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Participant Guide
Aircraft Wiring PracticesAn Interactive Training and Self-Study Course (25827)
Presented by
Brett PortwoodFAA Technical Specialist, Safety and Integration
Massoud SadeghiAging Systems Program Manager
Federal Aviation AdministrationMarch 28 & 29, 2001
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Table of Contents
INTRODUCTORY MATERIALS
Course Orientation .......................................................................................... 2About This Course................................................................................... 2
Who Is the Target Audience?.................................................................. 2
Who Are the Instructors? ........................................................................ 2
What Will You Learn? ............................................................................ 14
How Will This Course Help You On-the-Job?....................................... 14
Self-Assessment ................................................................................................ 6
Pre- & Post-Course Self-Assessment Questions..................................... 6
COURSE MATERIALS
Background ...................................................................................................... 10
Introduction ............................................................................................. 10
Aging Systems Program.......................................................................... 11
ASTRAC findings ................................................................................... 15
Accident service history .......................................................................... 19
Aging wiring overview..................................................................................... 25
Introduction ............................................................................................. 25Causes of wiring degradation.................................................................. 26
Current FAA guidance.................................................................................... 28
Overview ................................................................................................. 31
Advisory Circular 43.13-1b ............................................................................ 31
Topics to be addressed ............................................................................ 31
Electrical load determination .................................................................. 31
Breaker and wire sizing/selection ........................................................... 33
Exercise 1: Circuit breaker size calculation...................................... 35Figure 11-2 from 43.13-1b................................................................. 39
Exercise 2: Wire size calculation...................................................... 42
Figure 11-3 from 43.13-1b................................................................. 44
Figure 11-4a from 43.13-1b ............................................................... 45
Figure 11-6 from 43.13-1b................................................................. 46
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Figure 11-5 from 43.13-1b................................................................. 47
Exercise 3: Wire harness current capacity ........................................ 50
Routing, clamping, and bend radii .......................................................... 53
Exercise 4: Circuit breaker size calculation...................................... 75
Wire replacement and splicing ................................................................ 81
Wire terminals ......................................................................................... 88
Exercise 5: Terminal build up...........................................................102
Grounding and bonding...........................................................................103
Wire marking...........................................................................................109
Connectors and conduits .........................................................................112
Exercise 6: Pin arrangement...............................................................115
Exercise 7: Bend radius......................................................................123
Wire insulation properties .......................................................................124
AC 25-16 requirements ...................................................................................129
Electrical fault and fire detection ............................................................129
Circuit protection devices........................................................................130
Wire separation................................................................................................132
Introduction .............................................................................................132
Wire separation: 25.1309(b)...................................................................133
Wire separation: 25.903(d).....................................................................135
Wire separation: 25.1353(b)...................................................................136
Wire separation: 25.631 .........................................................................137
Post-TC wire separation ..........................................................................138
Instructions for Continued Airworthiness ....................................................139
General information/overview ................................................................139
Cleaning requirements/practices .............................................................141
Wiring general visual inspections (WGVI).............................................142
Non-destructive wire testing (NDT) methods.........................................145Preemptive wire splice repair and/or wire replacement..........................145
Wiring installation certification .....................................................................149
Introduction .............................................................................................149
Wiring diagrams......................................................................................150
Actual wiring diagram........................................................................152
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Wiring installation drawings ...................................................................153
Actual wire routing drawing ..............................................................156
Actual wiring installation and sub assemblies ...................................157
Actual wiring installation drawing parts list ......................................158
Questions and wrap-up ...................................................................................159
Appendices........................................................................................................160
AC 43.13-1b, Chapter 11
AC 25-16
Course Evaluation Forms
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Aircraft Wiring Practices
Introductory Materials
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Course Orientation
Aircraft Wiring Practices is designed to update
participants about a wide variety of wiring issues.Through the two-day (four hours per day) Interactive
Training format,Brett Portwood, FAA Technical
Specialist, Safety and Integration,andMassoud Sadeghi,
Aging Systems Program Manager, will provide you with
the basic concepts ofAircraft Wiring Practices, a course
that provides an overview of the aging wiring history, an
update on current FAA guidance, detailed information on
AC 43.13-1b, AC 25-16, wire separation, and
Instructions for Continued Airworthiness, and a reviewof what to look for on wiring diagrams and wiring
installation drawings.
This course is designed for new and experienced Systems
and Propulsion Transport Aircraft engineers who require
enough knowledge of wiring to be able to review data
submitted by manufacturers.
Brett Portwoodis the FAA Technical Specialist for
Safety and Integration. Brett has 11 years experience
with the FAA in certification of transport avionics
systems, including fly-by-wire flight guidance systems,
flight management systems, and electronic displays. As a
Technical Specialist, he provides expertise in safety
assessment methods and associated integration issues.
Brett is active in the FAAs Aging System Program,ATSRAC, and wiring installation and maintenance
practices. He assisted with the investigation (aircraft
wiring) of the MD-11 Swissair 111 accident. He worked
with Boeing to develop wiring practices workshops for
FAA certification engineers and inspectors. Brett also
was the FAA representative on the SAE S-18 System
About This
Course
Who Is the
Target
Audience?
Brett Portwood
Who Are the
Instructors?
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Safety Assessment commitee that authored ARP 4761,
Guidelines and Methods of Conducting the Safety
Assessment Process on Civil Airborne Systems and
Equipment.
Prior to joining the FAA, Brett spent 12 years performingfault/failure analyses for industry and the Navy nuclear
program.
Mr. Portwood has a BS degree in Physics from San
Diego State University and has published professional
papers on system safety assessment methods.
Massoud Sadeghi is the FAA Transport Aging SystemsProgram Manager responsible for implementing
improvements in the requirements of design, installation,
mainenance, repair, and certification processes for
airplane wiring. Massouds previous FAA
responsibilities include: SAE, ARAC, certification,
validations, and policy and rulemaking in the areas of
electrical systems, HIRF, and lightning.
Prior to the FAA, Massouds industry experience
included Boeing Military Airplanes (Wichita), re-engine,upgrading electrical systems, and rewiring military
airplanes (KC-135s); McDonnell Douglas, designing new
electrical systems for the new MD-90; and Boeing
(Seattle), designing new electrical systems for the new
777s. Before college, Massoud did electrical wiring of
commercial and residential buildings.
Mr. Sadeghi has taught college technical classes and
company classes on Modern Aircraft Electrical Systems.
He has both a BS and MS in Electrical Engineering from
the University of Missouri-Columbia.
Massoud Sadeghi
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After completing this course you will be able to
Apply the concepts/aspects of aging wiring.
Identify wiring factors used when approving wiring
diagrams. Identify the main purpose of reviewing wiring
installation drawings and the wiring factors used when
approving these installation drawings.
Describe the requirements for Instructions for
Continued Airworthiness as they relate to wiring.
The purpose of this course is to deliver a detailed
presentation of all aspects of aging wiring. It covers
applicable 14 CFRs, policy, and industry practices in the
area of wiring. It will introduce primary factors
associated with wire degradation. The course will also
include TC/STC data package requirements, wire
selection/protection, routing, clamping, splicing, and
termination practices, along with various examples,
pictures, mockups, videos, etc. The course includes
wiring maintenance concepts (e.g., cleans as you go),
including how to perform a wiring general visual
inspection.
Given appropriate wiring materials to review for
certification, after completing this course you should be
able to
Describe the major factors of wiring degradation and
list the characteristics of aging wiring.
Identify and use the current FAA wiring regulations
and guidance.
Determine if the circuit breakers, conductors, and
connectors are sized appropriately.
