25827

Participant Guide Aircraft Wiring Practices An Interactive Training and Self-Study Course (25827) Presented by Brett Portwood FAA Technical Specialist, Safety and Integration Massoud Sadeghi Aging Systems Program Manager Federal Aviation Administration March 28 & 29, 2001 Aircraft Wiring Practices Table of Contents INTRODUCTORY MATERIALS Course Orientation .......................................................................................... About This Course................................................................................... Who Is the Target Audience?.................................................................. Who Are the Instructors? ........................................................................ What Will You Learn? ............................................................................ How Will This Course Help You On-the-Job? ....................................... 2 2 2 2 14 14 Self-Assessment ................................................................................................ 6 Pre- & Post-Course Self-Assessment Questions..................................... 6 COURSE MATERIALS Background ...................................................................................................... Introduction ............................................................................................. Aging Systems Program.......................................................................... ASTRAC findings ................................................................................... Accident service history .......................................................................... 10 10 11 15 19 Aging wiring overview..................................................................................... 25 Introduction ............................................................................................. 25 Causes of wiring degradation.................................................................. 26 Current FAA guidance.................................................................................... 28 Overview ................................................................................................. 31 Advisory Circular 43.13-1b ............................................................................ Topics to be addressed ............................................................................ Electrical load determination .................................................................. Breaker and wire sizing/selection ........................................................... Exercise 1: Circuit breaker size calculation...................................... Figure 11-2 from 43.13-1b................................................................. Exercise 2: Wire size calculation ...................................................... Figure 11-3 from 43.13-1b................................................................. Figure 11-4a from 43.13-1b ............................................................... Figure 11-6 from 43.13-1b................................................................. 31 31 31 33 35 39 42 44 45 46 Participant Guide Version 1.0 page ii Aircraft Wiring Practices 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.........................................145 Preemptive wire splice repair and/or wire replacement..........................145 Wiring installation certification .....................................................................149 Introduction .............................................................................................149 Wiring diagrams ......................................................................................150 Actual wiring diagram........................................................................152 Participant Guide Version 1.0 page iii Aircraft Wiring Practices 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 Participant Guide Version 1.0 page iv Aircraft Wiring Practices Aircraft Wiring Practices Introductory Materials Participant Guide Version 1.0 page 1 Aircraft Wiring Practices Course Orientation About This Course 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, and Massoud Sadeghi, Aging Systems Program Manager, will provide you with the basic concepts of Aircraft 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 review of what to look for on wiring diagrams and wiring installation drawings. Who Is the Target Audience? 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. Who Are the Instructors? Brett Portwood is 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 FAA’s 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 Version 1.0 page 2 Brett Portwood Participant Guide Aircraft Wiring Practices 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 performing fault/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 Massoud Sadeghi is the FAA Transport Aging Systems Program Manager responsible for implementing improvements in the requirements of design, installation, mainenance, repair, and certification processes for airplane wiring. Massoud’s 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, Massoud’s 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. Participant Guide Version 1.0 page 3 Aircraft Wiring Practices What Will You Learn? 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. How Will This Course Help You On-theJob? 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. Participant Guide Version 1.0 page 4 Aircraft Wiring Practices • 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. Participant Guide Version 1.0 page 5 Aircraft Wiring Practices Self-Assessment Self-Assessment Questions The instructor will ask you at the begining of the presentation to respond to the following questions about aircraft 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. Participant Guide Version 1.0 page 6 Aircraft Wiring Practices 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 is a. required for high vibration areas. b. required for high temperature areas. c. required when stacking dissimilar materials. d. not required. Participant Guide Version 1.0 page 7 Aircraft Wiring Practices 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 general wiring 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. Participant Guide Version 1.0 page 8 Aircraft Wiring Practices Aircraft Wiring Practices Course Materials Participant Guide Version 1.0 page 9 Aircraft Wiring Practices Aircraft Wiring Practices Brett Portwood: [email protected] FAA Technical Specialist, Safety and Integration Los Angeles ACO; ANM-130L (562)627-5350 Massoud Sadeghi: [email protected] Aging Systems Program Manager Transport Airplane Directorate; ANM-114 (425)227-2117 Version 1.0 1 I. Background Background Why the need for wiring practices training? Aging Systems Program Aging Transport Systems Rulemaking Advisory Committee (ATSRAC) Accident Service History Version 1.0 2 A. Introduction 1. Historically, wiring was installed without much thought given to the aging aspects: a) Fit and forget. Participant Guide Version 1.0 page 10 Aircraft Wiring Practices 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 Aging Systems Program Instituted a comprehensive aging non-structural systems program Research to