Massoud Sadeghi: massoud.sadeghi@faa.gov FAA Aging Systems Program Manager Transport Airplane Directorate; ANM-117 (425)227-2117 Brett Portwood: brett.portwood@faa.gov FAA Technical Specialist for Safety and integration Los Angeles ACO; ANM-130L (562)627-5350 1
Topic Outline Electrical load determination Breaker and wire sizing/selection Routing/clamping/bend radii Splicing Wire terminals Grounding and bonding Wire marking Connectors and conduits Wire insulation properties 2
Electrical Load Determination Load analysis New or additional electrical devices should not be installed without an electrical load analysis (AC 43.13-1b) 3
AC 43.13-1b Topic Outline, cont. Electrical load determination Breaker and wire sizing/selection Routing/clamping/bend radii Splicing Wire terminals Grounding and bonding Wire marking Connectors and conduits Wire insulation properties 4
Circuit Breaker Protection A circuit breaker must always open before any component downstream can overheat and generate smoke or fire. (AC 43.13-1b, para. 11-48) Circuit breakers are designed as circuit protection for the wire, not for protection of black boxes or components... (AC 43.13-1b, para. 11-51) 5
Circuit Breaker Protection, cont. Use of a circuit breaker as a switch is not recommended Repeated opening and closing of contacts can lead to damage and premature failure of circuit breakers Most circuit breaker failures are latent 6
Wire Selection Size wires so they: Have sufficient mechanical strength Do not exceed allowable voltage drop levels Are protected by circuit protection devices Meet circuit current-carrying requirements 7
Wire Selection, cont. Mechanical strength of wire sizes less than #20 Do not use wire with less than 19 strands Provide additional support at terminations Should not be used when subject to excessive vibration, repeated bending, or frequent disconnection (ref. para. 11-66(a), page 11-21) 8
AC 43.13-1b Topic Outline, cont. Electrical load determination Breaker and wire sizing/selection Routing/clamping/bend radii Splicing Wire terminals Grounding and bonding Wire marking Connectors and conduits Wire insulation properties 9
Wiring Routing Eliminate potential for chafing against structure or other components Position to eliminate/minimize use as handhold or support Minimize exposure to damage by maintenance crews or shifting cargo Avoid battery electrolytes or other corrosive fluids 10
Wire Riding on Structure Power cables riding on structure can cause damage to the power cables A B 11
Wires Riding on Other Wires B Wire bundles that cross should be secured together to avoid chafing 12
Wires Riding on Other Wires Wire bundles that cross should be secured Btogether as shown 13
Wires Riding on Lightening Hole If the wire is not supported and grommet is too short, then there is wire bundle chafing 14
Wires Properly Installed on Lightening Hole Wires supported and proper grommet installation 15
Wiring as a Handhold 16
Wiring Routing, cont. Protect wires in wheel wells and other exposed areas Route wires above fluid lines, if practicable Use drip loops to control fluids or condensed moisture Keep slack to allow maintenance and prevent mechanical strain 17
Wire Bundles Above Fluid Lines Path of exposed end Broken wire shall not make contact with fluid line 18
Wires improperly tied, riding on hydraulic lines, contaminated with caustic fluid 19
Y Type Wire Bundle Breakouts Figure 8 loop may be located before or after tail of Y Before After Wire bundle breakout Wire bundles Head of strap shall not be located in this area or touching anything to cause chafing Plastic mechanical strapping 20
T Type Wire Bundle Breakouts Head of strap shall not be located in this area or touching anything to cause chafing Wire bundle breakout Wire bundle Plastic mechanical strapping 21
Complex Type Wire Bundle Breakouts 22
Stand-offs Use stand-offs to maintain clearance between wires and structure Employing tape or tubing is generally not acceptable as an alternative Exception: Exception: Where impossible to install off-angle clamps to maintain wiring separation in holes, bulkheads, floors, etc. 23
Exercise: Using Stand-offs A B 24
Bundle riding on structure 25
Wire bundle riding on control cable 26
Clamping Support wires by suitable clamps, grommets, or other devices at intervals of not more that 24 inches Supporting devices should be of suitable size and type with wire and/or cables held securely in place without damage to wire or wire insulation 27
Clamps Wire bundles should be snug in clamp (no movement) Cable not able to move axially RF cables: Do Not Crush Mount clamps with attachment hardware on top Tying not to be used as alternative to clamping 28
Example of Correct Cable Slack Appropriate slack 29
Clamp Distortion Correct clamp position Incorrect clamp position Distortion of rubber on clamp is NOT acceptable 30 WF2