What Will You
Learn?
How Will This
Course Help
You On-the-
Job?
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Determine if the type of wiring protection is
appropriate for a given environment.
Determine if the number and type of clamps, the feed
throughs/pass throughs, and conduits selected are
appropriate.
Evaluate the routing of the wire to ensure it has been
done in an optimum manner to prevent damage.
Identify what wiring information has to be in the
Instructions for Continued Airworthiness.
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Self-Assessment
The instructor will ask you at the begining of the
presentation to respond to the following questions aboutaircraft wiring practices.
During the live broadcast, use the keypad to answer
these questions.
1. What are the critical factors in addition to vibration that impact
wiring degradation?
a. Moisture, heat, improper installation.
b. Improper installation, heat, length.c. Moisture, age, resistance.
d. Heat, age, length.
2. What is the minimum bend radius for unsupported wire?
a. 3 times the largest diameter of the wire or cable in a bundle.
b. 3 times the smallest diameter of the wire or cable in a
bundle.
c. 10 times the largest diameter of the wire or cable in a bundle.
d. 10 times the smallest diameter of the wire or cable in a
bundle.
3. AC 25-16 is about
a. electrical load analysis.
b. electrical fault and fire detection.
c. wire routing.
d. wire maintenance and repair.
Self-Assessment
Questions
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4. What is the primary function of the circuit breaker in an
aircraft?
a. To remove power from aircraft systems.
b. To protect aircraft equipment.c. To protect aircraft wiring.
d. To protect electrical power sources.
5. What is a key factor used in selecting wire?
a. Marking method.
b. Breaker size.
c. Elasticity.d. Voltage drop.
6. Wire current-carrying capacity decreases with altitude.
a. True.
b. False.
7. What is the primary purpose of conduits?
a. Facilitation of fluid drainage from wire bundles.
b. Ease of wire routing.
c. Protection of wire bundles against atmospheric pressure.
d. Mechanical protection of wires and cables.
8. During the build up of terminal studs, a cadmium-plated washer
isa. required for high vibration areas.
b. required for high temperature areas.
c. required when stacking dissimilar materials.
d. not required.
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9. To ensure proper integrity and health of an aircraft wiring
system, the Instructions for Continued Airworthiness must be
submitted for
a. aircraft with extended range operation within 60 days after
certification.
b. aircraft with extended range operation prior to certification.
c. all aircraft within 60 days after certification.
d. all aircraft prior to certification.
10. In addition to reviewing the wire installation drawings, an FAA
engineer or designee should perform a first-of-a-model generalwiring compliance inspection.
a. True.
b. False.
11. When reviewing the wire installation drawing, ensure that
a. connector pin numbers are specified for all terminations.
b. wire routing is specified end to end.c. standard practices are referenced for all wire routing.
d. at least the safety-critical wire routing is clearly specified.
12. Check all items that should be submitted (as a minimum) as part
of the wiring installation data package.
a. Wiring separation diagram.
b. Wire installation drawing.
c. Wiring diagram.
d. Wiring repair manual.
e. Instructions for Continued Airworthiness.
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Aircraft Wiring Practices
Course Materials
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Version 1.0 1
Aircraft Wiring Practices
IBrett Portwood: [email protected]
FAA Technical Specialist, Safety and Integration
Los Angeles ACO; ANM-130L
(562)627-5350
IMassoud Sadeghi: [email protected]
Aging Systems Program Manager
Transport Airplane Directorate; ANM-114
(425)227-2117
I. Background
Version 1.0 2
Background
IWhy the need for wiring practices
training?
z Aging Systems Program
z Aging Transport Systems Rulemaking
Advisory Commit tee (ATSRAC)
z Accident Service History
A. Introduction
1. Historically, wiring was installed without much thought given to
the aging aspects:
a) Fit and forget.
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b)Unanticipated failure modes and their severity.
(1) Arc tracking.
(2) Arcing.
(3) Insulation flashover.
2. Maintenance programs often did not address these aging aspects.
Service history also indicates that Foreign Object Damage (FOD)
such as drill shavings, caustic liquids, etc. does cause wiring
degradation that can lead to wiring faults.
B. Aging Systems Program
Version 1.0 3
Aging Systems Program
I Instituted a comprehensive aging
non-structural systems program
z Research to identify and prio ritize
opportunities to enhance safety
z A data-driven program based on
inspections and service history reviewsz Multi-pronged solutions developed in
conjunction with aviation community
z Modeled after successfu l aging structures
program
1. Addresses a recommendation from the White House Commission
on Aviation Safety to add non-structural systems to the aging
aircraft program.
a) FAA using a data-driven approach to address safety concerns.
b)Data collected from research and development, various
inspections, service history review and surveys of industry.
c)Analysis of the data will result in revisions to maintenance
programs, training programs and improved design solutions
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for wire bundle and component installations. The goal is to
preclude accidents that may result from wire degradation.
Version 1.0 4
FAA Aging Transport Non-
Structural Systems Plan
IAir Transport Assoc. (ATA) s tudy team:
z Using lessons learned from TWA 800
and Swissair 111
z Addressing recommendations from
Gore Commission
z Collecting data from On-site evaluations
Meetings with PMIs, Airbus, and Boeing
Analysis of aging systems using NASDAC
data bases
2. Following the TWA 800 accident, the FAA initiated
investigations into fuel tank wiring. These investigations
revealed a need for a comprehensive review of all systems wiring.
Around this same time the White House Commission on AviationSafety and Security, or informally known as the Gore
Commission, recommended that the FAA, in cooperation with
airlines and manufacturers, expand the FAAs Aging Aircraft
Program to cover non-structural systems. The ongoing Swissair
111 accident investigation has provided additional focus on
wiring practices.
a) The FAA requested that ATA lead an effort to address aging
non-structural systems. ATA responded by forming the Aging
Systems Task Force (ASTF).
b)The FAA formed the Aging Non-Structural Systems Study
team. This team made detailed on-site evaluations of three
representative aging aircraft.
c)Based on the on-site evaluations, meetings with industry, and
analysis of data bases of service data, a plan was developed to
address our aging transport airplane systems.
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Version 1.0 5
FAA Aging Transport Non-
Structural Systems Plan, cont.
IStudy team, cont.
z Established ATSRAC to coordinate
aging systems initiatives with the FAA
z Incorporated the Air Transport
Associations (ATA) aging system task
force (ASTF) activities into ATSRAC
d)This plan called for the establishment of an Aging Transport
Systems Oversight Committee to coordinate the various aging
systems initiatives within the FAA. This task has been met
with the formulation of the Aging Transport Systems
Rulemaking Advisory Committee or also known as ATSRAC.
ATSRAC is a formal advisory committee to the Administrator
and holds public meetings every quarter.
Aging Systems Program
ATSRACATSRAC
Fleet sampling inspections
Service data review
Working group outputs
FAAFAAStudy team inspections
Inspection support
Service data review
Research and development
ProductsProducts
Corrective
actions
Inspection &
maintenance practice
improvements
Improved
design
practices
Improved
system data
reporting
Improved
training
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3. This chart provides a conceptual look at the ATSRAC process
and identifies multi-pronged solutions. The products are a result
of data collection from a sampling of the fleet, review of service
data, and ongoing research and development.a) The primary use of these products will be to determine
whether there are changes needed to design, manufacturing,
inspection, maintenance, and modification processes for the
wiring on transport airplanes to assure the continued safe
operation of these airplanes.
Version 1.0 7
Aging Systems Program, cont.