identify and prioritize opportunities to enhance safety A data-driven program based on inspections and service history reviews Multi-pronged solutions developed in conjunction with aviation community Modeled after successful aging structures program Version 1.0 3 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 Participant Guide Version 1.0 page 11 Aircraft Wiring Practices for wire bundle and component installations. The goal is to preclude accidents that may result from wire degradation. FAA Aging Transport NonStructural Systems Plan Air Transport Assoc. (ATA) study team: Using lessons learned from TWA 800 and Swissair 111 Addressing recommendations from Gore Commission Collecting data from – On-site evaluations – Meetings with PMIs, Airbus, and Boeing – Analysis of aging systems using NASDAC data bases Version 1.0 4 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 Aviation Safety and Security, or informally known as the Gore Commission, recommended that the FAA, in cooperation with airlines and manufacturers, expand the FAA’s 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. Participant Guide Version 1.0 page 12 Aircraft Wiring Practices FAA Aging Transport NonStructural Systems Plan, cont. Study team, cont. Established ATSRAC to coordinate aging systems’ initiatives with the FAA Incorporated the Air Transport Association’s (ATA) aging system task force (ASTF) activities into ATSRAC Version 1.0 5 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 ATSRAC •Fleet sampling inspections •Service data review •Working group outputs FAA •Study team inspections •Inspection support •Service data review •Research and development Products Corrective actions Improved Inspection & design maintenance practice practices improvements Improved Improved system data training reporting Participant Guide Version 1.0 page 13 Aircraft Wiring Practices 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. Aging Systems Program, cont. Aging systems research, engineering, and development (R,E,&D) FAA R,E,&D – Intrusive inspections – Arc fault circuit breaker development – Interconnect system testing and assessment – Inspection and testing technology development Version 1.0 7 4. The programs shown on the slide are some of the R, E, & D programs currently in progress. Participant Guide Version 1.0 page 14 Aircraft Wiring Practices C. ATSRAC findings ATSRAC Findings Inspected 6 recently retired aircraft 4 wire types Intensive detailed visual inspection Nondestructive testing (NDT) Laboratory analysis Purpose: Determine the state of wire Purpose on aged aircraft Version 1.0 8 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-related deterioration. Participant Guide Version 1.0 page 15 Aircraft Wiring Practices ATSRAC Findings, cont. ~1000 visual findings in the field Mostly mis-installation or traumatic damage On-aircraft NDT/lab testing resulted in many additional findings Non-negligible degradation on wire, connectors, and terminals Version 1.0 9 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. Participant Guide Version 1.0 page 16 Aircraft Wiring Practices ATSRAC Findings, cont. Results: Visual inspection effective in identifying certain conditions (heat damaged/burnt wire and vibration damage or chafing) Cannot be relied upon to find other conditions (cracked insulation, arcing, insulation delamination, and degraded repairs or splices) Version 1.0 10 ATSRAC Findings, cont. Risk assessment made on wiring faults Definite potential for long-term safety impacts in most cases Recommendations: Make changes and additions to current maintenance programs for wires Version 1.0 11 3. The conclusions are not sufficiently specific to serve as mandatory design or maintenance requirements. Participant Guide Version 1.0 page 17 Aircraft Wiring Practices ATSRAC Findings, cont. Additional maintenance/design possibilities Periodic visual inspections Periodic signal path resistance checks Preemptive splice repair or wire replacement In-situ NDT Reduce moisture intrusion/drip shields Version 1.0 12 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. Furthermore, the working group’s recommendations should not be 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. 5. Participant Guide Version 1.0 page 18 Aircraft Wiring Practices ATSRAC Findings, cont. Additional possibilities, cont. Minimize proximate flammable materials Use of heat shields Maintain separation of critical systems wiring Emphasis on clean-as-you-go philosophy Use of arc fault circuit breakers Version 1.0 13 D. Accident service history TWA 800 Accident 7/17/1996, Boeing 747-131, broke up in flight and crashed in Atlantic near New York Ignition energy for center wing tank explosion most likely entered through fuel quantity indication system (FQIS) wiring Neither energy release mechanism or location of ignition determined Version 1.0 14 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 Version 1.0 page 19 Participant Guide Aircraft Wiring Practices 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. Participant Guide Version 1.0 page 20 Aircraft Wiring Practices Wiring Lessons Learned Wiring to pumps located in metallic conduits Wear of teflon sleeving and wiring insulation has allowed arcing inside conduits, causing a potential ignition source in fuel tank Fuel pump connectors Arcing at connections within electrical connectors occurred due to bent pins or corrosion Version 1.0 15 Wiring Lessons Learned, cont. FQIS wiring Wire bundles with degraded and corroded wires mixed with high voltage wires FQIS probes Corrosion caused reduced breakdown voltage in FQIS wiring; fuel tank contamination led to reduced arc path between FQIS probe walls Version 1.0 16 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. Participant Guide Version 1.0 page 21 Aircraft Wiring Practices Wiring Lessons Learned, cont. Bonding straps Corrosion, inappropriately attached connections Worn static bonds on fuel system plumbing Corroded bonding surfaces near fuel tank access panels Version 1.0 17 Wiring Lessons Learned, cont. Electrostatic charge Use of non-conductive reticulated polyurethane foam allowed charge build up Fuel tank refueling nozzles caused increased fuel charging Version 1.0 18 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. Participant Guide Version 1.0 page 22 Aircraft Wiring Practices Swissair 111 Accident Crashed off coast of Nova Scotia on September 2, 1998 Smoke in cockpit Fire in cockpit overhead area Metalized mylar insulation blankets 23 wires found with arcing damage Investigation on-going Version 1.0 19 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 and the 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 MD11 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. Participant Guide Version 1.0 page 23 Aircraft Wiring Practices Swissair 111 - FAA Plan of Action AVR-1 Directive (November 1998) Minimize potential fuel sources –Replace metalized mylar insulation blankets Minimize potential ignition sources –Focus on wiring Version 1.0 20 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. Participant Guide Version 1.0 page 24 Aircraft Wiring Practices II. Aging wiring overview A. Introduction Wiring Overview Physical Properties Age Wire Degradation Installation Maintenance Version 1.0 Environment 21 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 potential to degrade at an accelerated rate. Therefore, good aircraft wiring practices are a fundamental requirement for wiring to remain safely intact. Participant Guide Version 1.0 page 25 Aircraft Wiring Practices B. Causes of wiring degradation Causes of Wiring Degradation Vibration Moisture Maintenance Version 1.0 22 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. Moisture – accelerates corrosion of terminals, pins, sockets, and conductors. Wiring installed in clean, dry areas with moderate temperatures appears to hold up well. 