Electrical Cables & Connectors
Aircraft wire and AWG, circuit protection sized to the wire, crimped terminations, connectors and screening.
Electrical cables & connectors, summary notes
- Aircraft wire uses a copper (sometimes copper-alloy) conductor, often tinned, silver- or nickel-plated for corrosion and temperature resistance, with high-performance insulation (PTFE, ETFE/Tefzel, modern low-smoke types). Size is given in American Wire Gauge (AWG).
- AWG runs backwards: a SMALLER AWG number means a THICKER conductor that carries more current. Wire is selected for current-carrying capacity (ampacity, derated in bundles and at altitude), allowable voltage drop and mechanical strength.
- Circuit protection (circuit breaker or fuse) is sized to protect the WIRE, not the equipment, it must open before the wire overheats. This is why re-rating a breaker to stop nuisance trips is not permitted.
- Terminations: crimped terminals and splices made with a calibrated crimp tool and the correct barrel are preferred where there is vibration; soldered joints are avoided in high-vibration/high-heat areas. Connectors (circular MS bayonet/threaded, rack-and-panel, coaxial, fibre-optic) are keyed to prevent mis-mating and use pin/socket contacts with a backshell and strain relief.
- Screening/shielding and bonding control EMI; coaxial cable (with its characteristic impedance) feeds antennas and RF. Route and clamp wiring to avoid chafing, keep drip loops, and separate power from signal runs.
- ⚠ Exam trap: the circuit breaker/fuse protects the WIRE and is sized to the wire, not the load; and a LOWER AWG number is a THICKER wire (more current), the numbering is reversed. Crimped joints are preferred to soldered where vibration is present.
A repeatedly tripping circuit breaker is 'fixed' by fitting a higher-rated breaker so it stops nuisance-tripping. Why is this dangerous?
The breaker is sized to protect the wire from overheating, not to suit the load. A higher-rated breaker lets more current flow through a wire that may not be rated for it, so a fault or overload can now overheat the insulation and start a fire before the breaker opens. The correct action is to find why it trips (short, overload, chafe) and rectify it, keeping the original wire-matched rating.
Cables & connectors concept map
Electrical Cables & Connectors
Electrical cables & connectors quiz
Electrical Cables & Connectors, quiz
1. In American Wire Gauge (AWG), a smaller number means a:
Thicker conductor carrying more currentThinner conductorHigher voltage rating only2. A circuit breaker or fuse is sized to protect the:
Wire, so it opens before the wire overheatsEquipment, regardless of the wireConnector only3. Fitting a higher-rated breaker to stop nuisance trips is:
Unsafe, the wire may overheat before it opensGood practiceRequired by the AMM4. Aircraft conductors are usually:
Copper, often plated for corrosion/temperatureSolid steelAluminium only, unplated5. Where vibration is present, the preferred joint is:
A properly crimped terminalA soldered jointA twisted pair with tape6. Aircraft connectors are keyed mainly to:
Prevent mis-mating (wrong connector/orientation)Add weightImprove the colour scheme7. Coaxial cable is used mainly for:
RF/antenna feeds with a defined characteristic impedanceHigh-current power feedersControl cables8. Wire ampacity (current-carrying capacity) must be:
Derated in bundles and at altitudeIncreased in bundlesIgnored below 28 V