Neets Module 4 Assignment 1
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State the reason for the establishment of a "unit size" for conductors.
To allow comparisons between conductors of different sizes and resistance.
Calculate the diameter in MILS of a conductor that has a diameter of 0.375 inch.
375 mils (move the decimal three places to the right).
Define a mil-foot.
A circular conductor with a diameter of 1 mil and a length of 1 foot.
Define a square mil as it relates to a square conductor.
The cross-sectional area of a square conductor with a side of 1 mil.
Define a circular mil.
The cross-sectional area of a circular conductor with a diameter of 1 mil.
What is the circular mil area of a 19-strand conductor if each strand is 0.004 inch?
Circular mil area (CMA) = D2 (in mils) � number of strands 0.0004 inch = 4 mils (CMA) = 4 2 � 19 (strands)(CMA) = 16 � 19 = 304 mils.
Define specific resistance.
The resistance of a unit volume of a substance.
List the three factors used to calculate resistance of a particular conductor in ohms.
- Cross-sectional area
- Specific resistance of a unit volume of the substance from which the conductor is made.
When using an American Standard Wire Gauge to determine the size of a wire, where should you place the wire in the gauge to get the correct measurement?
In the parallel walled slot not the circular area.
List the four factors you should use to select wire for a specified current rating.
- Conductor size
- The material it is made of the location of the wire in a circuit
- The type of insulation used.
What are three types of nonmetallic insulating materials that can be used in a high-temperature environments?
- Extruded polytetrafluoroethylene
- Silicone rubber.
State why it is important for you to consider the ambient (surrounding) temperature of a conductor when selecting wire size.
The heat surrounding the conductor is an important part of total conductor heating.
State two advantages of using aluminum wire for carrying electricity over long distances.
- It is light
- Reduces corona.
State four advantages of copper over aluminum as a conductor.
It has higher conductivity, it is more ductile, it has relatively high tensile strength, and it can be easily soldered.
Define the temperature coefficient of resistance.
The amount of increase in the resistance of a 1-ohm sample of the conductor per degree of temperature rise above 0� C
What happens to the resistance of copper when it is heated?
Compare the resistance of a conductor to that of an insulator.
Conductors have a very low resistance and insulators have a resistance that is so great that, for all practical purposes, they are nonconductors.
State two fundamental properties of insulating materials.
Insulation resistance and dielectric strength.
Define insulation resistance.
The resistance to current leakage through the insulation.
Define dielectric strength.
The ability of the insulation material to withstand potential difference.
How is the dielectric strength of an insulator determined?
By raising the voltage on a test sample until it breaks down.
What is the purpose of coating a copper conductor with tin when rubber insulation is used?
To prevent the rubber insulation from deteriorating due to chemical action.
What safety precaution should you take when working with extruded polytetrafluoroethylene insulated wiring?
Avoid breathing the vapors when the insulation is heated.
State the reasons that the Navy is getting away from the use of asbestos insulation.
Breathing asbestos fibers can cause lung disease and/or cancer
State what happens to the insulating characteristics of asbestos when it gets wet.
It will become a conductor.
What are the most common insulators used for extremely high voltages?
Varnished cambric and oil-impregnated paper.
What is the common name for enamel-insulated wire?
If a cable is installed where it receives rough treatment, what should be added?
How many categories of nonmetallic protective coverings are there?
What is the most common type of nonmetallic material used to protect wires and cables?
What are the most common types of fibrous tape?
Rubber-filled cloth tape and a combination of cotton cloth and rubber.
What materials are commonly used as cushions between cable insulation and metallic armor?
Jute and Asphalt coverings.
What are the two types of metallic protection?
Sheath and armor
What are the three types of lead-sheathed cables?
- Alloy lead
- Pure lead
- Reinforced lead.
What are the three examples of metallic armor cable that were discussed?
- Wire braid
- Steel tape
- Wire armor
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