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. 2. 3. Participant Guide Version 1.0 page 26 Aircraft Wiring Practices Causes of Wiring Degradation, cont. Indirect damage Chemical contamination Heat Installation Version 1.0 23 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. 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. Recommended original 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. 5. 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 long periods of time. This type of degradation is sometimes seen on engines, in galleys, and behind lights. Installation – improper installation accelerates the wiring degradation process. 7. Participant Guide Version 1.0 page 27 Aircraft Wiring Practices III. Current FAA guidance A. Overview Current FAA Guidance 25.1301/1309 25.1529 25.1353 25.869 Wiring Practices Policy memo AC 43.13-1b Version 1.0 AC 25-16 AC 25-10 24 1. 2. Sections 25.1301 and 25.1309 apply in a general sense in that a system must perform its intended function in a safe manner. There are some specific electrical power wiring requirements, such as 25.1353, but they do not specifically address all aircraft wiring. 14 CFR 25.1529 requires that instructions for continued airworthiness are specified, which would include maintenance manuals/procedures for wiring. In support, 43.13(a) states that each person performing maintenance on an aircraft shall use the methods, techniques, and practices prescribed in the current manufacturer’s maintenance manual or Instructions for Continued Airworthiness. A large body of FAA guidance for wiring practices is in Chapter 11 of AC 43.13-1b. However, this section contains methods, techniques, and practices acceptable to the Administrator for the repair of “non-pressurized areas” of civil aircraft, so it seemingly would not apply to pressurized transport aircraft. [Chapter 11 of AC 43.13-1b is an appendix of this Guide.] Version 1.0 page 28 3. 4. Participant Guide Aircraft Wiring Practices 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 ties everything together, however the FAA is in the process of initiating a part 25 rulemaking activity to address wiring installations. Guidance: AC 43.13-1b AC 43.13-1b: Acceptable Methods, Techniques, and Practices Aircraft Inspection and Repair Flight Standards AC Chapter 11- Aircraft Electrical Systems –See Appendix in Participant Guide Version 1.0 25 6. AC 43.13-1b covers a fairly comprehensive wide range of basic wiring practices topics. Participant Guide Version 1.0 page 29 Aircraft Wiring Practices Guidance: AC 25-16 AC 25 -16: Electrical Fault and Fire Prevention and Protection (4/5/91) Provides acceptable means to address electrically caused faults, overheat, smoke, and fire in transport category airplanes – See Appendix in Participant Guide 26 Version 1.0 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. Guidance: AC 25-10 AC 25 -10: Guidance for Installation of Miscellaneous, Non-required Electrical Equipment (3/6/87) Provides acceptable means to comply with applicable 14 CFRs associated with installation of electrical equipment such as galleys and passenger entertainment systems Version 1.0 27 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. Participant Guide Version 1.0 page 30 Aircraft Wiring Practices IV. Advisory Circular 43.13-1b A. Topics to be addressed AC 43.13-1b Topic Outline Electrical load determination Breaker and wire sizing/selection Routing/clamping/bend radii Splicing Wire terminals Grounding and bonding Wire marking Connectors and conduits Wire insulation properties Version 1.0 28 B. Electrical load determination Electrical Load Determination Load analysis Ensure that total electrical load can be safely controlled or managed within rated limits of affected components of aircraft’s electrical system (25.1351) New or additional electrical devices should not be installed without an electrical load analysis (AC 43.13-1b) Version 1.0 29 1. Each aircraft electrical bus can safely support a predetermined amount of electrical load that is based on the electrical capacity of Version 1.0 page 31 Participant Guide Aircraft Wiring Practices the aircraft generators and the aircraft’s overall electrical distribution system. 2. Where necessary as determined by a load analysis, wire, wire bundles, and circuit protective devices having the correct ratings should be added or replaced. C. Breaker and wire sizing/selection AC 43.13-1b Topic Outline, cont. Electrical load determination Breaker and wire sizing/selection Routing/clamping/bend radii Splicing Wire terminals Grounding and bonding Wire marking Connectors and conduits Wire insulation properties Version 1.0 30 Participant Guide Version 1.0 page 32 Aircraft Wiring Practices 1. Breaker and wire sizing/selection: Circuit breaker sizing and selection Circuit Breaker Devices Must 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 31 Circuit Breaker Protection “A circuit breaker must always open before any component downstream can overheat and generate smoke or fire.” (AC 43.13-1b, para. 11-48) “Circuit breakers are designed as circuit protection for the wire, not for protection of black boxes or components . . .” (AC 43.13-1b, para. 11-51) Version 1.0 32 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. Participant Guide Version 1.0 page 33 Aircraft Wiring Practices 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. Circuit Breaker Protection, cont. Use of a circuit breaker as a switch is not recommended Repeated opening and closing of contacts can lead to damage and premature failure of circuit breakers Most circuit breaker failures are latent Version 1.0 33 c) For the most part, you won’t know a circuit breaker has failed until you need it. Participant Guide Version 1.0 page 34 Aircraft Wiring Practices 2. Exercise 1: Determining circuit breaker size Exercise 1 Bus A Determine appropriate size for circuit breakers #1-6. Decide which circuit breaker to size first. 90 k VA 115v, 400 Hz T T T #1 Bus C Bus B #2 #3 #4 TRU 115Vac to 28Vdc T T R = 10Ω Assume power factor =1, and system loads will not change. T #5 #6 T R = 5Ω R = 10Ω R = 5Ω a) The maximum continuous current through a circuit breaker must be no more than 85% of its rating. Determining Breaker Size 1. Determine current flow available voltage load resistance of load protecting 2. Determine breaker size breaker current flow 85% rating factor Version 1.0 T 35 b) This is the formula for determining breaker size. Participant Guide Version 1.0 page 35 Aircraft Wiring Practices Determining Breaker Size, CB #5 1. Determine current flow available voltage 28 load resistance of load protecting 10 2. Determine breaker size breaker current flow 2.8 85% rating factor .85 = 3.29 A Version 1.0 36 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. What is the Standard Circuit Breaker Size? CB1 =44.38 = 45 A CB2 =13.53 = ? A CB3 =27.05 = ? A CB4 =11.88 = ? A CB5 = 3.29 = ? A CB6 = 6.59 = ? A Version 1.0 Ensure wire size compatible with circuit breaker rating. Dangerous to have small wires using large circuit breakers. 