Lesson 1: Building Wire Construction and Insulation Properties Flashcards
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.
utilization / effects
_______ 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 ________
Heat / electrical insulation
Conductors are assigned a ________ ampacity that reflects the insulation’s ability to handle and dissipate heat under _______ conditions.
specific / varying
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 ____.
- bare
- covered
- insulated
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
identified / recognized
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.
of use / life
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 ____.
310.10(C)(2)
The specific insulation types listed for use in wet locations contain the letter ____ in the type designator.
W
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.
60°C, 75°C, and 90°C / maximum
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.
ambient / internal
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.
conductivity / ampacity
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.
vertical raceways / shorter
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.
True
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.
assemblies
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.
True
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.
conductivity
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.
joint compounds
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.
identified
Manufacturers provide ____ specifications for terminations. The termination should be tightened to those specifications to ensure that the connection is electrically sound.
torquing
Copper-clad conductors are constructed using a minimum of ____ copper, which is bonded metallurgically to the aluminum.
10%
Solid conductors are constructed of a single piece of wire (strand). Stranded conductors are constructed of multiple wire (strands).
True
Chapter 9, Table ____ of the NEC lists conductor properties.
8
Maximum Temperature Ratings:
RHW = XHHW (wet) = MTW = TFE = UF = XHHW (dry) = THWN-2 =
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
In Table 8, Chapter 9 of the NEC, Conductors are listed from size #___, the smallest, to #___, the largest.
18 AWG / 2,000 kcmil
A circular mil (CM) is the area of a circle with a diameter of _____.
one mil
As the diameter of the wire increases, the AWG number ____, and the resistance of the conductor ____.
decreases / decreases
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.
specific resistance
The K of a material is defined as the resistance of the wire made from that material which is ____ long, and ____ in diameter.
1 foot / 1 mil
What happens to the resistance of most conductors as the temperature increases?
it increases
The K factor of a copper conductor at 68° is ____.
10.4
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
MTW = Machine tool wire FCC = Flat conductor AC = Armored MI = Mineral insulated NM = Nonmetallic-sheathed THW = Thermoplastic UF = Underground feeder SE = Service entrance cable
What is the difference between insulation types THW and THWN?
THWN has a nylon jacket
Conductors, type SIS, for switchboard wiring, have a maximum operating temperature of ____.
194°F
THW wire is available in sizes from ___ to ___.
14 AWG / 2,000 kcmil
Indicate which two of the following cable types are allowed for use in wet locations:
I. RHH
II. RHW
III. RHW-2
IV. XHH
RHW & RHW-2
Type XHHW conductors are listed for use in ____ location(s).
all of the above
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.
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