ASTM F2639-18

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation:F2639 −18
Standard Practice for
Design, Alteration, and Certification of Aircraft Electrical
Wiring Systems
This standard is issued under the fixed designation F2639; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
Grounding and Bonding 5.5
Electrical Wire Chart 5.6
1.1 Definition—This practice defines acceptable practices
Wire and Cable Identification 6
and processes for the design, alteration, and certification of General 6.1
Wire and Cable Identification 6.2
electric systems and installations in general aviation aircraft.
Types of Markings 6.3
This practice does not change or create any additional regula-
Sleeve and Cable Marker Selection 6.4
tory requirements nor does it authorize changes in or permit Placement of Identification Markings 6.5
Wiring Installation 7
deviations from existing regulatory requirements.
General 7.1
Wire Harness Installation 7.2
1.2 Applicability—The guidance provided in this practice is
Power Feeders 7.3
directed to air carriers, air operators, design approval holders,
Service Loops 7.4
Supplemental Type Certificate (STC) holders, maintenance
Drip Loops 7.5
Soldering 7.6
providers, repair stations, and anyone performing field ap-
Strain Relief 7.7
proval modifications or repairs.
Grounding and Bonding 7.8
Splicing 7.9
1.3 Protections and Cautions—This practice provides guid-
Fuel Tank Wiring 7.10
ance for developing actions and cautionary statements to be
Corrosion Preventative Compounds (CPC) 7.11
(MIL-C-81309)
added to maintenance instructions for the protection of wire
Electrical Load Considerations 8
and wire configurations. Maintenance personnel will use these
General 8.1
enhanced procedures to minimize contamination and acciden-
Methods for Determining the Current-Carrying 8.2
Capacity of Wires
tal damage to electrical wiring interconnection system (EWIS)
Acceptable Means of Monitoring and 8.3
while working on aircraft.
Controlling the Electrical Load
Electrical System Components 9
1.4 “Protect and Clean As You Go” Philosophy—This
General 9.1
philosophy is applied to aircraft wiring through inclusion in
Alternators 9.2
operators’maintenanceandtrainingprograms.Thisphilosophy
Generators 9.3
Ground Power Units 9.4
stresses the importance of protective measures when working
Auxiliary Power Units 9.5
on or around wire bundles and connectors. It stresses how
Batteries 9.6
important it is to protect EWIS during structural repairs, STC
Circuit Protection Devices 9.7
Conduit 9.8
installations, or other alterations by making sure that metal
Connectors 9.9
shavings, debris, and contamination resulting from such work
Inverters and Power Converters 9.10
are removed. Junctions 9.11
Junction Boxes 9.12
1.5 This practice includes the following sections:
Electronic Assemblies 9.13
Relays 9.14
Title Section
Studs 9.15
Wire Selection 5
Switches 9.16
General 5.1
Terminals and Terminal Blocks 9.17
Aircraft Wire Materials 5.2
Waveguides 9.18
Table of Acceptable Wires 5.3
Electrical System Component Installation 10
Severe Wind and Moisture Problems (SWAMP) 5.4
General 10.1
Alternators 10.2
Generators 10.3
Auxiliary Power Units (APUs) 10.4
This practice is under the jurisdiction of ASTM Committee F39 on Aircraft
Batteries 10.5
Systems and is the direct responsibility of Subcommittee F39.01 on Design,
Circuit Protection Devices 10.6
Alteration, and Certification of Electrical Systems.