38 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. Participant Guide Version 1.0 page 36 Aircraft Wiring Practices 3. Breaker and wire sizing/selection: Wire sizing and selection Wire Selection Size wires so they: Have sufficient mechanical strength Do not exceed allowable voltage drop levels Are protected by circuit protection devices Meet circuit current-carrying requirements Version 1.0 40 (allowable voltage drop between bus and utilization equipment ground) Table 11-6. Tabulation chart Nominal System Voltage 12 28 115 200 Version 1.0 Allowable Voltage Drop Continuous 0.5 1 4 7 Allowable Voltage Drop Intermittent 1 2 8 14 41 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. Participant Guide Version 1.0 page 37 Aircraft Wiring Practices (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. Table 11-7. Examples of Determining Required Wire Size Using Figure 11-2 Voltage Run Circuit Wire Drop Length Current Size 1V 0.5 V 4V 7V Version 1.0 Check Calculated Voltage Drop (.000445 ohm/ft) (100 ft) (20 A) = 0.89 V (.000183 ohm/ft) (50 ft) (40 A) = 0.366 V (.00202 ohm/ft) (100 ft) (20 A) = 4.04 V (.00304 ohm/ft) (100 ft) (20 A) = 6.08 V 42 100 ft 50 ft 100 ft 100 ft 20 A 40 A 20 A 20 A #6 #2 ? #14 b) This table is on page 11-22 of AC 43.13-1B. These calculations are based on standard conditions at 20°C. 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. Participant Guide Version 1.0 page 38 Aircraft Wiring Practices Participant Guide Version 1.0 page 39 Aircraft Wiring Practices Wire Selection, cont. Mechanical strength of wire sizes less than #20 Do not use wire with less than 19 strands Provide additional support at terminations Should not be used when subject to excessive vibration, repeated bending, or frequent disconnection (ref. para. 11-66(a), page 11-21) Version 1.0 43 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. Participant Guide Version 1.0 page 40 Aircraft Wiring Practices 4. Breaker and wire sizing/selection: Current capacity Determining Current-Carrying Capacity Effect of heat on wire insulation Maximum operating temperature Single wire or wires in a harness Altitude Version 1.0 44 Participant Guide Version 1.0 page 41 Aircraft Wiring Practices 5. Breaker and wire sizing/selection: Exercise 2: Wire size calculation Exercise 2: Wire Size Calculation Calculate the wire size for this example. Use AC 43.13: Wire length = 40 ft Circuit current = 20 A Source voltage = 28 V Wire type = 200° C Max ambient temperature = 50° C Max altitude = 20,000 ft 8 wires in a bundle Figure 11-3 for wire gauge Calculate temperature rise Figure 11-4a for temperature derating factor Figure 11-6 for altitude derating factor Figure 11.5 for bundle Calculate estimated operating temperature using the formula: T2 = T1 + (TR - T1) [(I2 / Imax)1/2] a) Determine if an appropriate wire size has been selected. The estimated operating temperature must be less than conductorrated 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 formula’s components. Participant Guide Version 1.0 page 42 Aircraft Wiring Practices Exercise 2: Wire Size Calculation Calculating wire size Calculate estimated operating temperature using the formula below (ref. page 11-26): T2 = T1 + (TR - T1) [(I2 / Imax)1/2] Where : T2 = est. operating temperature T1 = ambient temperature TR = conductor-rated temperature I2 = circuit current Imax = calculated current Version 1.0 46 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 150°C. 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). Participant Guide Version 1.0 page 43 Aircraft Wiring Practices Participant Guide Version 1.0 page 44 Aircraft Wiring Practices Participant Guide Version 1.0 page 45 Aircraft Wiring Practices Participant Guide Version 1.0 page 46 Aircraft Wiring Practices Participant Guide Version 1.0 page 47 Aircraft Wiring Practices Wire Size Calculation Wire gauge = #12 Current for #12 wire at 150° C = 60 A Altitude derating factor for 20,000 ft. = 0.92 x 60 = 55.2 A Bundle of 8 wires = 0.5 x 55.2 = 27.6 A Calculate estimated operating temperature T2 = T1 + (TR - T1) [(I2 / Imax)1/2] T2 = T2 = Compare T2 to rating for wire type to ensure T2 less Version 1.0 47 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. Participant Guide Version 1.0 page 48 Aircraft Wiring Practices 6. Breaker and wire sizing/selection: Wire system design Determining Wire System Design AC 43.13-1b, Section 5: tables and figures provide an acceptable method of determining wire system design Version 1.0 49 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. Participant Guide Version 1.0 page 49 Aircraft Wiring Practices 7. Breaker and wire sizing/selection: Exercise 3: Wire harness current capacity Exercise 3: Wire Harness Current Capacity Determine if wires are sized properly for bundle assembly. Wire harness = 10 #20 wires; 200° C 25 #22 wires; 200° C Max. ambient temperature = 60° C Max operating altitude = 60,000 ft Circuit analysis = 7 of 35 wires carrying current at or near full capacity (7/35 = 20%) Use AC 43.13 Figure 11-4a for current Figure 11-5 for bundle Figure 11-6 for altitude derating factor 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. Participant Guide Version 1.0 page 50 Aircraft Wiring Practices 8. Breaker and wire sizing/selection: Wire selection Wire Selection Conductor stranding Minimizes fatigue breakage Platings for all copper aircraft wiring Plated because bare copper develops surface oxide film — a poor conductor – Tin < 150° C – Silver < 200° C – Nickel < 260° C Version 1.0 52 a) Elevated temperature degradation of tin- and silver-plated copper conductors will occur if they are exposed to continuous operation at elevated levels. (1) For tin-plated conductors, tin-copper intermetallics will form, resulting in an increase in conductor resistance. (2) For silver-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 to continuous elevated temperature. Participant Guide Version 1.0 page 51 Aircraft Wiring Practices 9. Breaker and wire sizing/selection: Wire substitution Wire Substitution for Repairs and Maintenance When replacement wire is required, review aircraft maintenance manual to determine if original aircraft manufacturer (OAM) has approved any substitution If not approved, then contact OAM for an acceptable replacement 53 Version 1.0 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. Participant Guide Version 1.0 page 52 Aircraft Wiring Practices D. Routing, clamping, and bend radii AC 43.13-1b Topic Outline, cont. Electrical load determination Breaker and wire sizing/selection Routing/clamping/bend radii Splicing Wire terminals Grounding and bonding Wire marking Connectors and conduits Wire insulation properties Version 1.0 54 1. Routing, clamping, and bend radii: Routing Wiring Routing Eliminate potential for chafing against structure or other components Position to eliminate/minimize use as handhold or support Minimize exposure to damage by maintenance crews or shifting cargo Avoid battery electrolytes or other corrosive