IAging systems research, engineering,
and development (R,E,&D)
z FAA R,E,&D
Intrusive inspections
Arc faul t c ircuit breaker development
Interconnect system testing and
assessment
Inspection and testing technology
development
4. The programs shown on the slide are some of the R, E, & D
programs currently in progress.
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C. ATSRAC findings
Version 1.0 8
ATSRAC Findings
I Inspected 6 recently retired aircraft
z 4 wire types
z Intensive detailed visual inspection
z Nondestructive testing (NDT)
z Laboratory analysis
IIPurposePurpose: Determine the state of wireon aged aircraft
1. Results of detailed visual inspection, nondestructive testing, and
laboratory analysis were analyzed to determine the state of wire
on aged aircraft as a function of wire type and service history. In
addition, the results of visual inspection were compared with the
nondestructive testing and laboratory analysis to determine the
efficacy of visual inspection for the detection of age-relateddeterioration.
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ATSRAC Findings, cont.
I~1000 visual findings in the field
z Mostly mis-installation or t raumatic
damage
IOn-aircraft NDT/lab testing resulted
in many additional findings
z Non-negligible degradation on wire,
connectors, and terminals
2. The working group choose to focus on six important categories of
wire degradation:
a)Degraded wire repairs or splices,
b)Heat damaged or burnt wire,
c)Vibration damage or chafing,
d)Cracked insulation,
e)Arcing, and
f) Insulation delamination.
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Version 1.0 10
ATSRAC Findings, cont.
IIResults:Results: Visual inspection effective
in identifying certain conditions
(heat damaged/burnt wire and
vibration damage or chafing)
z Cannot be relied upon to find other
conditions (cracked insulation, arcing,
insulation delamination, and degraded
repairs or splices)
Version 1.0 11
ATSRAC Findings, cont.
IRisk assessment made on wiringfaults
z Definite potential for long-term
safety impacts in most cases
IIRecommendations:Recommendations: Make
changes and additions to current
maintenance programs for wires
3. The conclusions are not sufficiently specific to serve as
mandatory design or maintenance requirements.
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Version 1.0 12
ATSRAC Findings, cont.
IAddi tional maintenance/design
possibilities
z Periodic visual inspections
z Periodic signal path resistance checks
z Preemptive splice repair or wire
replacement
z In-situ NDT
z Reduce moisture int rusion/drip shields
4. The recommendations resulting from this analysis (shown on this
slide and the next ) suggest changes and additions to maintenance
programs for wires subject to the conditions and influencing
factors that occur in the transport aircraft operating environment.
The recommendations specifically document how repairs should
be effected once the condition has been observed. Current best
practice is sufficient in this regard.
5. Furthermore, the working groups recommendations should notbe considered a comprehensive set of design and maintenance
requirements for wire installations, nor should they be considered
a substitute for specific detailed analysis. Each individual wire
installation requires an analysis that considers, in addition to
these recommendations, application-specific requirements.
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Version 1.0 13
ATSRAC Findings, cont.
IAdditional possibi lit ies, cont.
z Minimize proximate flammable materials
z Use of heat shields
z Maintain separation of c ritical systems
wiring
z Emphasis on clean-as-you-go
philosophy
z Use of arc fault circui t breakers
D. Accident service history
Version 1.0 14
TWA 800 Accident
I7/17/1996, Boeing 747-131, broke up
in flight and crashed in Atlantic near
New York
I Ignition energy for center wing tank
explosion most li kely entered
through fuel quantity indication
system (FQIS) wir ing
INeither energy release mechanism
or location of igni tion determined
1. On July 17, 1996, about 8:30 p.m., TWA flight 800, a Boeing
747-131, broke up in flight and crashed in the Atlantic Ocean
near East Moriches, New York. TWA flight 800 was operating
under part 121 as a scheduled international passenger flight from
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John F. Kennedy International Airport (JFK), to Charles
DeGaulle International Airport. The flight departed JFK at 8:19
p.m. All 230 people on board were killed and the airplane was
destroyed.a) The Transport Airplane Directorate is currently in the
rulemaking process to address certification aspects of fuel tank
design with regard to minimizing the potential for fuel vapor
ignition. As part of the rulemaking focus, wiring as a source
of direct and indirect arcing is addressed.
(1) The next slides present some wiring lessons learned from
reviewing the TWA accident and in-service aircraft.
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Version 1.0 15
Wiring Lessons Learned
IWiring to pumps located in metallicconduitsz Wear of teflon sleeving and wiring
insulation has allowed arcing ins ide
conduits , causing a potential ignition
source in fuel tank
IFuel pump connectorsz Arcing at connections within elect rical
connectors occurred due to bent pins
or corrosion
Version 1.0 16
Wiring Lessons Learned, cont.
IFQIS wiringz Wire bundles with degraded and
corroded wires mixed with high
voltage wires
IFQIS probes
z Corrosion caused reduced breakdown
voltage in FQIS wiring; fuel tank
contamination led to reduced arc path
between FQIS probe walls
2. FQIS probes
a)Contamination in the fuel tanks (such as steel wool, lock wire,
nuts, rivets, bolts; and mechanical impact damage) caused
reduced arc path resistance between FQIS probe walls.
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Version 1.0 17
Wiring Lessons Learned, cont.
IBonding straps
z Corrosion, inappropriately attached
connections
z Worn static bonds on fuel system
plumbing
z Corroded bonding surfaces near
fuel tank access panels
Version 1.0 18
Wiring Lessons Learned, cont.
IElectrostatic charge
z Use of non-conduct ive reticulated
polyurethane foam allowed charge
build up
z Fuel tank refueling nozzles caused
increased fuel charging
3. Electrostatic charge
a) In another case, the fuel tank refueling nozzles caused spraying
of fuel into fuel tanks in such a manner that increased fuel
charging, which also can lead to arcing inside the fuel tank.
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Version 1.0 19
Swissair 111 Accident
ICrashed off coast of Nova Scotia onSeptember 2, 1998
ISmoke in cockpit
IFire in cockpit overhead area
IMetalized mylar insulation blankets
I23 wires found with arcing damage
I Investigation on-going
4. The aircraft, enroute from JF Kennedy, NY, to Geneva
Switzerland, crashed in the ocean approximately 40 miles
southwest Halifax Nova Scotia following a report of smoke in
the cockpit. There were no survivors.
a)By September, 1999, the TSB had recovered approximately 98
percent of the aircraft by weight. The TSB elected to
reconstruct the forward 10 meters of the MD-11 fuselage. Most
of the aircraft pieces were about 6 to 12 inches in diameter andthe components had to be molded and sewn together. The
assembled fuselage presented a distinct footprint of fire damage
in the overhead cockpit and overhead first class area.
b) Investigation into a number of in-flight/ground fires on MD-
11 and MD-80 series airplanes has revealed that insulation
blankets covered with film material, also know as metalized
mylar film material, may contribute to the spread of a fire
when ignition occurs from small ignition sources such as
electrical arcing and sparking.
c) It can not be determined at this time if the arcing initiated the
fire or whether the arcing was a result of the fire.
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Version 1.0 20
Swissair 111 -FAA Plan of Action
IAVR-1 Directive (November 1998)
z Minimize potential fuel sources
Replace metalized mylar insulation
blankets
z Minimize potential ignit ion sources
Focus on wiring
5. Since results from flammability testing at the FAA Tech Center
indicated that the metalized mylar insulation blankets can spread
a fire from an arcing incident (the original test method was
determined to be insufficient and has been updated), the FAA
developed a plan to replace all metalized mylar insulation
blankets.
