aircraft wiring ref

7/28/2019 Aircraft Wiring Ref

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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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Aircraft Wiring Practices

Participant Guide Version 1.0 page ii

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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Participant Guide Version 1.0 page iii

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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Participant Guide Version 1.0 page iv

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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Participant Guide Version 1.0 page 1


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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Course Materials


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Version 1.0 1


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

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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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Version 1.0 9

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


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


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


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


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


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


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.




ISplicing

IWire terminals

IGrounding and bonding

IWire marking

IConnectors and condui ts



37/167



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.


43/167




44/167



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


46/167



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.


56/167



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.




ISplicing

IWire terminals


IWire markingIConnectors and condui ts


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


59/167



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


60/167



(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.


64/167



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.


65/167



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.




ISplicing

IWire terminals


IWire markingIConnectors and condui ts


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.




ISplicingIWire terminals


IWire marking

IConnectors and conduits



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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

aircraft wiring ref

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