled
on top to cause distortion. Gloves should not be stored near vehicle heaters.
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Sleeves should be stored flat with inserts rolled up lengthwise, or placed in a tube shaped bag.
Nothing should be placed on top of sleeves or stored near vehicle heaters.
7.4.14 PLACING OF INSULATING
GOODS ON CONDUCTORS
When workers are about to begin work that requires the use of rubber goods, they should
climb or raise the bucket to a position just below the first line of conductors. When climbing they should
then determine their working position and what lines and other conductors should be covered. They should then
request the required rubber goods. Before proceeding further, the workers shall put on the rubber gloves and
leather protectors and make certain that they are in good order. Rubber goods shall be raised in a secure
manner.
As the workers ascend to their working position, they shall cover all conductors which provide a hazard.
This should be done from below whenever possible. At no time shall workers pass
through energized equipment before it is covered with rubber goods (line guards). All conductors and grounds
adjacent to working space shall be considered, including those near any possible change of position that may be
necessary. When line hose is applied to vertical or sagging wires, it should be fastened to the line to prevent
its slipping from position. When blankets are used for covering items such as dead ends, potheads, secondary
racks, and transformers, they should be secured by wooden or plastic clamp pins or tie thongs. After the
protective equipment has been placed, care should be taken to prevent damage to the rubber from tie wires,
spurs, or other objects.
7.4.15 REMOVING INSULATING GOODS FROM CONDUCTORS
When the job is completed,
the protectors should be removed in the reverse order of installation. Remote conductors are removed first and
the wires nearest the workers last. After being detached, the equipment should immediately be lowered to the
ground.
7.4.16 CLEANING AND INSPECTING
After the rubber goods have been lowered to the ground, they should be cleaned and visually
inspected before being placed in the carrier compartments of the truck.
7.5 PROTECTIVE GROUNDING OF LINES
AND EQUIPMENT
Grounding is the most effective way of protecting electrical workers from electric shock.
That is why it is important to ensure that all deenergized lines and equipment are grounded.
7.5.1
PURPOSE
Blankets should be rolled up and placed in canisters or protective canvas holders. Do not fold,
hold together with tape, pile materials on top of, or store blankets near vehicle heaters. This section
provides information concerning protection for workers repairing, servicing, or working on high-voltage power
lines.
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Figure 7-2. Equipotential grounding is the most effective way of protecting employees who are working on
high-voltage systems and equipment.
7.5.1.1 REDUCE THE POTENTIAL VOLTAGE DIFFERENCES ACROSS THE WORKER
The primary function of personal protective grounds is to provide maximum safety for personnel while they are
working on deenergized lines or equipment. This will be accomplished by making provisions that will reduce the
potential voltage differences at the work site (voltage differences across the worker) to a safe value in the
event that line or equipment being worked on is accidentally reenergized, voltages induced from other energized
lines, an energized line falls on the line being worked, or there is a lightning strike near the line being
worked.
The personal protective grounds should provide a low-impedance path to ground to ensure prompt
operation of the circuit protective devices.
7.5.2 APPLICATION
Certain methods and steps should be exercised when placing grounds and loads to protect
workers from high-voltage hazards.
7.5.2.1 DEENERGIZED LINES
When an energized line or equipment in
excess of 600 V is removed from service to be worked on, it shall be treated as energized until it is
deenergized, tagged, locked if necessary, tested, and grounded.
Figure 7-2. Equipotential grounding is the most effective way of protecting employees who are working on
high-voltage systems and equipment.
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7.5.2.2 NEW CONSTRUCTION OR DISMANTLING OF FACILITIES
If isolating devices are not in place and
energization is impossible from any source, single-phase grounding is appropriate, acceptable, and safe. If
energization is possible by the closure of a jumper or isolating device, shorts and grounds shall be used
unless conductor handling activity makes this impractical or impossible because of line design or construction
process.
7.5.2.3 MINIMUM APPROACH DISTANCE FROM UNGROUNDED CONDUCTORS
The minimum approach distances
in Section 2.13.4.1 shall be maintained from ungrounded conductors at the work location. The ground may be
omitted if the making of the ground is impractical or the resulting conditions are more hazardous than working
on the lines or equipment without grounding. However, all work shall be done as if the line or equipment were
energized.