Conduit 10.7
Current edition approved Oct. 1, 2018. Published November 2018. Originally
Connectors 10.8
approved in 2007. Last previous edition approved in 2015 as F2639–15. DOI:
Inverters and Power Converters 10.9
10.1520/F2639-18.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2639−18
ANSI EIA/TIA-568-BCommercial Building Telecommuni-
Junctions 10.10
Junction Boxes, Panels, Shields, and 10.11
cations Cabling Standard
Microswitch Housings
ANSI J-STD-004Requirements for Soldering Fluxes
PC Board Assemblies 10.12
Relays 10.13
2.4 FAA Standards:
Studs 10.14
Advisory Circular 20-53()Protection of Aircraft Fuel Sys-
Switches 10.15
Terminals and Terminal Blocks 10.16 tems Against Fuel Vapor Ignition Due To Lightning
Waveguides 10.17
AC 20-136()Protection of Aircraft Electrical/Electronic
EMI/RFI 11
Systems Against the Indirect Effects of Lightning
General 11.1
Grounding and Bonding 11.2 AC 21-16()RTCA Document DO-160D/E/F/G
HIRF 11.3
AC 23.1309-1ESystems Safety Analysis and Assessment
Lightning 11.4
for Part 23 Airplanes
Alterations 12
General 12.1 AC 25-16Electrical Fault and Fire Prevention and Protec-
Wire Substitutions 12.2
tion
Commercial Off-the-Shelf (COTS) Components 12.3
AC25.869-1()ElectricalSystemFireandSmokeProtection
Electrical Load Considerations 12.4
Batteries 12.5 AC 25.981-1( ) Fuel Tank Ignition Source Prevention
Circuit Breakers 12.6
Guidelines
Junction Boxes 12.7
AC 25.1353-1()Electrical Equipment and Installations
Relays 12.8
Switches 12.9 AC 25.1357-1()Circuit Protective Device Accessibility
Wire Marking 12.10
AC 27-1BCertification of Normal Category Rotorcraft
Wire Bundle Routing 12.11
AC 29-2CCertification of Transport Category Rotorcraft
Wire Bundle Combing 12.12
Interference Tests 12.13
DOT/FAA/CT86/8DeterminationofElectricalPropertiesof
System Safety Assessments 12.14
Bonding and Fastening Techniques
Certification Processes 13
DOT/FAA/CT-83/3Users Manual for FAAAdvisory Circu-
General 13.1
Certification 13.2 lar 20-53a
Alterations and Maintenance 13.3
DOT/FAA/CT-89-22Aircraft Lightning Protection Hand-
1.6 Values—The values given in inch-pound units are to be
book
regarded as the standard. The values in parentheses are for
Title14 Code of Federal Regulations Part 23Airworthiness
information only. See Appendix X2 for SI-based prefixes and
Standards: Normal, Utility, Acrobatic, and Commuter
powers of 10.
Category Airplanes
NOTE 1—Where SI units are required, refer to Annex 5 of ICAO.
Title14 Code of Federal Regulations Part 25Airworthiness
1.7 This standard does not purport to address all of the
Standards: Transport Category Airplanes
safety concerns, if any, associated with its use. It is the Title14 Code of Federal Regulations Part 27Airworthiness
responsibility of the user of this standard to establish appro-
Standards: Normal Category Rotorcraft
priate safety, health, and environmental practices and deter- Title14 Code of Federal Regulations Part 29Airworthiness
mine the applicability of regulatory limitations prior to use.
Standards: Transport Category Rotorcraft
1.8 This international standard was developed in accor- Title14 Code of Federal Regulations Part 31Airworthiness
dance with internationally recognized principles on standard-
Standards: Manned Free Balloons
ization established in the Decision on Principles for the Title14 Code of Federal Regulations Part 33Airworthiness
Development of International Standards, Guides and Recom- Standards: Aircraft Engines
mendations issued by the World Trade Organization Technical Title14 Code of Federal Regulations Part 34Fuel Venting
Barriers to Trade (TBT) Committee. and Exhaust Emission Requirements for Turbine Engine
Powered Airplanes
2. Referenced Documents
Title14 Code of Federal Regulations Part 35Airworthiness
Standards: Propellers
2.1 Unlessapprovedbytheadministrator,thelatestrevision
Title14 Code of Federal Regulations Part 36Noise Stan-
of the listed documents shall be used for reference.