fluids Version 1.0 55 a) In general, wiring should be routed in such a manner to ensure reliability and to offer protection from the following potential hazards: Participant Guide Version 1.0 page 53 Aircraft Wiring Practices (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 Participant Guide Version 1.0 page 54 Aircraft Wiring Practices Wires Riding on Lightening Hole If the grommet is too short, then there is wire bundle chafing A B (2) Use as a handhold or as a support for maintenance personnel. Wiring as a Handhold Participant Guide Version 1.0 page 55 Aircraft Wiring Practices (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 moistureprone (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. Participant Guide Version 1.0 page 56 Aircraft Wiring Practices Wiring Routing, cont. Protect wires in wheel wells and other exposed areas Route wires above fluid lines, if practicable Use drip loops to control fluids or condensed moisture Keep slack to allow maintenance and prevent mechanical strain Version 1.0 60 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 or related 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 loop is 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 installed in 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. Participant Guide Version 1.0 page 57 Aircraft Wiring Practices Wire Bundles Above Fluid Lines Path of exposed end Broken wire shall not make contact with fluid line 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: Participant Guide Version 1.0 page 58 Aircraft Wiring Practices (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. Y Type Wire Bundle Breakouts Figure 8 loop may be located before Afte or after r tail of Y Be re fo Wire bundle breakout Wire bundles Head of strap shall not be located in this area or touching anything to cause chafing Plastic mechanical strapping (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 wire bundle at the breakout junction. Participant Guide Version 1.0 page 59 Aircraft Wiring Practices T Type Wire Bundle Breakouts Head of strap shall not be located in this area or touching anything to cause chafing Wire bundle breakout Wire bundle Plastic mechanical strapping (2) The “T” type of breakout (also called 90° breakout) is used when portions of wiring from both directions in the wire bundle depart the bundle to be routed in another direction. Complex Type Wire 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. Participant Guide Version 1.0 page 60 Aircraft Wiring Practices 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 Stand-offs Use stand-offs to maintain clearance between wires and structure Employing tape or tubing is generally not acceptable as an alternative Exception: Where impossible to install off-angle clamps to maintain wiring separation in holes, bulkheads, floors, etc. Version 1.0 66 (1) The wiring design should preclude wire bundles from contacting structure. Participant Guide Version 1.0 page 61 Aircraft Wiring Practices 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. Participant Guide Version 1.0 page 62 Aircraft Wiring Practices 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. Participant Guide Version 1.0 page 63 Aircraft Wiring Practices 3. Routing, clamping, and bend radii: Clamping Clamping Support wires by suitable clamps, grommets, or other devices at intervals of not more that 24 inches Supporting devices should be of suitable size and type with wire and/or cables held securely in place without damage to wire or wire insulation 70 Version 1.0 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. Participant Guide Version 1.0 page 64 Aircraft Wiring Practices Clamps Wire bundles should be snug in clamp (no movement) Cable not able to move axially RF cables: do not crush Mount clamps with attachment hardware on top Tying NOT used as alternative to clamping Version 1.0 71 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 achieve this 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 attachment hardware 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. Participant Guide Version 1.0 page 65 Aircraft Wiring Practices Example of Correct Cable Slack Appropriate slack 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. Participant Guide Version 1.0 page 66 Aircraft Wiring Practices Clamp Distortion Correct clamp position Incorrect clamp position Distortion of rubber on clamp is NOT acceptable 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. Participant Guide Version 1.0 page 67 Aircraft Wiring Practices Clamp Orientation 90±5° Correct Incorrect 90±5° Correct Incorrect 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. Participant Guide Version 1.0 page 68 Aircraft Wiring Practices Plastic Snap-in Clamp (Tie Mount) support bracket snap-in tie mount release tab tail 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. Participant Guide Version 1.0 page 69 Aircraft Wiring Practices Typical Rubber Clamp Rubber cushion All wires contained in rubber cushion Clamp tabs Wedge No pinching Stand off j) Clamps on wire bundles should be selected so that they have a snug fit without pinching wires. Typical Nylon Closed-Face Clamp 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. Participant Guide Version 1.0 page 70 Aircraft Wiring Practices Engage Clamp Tab in Slot Incorrect Clamp tab Clamp slot 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. Participant Guide Version 1.0 page 71 Aircraft Wiring Practices Clamp Pinching Incorrect Do not pinch wires here Correct 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 manufacturer’s wiring specifications allow for wire cable build-up under certain circumstances. Participant Guide Version 1.0 page 72 Aircraft Wiring Practices Exercise: Clamping A B 4. Routing, clamping, and bend radii: Wire bend radii Wire Bend Radii Minimum bend radius - 10 times the outside diameter of the largest wire or cable in the group — unsupported 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 Version 1.0 83 a) Where it is not practical to install wiring or cables within the radius requirements, the bend should be enclosed in insulating tubing. Participant Guide Version 1.0 page 73 Aircraft Wiring Practices Minimum Bend Radii No support at end of bend Min. bend radius - 10 x parameter of wire or cable Min. bend radius 3 x diameter of wire Diameter of wire or cable Support at both ends of wire bend b) This illustration shows the proper bend radii for three different scenarios. Bend radii okayGreater than 3 times diameter (secured at both ends of loop) Participant Guide Version 1.0 page 74 Aircraft Wiring Practices Bend radii problemLess 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. Exercise 4: Wiring Problems Find the wiring problems illustrated in these photos. Passenger Seat A B Participant Guide Version 1.0 page 75 Aircraft Wiring Practices 5. Routing, clamping, and bend radii: Spare wire and connector contacts Unused Wires Secured Tied into a bundle or secured to a permanent structure Individually cut with strands even with insulation Pre-insulated, closed-end connector or 1-inch piece of insulating tubing folded and tied back Version 1.0 88 a) The following three slides depict an acceptable method of insulating and physically securing a spare connector contact within a wire bundle. Spare Connector