7.5.2.4 VISIBLE THREE-PHASE SHORT AND GROUND REQUIRED
Visible three-phase short circuiting may be accomplished through conductive parts such as guy wires and
unpainted metal tower members, but shall not be effected through a grounding mat or other concealed conductors.
7.5.2.5 GROUND CIRCUIT
No power disconnect switch, power circuit breaker, transformer, wave trap, or fuse
shall be part of the protective grounding circuit.
Table 7-2. AC live-line work minimum approach
distance.
Note 1: These distances take into consideration the highest switching surge an employee will be exposed
tto on any system with air as the insulating medium and the maximum voltage shown.
Note 2: The clear live
line tool distances shall equal or exceed the values for the indicated voltage ranges.
Note 3: See 29 CFR
1910.269, Appendix B for information on how the minimum approach distances were derived.
7-10
7.5.3 GROUNDING EQUIPMENT
ASTM Committee F-18, Electrical Protective Equipment for Workers, has
developed and published a consensus standard for protective grounds, ASTM Designation: F-855. This voluntary
consensus standard may be used by all Federal agencies for procurement purposes. Therefore, grounding cables,
clamps, and ferrules purchased should meet all the requirements of ASTM Designation: F-855. Aluminum cables
shall not be used for personal grounds. The grounding of high-voltage lines and equipment will provide workers
with additional
protection from electric shock if grounds are sized, selected, and installed properly.
7.5.3.1 AVAILABILITY
Grounding cables shall be available for use when work is being done on deenergized
lines or equipment.
7.5.3.2 APPROVED CAPACITY
Grounding cables shall accommodate the maximum
fault current to which the cable or equipment might be subjected.
7.5.3.3 GROUNDING CABLES AND HARDWARE
Personal protective grounding cables consist of appropriate
lengths of suitable copper grounding cable, with electrically and mechanically compatible ferrules and clamps
at each end. In addition, appropriate hot sticks are required for installing and removing the conductor-end
clamps to the conductors. Hot sticks are required for attaching ground-end clamps if the grounded system and
the worker are at different potentials. Cluster bars provide a low resistance means of connecting the
ground-end clamps. Each of these components will be discussed in the following subsections.
7.5.3.4
GROUNDING CABLES
Most of the grounding cables in use today (and available for purchase) are actually manufactured for
another purpose-principally as welding cable. These extra-flexible copper cables with jackets are manufactured
according to appropriate ASTM standards for both cables and jackets, and can be expected to perform
satisfactorily as grounding cables.
7.5.3.4.1 STRANDING
There are several classes of flexible cable
with various stranding in the sizes normally used for
grounding cables.
7.5.3.4.2 JACKETS
Welding cables are nominally insulated at 600 volts. When used
as grounding cable, the insulation or jacket serves primarily for mechanical protection of the conductor. The
flexible elastomer or thermoplastic jackets are manufactured, applied, and tested according to ASTM
standards. Black, red, and yellow jackets are usually neoprene rubber compounds, while clear jackets are
ultraviolet-inhibited polyvinyl chloride (PVC). All jackets should have the AWG size stamped or printed
repeatedly along the length of the cable. The clear jacket allows easy visual
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inspection of the conductor for strand breakage, but becomes stiff and hard to handle at low
temperatures. The clear jacket will split or shatter at very low temperatures.
7.5.3.4.3 FERRULES
Ferrules should be threaded-stud copper base compression type. Ferrules should have
the filler compound vent hole at the bottom of the cable so that employees can visually check that the cable
is fully inserted into the ferrule. Compound should be used with crimped ferrules. The ferrules should be
crimped with the ferrule manufacturer's recommended die. The press shall have enough pressure to completely
close the die. The area covering the inserted cable jacket should not be compressed. Heat shrink or springs
should be installed over a portion of the ferrule to minimize strand breakage caused by bending. In all cases,
the manufacturer's recommendations should be followed.
7.5.3.4.4 HANDLING OF GROUNDING CABLE
Personal protective grounds are usually handled and lifted by the cable. However, continuous flexing eventually
breaks the conductor strands beneath the jacket. Therefore, employees
should minimize the use of sharp bends in the cable.