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II. Aging wiring overview
A. Introduction
Version 1.0 21
Maintenance
Age
Installation Environment
Physical
Properties
Wiring Overview
WireWire
DegradationDegradation
1. Wiring degradation
a)Wire degradation is a process that is a function of several
variables; aging is only one of these. Other main factors that
influence wire degradation are shown in the above slide.
2. Characteristics of aging wiring
a) The manner in which wiring degrades is therefore dependent
upon the wire type, how it was originally installed, the overall
time and environment exposed to in service, and how the
wiring was maintained.
b)Service history shows that how the wiring is installed has a
direct effect on wire degradation. In other words, wiring that
is not selected or installed properly has an increased potentialto degrade at an accelerated rate. Therefore, good aircraft
wiring practices are a fundamental requirement for wiring to
remain safely intact.
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B. Causes of wiring degradation
Version 1.0 22
Causes of Wiring Degradation
IVibration
IMoisture
IMaintenance
1. Vibration accelerates degradation over time, resulting in
"chattering" contacts and intermittent symptoms. High vibration
can also cause tie-wraps, or string-ties to damage insulation. In
addition, high vibration will exacerbate any existing problem with
wire insulation cracking.
2. Moisture accelerates corrosion of terminals, pins, sockets, and
conductors. Wiring installed in clean, dry areas with moderate
temperatures appears to hold up well.
3. Maintenance improperly done may contribute to long term
problems and wiring degradation. Repairs that do not meet
minimum airworthiness standards may have limited durability.
Repairs that conform to manufacturers recommended
maintenance practices are generally considered permanent and
should not require rework if properly maintained.
a)Care should be taken to protect wire bundles and connectors
during modification work, and to ensure all shavings and
debris are cleaned up after work is completed.
b)Wiring that is undisturbed will have less degradation than
wiring that is reworked. As wiring and components become
more brittle with age, this effect becomes more pronounced.
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Version 1.0 23
Causes of Wiring Degradation ,cont.
I Indirect damage
IChemical contamination
IHeat
I Installation
4. Indirect damage events such as pneumatic duct ruptures can
cause damage that can later cause wiring problems. When such
an event has occurred, surrounding wire should be carefully
inspected to ensure no damage is evident.
5. Chemical contamination chemicals such as hydraulic fluid,
battery electrolytes, fuel, corrosion inhibiting compounds, waste
system chemicals, cleaning agents, deicing fluids, paint, and soft
drinks can contribute to degradation of wiring. Recommendedoriginal equipment manufacturer cleaning instructions should be
followed.
a)Hydraulic fluid is very damaging to connector grommet and
wire bundle clamps, leading to indirect damage, such as arcing
and chafing.
6. Heat accelerates degradation, insulation dryness, and cracking.
Direct contact with a high heat source can quickly damage
insulation, low levels of heat can degrade wiring over longperiods of time. This type of degradation is sometimes seen on
engines, in galleys, and behind lights.
7. Installation improper installation accelerates the wiring
degradation process.
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5. So the question is where do I go to find FAA guidance for
acceptable wiring practices ? The answer: 14 CFR 25.869, AC
43.13-1b, AC 25-16, and AC 25-10 all provide aspects of good
wiring practices. For now, there is no one rule or AC that tieseverything together, however the FAA is in the process of
initiating a part 25 rulemaking activity to address wiring
installations.
Version 1.0 25
Guidance: AC 43.13-1b
IIAC 43.13-1b:AC 43.13-1b: Acceptable Methods,
Techniques, and Practices -
Aircraft Inspection and Repair
z Flight Standards AC
z Chapter 11- Aircraft Electrical
Systems
See Appendix in Participant Guide
6. AC 43.13-1b covers a fairly comprehensive wide range of basic
wiring practices topics.
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Version 1.0 26
Guidance: AC 25-16
IIAC 25 -16:AC 25 -16: Elect rical Fault and Fi re
Prevention and Protection (4/5/91)
z Provides acceptable means to
address electrically caused faults,
overheat, smoke, and fire in
transport category airplanes
See Appendix in Partic ipant Guide
7. AC 25-16 has an emphasis on wiring flammability, circuit breaker
protection, wiring near flammable fluids, and associated acceptable
test methods. This AC is being considered for updating.
Version 1.0 27
Guidance: AC 25-10
IIAC 25 -10:AC 25 -10: Guidance for Instal lation
of Miscellaneous, Non-required
Electrical Equipment (3/6/87)
z Provides acceptable means to
comply wi th appl icable 14 CFRs
associated with installation of
electrical equipment such as galleys
and passenger entertainment systems
8. AC 25-10 contains minimal wiring practices specifics, including
general load analysis requirements and circuit breaker protection
requirements, which are more thoroughly covered in AC 43.13-1b
and AC 25-16.
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IV. Advisory Circular 43.13-1b
A. Topics to be addressed
Version 1.0 28
AC 43.13-1b Topic Out line
IElectrical load determination
IBreaker and wire sizing/selection
IRouting/clamping/bend radii
ISplicing
IWire terminals
IGrounding and bondingIWire marking
IConnectors and conduits
IWire insulation properties
B. Electrical load determination
Version 1.0 29
Electrical Load Determination
ILoad analysis
z Ensure that total electrical load can be
safely cont rolled or managed within
rated limits of affected components of
aircraft s electrical system (25.1351)
z New or addit ional electrical devices
should not be installed without an
electrical load analysis (AC 43.13-1b)
1. Each aircraft electrical bus can safely support a predetermined
amount of electrical load that is based on the electrical capacity of
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the aircraft generators and the aircrafts overall electrical
distribution system.
2. Where necessary as determined by a load analysis, wire, wire
bundles, and circuit protective devices having the correct ratingsshould be added or replaced.
C. Breaker and wire sizing/selection
Version 1.0 30
AC 43.13-1b Topic Out line,cont.
IElectrical load determination
IBreaker and wire sizing/selection
IRouting/clamping/bend radii
ISplicing
IWire terminals
IGrounding and bonding
IWire marking
IConnectors and condui ts
IWire insulation properties
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1. Breaker and wire sizing/selection: Circuit breaker sizing and
selection
Version 1.0 31
Circuit Breaker Devices
IMust be sized to open before
current rating of attached
wire is exceeded, or before
cumulative rating of all
connected loads are exceeded,
whichever is lowest (25.1357)
Version 1.0 32
Circuit Breaker Protection
I A circui t breaker must always open
before any component downstream
can overheat and generate smoke
or fi re. (AC 43.13-1b, para. 11-48)
I 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)
a)Breakers are sized to protect the aircraft wiring as the main
design constraint. Any further protection of components or
LRUs is desirable but not mandatory.
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b) Ideally, circuit breakers should protect against any wiring fault
that leads to arcing, sparking, flames, or smoke. But as we
will learn, thermal circuit breakers do not always detect arcing
events.
Version 1.0 33
Circuit Breaker Protection, cont.
IUse of a circui t breaker as a
switch is not recommended
z Repeated opening and clos ingof contacts can lead to damage
and premature failure of circuit
breakers
z Most circuit breaker failures
are latent
c) For the most part, you wont know a circuit breaker has failed
until you need it.
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2. Exercise 1: Determining circuit breaker size
Determine appropriatesize for circuitbreakers #1-6.
Decide which circuit
breaker to size first.
Assume power factor =1,and system loads will notchange.
Bus A Bus C
R = 5
#2
#1
#4#3
#5 #6
T T
T T T
T
T
Bus B
R = 10
R = 10 R = 5
TRU115Vac to 28Vdc
Exercise 190 k VA
115v, 400 Hz
T
a) The maximum continuous current through a circuit breaker
must be no more than 85% of its rating.