dards: Aircraft Type and Airworthiness Certification
2.2 ASTM Standards:
2.5 SAE Standards:
F2490Guide forAircraft Electrical Load and Power Source
AMS-S-8802Sealing Compound, Temperature-Resistant,
Capacity Analysis
IntegralFuelTanksandFuelCellCavities,HighAdhesion
2.3 ANSI Standards:
(Replaces MIL-S-8802)
ANSI/EIA-5200000Generic Specification for Special-Use
ARP1199Selection,Application, and Inspection of Electric
Electromechanical Switches of Certified Quality
Overcurrent Protective Devices
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
Standards volume information, refer to the standard’s Document Summary page on 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http://
the ASTM website. www.access.gpo.gov.
3 5
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St., Available from Society of Automotive Engineers (SAE), 400 Commonwealth
4th Floor, New York, NY 10036, http://www.ansi.org. Dr., Warrendale, PA 15096-0001, http://www.sae.org.
F2639−18
ARP 1308Preferred Electrical Connectors for Aerospace A-A-52083Tape, Lacing andTying, Glass (replaces MIL-T-
Vehicles and Associated Equipment 43435)
ARP 1870 Aerospace Systems Electrical Bonding and A-A-52084Tape, Lacing andTying,Aramid (replaces MIL-
T-43435)
Grounding for Electromagnetic Compatibility and Safety
A-A-59163Insulation Tape, Electrical, Self Adhering, Un-
ARP 1928Torque Recommendations for Attaching Electri-
supported Silicone Rubber
cal Wiring Devices to Terminal Boards or Blocks, Studs,
AN735Clamp
Posts, Etc
AN960JD10LConductive Washer
ARP 4761Guidelines and Methods for Conducting the
MIL-C-22520Wire Termination Crimp Tools
SafetyAssessmentProcessonCivilAirborneSystemsand
MIL-C-26482Connectors, Electrical, (Circular, Miniature,
Equipment
Quick Disconnect, Environment Resisting), Receptacles
ARP5369GuidelinesforWireIdentificationMarkingUsing
and Plugs, General Specification for
the Hot Stamp Process
MIL-C-39029 Contacts, Electrical Connector, General
ARP 5414Aircraft Lightning Zoning
Specification for
ARP 5583Guide to Certification of Aircraft in a High
MIL-PRF-81309Corrosion Preventative Compounds,Water
Intensity Radiated Field (HIRF) Environment
Displacing, Ultra-Thin Film
AS 4372Performance Requirements for Wire, Electric, In-
MIL-DTL-22520Crimping Tools, Wire Termination, Gen-
sulated Copper or Copper Alloy
eral Specification for (replaces MIL-C-22520/2)
AS 4373Test Methods for Insulated Electric Wire
MIL-DTL-27500Cable,Power,ElectricalandCableSpecial
AS 4461Assembly and Soldering Criteria for High Quality/
Purpose, Electrical Shielded and Unshielded, General
High Reliability
Specification for
AS 6136Conduit, Electrical, Flexible, Shielded, Aluminum
MIL-DTL-5015 Connectors, Electrical, Circular Threaded,
Alloy for Aircraft Installations. (Replaces MIL-C-6136)
AN Type, General Specification for
AS 7351Clamp, Loop Type Bonding-FSC 5340 (replaces
MIL-DTL-83723Connectors, Electrical, (Circular, Environ-
AN735)
ment Resisting), Receptacles and Plugs, General Specifi-
AS 7431 Bracket, Support Clamp-FSC 5340 (replaces
cation for
AN743)
MIL-F-14256F Flux, Soldering, Liquid, Paste Flux, Solder
AS 7928Terminals, Lug: Splices, Conductor: Crimp Style,
Paste and Solder-Paste Flux (for Electronic/Electrical
Copper,GeneralSpecificationfor(ReplacesMIL-T-7928)
use), General Specification for
AS 22759Wire, Electrical, Fluoropolymer-Insulated, Cop-
MIL-M-81531Marking of Electrical Insulating Materials
per or Copper Alloy. (Replaces MIL-W-22759)
MIL-PRF-39016 Relays Electromagnetic, Established
AS 23190Straps, Clamps, Plastic and Metal, and Mounting
Reliability, General Specification for
Hardware, Plastic for Cable Harness Tying and Support
MIL-PRF-5757Relays, Hermetically Sealed
Clamp, Loop, Metal, Cushioned, Adjustable, Wire
MIL-PRF-6106Relays,Electromagnetic,GeneralSpecifica-
Support, Type V, Class 1-FSC (replaces MIL-S-23190)
tion for
AS 25064Conduit, Flexible, Radio Frequency Shielding
MIL-PRF-83536 Relays, Electromagnetic, Established
[use in place of MIL-C-7931?]