7.5.3.4.5 SIZE OF GROUNDING CABLE
The size of the grounding cable must be selected to handle the maximum calculated fault
current of the power system or specific portion thereof. The minimum size that shall be used for
grounding cables is #2 AWG flexible copper. In larger substations, the maximum available fault
current may require larger cables. If larger cables are not available, parallel cables (with the
appropriate derating factor) may be used.
Most manufacturers and suppliers of grounding cables publish
tables to assist the user in selecting the proper cable size for a given fault current. These tables show the
maximum fault current capability for several sizes of copper grounding cables.
7.5.3.4.6 GROUNDING CABLE
LENGTH
Excessive cable lengths should be avoided. Therefore, slack in the installed cables should be
minimal to reduce possible injury to workers. Resistance in the cable increases with cable length, and
excessive length could exceed the tolerable voltage drop across the body. Longer than necessary cables also
tend to twist or coil, which reduces the effectiveness of the cable.
7.5.3.4.7 GROUNDING CLAMPS
Grounding clamps are normally made of copper or aluminum alloys; sized to meet or exceed
the current-carrying capacity of the cable; and designed to provide a strong mechanical connection to the
conductor, metal structure, or ground wire/rod.
7.5.3.4.7.1 CLAMP TYPES
Clamps are furnished in, but
not limited to, three types according to their function and methods of installation:
1. Type I clamps,
for installation on deenergized conductors, are equipped with eyes for installation with removable hot sticks.
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2. Type III clamps, for installation on permanently grounded conductor or metal structures,
have T-handles, eyes, and/or square-or hexagon-head screws.
3. Other types of special clamps are designed
for specific applications, such as cluster grounds, underground equipment grounding, and so on.
7.5.3.4.7.2 CLAMP JAWS
Bus clamps should be furnished with smooth jaws for installation on copper,
aluminum, or silverplated bus work without marring the surface. Conductor or metal structure clamps should
be furnished with serrations or cross-hatching designed to abrade or bite through corrosion products on
surfaces of the conductor or the metal structure being clamped. Several styles of conductor and ground-end
clamps have jaws that can be replaced when the serrations have worn. Self-cleaning jaws are recommended for
conductor-end clamps used on aluminum or aluminum conductor steel reinforced (ACSR) conductors. Several styles
of ground-end clamps are designed with a cup-point set screw which should be tightened with a wrench (after the
serrated jaws have been securely tightened) to break through paint, rust, galvanized coating, or corrosion on
the surface that is to be clamped.
A typical grounding cable for transmission line work used by line crews
consists of a 2/0 AWG copper cable with an insulating jacket, terminated with an all-angle, self-cleaning
aluminum conductor clamp at one end, and a flat-faced clamp with a set screw at the other end for connecting
to a tower leg or ground wire/rod.
7.5.3.4.8 GROUNDING CLUSTER BARS
When climbing wood-pole
structures, workers may use a grounding cluster bar to connect the phase cables to the pole ground wire, if the
ground wire has sufficient capacity to carry the fault current. Cluster bars must have an attached bonding
lead. If there is no pole ground wire, the cluster bar for each pole is connected to a common driven or
screw-in ground rod with a grounding cable (or cables). In substation grounding, a copper bar is sometimes used
to connect the three-phase cables and a fourth cable to a riser from the station ground mat. When installing
personal grounds on wood structures from a bucket, the ground cables may be connected between the overhead
ground wire (OGW), and the phases without the use of cluster bars provided that an electrical bond of
sufficient current carrying capacity exists between the OGW and the structure ground.
7.5.3.4.9 TEMPORARY GROUND RODS
Some typical examples of temporary ground rods used for grounding
ungrounded structures or mobile equipment, or during conductor splicing operations, are either:
1. A
minimum ⅝-inch diameter bronze, copper, or copper-weld rod at least 6 feet long, driven to a depth of at least
5 feet; or
2. A 6-foot, screw-type ground rod, consisting of a minimum ⅝-inch diameter copper-weld shaft
with a bronze auger bit and bronze T-handle, screwed to a depth of at least 5 feet (preferred). The T-handle
must be tightly connected to the rod.