Version 1.0 35
Determining Breaker Size
1. Determine current flow
available voltage
load resistance of load protecting
2. Determine breaker sizebreaker current f low
85% rating factor
b)This is the formula for determining breaker size.
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Version 1.0 36
Determining Breaker Size, CB #5
1. Determine current flow
available voltage 2828
load resistance of load protecting 1010
2. Determine breaker size
breaker current flow 2.82.8
85% rating factor .85.85
= 3.29 A= 3.29 A
c)After determining the actual breaker size, select the standard
size for circuit breaker that is the closest to the wire current
without being less.
Version 1.0 38
What is the Standard Circuit
Breaker Size?
II CBCB11 =44.38 = 45 A
II CBCB22 =13.53 = ? A
II CBCB33 =27.05 = ? A
II CBCB44 =11.88 = ? A
II CBCB55 = 3.29 = ? A
II CBCB66 = 6.59 = ? A
Ensure wire sizecompatible withcircuit breaker
rating.
Dangerous tohave small wires
using large
circuit breakers.
d)Care must be taken to ensure that wire size is compatible with
the circuit breaker rating. It is dangerous to have small wires
using large circuit breakers.
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3. Breaker and wire sizing/selection: Wire sizing and selection
Version 1.0 40
Wire Selection
ISize wires so they:
z Have suff icient mechanical s trength
z Do not exceed allowable voltage drop
levels
z Are protected by ci rcui t protect ion
devices
z Meet circu it current-carrying
requirements
Version 1.0 41
Nominal
System
Voltage
12
28
115
200
Al lowable
Voltage Drop
Continuous
0.5
1
4
7
1
2
8
14
Al lowable
Voltage Drop
Intermittent
Table 11-6. Tabulation chart (allowablevoltage drop between bus and utilization equipment ground)
AC 43.13-1B, page 11-21
a) The voltage drop in the main power wires from the generation
source or the battery to the bus should not exceed 2% of the
regulated voltage when the generator is carrying rated current
or the battery is being discharged.
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(1) As a rule of thumb, Table 11-6 (as shown in the slide)
defines the maximum acceptable voltage drop in the load
circuits between the bus and the utilization equipment
ground.
Version 1.0 42
Table 11-7. Examples of Determining
Required Wire Size Using Figure 11-2
Voltage Run Circuit Wire CheckDrop Length Current Size Calculated
Voltage Drop
1 V 100 ft 20 A # 6 (.000445 ohm/ft)(100 ft) (20 A) = 0.89 V
0.5 V 50 ft 40 A # 2 (.000183 ohm/ft)(50 ft) (40 A) = 0.366 V
4 V 100 ft 20 A ?? (.00202 ohm/ft)(100 ft) (20 A) = 4.04 V
7 V 100 ft 20 A #14 (.00304 ohm/ft)(100 ft) (20 A) = 6.08 V
b)This table is on page 11-22 of AC 43.13-1B. These
calculations are based on standard conditions at 20C. For
higher temperatures, the formula shown in Figure 11-2 should
be used. For calculating voltage drop, resistance of wire per
unit length can be found in Table 11.9 of 43.13-1b.
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Version 1.0 43
Wire Selection,cont.
IMechanical strength of wire sizes less
than #20
z Do not use wire with less than 19 strands
z Provide additional support at
terminations
z Should not be used when subject to
excessive vibration, repeated bending, or
frequent disconnection
(ref. para. 11-66(a), page 11-21)
c) If it is desirable to select wire sizes smaller than #20, particular
attention should be given to the mechanical strength and
installation handling of these wires (ref. paragraph 11-66,
section 5, page 21, AC 43-13.1b).
(1) Consideration should be given to the use of high-strength
alloy conductors in small gauge wires to increase
mechanical strength.
(2) As a general practice, wires smaller than #20 should be
provided with additional clamps and be grouped with at
least three other wires.
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4. Breaker and wire sizing/selection: Current capacity
Version 1.0 44
Determining Current-CarryingCapacity
IEffect of heat on wire insulation
z Maximum operating temperature
z Single wire or wires in a harness
zAlt itude
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5. Breaker and wire sizing/selection: Exercise 2: Wire size
calculation
Exercise 2: Wire Size Calculation
I Wire length = 40 ft
I Circuit current = 20 A
I Source voltage = 28 V
I Wire type = 200 C
I Max ambient
temperature = 50 C
I Max altitude = 20,000 ft
I 8 wires in a bundle
I Use AC 43.13:
z Figure 11-3 for wire gauge
z Calculate temperature rise
z Figure 11-4a for temperature
derating factor
z Figure 11-6 for altitude
derating factorz Figure 11.5 for bundle
I Calculate estimated operating
temperature using theformula:
T2 = T1 + (TR - T1) [(I2 / Imax)1/2]
Calculate the wire size for this example.
a)Determine if an appropriate wire size has been selected. The
estimated operating temperature must be less than conductor-
rated temperature. If this is not the case, then the wire size
must be increased.
b)The next slide provides a larger version of the formula and an
explanation of each of the formulas components.
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Version 1.0 46
Exercise 2: Wire Size Calculation
I Calculate estimated operating temperatureusing the formula below (ref. page 11-26):
TT22 = T= T11 + (T+ (TRR - T- T11) [(I) [(I22 / I/ Imaxmax ))1/21/2]]
I Where : T2 = est. operating temperature
T1 = ambient temperature
TR = conductor-rated temperature
I2 = circuit current
Imax = calculated current
Calculating wire size
c) This formula is from AC 43.13.1b (ref. page 11-29).
d)Step 1. Determine the maximum allowable temperature rise,
which is the wire-rated temperature minus the maximum
ambient temperature.
e) Step 2. Use figure 11-3 for wire gauge.
f) Step 3. Use figure 11-4a to determine current for #12 wire at
150C.
g)Step 4. Use figure 11-6 for altitude derating factor for 20,000
ft.
h)Step 5. Use figure 11-5 for bundle of 8 wires (assuming
100% loading).
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Version 1.0 47
Wire Size Calculation
IWire gauge = #12
ICurrent for #12 wire at 150 C = 60 A
IAl ti tude derat ing factor for 20,000 f t. = 0.92 x 60 = 55.2 A
IBundle of 8 wires = 0.5 x 55.2 = 27.6 A
ICalculate estimated operating temperature
T2 = T1 + (TR - T1) [(I2 / Imax)1/2]
T2 =
T2 =
ICompare T2 to rating for wire type to ensure T2 less
i) Step 6. Where : T2 = estimated operating temperature
T1 = ambient temperature
TR= conductor-rated temperature
I2 = circuit current
Imax = calculated current
j) Note: Estimated operating temperature must be less than
conductor-rated temperature. If this is not the case, then the
wire size must be increased.
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6. Breaker and wire sizing/selection: Wire system design
Version 1.0 49
Determining Wire System Design
IIAC 43.13-1b, Section 5:AC 43.13-1b, Section 5:
tables and figures provide
an acceptable method of
determining wire system
design
a) The applicant should ensure that the maximum ambient
temperature that the wire bundles will be subjected to, plus the
temperature rise due to the wire current loads, does not exceed
the maximum conductor temperature rating.
b) In smaller harnesses, the allowable percentage of total current
may be increased as the harness approaches the single wire
configuration.
c) The continuous current ratings contained in the tables and
figures in AC 43.13-1b were derived only for wire application,
and cannot be applied directly to associated wire termination
devices (e.g., connector contacts, relays, circuit breakers,
switches). The current ratings for devices are limited by the
design characteristics of the device. Care should be taken to
ensure that the continuous current value chosen for a particular
system circuit shall not create hot spots within any circuit
element which could lead to premature failure.