Contact: Preparing Single Contact Tubing Wire Contact 3 times length of contact Participant Guide Version 1.0 page 76 Aircraft Wiring Practices Spare Connector Contact: Folding Tube and Tying Single Contact 0.75 ± 0.15 in. Tying tape Fold Spare Connector Contact: Single Contact Attachment to Wire Bundle Wire bundle Tying tape Participant Guide Version 1.0 page 77 Aircraft Wiring Practices b) Spare wire termination using an endcap. This is another way to protect unused wiring. Spare Wire Termination Using Endcap Wire and end cap in position Install end cap over wire end. Shrink in place. Adhesive tape Wire bundle End caps Fiberglass tying tape (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) Participant Guide Version 1.0 page 78 Aircraft Wiring Practices c) Coil and stow methods Coil and Stow Methods Wire bundle Wire bundle ties Clamp Coil and stow short wire bundles in low vibration areas (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. Participant Guide Version 1.0 page 79 Aircraft Wiring Practices Coil and Stow Methods, cont. Wire bundle ties Clamp Wire bundle Excess wire Coil and stow long wire bundles in low vibration areas Coil and Stow Methods, cont. Wire bundle Teflon tape Wire bundle ties Adjacent wire bundle Coil and stow in medium and high vibration areas (3) Coil and stow in medium and high vibration areas requires additional tie straps, sleeving, and support. Participant Guide Version 1.0 page 80 Aircraft Wiring Practices Exercise: Stowing Unused Wires A B E. Wire replacement and splicing 1. Wire replacement and splicing: Wire replacement Wire Replacement Wires should be replaced when: Chafed or frayed Insulation suspected of being penetrated Outer insulation is cracking Damaged by or known to have been exposed to electrolyte, oil, hydraulic fluid, etc. Evidence of overheating can be seen Version 1.0 98 Participant Guide Version 1.0 page 81 Aircraft Wiring Practices 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. Participant Guide Version 1.0 page 82 Aircraft Wiring Practices Wire Replacement, cont. Wire should be replaced when: Wire bears evidence of being crushed or kinked Shield on shielded wire if frayed and/or corroded Wire shows evidence of breaks, cracks, dirt, or moisture in plastic sleeving Sections of wire have splices occurring at less than 10-ft intervals Version 1.0 100 b) Continuing, this slide shows additional circumstances that warrant replacing wiring. c) Shielding requirements Wire Replacement, cont. Shielding requirements Replacement wires must have the same shielding characteristics as the original wire, such as shield optical coverage and resistance per unit length Replacement wires should not be installed outside the bundle shield Version 1.0 101 (1) For more information on shielding, the Lightning/HIRF Video and Self-study Guide is available. (To obtain, see your Directorate training manager.) Participant Guide Version 1.0 page 83 Aircraft Wiring Practices d) Adding or replacing wires on a bundle Adding or Replacing Wires on a Bundle Chafing Incorrect procedure Correct procedure (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 a Bundle A B Participant Guide Version 1.0 page 84 Aircraft Wiring Practices 2. Wire replacement and splicing: Splicing AC 43.13-1b Topic Outline, cont. Electrical load determination Breaker and wire sizing/selection Routing/clamping/bend radii Splicing Wire terminals Grounding and bonding Wire marking Connectors and conduits Wire insulation properties Version 1.0 104 Wire Splicing Keep to a minimum Avoid in high vibration areas Locate to permit inspection Stagger in bundles to minimize increase in bundle size Use self-insulated splice connector, if possible Version 1.0 105 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 can’t be Participant Guide Version 1.0 page 85 Aircraft Wiring Practices 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-T7928 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. Participant Guide Version 1.0 page 86 Aircraft Wiring Practices Overheated wire at the splice d) Splices that are not crimped properly (under or over) can cause increased resistance leading to overheat conditions. Ganged wire splices 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. Participant Guide Version 1.0 page 87 Aircraft Wiring Practices 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 AC 43.13-1b Topic Outline, cont. Electrical load determination Breaker and wire sizing/selection Routing/clamping/bend radii Splicing Wire terminals Grounding and bonding Wire marking Connectors and conduits Wire insulation properties Version 1.0 110 Participant Guide Version 1.0 page 88 Aircraft Wiring Practices Terminals Tensile strength of the wire-toterminal joint should be at least the equivalent tensile strength of the wire Resistance of the wire-to-terminal joint should be negligible relative to the normal resistance of the wire Version 1.0 111 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. Participant Guide Version 1.0 page 89 Aircraft Wiring Practices 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 one post. 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 usually result in mechanical weakening or damage to the terminal. e) This slide is an example of limits established by the OAM with regard to bending the terminal prior to installation. Bending of Straight Copper Terminals Brazed joint Position of tongue before bending Participant Guide Version 1.0 page 90 Aircraft Wiring Practices 3. Terminal strips Terminal Strips Barriers to prevent adjacent studs from contacting each other Current should be carried by terminal contact surface and not by stud Studs anchored against rotation Replace defective studs with studs of same size and material, mount securely, tighten terminal securing nut Version 1.0 113 a) Wires are usually joined at terminal strips fitted with barriers. (1) When more than four terminals are to be connected together, a small metal bus should be mounted across two or more adjacent studs. Terminal Strips, cont. Mount strips so loose metallic objects cannot fall across terminal Provide spare stud for breaks and future expansion Inspect terminal periodically for loose connections, metallic objects, dirt, and grease accumulation – Can cause arcing, resulting in fire or systems failure Version 1.0 114 Participant Guide Version 1.0 page 91 Aircraft Wiring Practices Terminals on circuit breakers b) Every possibility of terminals not being torqued properly, due to misinstallation, poor maintenance, and service life, should be addressed in the design. (1) Electrical equipment malfunction has frequently been traced to poor terminal connections at terminal boards. (2) Loose contact surfaces can produce localized heating that may ignite nearby combustible materials or overheat adjacent wire insulation. (3) The green torque stripes painted on the terminal fasteners in this picture. This is an excellent method to quickly determine if a terminal fastener is still torqued to its original value. Participant Guide Version 1.0 page 92 Aircraft Wiring Practices Power feeder terminals c) High current terminals are more sensitive to increased resistance due to a improperly torqued terminal. (1) The power feeder cables should not be touching each other without being suitably tied with spacers