If a temporary rod cannot be driven or screwed to a depth of 5 feet,
additional rod(s) should be driven or screwed so that a total of at least 5 feet of rod is buried. These rods
shall be bonded
7-13
together with grounding cables prior to installing phase grounds. The rods should be placed 6 to 8 feet
apart; however, the 10-foot clearance from the rods should be maintained. OGWs may be used at any time to bond
the conductors provided that these wires are electrically bonded to the structure ground, either permanently or
by personal grounds.
Groundsmen should stay clear (at least 10 feet where feasible) of items such as down
guys, ground rods, maintenance vehicles, and structure legs or ground wires while they are bonded to
protective grounds which are in place. When it is absolutely necessary to work on or near these features,
employees should use bonded conductive or insulated platforms, or approved insulated shoes to minimize the
hazard from step and touch potentials.
7.5.4 TESTING BEFORE INSTALLING GROUNDS
Before grounds are installed, the deenergized line or equipment shall be tested for voltage.
Appropriate testers for the nominal voltage involved (audio or visual) should be used. They shall
be tested immediately before and after use to verify that they are in good working condition.
7.5.5 ATTACHING AND REMOVING GROUNDS
Employees attaching and removing grounds shall comply with the
following:
1. Grounding equipment should be visually inspected and all mechanical connections checked
for tightness before each use.
2. The surface to which the ground is to be attached should be clean before
the grounding clamp is installed or a self-cleaning clamp shall be used.
3. No ground shall be removed
until all personnel are clear of the temporary grounded lines or equipment. When the grounding set is removed,
it shall be disconnected from the line or equipment end first with an approved hot-line tool and moved to a
point clear of energized conductors before the ground end is disconnected.
7.5.6 GROUNDING METHODS AND
LOCATION OF GROUNDS IN ORDER OF PREFERENCE
Employees installing grounds shall install them using the
information given in the following sections.
7.5.6.1 WORK LOCATION
Grounds should be installed at the work location with all grounded parts of different potential
bonded together (on wood poles, all down guys, overhead ground wire, neutral conductor, and
pole ground). The cluster bar assembly should be installed below the working area and jumper
to the ground point or the neutral conductor and the phase conductor, a method of grounding
termed "equipotential" grounding. It provides the greatest margin of safety for the lineworker by placing
everything at equal potential, eliminating the possibility of the lineworker getting in series to ground.
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7.5.6.2 MULTIPLE WORK LOCATIONS AND SINGLE-PHASE GROUNDING AT WORK LOCATION
If work is to be
performed at more than one place in a line section, the line section shall be
grounded at one location and the conductor be grounded at each work location to reduce the
potential voltage difference across the work site.
7.5.6.3 OTHER LOCATIONS
Grounds shall be placed
at the work location or at each side of the work location and as close as practical to it.
7.5.7 TESTING
WITHOUT GROUNDS
Grounds may be temporarily removed when necessary for testing. Each employee shall use
insulating equipment and be isolated from any hazard involved. Additional measures may be necessary to protect
each exposed employee in case previously grounded lines or equipment become energized.
7.5.8 GROUND
PERSONNEL
In cases where ground rods or pole grounds are used for personal protective grounding,
personnel working on the ground shall either maintain a safe distance from such equipment or use the
appropriate equipment designed to prevent touch-and-step potential hazards. The term "touch potential hazard"
refers to the difference in voltage measured between the grounding equipment and a worker in contact with the
grounding equipment at the time it is accidentally energized. The term "step potential hazard" refers to the
difference in voltage measured between each foot of the worker standing or walking in an electrical field
created by high voltage brought to earth.
7.6 INSTALLING OR REMOVING CONDUCTORS
Employees installing or removing conductors should follow certain
guidelines to ensure safety.
7.6.1 WORKING ON ENERGIZED LINE OR EQUIPMENT
Employees working on energized lines or equipment should comply with the following: 1. Work on electrical
equipment and circuits other than electrical utility lines and equipment,
operating a 50 V or more ground, should be worked on following the guidelines of Section 2
of the handbook.
2. Line or equipment carrying an ac voltage in excess of 600 V phase-to-phase should be
worked on with rubber gloves or live line tools. All other necessary protective devices such as line hose,
hoods, covers, sleeves, and rubber blankets should be used. (See Section
2.1.2).