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7. Breaker and wire sizing/selection: Exercise 3: Wire harness
current capacity
Exercise 3: Wire Harness Current Capacity
I Wire harness = 10 #20 wires; 200 C
25 #22 wires; 200 C
I Max. ambient temperature = 60 C
I Max operating altitude = 60,000 ft
I Circuit analysis = 7 of 35 wires carrying
current at or near ful l capacity (7/35 = 20%)
I Use AC 43.13
z Figure 11-4a for current
z Figure 11-5 for bundle
z Figure 11-6 for altitude derating factor
Determine if wires are sized properly forbundle assembly.
a) The previous exercise looked at determining the size of a
single wire. This activity looks at determining the sizes and
numbers of wires in a bundle. The number of wires in a
bundle reduces the overall bundle load capacity.
b)First calculate the temperature rise due to current.
c) Figure 11-4a to determine current for size 20 and 22 wires at
140 C.
d)Figure 11.5 for bundle derating for 20% curve and 35 wires.
e) Figure 11-6 to determine altitude derating factor for 60,000 ft.
f) Calculate the total harness capacity for #20 and #22 wires and
for the total harness.
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8. Breaker and wire sizing/selection: Wire selection
Version 1.0 52
Wire Selection
IConductor stranding
z Minimizes fatigue breakage
IPlatings for all copper aircraft wiring
z Plated because bare copper develops
surface oxide film a poor conductor
Tin < 150 C
Silver < 200 C Nickel < 260 C
a) Elevated temperature degradation of tin- and silver-plated
copper conductors will occur if they are exposed to continuous
operation at elevated levels.
(1) Fortin-plated conductors, tin-copper intermetallics will
form, resulting in an increase in conductor resistance.
(2) Forsilver-plated conductors, degradation in the form of
interstrand bonding, silver migration, and oxidation of the
copper strands will occur with continuous operation near
rated temperature, resulting in loss of wire flexibility.
Also, due to potential fire hazard, silver-plated
conductors shall not be used in areas where they are
subject to contamination by ethylene glycol solutions.
(3) Both tin- and silver-plated copper conductors will
exhibit degraded solderability after exposure tocontinuous elevated temperature.
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9. Breaker and wire sizing/selection: Wire substitution
Version 1.0 53
Wire Subst itut ion for Repairs
and Maintenance
IWhen replacement wire is required,
review aircraft maintenance manual
to determine iforiginal aircraft
manufacturer(OAM) has approved
any substitution
z If not approved, then contact OAM
for an acceptable replacement
a)Most aircraft wire designs are to specifications that require
manufacturers to pass rigorous testing of wires before they are
approved or added to a Qualified Products List. Aircraft
manufacturers who maintain their own wire specifications
exercise close control of their approved sources.
b)The original aircraft manufacturer (OAM) may have special
concerns regarding shielding, insulation, etc. for certain wiring
on the aircraft that perform critical functions or wiring that is
chosen based on a set of unique circumstances.
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D. Routing, clamping, and bend radii
Version 1.0 54
AC 43.13-1b Topic Out line,cont.
IElectrical load determination
IBreaker and wire sizing/selection
IRouting/clamping/bend radii
ISplicing
IWire terminals
IGrounding and bonding
IWire markingIConnectors and condui ts
IWire insulation properties
1. Routing, clamping, and bend radii: Routing
Version 1.0 55
Wiring Routing
IEliminate potential for chafing against
structure or other components
IPosition to eliminate/minimize use as
handhold or support
IMinimize exposure to damage by
maintenance crews or shifting cargo
IAvoid battery electrolytes or othercorrosive fluids
a) In general, wiring should be routed in such a manner to
ensure reliability and to offer protection from the following
potential hazards:
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(1) Wire chafing
Wire Riding on Structure
Power cables riding
on structure can
cause damage to the
power cables
A
B
Wires Riding on Other Wires
Wire bundles that
cross should be
secured together to
avoid chafing
A
B
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Wires Riding on Lightening Hole
If the grommet is tooshort, then there is
wire bundle chafing
A
B
(2) Use as a handhold or as a support for maintenance
personnel.
Wiring as a Handhold
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(3) Damage by personnel moving within the aircraft.
(4) Damage by stowage or shifting cargo.
(5) Damage by battery or acidic fumes or fluids.
(6) Abrasion in wheel wells where exposed to rocks, ice,
mud, etc.
(7) Damage from external events (zonal analysis/particular
risks analysis demands).
(8) Harsh environments such as severe wind and moisture-
prone (SWAMP) areas, high temperatures, or areas
susceptible to significant fluid or fume concentration.
b) In addition, wiring should be routed to permit free movement
of shock and vibration mounted equipment, designed to
prevent strain on wires, junctions, and supports, and, the
wiring installation should permit shifting of wiring and
equipment necessary to perform maintenance within the
aircraft. In addition, wire lengths should be chosen to allow
for at least two reterminations.
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Version 1.0 60
Wiring Routing, cont.
IProtect wires in wheel wells and otherexposed areas
IRoute wires above fluid lines, ifpracticable
IUse drip loops to control fluids orcondensed moisture
IKeep slack to allow maintenance andprevent mechanical strain
c)Ensure that wires and cables are adequately protected in
wheel wells and other areas where they may be exposed to
damage from impact of rocks, ice, mud, etc. This type of
installation must be held to a minimum.
(1) Wires and cables routed within 6 inches of any
flammable liquid, fuel, or oxygen line should be closely
clamped and rigidly supported. A minimum of 2 inches
must be maintained between wiring and such lines orrelated equipment, except when the wiring is positively
clamped to maintain at least 1/2-inch separation or when
it must be connected directly to the fluid-carrying
equipment.
(2) Ensure that a trap or drip loopis provided to prevent
fluids or condensed moisture from running into wires and
cables dressed downward to a connector, terminal block,
panel, or junction box.
(3) Wires and cables installedin bilges and other locations
where fluids may be trapped are routed as far from the
lowest point as possible or otherwise provided with a
moisture-proof covering.
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Path of exposed end
Broken wire shall not make
contact with fluid line
Wire Bundles Above Fluid Lines
2. Wire bundles above fluid lines. The clamps should be a
compression type and should be spaced so that, assuming a wire
break, the broken wire will not contact hydraulic lines, oxygen
lines, pneumatic lines, or other equipment whose subsequent
failure caused by arcing could cause further damage.
Wires improperly tied,
riding on hydraulic lines,
contaminated with
caustic fluid
a) This slide shows a number of problems:
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(1) Wires in the bundles are not tied properly.
(2) The wire bundle is riding hard on the hydraulic lines.
(3) The wire bundles appears to be contaminated with
hydraulic fluid residue.
b)Wire bundle breakouts. There are three basic wire bundle
breakout types used in routing aircraft wiring. They are called
the Y, T, and Complex types.
Wire bundlebreakout
Figure 8 loop maybe located beforeor aftertail of Y
Plastic mechanical strapping
Wirebundles
Befo
re
After
Y Type Wire Bundle Breakouts
Head of strap shall notbe located in this areaor touching anythingto cause chafing
(1) The Y type of breakout is used when a portion of
wiring from one direction of the wire bundle departs the
bundle to be routed in another direction.
Care should be taken when plastic tie wraps are used to
provide wire containment at the breakout so that the tie
wrap head does not cause chafing damage to the wirebundle at the breakout junction.
