Worksheet 53-Aircraft Wiring Flashcards
What US standards must aircraft wire meet to be eligible for installation in aircraft?
Aircraft wiring must be FAA specifications and be installed and maintained in accordance with FAA approved processes. The FAA standards may be referenced industry standards along with MIL-spec standards or could meet original specifications during aircraft certification.
What are the general physical characteristics of aircraft wire that make it different from automotive or industrial wire?
Aircraft wire is designed to be lightweight, corrosion resistant, uniform construction, meet flammability standards (doesn’t produce dangerous fumes when burned), and can withstand motion and flexing without breaking.
What are the general forms or types of aircraft wire?
Forms of wires are single wires, not used in aircraft except for thermocouples, etc. and multiple conductor wire that form cables when they are run concurrently with additional conductors they are termed wire bundles. The properties of these conductors and cables accept soldering and crimping connection well.
Name two of the best conductive materials and what in their construction makes them the best? Name two of the best insulating materials and explain what makes them the best.
Two of the best conductors are gold and silver because valance orbits are nearly empty and contain only 1 electron each.
Two of the best insulators are neon and helium because their valence orbits are full.
What are the two best insulating materials and what is the unique atomic structure is responsible for these insulating characteristics?
The most common aircraft wire is stranded copper to achieve maximum flexibility. The wire is 7 or 19 strands based on the gauge of the wire. The wire is coated to prevent oxidation and promote solder-ability. The coating materials are rated by their ability to withstand the heat generated by the circuit. Tin-lead is rated to 105C, silver is rated to 200C, and nickel is rated to 260C.
Identify the makeup and construction of the most common aircraft wire including the wire coatings and temperature ratings.
Insulators are materials that have more than four valance electrons that inhibit electron flow. Insulator material is governed by cost, operating temperature, insulation resistance, chemical resistance and strength.
Identify the characteristics of an insulator that inhibits the flow of electrons.
Shielding is used to protect the wire from radio frequency interference (RFI) both from the wire itself and from outside sources. Shielding does not eliminate RFI but it does direct the energy to ground.
Identify the causes of radio frequency interference (RFI) and how it is dealt with in aircraft construction.
Coaxial cables have some shielding properties as part of its construction. The primary concern is to maintain precise dimensions between the conductor and the outer shield to establish precise impedance values. Typically, aircraft coax cables are designed for 50Ω impedance.
What is the minimum size of aluminum wire that can be used in aircraft and what consideration must be made for aluminum wire connections?
Aluminum wire is approves for some aircraft applications where weight reduction is necessary but there are several considerations necessary for its use. The minimum aluminum wire size is #6AWG or larger and special connections are necessary to prevent galvanic corrosion and special hardware is needed to prevent electrolytic corrosion.
What is the industry standard used to specify wire diameters and what is the incremental size number that will either double or half the size of the wire?
American Wire Gauge (AWG) protocols are used to specify wire diameters. The numbers assigned are inverse to the actual diameters. For example, #20AWG wire is 0.032” in diameter and #0 AWG wire is 0.325” in diameter.
What is the purpose of the wire usage chart and what document can a technician to refer to to find this chart?
The wire usage chart is designed for technicians and installers to select the correct wire for a specific environment. The chart is published in the FAA Advisory Circular AC 43-13-1B and has complete instructions for its use.
Using the chart find the minimum wire size needed for a voltage of 28VDC, for a length of 40’, with a load of 5A of wire in a conduit.
20AWG
Using the chart, find the minimum wire size needed for a voltage of 115VAC with a length of 96’ with a load of 30A in free air.
12AWG
Using the chart, find the minimum wire size needed for a 14VDC system with a length of 10’ and a load of 10A in free air.
18AWG