3. Energized line should be worked on from below whenever possible. When working
energized line or equipment carrying 600 V or more to ground, there shall be two qualified
workers performing the work (see Section 2.1.2). Work shall not be performed on energized
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lines or equipment during rain, snow, sleet, fog, and other damp conditions, except in
extreme emergencies if in the opinion of supervision and line crew it can be done safely.
4. While working on the same pole, workers shall not work simultaneously on wires that have a difference of
potential.
5. Rubber gloves of appropriate voltage rating shall be worn when working within reach of a
fellow employee who is working on or within reach of wires or equipment carrying voltage in excess of 600 V.
6. Insulated tongs or disconnect sticks shall be used to open or close plugs or fuses or to disconnect blades.
7.6.2 STRINGING OR REMOVING DEENERGIZED CONDUCTORS
Employees stringing or removing deenergized conductors
should follow certain safe work practices. Consideration should be given to the following:
1. When it is necessary to conduct any work on poles or structures carrying more than one
circuit and where there is not safe working clearance between circuits, the conductors not
being worked on shall be either:
a. Untied and separated with proper clearance from the pole or structure,
b. Deenergized and grounded, or c. Covered with the necessary protective devices.
2. Prior to stringing
operations, a job briefing shall be held setting forth the plan of operation and specifying the type of
equipment to be used, grounding devices to be used and instructions to be followed, crossover methods to be
employed, and clearance authorization
required.
3. Where there is a possibility that the conductor will accidentally contact an energized circuit
or receive a dangerous induced voltage buildup, to protect the employee from the hazards of the conductor, the
conductor being installed or removed shall be grounded or provisions made to insulate or isolate the employee.
4. If the existing line is deenergized, proper clearance authorization should be secured and the line grounded
on both sides of the crossover, or the line being strung or removed should be considered and worked on as
energized.
5. When workers cross over energized conductors, rope nets or guard structures shall be
installed unless provisions are made to isolate or insulate the workers or the energized conductor. Where
practical, the automatic reclosing feature of the circuit-interrupting device should be made inoperative. In
addition, the line being strung should be grounded on either side of the crossover or considered and worked on
as energized.
6. Conductors being strung or removed should be kept under positive control by the use of
adequate tension reels, guard structures, tielines, or other means to prevent accidental contact with energized
circuits.
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7. Guard structure members should be sound, of adequate dimension and strength, and
adequately supported.
8. Catch-off anchors, rigging, and hoists should be of ample capacity to prevent loss
of lines.
9. The manufacturer's load rating should not be exceeded for stringing lines, pulling lines, sock
connections, and all load-bearing hardware and accessories.
10. Pulling lines and accessories should be inspected regularly and replaced or repaired when
damaged or when their dependability is doubtful.
11. Conductor grips should not be used on wire rope unless
designed for this application.
12. While the conductor or pulling line is being pulled (in motion), workers
should not be permitted directly under overhead operations, nor should any employee be permitted on the
cross arm.
13. A transmission clipping crew should have a minimum of two structures clipped between the
crew and the conductor being sagged. When working on conductors, clipping crews should install grounds at the
work location. The grounds should remain intact until the conductors are clipped in, except on dead-end
structures.
14. Except during emergency restoration activities, work from structures should be discontinued
when adverse weather (such as high wind or ice on structures) makes the work hazardous.
15. Stringing and clipping operations should be discontinued during an electrical storm in the immediate
vicinity.
16. Reel-handling equipment, including pulling and braking machines, should have ample
capacity, operate smoothly, and be leveled and aligned in accordance with the manufacturer's operating
instructions.
17. Reliable means of communication between the reel tender and pulling rig operator should
be provided.
18. Each pull should be snubbed or dead-ended at both ends before subsequent pulls.
7.6.3 STRINGING ADJACENT TO ENERGIZED LINES
Employees stringing adjacent to energized lines should follow
certain safe work practices. Consideration should be given to the following:
1. When performing work
from structures, clipping crews and all others working on conductors, subconductors, or overhead grounding
conductors should be protected by individual grounds installed at every work location.