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Plastic mechanical strapping
Wire bundle breakout
Wirebundle
Head of s trap shallnot be located in
this area ortouching anything
to cause chafing
T Type Wire Bundle Breakouts
(2) The T type of breakout (also called90 breakout) is
used when portions of wiring from both directions in the
wire bundle depart the bundle to be routed in another
direction.
Complex TypeWire Bundle Breakouts
(3) A Complex type of breakout is generally used to route
certain wires out of a wire bundle to a terminal strip,
module block, or other termination.
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c) For all types of breakouts, there should be sufficient slack in
the wires that are being broken out of the bundle to avoid
strain on the wire between the wire bundle and the
termination.
d)Use of stand-offs
Version 1.0 66
Stand-offs
IUse stand-offs to maintain c learancebetween wires and structure
z Employing tape or tubing is generally
notnot acceptable as an alternative
IIException:Exception: Where impossib le to
install off -angle clamps to maintain
wir ing separation in holes,
bulkheads, floors, etc.
(1) The wiring design should preclude wire bundles from
contacting structure.
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Exercise: Using Stand-offs
A
B
e)Examples of bundle problems
Bundle riding on structure
(1) One of the more common aircraft wiring problems is
chafing due to wire bundles coming into contact with
aircraft structure or other aircraft equipment.
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Wire bundle riding
on control cable
(2) This picture shows a wire bundle that is in close contact
with a control cable. Adequate distance between wire
bundles and control cables should be maintained to
account for movement due to slack and maintenance.
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3. Routing, clamping, and bend radii: Clamping
Version 1.0 70
Clamping
ISupport wires by suitable clamps,
grommets, or other devices at
intervals of not more that 24 inches
ISupporting devices should be of
suitable size and type with wire and/or
cables held securely in place without
damage to wire or wire insulation
a)Wire supports and intervals. Clamps and other primary
support devices should be constructed of materials that are
compatible with their installation and environment, in terms of
temperature, fluid resistance, exposure to ultraviolet light, and
wire bundle mechanical loads.
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Version 1.0 71
Clamps
IWire bundles should be snug in
clamp (no movement)
z Cable not able to move axially
IRF cables: do not crush
IMount clamps with attachment
hardware on top
ITying NOT used as alternative to
clamping
b)Clamps on wire bundles should not allow the bundle to move
through the clamp when a slight axial pull is applied.
c)Clamps on RF cables must fit without crushing and must be
snug enough to prevent the cable from moving freely through
the clamp, but may allow the cable to slide through the clamp
when a light axial pull is applied. The cable or wire bundle
may be wrapped with one or more turns of tape or other
material suitable for the environment when required to achievethis fit.
(1) Plastic clamps or cable ties must not be used where their
failure could result in interference with movable controls,
wire bundle contact with movable equipment, or chafing
damage to essential or unprotected wiring. They must not
be used on vertical runs where inadvertent slack
migration could result in chafing or other damage.
(2)
Clamps must be installed with their attachmenthardware positioned above them, wherever practicable,
so that they are unlikely to rotate as the result of wire
bundle weight or wire bundle chafing.
d)Clamps lined with nonmetallic material should be used to
support the wire bundle along the run.
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Example of Correct Cable Slack
Appropriate s lack
e)Appropriate slack protects the wires from stress and from
contact with inappropriate surfaces.
(1) Too much cable slack can allow the cable to contact
structure or other equipment which could damage the
wire bundle.
(2) Too little slack can cause a pre-load condition on the
cable which could cause damage to the wire bundle
and/or clamps as well.
(3) Also, sufficient slack should be left between the last
clamp and the termination or electrical equipment to
prevent strain at the terminal and to minimize adverse
effects of shock-mounted equipment.
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Clamp Distort ion
Incorrect clamp position
Distortion of rubber on
clamp is NOT acceptable
Correct clamp position
f) As is shown in the top graphic, the wire bundles are routed
perpendicular to the clamp.
(1) If wire bundles are not routed perpendicular to the clamp
(bottom graphic), stress can be created against the clamp
and clamp grommet which can distort the clamp and/or
clamp grommet. Distorted clamps/clamp grommets can
cause wire bundle damage over time.
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Correct
Correct Incorrect
Incorrect
905
Clamp Orientation
905
g)This slide further illustrates correct and incorrect clamp
orientations. Incorrect clamp orientation can lead to wire
bundle damage.
Example - Clamp Distortion
h)Note that the wire bundle is not perpendicular to the clamp.
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release
tab
support
bracket
tail
snap-in tie
mount
Plastic Snap-in Clamp (Tie Mount)
i) These types of clamps are not suitable for large wire bundles
and should not be used in high temperature or high vibration
areas.
(1) Any type of plastic clamp or cable tie should not be used
where their failure could result in interference with
movable controls, wire bundle contact with movable
equipment, or chafing damage to essential or unprotected
wiring.
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Stand off
No
pinching
Clamp
tabs
Rubber cushion
Wedge
Typical Rubber Clamp
Al l wires containedin rubber cushion
j) Clamps on wire bundles should be selected so that they have a
snug fit without pinching wires.
Typical Nylon Closed-FaceClamp Installation
Do not pinch
wire here
k) It is important when adding wiring to an existing wire bundle
to evaluate the existing clamp sizing in order to avoid possible
clamp pinching. In some cases it may be necessary to increase
the size of the clamps to accommodate the new wiring.
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Engage Clamp Tab in Slot
Incorrect
Clampslot
Clamp
tab
Correct
l) When using clamp tabs, make sure that the tabs are properly
engaged. Otherwise, the tab could become loose and cause
subsequent wire damage.
(1) Ensure that the clamp is snapped before installing and
tightening the bolt.
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Do not pinch
wires here
Correct
Incorrect
Clamp Pinching
m)This slide further illustrates how wires can be pinched and
damaged due to improper clamp installation.
Open-faced nylon clamp with cable
build-up (missing hardware)
n)Note the missing clamp hardware. Also note that the black
cable was using a tape build-up at the clamp. Some
manufacturers wiring specifications allow for wire cable
build-up under certain circumstances.
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Exercise: Clamping
A
B
4. Routing, clamping, and bend radii: Wire bend radii
Version 1.0 83
Wire Bend Radii
IMinimum bend radius - 10 times the
outside diameter of the largest wire
or cable in the group unsupported
z Exceptions
Terminations/reversing direction in bundle
(supported at both ends of loop) -
3 times the diameter
RF cables - 6 times the diameter
Thermocouple wire - 20 times the diameter
a)Where it is not practical to install wiring or cables within the
radius requirements, the bend should be enclosed in insulating
tubing.
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No support atend of bend
Min. bend radius - 10 xparameter of wire or cable
Support at both
ends of wire bend
Diameter of
wire or cable
Min. bend radius3 x diameter of w ire
Minimum Bend Radii
b)This illustration shows the proper bend radii for three different
scenarios.
Bend radii okay-
Greater than 3 t imes diameter(secured at both ends of loop)
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Bend radii problem-
Less than 3 times the diameter
c)Although supported, this wire bundle does not meet bend
radius standards due to the large wires in the bundle.
A
Exercise 4: Wiring Problems
B
Passenger Seat
Find the wiringproblems illustratedin these photos.
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5. Routing, clamping, and bend radii: Spare wire and connector
contacts
Version 1.0 88
Unused Wires
ISecured
z Tied into a bundle or secured to a
permanent structure
I Individually cut with strands even
with insulation
IPre-insulated, closed-end connectoror 1-inch piece of insulating tubing
folded and tied back
a) The following three slides depict an acceptable method of
insulating and physically securing a spare connector contact
within a wire bundle.
