5-1) Aircraft Wiring

Question 1

What are some characteristics of aircraft wiring?

Answer 1

lighter weight, corrosion resistant, consistent construction, don’t product dangerous fumes when burned, better able to withstand vibration/motion without breaking

Question 2

What types of wires are used on cars vs. aircraft?

Answer 2

Cars and trailers typically use solid core wire. Aircraft typically use stranded core wire, which accept solder and crimp better.

Question 2

What types of wires are used on cars vs. aircraft?

Answer 2

Cars and trailers typically use solid core wire. Aircraft typically use stranded core wire, which accept solder and crimp better.

Question 3

What are the two best metal conductors?

Answer 3

Gold and silver

Question 4

What are the two best insulators?

Answer 4

Neon and helium

Question 5

Why do aircraft use stranded copper wire?

Answer 5

flexibility and resistance to vibration damage

Question 6

Why aren’t solid core wires used in aircraft?

Answer 6

They are susceptible to work hardening from movement and vibration that can cause cracking and stress fractures.

Question 7

What two quantities of strands in an aircraft wire are typically used?

Answer 7

7-strand and 19-strand

Question 8

What process to aircraft wires undergo to prevent oxidation and promote solderability?

Answer 8

Coating / pre-tinning with a protective coating

Question 9

How are coating materials rated?

Answer 9

According to their ability to withstand heat

Question 10

What is the key source of heat in question that the wire needs protection against?

Answer 10

Heat generated by flow of current in the wire, not by heat around the wire in the aircraft

Question 10

What is the key source of heat in question that the wire needs protection against?

Answer 10

Heat generated by flow of current in the wire, not by heat around the wire in the aircraft

Question 11

What temperature can tin-lead coating protect up to?

Answer 11

105°C

Question 12

What temperature can silver coating protect up to?

Answer 12

200°C

Question 13

What temperature range can nickel coating protect up to?

Answer 13

200-260°C

Question 14

What atomic properties do good insulators have?

Answer 14

They have more than 4 valance electrons. Insulators will not accept the extra electrons from current flow easily, therefore they are considered to have high resistance.

Question 14

What atomic properties do good insulators have?

Answer 14

They have more than 4 valance electrons. Insulators will not accept the extra electrons from current flow easily, therefore they are considered to have high resistance.

Question 15

What are general physical properties of insulation material?

Answer 15

operating temperature, insulation resistance, abrasion resistance, chemical resistance, strength

Question 16

What is a particular kind of wire insulation that was a total failure that technicians needs to be aware of?

Answer 16

Kapton

Question 17

What hazards does Kapton insulation pose?

Answer 17

Does not age well. Prone to extreme arcing and flashover. Recognized by its woven cover and metallic shield.

Question 18

What kind of insulated wire is this?

Answer 18

Kapton

Question 19

Under what circumstances can Kapton insulated wire be used even though its dangers are well known?

Answer 19

Manufacturer requires its use.

Question 20

Why do some wires/cables come with shielding?

Answer 20

Shielding is for protection from radio frequency interference (RFI) both from the wire itself and from outside sources getting into the wire.

Question 21

Does wire shielding totally nullify electromagnetic interference?

Answer 21

No, but it can redirect that energy into the ground to minimize the introduction of noice/interference into the wire

Question 22

What are coaxial cables designed to do?

Answer 22

They are designed to pass on high-frequency signals from a source to an antenna.

Question 23

What is the typical impedance of coaxial cable on an aircraft?

Answer 23

50Ω

Question 24

What makes aluminum wire desirable for some aircraft applications?

Answer 24

Lighter weight than copper wire

Question 25

What is the minimum wire gauge size for aluminum wire in an aircraft?

Answer 25

6AWH

Question 26

What precautions must be made when using aluminum wiring?

Answer 26

Aluminum wire is more susceptible to work hardening than copper wire. Terminations must be made for the aluminum wire to prevent galvanic corrosion that would be present when two dissimilar metals are attached. Hardware must be compatible to avoid electronic corrosion.

Question 27

What standard is used to specify wire diameters?

Answer 27

American Wire Gauge (AWG)

Question 28

What is the proportional relationship between wire diameter and wire gauge?

Answer 28

Wire diameter doubles (or halves) for every 3 wire gauge sizes.

Question 29

What is the diameter of #20 AWG wire?

Answer 29

0.032 inches

Question 30

What is the diameter of #0 AWG wire?

Answer 30

0.325 inches

Question 31

What unit is used to specify a wire's cross-sectional area?

Answer 31

Circular mil area

Question 32

How is circular mil area calculated?

Answer 32

Wire diameter (in inches) is squared Example: #20 AWG is 0.032" diamater 0.032²=1024 circular mils

Question 33

What are the characteristics of MIL-W-5086 Type I wire?

Answer 33

Type I is an unshielded aircraft wire. MIL-spec wire is constructed of a stranded tinned copper conductor, white polyvinyl chloride insulation, and a clear nylon outer jacket. MIL-spec wire may be used in electronic or electrical applications.

Question 34

What are the characteristics of MIL-W-5086 Type II wire?

Answer 34

Also an unshielded aircraft wire. #22 AWG through #12 AWG are constructed of stranded tinned copper conductor with a white PVC insulation and a white class yarn braid. MIL-spec wire has a clear nylon outer jacket. Gauges #10 AWG through #0000 AWG are constructed of stranded tinned copper conductor with a white PVC insulation and a white class yarn braid. Wire has a flame retardant nylon lacquered glass with yarn braid overall. MIL-W-5086 Type II may be used as airframe wire at temperatures within the range of -55°C to +105°C.

Question 35

What is the voltage rating for MIL-spec wire?

Answer 35

600 volts

Question 36

What are common physical properties for both Type I and II MIL-W-5086 wire?

Answer 36

Resistant to: water, aircraft fuels, hydraulic fluids, oils, Skydrol (fire resistant aviation hydraulic fluid), dilute acids, ethylene glycol, alkalis, alcohol, fungus, abrasion.

Question 37

Under was extreme conditions may MIL-spec wires be used?

Answer 37

Any application where it may be exposed to abrasion, high impact loads or chemical abuse

Question 37

Under was extreme conditions may MIL-spec wires be used?

Answer 37

Any application where it may be exposed to abrasion, high impact loads or chemical abuse

Question 38

Explain the steps to take to use this wire selection chart.

Answer 38

1. Select column for circuit voltage on the left 2. Select the length of wire from the correct circuit voltage column 3. Look to the right and find the correct diagonal line corresponding to the current (amperes) to be used 4. Find the intersection of that current rating with the wire size from the X-axis 5. Based on the use “Continuous Rating-Cables in a Bundle,” “Continuous Rating-Wire in Free Air,” “Intermittent Rating” etc., make sure that the point of intersection of length, amperes and wire gauge is ABOVE the selected curve for the wire's use. 6. If the point of intersection is not ABOVE the curve, move up in wire gauge size (larger wire, lower AWG number to the right). 1. If the determined point for length and current falls between two wire gauge sizes, always move up to the next larger wire size.