2. When workers are stringing adjacent to energized lines, the tension-stringing method or
other methods that prevent unintentional contact between the lines being pulled and any worker should be used.
3. All pulling and tensioning equipment should be effectively grounded.
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4. A ground should be installed between the tensioning reel setup and the first structure to ground
each bare conductor, subconductor, and overhead grounding conductor during stringing across or adjacent to
energized lines.
5. During stringing operations, each bare conductor, subconductor, and overhead grounding
conductor should be grounded at the first tower adjacent to both the tensioning and pulling setup and at
appropriate intervals. The grounds should be left in place until conductor installation is completed. Except
for moving-type grounds, the grounds should be placed and removed with a hot stick.
6. Conductors,
subconductors, and overhead grounding conductors should be grounded at all dead-end or catch-off points.
7. A ground should be located at each side and within 10 ft. of working areas where conductors,
subconductors, or overhead grounding conductors are being spliced at ground level. The two ends to be spliced
should be bonded to each other. It is recommended that splicing be carried out on either an insulated platform
or on a conductive metallic grounding mat bonded to both grounds. When a grounding mat is used, it should be
roped off and an insulated walkway provided for access to the mat.
7.7 SPECIAL TOOLS
Line workers
shall be familiar with special tools that are used for climbing, such as climber gaffs, climber straps, and
body belts shall properly store and maintain such equipment.
7.7.1 LINEWORKERS’ CLIMBING TOOLS
Employees should apply the following:
1. All climbers should be inspected frequently by the worker using
them.
2. Climber gaffs should be kept sharp.
3. A climber shall not be used when its gaff becomes
shorter than 1-1/4 in. inside measurement.
4. Climber straps that are worn or otherwise defective shall be
replaced.
7.7.2 BODY BELTS AND SAFETY STRAPS
Employees using body belts and safety straps (work positioning equipment) should apply the
following:
1. All body belts and safety straps shall be inspected before each use by the employee who uses
them.
2. Workers shall use their body belts and safety straps when doing any work involving danger of
falling.
3. Body belts and safety straps should not be stored with unguarded sharp tools or devices.
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Figure 7-3. Employees using special tools for climbing and for servicing high voltage systems shall be trained
on how to use such tools and equipment.
4. Heat, sharp bends, and overstressing of body belts and safety
straps should be avoided as they are injurious to leather. Wet leather should be dried slowly at moderate
temperatures.
7.7.3 TOOL BAG AND EQUIPMENT
Tools, small equipment, and materials should be raised
and lowered in a tool bag. The tool bag should be inspected before use to see that it contains no broken glass
or other material on which the employee could cut his or her hand or rubber gloves. Tool bags should not have
any metal in their construction.
7.7.4 TAPES AND RULERS
Workers should not use metal measuring
tapes or tapes having metal strands woven into the fabric, brass bound rules, or metal scales when working near
electrical equipment or conductors
7.7.5 SPOON AND SHOVELS
Tools of this type, especially those
having long wooden handles, shall not be used when the handles are cracked, split, or broken.
Figure
7-3. Employees using special tools for climbing and for servicing high voltage systems shall be trained on how
to use such tools and equipment.
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7.7.6 PIKE POLES
Pike poles shall comply with the following:
1. Cracked, broken, or slivered
pike poles should not be used;
2. Pike poles should not be thrown; and
3. When not in use and loaded
on the truck, the points should be protected so that they will not injure anyone.
7.7.7 HAND AXES AND
SHARP TOOLS
Hand axes and sharp tools shall comply with the following:
1. Hand axes should not be
used on overhead work; and
2. When not in use, sharp tools should be protected by the suitable guards or
containers.
7.7.8 HANDLINES AND TAGLINES
Use high quality, nonconductive hand lines and taglines. Keep them stored
in a clean, dry location and protected from damage and contamination. Wear clean gloves when handling hand
lines and taglines to avoid contaminating the rope. Remove wet, dirty, or damaged ropes from service.
7.8 TREE TRIMMING
Equipment used to trim trees shall be maintained in approved and proper working condition
to aid tree trimmers and protect them from hazards.
7.8.1 CARE AND USE OF TOOLS
Tools shall be
cared for using the following methods:
1. The handles of all tree-trimming tools shall be kept well dressed
and varnished.