or other securing device. Participant Guide Version 1.0 page 93 Aircraft Wiring Practices 4. Terminal lugs Terminal Lugs Connect wiring to terminal block studs No more than 4 lugs, or 3 lugs and a bus bar, per stud Lug hole size should match stud diameter Greatest diameter on bottom, smallest on top Tightening terminal connections should not deform lugs Version 1.0 117 a) Wire terminal lugs should be used to connect wiring to terminal block studs or equipment terminal studs. b) When the terminal lugs attached to a stud vary in diameter, the greatest diameter should be placed on the bottom and the smallest diameter on top. c) Terminal lugs should be so positioned that bending of the terminal lug is not required to remove the fastening screw or nut, and movement of the terminal lugs will tend to tighten the connection. Participant Guide Version 1.0 page 94 Aircraft Wiring Practices Terminal Lugs, cont. Aluminum lugs Crimped to aluminum wire only – Special attention needed to guard against excessive voltage drop at terminal junction • Inadequate terminal contact area • Stacking errors • Improper torquing Use calibrated crimp tools Version 1.0 118 d) The tongue of the aluminum terminal lugs or the total number of tongues of aluminum terminal lugs when stacked, should be sandwiched between two flat washers (cadmium plated) when terminated on terminal studs. Spacers or washers should not be used between the tongues of like material terminal lugs. (1) Examples of such conditions are improper installation of terminals and washers, improper torsion (“torquing” of nuts), and inadequate terminal contact areas. e) Aluminum wire is normally used in sizes of 10 gauge and larger to carry electrical power in large transport category aircraft in order to save weight. Although not as good a conductor as copper, aluminum is lighter when compared to copper and the weight savings can be significant for a large aircraft that may have several hundred feet of power feeder cable. f) Because aluminum is used primarily for high current power applications, the terminal junctions are more sensitive to conditions leading to increased junction resistance which can cause arcing and localized heat distress. Participant Guide Version 1.0 page 95 Aircraft Wiring Practices 5. Terminal stacking materials and methods a) Multiple wires often terminate onto a single terminal stud. Care should be taken to install the terminal properly. The materials that the terminals are constructed of will impact the type of stacking methods used. Dissimilar metals, when in contact, can produce electrolysis that can cause corrosion, thus degrading the terminal junction resistance and causing arcing or hot spots. Terminal Stacking (like materials) Nut Lock washer Flat washer Copper terminal lugs Terminal stud b) For stacking terminals that are made of like materials, the terminals can be stacked directly on top of each other. Participant Guide Version 1.0 page 96 Aircraft Wiring Practices Terminal Stacking (unlike materials) Copper terminal Flat washers Terminal stud Nut Lock washer Flat washer Aluminum terminals c) When stacking unlike materials together, use a cadmiumplated flat washer to isolate the dissimilar metals. Terminal Stacking Methods Crimp barrel (belly up) Nut Lock washer Flat washer Crimp barrel (belly down) One-Sided Entry With Two Terminals d) When two terminals are installed on one side of the terminal strip, ensure that the terminal crimp barrels do not interfere with one another. One method to avoid this problem is to install the terminals with the barrels “back to back.” Participant Guide Version 1.0 page 97 Aircraft Wiring Practices Terminal Stacking Methods, cont. Crimp barrel (belly down) in “V” split Nut Lock washer Flat washer Crimp barrel (belly up) in center of “V” One-Sided Entry With 3 Terminals Terminal Stacking Methods, cont. Nut Lock washer Flat washer Crimp barrel (belly up) in “V” split Crimp barrel (belly down) in “V” split One-Sided Entry With 4 Terminals e) The stacking method used to connect terminals to terminal strips should cause no interference between terminals that could compromise the integrity of the terminal junction. Participant Guide Version 1.0 page 98 Aircraft Wiring Practices 6. Terminal tightening hardware Terminal Tightening Hardware Incorrect Space Nut Lock washer Flat washer Correct Lock washer not compressed Lock washer compressed a) Service history has shown that hardware stack up at terminals is prone to human error. b) It is important to use the correct tightening hardware and install it correctly for a given installation. It is important to ensure the locking washer is fully compressed and is adjacent to the nut. c) There should be a minimum of two to three threads showing on the stud when the nut is properly torqued. Participant Guide Version 1.0 page 99 Aircraft Wiring Practices 7. Washer size selection Washer Size Selection Improperly-sized washer Raised portion of terminal Non-self locking nut Steel washers Split lock washer Correct Aluminum terminal a) Select and use the correct size washers in any termination. Undersized or oversized washers can lead to increased junction resistance and localized heat or arcing. b) An improperly sized washer can lead to insufficient contact between the terminal and terminal lug. Example: Terminal Stacking To prevent corrosion from dissimilar metals, put a cadmium washer between aluminum and copper terminals. A B Participant Guide Version 1.0 page 100 Aircraft Wiring Practices Example: Lock Washers Example: Lock Washers, cont. Participant Guide Version 1.0 page 101 Aircraft Wiring Practices 8. Exercise 5: Terminal build up Which of the terminal assemblies below is correct? nut lock washer aluminum lug copper lug nut lock washer cadmium washers aluminum lug flat washer nut lock washer flat washer cadmiumplated washers copper lug flat washer Exercise 5: Terminal Build Up A B aluminum lug C Participant Guide Version 1.0 page 102 Aircraft Wiring Practices G. Grounding and bonding AC 43.13-1b Topics Covered Electrical load determination Breaker and wire sizing/selection Routing/clamping/bend radii Splicing Wire terminals Grounding and bonding Wire marking Connectors and conduits Wire insulation properties Version 1.0 130 1. This is a high-level overview of grounding. For more detailed information, the Lightning/HIRF Video and Self-study Guide is available through your training manager. Grounding Definition Grounding is the process of electrically connecting conductive objects to either a conductive structure or some other conductive return path for the purpose of safely completing either a normal or fault circuit. Version 1.0 131 2. Grounding. One of the more important factors in the design and maintenance of aircraft electrical systems is proper bonding and grounding. Inadequate bonding or grounding can lead to Version 1.0 page 103 Participant Guide Aircraft Wiring Practices unreliable operation of systems, such as EMI, electrostatic discharge damage to sensitive electronics, personnel shock hazard, or damage from lightning strike. Grounding Types of grounding AC returns DC returns Others Avoid mixing return currents from various sources Noise will be coupled from one source to another and can be a major problem for digital systems Version 1.0 132 a) Mixing return