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bugsbunny2255
on FreezingBlue Flashcards.
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Why has a "unit size" for conductors been established?
To compare the size and resistance of one conductor with that of another
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What is the decimal equivalent of one (1)mil?
0.001 in
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What is the definition of a mil foot?
A conductor 1 foot in length with a diameter of 1 mil
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A square mil is defined as the area of a
square, the sides of which are each equal
in length to what dimension?
1 mil
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A circular mil is defined as the area of a
circle having what dimension?
A diameter of 1 mil
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What is the definition of specific resistance?
The resistance of a unit volume of a substance to the flow of current expressed in ohms
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When a wire gauge is used to determine
the size of a wire, the measurement
should be made in what part of thegauge?
In the slot
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What types of insulation are best suited
for use in a high-temperature environment?
Cotton, polytetrafluoroethylene, and oiled paper
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What is the "ambient" temperature of a
conductor?
It is the heat generated by external sources and affecting a conductor’s temperature
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Which of the following metals is the best
conductor of current?
Silver
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Because its resistance changes very little
with temperature changes, what conductor is best suited for use in measuring instruments?
Manganin
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What definition best describes an insulating material?
A material that has a very high resistance
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The dielectric strength of an insulating material is a measurement of the material's ability to resist electrostatic stress caused by what factor?
Voltage
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Insulation resistance can best be defined
as the ability of an insulating material to
resist what action?
Current leakage
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For a material to be a good insulator,
what two properties are most important?
High dielectric strength and high insulation resistance
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When rubber is used as the insulating
material over a copper conductor, why is
a thin coating of tin used between the
two materials?
- To prevent a chemical action from
- taking place between the copper and rubber
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What is the NEC for a rubber heatresistance
compound?
RHH
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Latex rubber is a high-grade compound consisting of what percentage of unmilled grainless rubber?
90%
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Plastic insulation is normally used for
what levels of voltage?
Medium to low
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When dealing with NEC type designators
for thermoplastics, the letter "W" stands for what type of insulation?
Moisture-resistant
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What is the common name for woven
covers?
Loom
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What percentage of tin is used in alloylead
sheathing?
2%
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Why is the use of asbestos being
discontinued as an insulating material in
the Navy?
It poses a health hazard to personnel
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What happens to asbestos insulationwhen it gets wet?
It becomes a conductor
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What insulating materials are best suitedfor use with high voltage?
Varnished cambric and oil impregnated paper
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What is the common name for enamel insulated wire?
Magnet wire
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What are the basic requirements for a splice or terminal connection?
To be mechanically and electrically effective
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The preferred method for removing
insulation from most types of insulated
wire is by using what tool?
Wire stripper
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When a Western Union splice is used to
connect two wires, why should the
twisted ends of the wires be pressed
down as close as possible to the straight
portion of the wire?
To prevent the wires from puncturing the tape covering
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When multiconductor cables are spliced,
why are the splices staggered?
To increase the strength of the individual splices
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When is a rattail joint normally used?
When a branch circuit is required and a junction box is used to join conduit
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If a fluorescent light is to be attached to a
branch circuit, which of the following
splices should normally be used?
Fixture joint
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When is a knotted tap joint normally used?
When a branch circuit is joined to a continuous wire (main wire)
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Which of the following splices is NOT butted?
Knotted tap joint
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Why is friction tape used over a splice?
To provide a protective covering over the rubber tape
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When noninsulated splices and terminal
lugs are insulated, what types of insulation are most commonly used?
Spaghetti and heat-shrinkable tubing
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When heat-shrinkable tubing is used, what is the maximum temperature to which the wire should be subjected?
300ºF
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When a large aluminum terminal lug or splice is installed, why is it NOT necessary to clean the aluminum wire?
The wire is cleaned by the abrasive compound in the lug or splice
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When aluminum terminals lugs or splices are installed, which of the following tools is generally recommended for use?
Power crimping tool
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Color codes are used on preinsulated terminal lugs and splices to indicate whatinformation?
The wire sizes on which they are to be used
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