2. When trimming trees near live conductors, the employee shall not work with wet tools or
ropes. Such equipment should be protected during rain showers.
3. A tree-trimming saw shall be protected by being put into its scabbard when it is not in use.
4. All
ropes shall be inspected frequently for cuts and wear.
7.8.2 CLIMBING
The following shall be applied for climbing:
1. An employee should use a ladder to climb a tree, unless
the employee is properly equipped and trained for tree climbing.
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2. Climber gaffs and straps shall be designed for tree climbing. The safety strap shall be constructed
to withstand contact with saws and other sharp objects. Workers in trees shall
be tied off.
7.9 SERIES STREET-LIGHTING CIRCUITS AND APPARATUS
Lighting circuits and apparatus used
for series street-lighting should comply with the following:
1. Rubber gloves or any other necessary
protective equipment should be used when working on a series street-lighting circuit, unless the circuit is
electrically isolated and grounded at the work location. Unless properly tagged and isolated, series street
lighting circuits should be considered as being energized.
2. The opening of a time clock, a
photoelectric relay, or remote control overcurrent control equipment shall not be considered as isolation
points that provide a safe work condition while employees work on series lighting circuits.
3. The use
of series lighting circuits is discouraged.
7.10 UNDERGROUND
Underground work requires a means of
safe entrance and exit from the workspace. Employees should follow the guidance given in the following
subsections to ensure safety in entering and leaving such work spaces.
7.10.1 WORKING IN MANHOLES, UTILITY TUNNELS, AND VAULTS
Manholes, utility tunnels, and vaults may be
considered confined spaces and shall comply with 29 CFR 1910.146,1910.269(e) and (t), and 1926.956. The
following may apply to employees working in manholes, utility tunnels, and vaults:
1. Employees who
enter manholes shall be trained in the hazards of the confined spaces, confined space entry procedures, and
confined space emergency and rescue procedures.
2. When opening a manhole, employees shall completely remove the manhole cover from the
opening. Manhole covers should be removed before the cable is rodded or installed and removed.
3. Open manholes shall be barricaded and protected by flags or guards as required. All open
manholes shall be protected as required by 29 CFR 1910.269(e).
4. Before the pit is entered, it shall be
tested for oxygen content and the flammable-gas explosive limit. Workers shall not smoke or use an open flame
while tests for an explosive mixture of gas are being made.
5. If the oxygen level is less than 19.5 percent or greater than 21 percent, the pit shall be ventilated
and retested before any work begins.
6. If the flammable-gas content is more than 10% of the lower
explosive limit, the pit shall be ventilated and retested before any work begins. When testing indicates that a
manhole contains either a mixture of explosive gas and air richer than safe working limits or
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flammable liquids, corrective measures shall be taken before work in the manhole is allowed
to proceed.
7. When nitrogen is used in manholes or confined areas, approved atmosphere testing devices
shall be placed in operation where they can be observed by people in the manhole. When the testing devices show
a deficiency of oxygen, all personnel shall leave the manhole until the proper atmosphere is restored.
8. The manhole shall be ventilated continuously when occupied.
9. An attendant is required topside with the
means to summon help without leaving his or her station. The attendant shall be capable of instituting a rescue
without entering the manhole. The attendant on the surface is responsible for the safety of the persons in the
manhole.
10. The topside attendant can perform other duties outside of the enclosed space if these duties
do not distract the attendant from monitoring employees within the space. All manholes over 4 ft. deep should
be entered with the use of a ladder as required by 29 CFR 1910.269 (t)(1).
11. Workers should open all
entrance bars or chains on the topside of manhole guards before entering or leaving a manhole. All chains or
bars should be closed at all other times, except when raising or lowering tools or materials.
12.
Operations involving chemical cleaning agents, solvents, volatile chemicals, cutting and welding equipment, and
other hazardous agents or tools require additional consideration. Consultation with and concurrence of
appropriate industrial safety and industrial hygiene personnel are required.
13. The employee shall enter or leave a manhole by means of a ladder. The employer shall not
use a cable, cable hanger, or manhole rack as a support for climbing. A manhole ladder should never be removed
while a worker is in the manhole unless absolutely necessary. In the instance of a ladder being removed to make
it easier to rescue a worker, the topside attendant shall fully devote his or her attention and efforts to
instituting a rescue using the worker's body harness and lifeline if necessary. The ladder shall be replaced as
soon as practical.
