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harlanjr
on FreezingBlue Flashcards.
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do personal protective grounds protect from lightning
no, there is no protection from lightning
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define fault current
the amount of current that a given system can deliver to a fault or short circuit
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where is the highest available fault current found
near the source
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how is static charge created on overhead conductors
warmer winds blowing across the surface of conductors
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which method of grounding provides the best protection for linemen
equipotential zone
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what are two main objectives of personal protective grounding
limit the amount of current flow and voltage drop across the lineworker's body; minimize the time that the current could flow through the lineworker's body
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what are 4 sources of induced voltage
existing energized lines; radio, television, and microwave towers.
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a line is not dead until it's _______
GROUNDED!!!!!!
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why is buzz testing not a good method of testing for the presence of voltage
relies on sound which can be masked, especially on lower voltages.
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three testing methods of testing for the presence of voltage
buzz, neon indicator, and audible tester
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what should be done if lightning is present when working on power lines
cease work
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the neutral is considered as an extension of the substation _____ ____
ground grid
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running or traveling grounds are used to protect an employee when conducting what type of work
stringing wire
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OSHA requires personal protective grounding cable to be a minimum of what size
#2 AWG copper
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where is a cluster bracket attached. how does it create a EPZ zone
the bracket functions as a terminal point for the grounding jumpers and provides contact with the pole to establish EPZ
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what potential hazard may be encountered while you are working on a denergized line adjacent to an energized line
induced voltage
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how is static charge created on denergized lines
warmer winds blowing across the surface of conductors
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in order to select grounds for a particular work location, that are large enough to carry the _____ ______ until the circuit protection equipment clears the fault, it is important to know the _____ ______ ______ for that part of the system.
fault current; fault current levels
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fault current is the _____ __ ______ that a given system can deliver to a fault or short circuit
amount of current
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where are fault currents the highest
near the source
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a potentially hazardous condition that can be encountered by lineworkers or the public where/ when walking may provide a potential for current to flow between two conductive objects to earth can be described as an example of
step potential
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bracket grounding provides
a low resistance short circuited connection from the line to earth at one or both sides of the work location
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this method of grounding is the most effective way of protecting the lineworker in the event the line or equipment becomes energized
EPZ grounding
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describe how EPZ grounding protects the line worker
diverts or shunts the flow of current around the line worker
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name four more common incidents that result in inadvertent energizing of a line
inadvertent operation of a switch, disconnect etc.; switch accidentally falling closed; generator back feed; line contacts foreign objects
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describe the fundamental concept of personal protective grounding
provides a low resistance path to ground for fault current through grounding devices that are designed to carry high levels of current in the event the line becomes accidentally energized
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what does OSHA standard 1910.269(n)(3) state about temporary protective grounds
temporary protective grounds shall be placed at such locations and arranged in such a manner as to prevent each employee from being exposed to hazardous difference in electrical potential
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list the two main objectives of personal protective grounding
limit the amount of current flow and voltage drop across the lineworkers body; minimize the time that the current could flow through the lineworkers body
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is a test probe designed for grounding
no
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steps for installing bracket grounding
neutral to center phase, center to outside phase, center to inside phase
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EPZ grounding provides
a low resistance short circuited connection from the line to the earth and shunts or diverts the flow of current around the line worker
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does it matter which side of the pole EPZ grounds are installed
no
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5 potential voltage sources
induced voltage or induction; lightning; capacitance; static charges; inadvertent energizing
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4 sources of induced voltages
adjacent energized lines; radio; television; microwave towers
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what is fault current
the amount of current that a given system can deliver to a fault or short circuit
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where are the fault current levels the highest
closest to the source
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how high can fault voltage levels be
30,000 amps to 40,000 amps
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step potential occurs between
a workers feet
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touch potential occurs between
a workers hands and feet
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a system neutral extends from
the substation grounding grid
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NESC requires that system grounds be placed where on a circuit
minimum of four times per mile
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what is a grounding elbow
used on 200a bushing to ground underground conductors or devices
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what is a portable feed through
used to isolate, test, and ground an underground cable or circuit
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what is a grounded bushing
one side of a portable feed through; temporary ground for elbows; used to bleed off capacitance
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what is a insulated protective cap
used to cover vacated bushings; it insulates, shields, and seals any load break bushing interface
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what is a grounding spike clamp
penetrating type clamp that is typically utilized to prove that a cable is deenergized at the work location
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ground cable length should be short as possible to minimize ________ ______
whipping effect
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OSHA requires that cable used for personal protective grounds never be smaller than
#2 AWG CU
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cluster bracket are used for what type PPE grounding
EPZ
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running grounds are used to
protect line workers on the ground when stringing conductors
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stringing block grounds are used to
bleed off induction and static when stringing conductors
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live front grounds
have exposed clamps similar to overhead grounds
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5 sources of electric energy
induced voltage or induction; lightning; capacitance; static charge; inadvertent energizing
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6 ground sources
substation ground grid; system neutral; static/ shielding wire; driven ground rod; anchor rods; metal structure
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grounding clamps form
the connection between the low resistance grounding cable and the conductor
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what does a difference of potential cause
current flow
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