currents. This interaction may not be a problem or it could be a major non-repeatable anomaly. (1) To minimize the interaction between various return currents, different types of grounds should be identified and used. As a minimum, the design should use three ground types: (1) AC returns, (2) DC returns, and (3) all others. (2) For distributed power systems, the power return point for an alternative power source would be separated. • For example, in a two-AC generator system (one on the right side and the other on the left side), if the right AC generator were supplying backup power to equipment located in the left side, (left equipment rack) the backup AC ground return should be labeled “AC Right.” The return currents for the left generator should be connected to a ground point labeled “AC Left.” Participant Guide Version 1.0 page 104 Aircraft Wiring Practices Grounding, cont. Design of ground path should be given as much attention as other leads in the system Grounding should provide a constant impedance Ground equipment items externally even when internally grounded Avoid direct connections to magnesium structure for ground return Version 1.0 133 b) Constant impedance. A requirement for proper ground connections is that they maintain an impedance that is essentially constant. (1) Ground return circuits should have a current rating and voltage drop adequate for satisfactory operation of the connected electrical and electronic equipment. (2) EMI problems, that can be caused by a system’s power wire, can be reduced substantially by locating the associated ground return near the origin of the power wiring (e.g., circuit breaker panel) and routing the power wire and its ground return in a twisted pair. (3) Special care should be exercised to ensure replacement on ground return leads. The use of numbered insulated wire leads instead of bare grounding jumpers may aid in this respect. c) External grounding of equipment items. Direct connections to a magnesium structure (which may create a fire hazard) must not be used for ground return. Participant Guide Version 1.0 page 105 Aircraft Wiring Practices Grounding, cont. Heavy current grounds Attach to individual grounding brackets attached to aircraft structure with a proper metal-to-metal bond Accommodate normal and fault currents of system without creating excessive voltage drop or damage to structure Give special attention to composite aircraft Version 1.0 134 d) Heavy-current grounds. Examples include power ground connections for generators, transformer rectifiers, batteries, and external power receptacles. (1) Use at least three fasteners, located in a triangular or rectangular pattern, must be used to secure such brackets in order to minimize susceptibility to loosening under vibration. (2) When using a material such as carbon fiber composite (CFC), which has a higher resistivity than aluminum or copper, provide an alternative ground path(s) for power return current. Participant Guide Version 1.0 page 106 Aircraft Wiring Practices 3. Bonding Bonding Equipment bonding Low impedance paths to aircraft structure required for electronic equipment to provide radio frequency return circuits Facilitates reduction in EMI for most electrical equipment – Cases of components that produce EMI should be grounded to structure Version 1.0 135 a) Equipment bonding. To ensure proper operation of electronic equipment, it is particularly important to conform the system’s installation specification when inter-connections, bonding, and grounding are being accomplished. Bonding, cont. Metallic surface bonding Electrically connecting conductive exterior airframe components through mechanical joints, conductive hinges, or bond straps – Protects against static charges and lightning strikes Version 1.0 136 b) Metallic surface bonding. Exceptions may be necessary for some objects such as antenna elements, whose function Participant Guide Version 1.0 page 107 Aircraft Wiring Practices requires them to be electrically isolated from the airframe. Such items should be provided with an alternative means to conduct static charges and/or lightning currents, as appropriate. Bonding, cont. Static bonds Required for all isolated conducting parts with area greater than 3 in2 and a linear dimension over 3" subjected to appreciable electrostatic charging due to precipitation, fluid, or air in motion – Resistance of less than 1 ohm when clean and dry usually ensures static dissipation on larger objects Version 1.0 137 c) Static bonds. All isolated conducting parts inside and outside the aircraft, having an area greater than 3 in2 and a linear dimension over 3 inches, that are subjected to appreciable electrostatic charging due to precipitation, fluid, or air in motion, should have a mechanically secure electrical connection to the aircraft structure of sufficient conductivity to dissipate possible static charges. (1) A resistance of less than 1 ohm when clean and dry will generally ensure such dissipation on larger objects. Higher resistances are permissible in connecting smaller objects to airframe structure. Participant Guide Version 1.0 page 108 Aircraft Wiring Practices H. Wire marking AC 43.13-1b Topics Covered Electrical load determination Breaker and wire sizing/selection Routing/clamping/bend radii Splicing Wire terminals Grounding and bonding Wire marking Connectors and conduits Wire insulation properties Version 1.0 138 1. Purpose Wire Marking Necessary for: Safety of operation Safety to maintenance personnel Ease of maintenance To identify performance capability, use wire material part number and five digit/letter code identifying manufacturer Version 1.0 139 2. Common manufacturer marking process. Each wire and cable should be marked with a part number. It is common practice for wire manufacturers to follow the wire material part number with the five digit/letter C.A.G.E. code identifying the wire Version 1.0 page 109 Participant Guide Aircraft Wiring Practices manufacturer. Using this code, existing installed wire that needs replacement can be identified as to its performance capabilities. This helps to prevent the inadvertent use of lower performance and unsuitable replacement wire. a) NOTE: Be careful when hot stamping wire. Service history has shown problems associated with hot stamping due to insulation damage caused during the process. b) The method of identification should not impair the characteristics of the wiring. c) Original wire identification. To facilitate installation and maintenance, retain the original wire-marking identification. The wire identification marks should consist of a combination of letters and numbers that identify the wire, the circuit it belongs to, its gauge size, and any other information to relate the wire to a wiring diagram. All markings should be legible in size, type, and color. d) Identification and information related to the wire and wiring diagrams. The wire identification marking should consist of similar information to relate the wire to a wiring diagram. Participant Guide Version 1.0 page 110 Aircraft Wiring Practices Wire Marking, cont. Wire identification marks identify wire, circuit, and gauge size Markings should be legible in size, type, and color at 15-inch maximum intervals along the wire [directly on wire or indirect (sleeve/tag)]