Lesson 1: Building Wire Construction and Insulation Properties

Question 1

The conductors that carry the current to electrical devices and ________ equipment are the heart of all electrical systems. There are associated _________ whenever current flows through a conductor.

Answer 1

utilization / effects

Question 2

_______ associated with the flow of current in a conductor is one of the most significant factors to be considered in designing electrical systems. The conductor’s rating is dependent upon its type of ________

Answer 2

Heat / electrical insulation

Question 3

Conductors are assigned a ________ ampacity that reflects the insulation’s ability to handle and dissipate heat under _______ conditions.

Answer 3

specific / varying

Question 4

Conductors used in electrical systems are often defined by the material, if any, that is used to encase the actual electrical conductor. Three classifications exist for electrical conductors; they are ___ , ___ , and ____.

Answer 4

• bare
• covered
• insulated

Question 5

Insulated conductors are the most common conductors installed in electrical systems. These conductors are constructed with a material that been _____ by the NEC as a _____ electrical insulation

Answer 5

identified / recognized

Question 6

There are numerous types of electrical insulations. The type of insulation selected depends upon the condition ____ of the conductor. For example, a conductor for direct burial requires an insulation that is suitable for the conditions it is likely to be exposed to over the ____ of the conductor.

Answer 6

of use / life

Question 7

When conductors are installed in wet locations, the insulated conductors and cables shall be either moisture-impervious metal-sheathed, be of a type listed for use in wet locations, or be of one of the types contained in ____.

Answer 7

310.10(C)(2)

Question 8

The specific insulation types listed for use in wet locations contain the letter ____ in the type designator.

Answer 8

W

Question 9

An important consideration in selecting conductor insulation type is the temperature limitations of the insulation. The three basic insulation temperature ratings listed for the conductors used for general wiring are ____. The ____ temperature that the conductor is exposed to along its entire length shall be used when determining the temperature rating of a conductor.

Answer 9

60°C, 75°C, and 90°C / maximum

Question 10

The common factors that can contribute to conductor insulation degradation because of excessive operating temperature are the ____ temperature in which the conductor insulation shall operate, the ____ heat created in the conductor as a result of current flow, the dissipation rate of the heat into the surrounding environment, and the heat generated by adjacent current-carrying conductors.

Answer 10

ambient / internal

Question 11

The two most common materials used for construction of electrical conductors are copper and aluminum. Copper has excellent ____ and therefore has a higher allowable ____ than a comparable aluminum conductor.

Answer 11

conductivity / ampacity

Question 12

A factor to consider when installing electrical conductors is the weight of the conductors. Copper conductors installed in ______ require support at _____ intervals than are required for aluminum conductors.

Answer 12

vertical raceways / shorter

Question 13

Copper conductors are available as hard-drawn, medium-hard-drawn, and soft-drawn. Hard-drawn copper has the greatest strength, but is difficult to work with. Because of the difficulty in shaping hard-drawn copper, its uses are limited.

Answer 13

True

Question 14

Soft-drawn copper is easy to work with and can be installed in many different types of raceways and cable ____. Most general building wires used in electrical distribution systems are made of soft-drawn copper.

Answer 14

assemblies

Question 15

Aluminum conductors have been used extensively for a number of years in the utility distribution and transmission field. More recently, aluminum conductors have found increasing applications in building electrical distribution systems.

Answer 15

True

Question 16

Despite the fact that aluminum is not as good a conductor as copper, its reduced ____ is compensated by the considerable cost savings in using aluminum conductors.

Answer 16

conductivity

Question 17

Because the surface of aluminum conductors oxidizes readily, terminations are generally made with the aid of ____ designed to prevent the oxide from re-forming in the installation process.

Answer 17

joint compounds

Question 18

Conductors of different materials, like copper and aluminum, should not be terminated in a manner that causes the dissimilar metals to come in direct contact with each other unless the termination or splicing device is _____ for such use.

Answer 18

identified

Question 19

Manufacturers provide ____ specifications for terminations. The termination should be tightened to those specifications to ensure that the connection is electrically sound.

Answer 19

torquing

Question 20

Copper-clad conductors are constructed using a minimum of ____ copper, which is bonded metallurgically to the aluminum.

Answer 20

10%

Question 21

Solid conductors are constructed of a single piece of wire (strand). Stranded conductors are constructed of multiple wire (strands).

Answer 21

True

Question 22

Chapter 9, Table ____ of the NEC lists conductor properties.

Answer 22

8

Question 23

Maximum Temperature Ratings:

RHW =     
XHHW (wet) =     
MTW =     
TFE =     
UF =     
XHHW (dry) =     
THWN-2 =

Answer 23

RHW =  75°C
XHHW (wet) =  75°C
MTW =  60°C and 90°C
TFE =  250°C    
UF = 60°C and 75°C    
XHHW (dry) =  90°C    
THWN-2 =  90°C

Question 24

In Table 8, Chapter 9 of the NEC, Conductors are listed from size #___, the smallest, to #___, the largest.

Answer 24

18 AWG / 2,000 kcmil

Question 25

A circular mil (CM) is the area of a circle with a diameter of _____.

Answer 25

one mil

Question 26

As the diameter of the wire increases, the AWG number ____, and the resistance of the conductor ____.

Answer 26

decreases / decreases

Question 27

Every electrical conducting material has a different resistance to current flow. In order to perform calculations to determine circuit resistance, you must know the _____ (abbreviated K) of a material.

Answer 27

specific resistance

Question 28

The K of a material is defined as the resistance of the wire made from that material which is ____ long, and ____ in diameter.

Answer 28

1 foot / 1 mil

Question 29

What happens to the resistance of most conductors as the temperature increases?

Answer 29

it increases

Question 30

The K factor of a copper conductor at 68° is ____.

Answer 30

10.4

Question 31

Cable Types:

I. Armored
II. Flat conductor
III. Mineral insulated
IV. Machine tool wire
V. Nonmetallic-sheathed
VI. Underground feeder
VII. Service entrance cable
VIII. Thermoplastic

Answer 31

MTW = Machine tool wire
FCC = Flat conductor
AC = Armored
MI = Mineral insulated
NM = Nonmetallic-sheathed
THW = Thermoplastic
UF = Underground feeder
SE = Service entrance cable

Question 32

What is the difference between insulation types THW and THWN?

Answer 32

THWN has a nylon jacket

Question 33

Conductors, type SIS, for switchboard wiring, have a maximum operating temperature of ____.

Answer 33

194°F

Question 34

THW wire is available in sizes from ___ to ___.

Answer 34

14 AWG / 2,000 kcmil

Question 35

Indicate which two of the following cable types are allowed for use in wet locations:

I. RHH
II. RHW
III. RHW-2
IV. XHH

Answer 35

RHW & RHW-2

Question 36

Type XHHW conductors are listed for use in ____ location(s).

Answer 36

all of the above

Question 37

Listed wire types designated with the suffix ___ shall be permitted to be used at a continuous 90°C operating temperature in both wet and dry locations.

Answer 37

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