Note: The other workers in the hole should be warned that the ladder is to be removed in
time to allow him or her to exit the hole if necessary.
14. Materials, tools, and equipment should be kept
at a sufficient distance from the entrance to the manhole to avoid any hazard to the occupant from falling
objects or from hot metal or spilled compounds.
15. Blowtorches and furnaces should be ignited before
being lowered into manholes unless this creates additional hazards.
16. Rags, tape, refuse, and
combustible and flammable materials should not be allowed to accumulate in a manhole.
17.
Instrumentation shall be calibrated per manufacturer's instructions. [See 29 CFR 1910.269(e)(8)]. A record of
calibration should be maintained.
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18. GFCIs shall be used for 120-V ac power unless such power is supplied by a portable or
vehicle-mounted two-wire, single-phase generator rated not more than 5 kW, where the
circuit conductors of the generator are insulated from the generator frame and all other grounded surfaces.
(See Section 6.4).
19. All cables and insulated wires that do not have grounded conducting sheaths or
shielding should be treated as bare conductors. They shall be considered energized unless approved methods
have been used to determine that they are deenergized. Barricade or cover these conductors with protective
equipment or devices that will be within reach of a worker's position.
20. Where multiple cables are
present the cable to be worked on shall be identified by electrical means unless its identity is obvious. [See
29 CFR 1910.269(t)(5)]. Where cable has one or more abnormalities that could be an indication of an impending
fault, the defective cable shall be deenergized, except when service load conditions and a lack of feasible
alternatives require that the cable remain energized. In that case, employees may enter the manhole if they
are protected by the affects of the failure by flash blankets or other devices capable of containing the
adverse effects of the fault. [See 29 CFR 1910.269(t)(7)].
7.10.2 WORKING ON ENERGIZED UNDERGROUND CABLES
In general, work should not be performed on energized
underground cables. However, strictly external work, not requiring an appreciable change in location of the
cable, may be performed under direct supervision. Energized cables that are to be moved shall be inspected for
defects. [See 29 CFR 1910.269(t)(6)].
7.10.3 TERMINALS OF UNDERGROUND CABLES (POTHEADS)
Before
work is started, the overhead line connections to a cable terminal upon which work is to be performed should be
either:
1. Deenergized and grounded or
2. Disconnected and covered with protective equipment.
7.11 FERRO-RESONANCE
Ferro-resonance can generate overvoltages of up to 12 times line-to-ground source voltage
upon opening of a single-phase device or a poorly synchronized three-phase device. Violent
failure can occur, exposing personnel to the high-voltage failure and accompanying conditions.
Ferro-resonant conditions can result in damage to lightning arresters, switching devices, buried
cable, transformers, and associated equipment.
Ferro-resonance can be initiated when all of the following
elements are present and the switching means at dip point or takeoff is either a single-phase device or an
unsynchronized three-phase device that does not operate all phases within one-half cycle: i. System grounded
at the source but with no ground at the transformer bank, such as a transformer or transformer bank connected
delta on a grounded-wye system.
ii. Shielded cable or overhead conductor length sufficient to create the capacitance necessary.
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iii. Transformer size that permits saturation of the iron core at the operating voltage
iv. Transformer unloaded or very lightly loaded.
Prevention or control of ferro-resonance may be
accomplished by any of the following measures:
1. Using a wye-wye transformer connection with both
neutrals grounded and tied to the system neutral.
2. Using only phase-to-neutral (not phase-to-phase)
transformer connections for single-phase transformers.
3. Limiting length of underground cable between transformers and single-pole or poorly
synchronized three-pole switching devices.
4. If single-pole or poorly synchronized switching devices must
be used, ensuring that transformer and underground cable are loaded in excess of 2% resistive load of the
transformer capacity.
5. If transformer primary is ungrounded-wye, temporarily grounding the neutrals of
the transformers being switched.
6. Installing close-coupled, high-speed, three-pole switching devices
to minimize the duration of the single-phase condition during opening and closing of the circuit
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