3 times length of contact
WireContact
Tubing
Spare Connector Contact:Preparing Single Contact
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Tying tape0.75 0.15 in.
Fold
Spare Connector Contact: FoldingTube and Tying Single Contact
Tying tapeWire
bundle
Spare Connector Contact: Single
Contact Attachment to Wire Bundle
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b)Spare wire termination using an endcap. This is another
way to protect unused wiring.
Wire and end cap
in positionInstall end cap over wire
end. Shrink in place.
Fiberglass
tying tape
Wire bundle
End caps
Adhesive tape
Spare Wire Termination Using Endcap
(1) Installing prefabricated end caps are an effective method
of protecting unused wires with exposed conductors.
Unused wiring -
Improper termination with exposed conductor
(should be properly insulated and
secured to bundle)
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c)Coil and stow methods
Wirebundle
ties
Coil and stow short wire bundlesin low vibration areas
Clamp
Coil and Stow Methods
Wire
bundle
(1) Coil and stow methods are often used to secure excess
length of a wire bundle or to secure wire bundles that are
not connected to any equipment, such as wiring
provisioning for a future installation.
(2) The key objective to coiling and stowing wiring is to
safely secure the wire bundle to prevent excessive
movement or contact with other equipment that could
damage the wiring.
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Coil and Stow Methods, cont.
Wire bundle
Wire bundle ties
Coil and stow long wire bundles
in low vibration areas
Clamp
Excess wire
Coil and stow in mediumand high vibration areas
Ad jacent wi re bundle
Wirebundle Wire
bundleties
Teflontape
Coil and Stow Methods, cont.
(3) Coil and stow in medium and high vibration areas
requires additional tie straps, sleeving, and support.
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Exercise: Stowing Unused Wires
A
B
E. Wire replacement and splicing
1. Wire replacement and splicing: Wire replacement
Version 1.0 98
Wire Replacement
IWires should be replaced when:
z Chafed or frayed
z Insulation suspected of being
penetrated
z Outer insu lation is cracking
z Damaged by or known to have been
exposed to electrolyte, oil, hydraulicfluid, etc.
z Evidence of overheating can be seen
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Heat Discoloration
a) This picture shows an example of heat discoloration on
protective sleeving which is part of the wire bundle. The large
clamp was moved to see the difference in color. In this case,
the wiring that is not covered in sleeving shows no signs of
heat distress. An adjacent light bulb was radiating enough
heat to cause discoloration over time to the protective
sleeving. Although this condition is not ideal, it is acceptable.
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Version 1.0 100
Wire Replacement, cont.
IWire should be replaced when:
z Wire bears evidence of being crushed
or kinked
z Shield on shielded wire if frayed
and/or corroded
z Wire shows evidence of breaks, cracks,
dirt, or moisture in plastic sleeving
z Sections of wire have splices occurring
at less than 10-ft in tervals
b)Continuing, this slide shows additional circumstances that
warrant replacing wiring.
c) Shielding requirements
Version 1.0 101
Wire Replacement, cont.
IShielding requirements
z Replacement wires must have the
same shielding characteristics as the
original wire, such as shield opt ical
coverage and resistance per unit
length
z Replacement wires should not be
installed outside the bundle shield
(1) For more information on shielding, theLightning/HIRF
Video and Self-study Guide is available. (To obtain, see
your Directorate training manager.)
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d)Adding or replacing wires on a bundle
Correctprocedure
Incorrect
procedure
Chafing
Adding or Replacing Wireson a Bundle
(1) When adding or replacing wires on a wire bundle, the
replacement or added wire should be routed in the same
manner as the other wires in the wire bundle.
When the new wire is installed, the ties and clamps
should be opened one at a time to avoid excessive
disassembly of the wire bundles.
Example: Adding Wires on aBundle
A
B
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2. Wire replacement and splicing: Splicing
Version 1.0 104
AC 43.13-1b Topic Out line, cont.
IElectrical load determination
IBreaker and wire sizing/selection
IRouting/clamping/bend radii
ISplicing
IWire terminals
IGrounding and bonding
IWire markingIConnectors and condui ts
IWire insulation properties
Version 1.0 105
Wire Splic ing
IKeep to a minimum
IAvoid in high vibration areas
ILocate to permit inspection
IStagger in bundles to minimize
increase in bundle size
IUse self-insulated splice
connector, if possible
a) Splicing is permitted on wiring as long as it does not affect the
reliability and the electro-mechanical characteristics of the
wiring. Splicing of power wires, co-axial cables, multiplex
bus, and large gauge wire should be avoided. If it cant be
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avoided, then the power wire splicing must have approved
data.
b)Many types of aircraft splice connectors are available for
use when splicing individual wires.
(1) A non-insulated splice connector may be used provided
the splice is covered with plastic sleeving that is secured
at both ends.
(2) Environmentally-sealed splices that conform to MIL-T-
7928 provide a reliable means of splicing in SWAMP
areas. However, a non-insulated splice connector may be
used, provided the splice is covered with dual wall shrink
sleeving of a suitable material.
Staggered Splices
c) Splices in bundles should be staggered so as to minimize any
increase in the size of the bundle that would:(1) Prevent bundle from fitting into designated space.
(2) Cause congestion adversely affecting maintenance.
(3) Cause stress on the wires.
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Overheated wire at the splice
d)Splices that are not crimped properly (under or over) can cause
increased resistance leading to overheat conditions.
Ganged
wiresplices
e) If splices are not staggered, proper strain relief should be
provided in order to avoid stress on the wires. In this
particular installation, strain relief was applied to avoid stress
on the wires.
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Ganged wire splices
f) The top two wires in this photo are experiencing stress due to
a preload condition. Also note that the wire bundle is not
properly clamped.
F. Wire terminals
Version 1.0 110
AC 43.13-1b Topic Outline, cont.
IElectrical load determination
IBreaker and wire sizing/selection
IRouting/clamping/bend radii
ISplicingIWire terminals
IGrounding and bonding
IWire marking
IConnectors and conduits
IWire insulation properties
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Version 1.0 111
Terminals
ITensile strength of the wire-to-
terminal joint should be at least
the equivalent tensile strength of
the wire
IResistance of the wire-to-terminal
joint should be negligible relative to
the normal resistance of the wire
1. Tensile strength terminals are attached to the ends of electrical
wires to facilitate connection of the wires to terminal strips or
items of equipment.
a) Selection of wire terminals. The following should be
considered in the selection of wire terminals:
(1) Current rating.
(2) Wire size (gauge) and insulation diameter.
(3) Conductor material compatibility.
(4) Stud size.
(5) Insulation material compatibility.
(6) Application environment.
(7) Solder/solderless.
2. Bending straight copper terminals
a) If bending of a terminal is necessary, care should be taken to
avoid over bending the terminal which can cause damage to
the terminal. Also, a terminal can only be bent once since any
additional bending can cause damage.
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b)Pre-insulated crimp-type ring-tongue terminals are preferred.
The strength, size, and supporting means of studs and binding
posts, as well as the wire size, should be considered when
determining the number of terminals to be attached to any onepost.
c) In high-temperature applications, the terminal temperature
rating must be greater than the ambient temperature plus
current related temperature rise. Use of nickel-plated
terminals and of uninsulated terminals with high-temperature
insulating sleeves should be considered. Terminal blocks
should be provided with adequate electrical clearance or
insulation strips between mounting hardware and conductive
parts.d)Terminals are sensitive to bending at the junction between the
terminal ring and the terminal crimp barrel. Bending the
terminal more than once or exceeding pre-determined terminal
bend limits will u