Reliability, 25Amperes and Below, General Specification
AS 25281Clamp, Loop, Plastic, Wire Support-FSC 5340
for
(replaces MS25281)
MIL-S-8516Sealing Compound, Polysulfide Rubber, Elec-
AS 25435Terminal-Lug, Crimp Style, Straight Type, for
tric Connectors and Electric Systems, Chemically Cured
Aluminum Aircraft Wire, Class 1 (Replaces MS254350)
MIL-STD-704Aircraft, Electrical Power Characteristics
AS25436Terminal-Lug,CrimpStyle,90°UprightType,for
MIL-T-8191Test and Checkout Equipment, Guided Missile
Aluminum Aircraft Wire, Class 1 (Replaces MS25436)
Weapons Systems, General Specification for [should this
AS25438Terminal-Lug,CrimpStyleRightAngleType,for
be SAE AMS-T-81914 replaces MIL-T-81914?]
Aluminum Aircraft Wire, Class 1 (Replaces MS25438)
MIL-W-25038 Wire, Electrical, High-Temperature, Fire
AS 33671 Strap, Tie Down, Electrical Components,
Resistant, and Flight Critical
Adjustable, Self Clinching, Plastic, Type I, Class 1 (Re-
MIL-W-81044 Wire, Electric, Crosslinked Polyalkene,
places MS3367)
CrosslinkedAlkine-Imide, or Polyarylene Insulated, Cop-
AS 50881AWiring Aerospace Vehicle (Replaces MIL-W-
per or Copper Alloy
5088)
MIL-W-81381Wire,Electric,Fluorocarbon/PolyimideInsu-
AS 70991 Terminal, Lug and Splice, Crimp Style
lated
Aluminum, forAluminumAircraft Wire. (Replaces MIL-
MS21919Cable Clamps
T-7099E)
MS25440 Flat Washer
2.6 Military Standards:
MS3057Cable Clamp Adapters
A-A-52080Nylon Lacing Tape (replaces MIL-T-43435) MS3109Boots, Heat-Shrinkable, Strain-Relief, RightAngle
A-A-52081 Polyester Lacing Tape (replaces MIL-T-43435) MS3115 Connectors, Receptacle, Electrical, Dummy
A-A-52082Tape, Lacing and Tying, TFE Fluorocarbon
Stowage, Bayonet Coupling, for MIL-C-26482
(tetra fluorocarbon) (replaces MIL-T-43435) Connectors, Series 1 and 2
F2639−18
MS3117Boots, Heat-Shrinkable, Strain-Relief, RightAngle NationalElectricalManufacturersAssociation(NEMA)WC
MS3142Connector, Receptacle, Electrical, Box Mounting, 27500Standards for Aerospace and Industrial Electric
Solder Contact Hermetic, AN Type Cable (replaces MIL-DTL-27500H)
MS3143 Connector, Receptacle, Electrical, Solder ICAOAnnex 5Units of Measurement to be used inAir and
Mounting, Solder Contact Hermetic, AN Type Ground Operations
MS3158BackshellsShrinkableBoot,forElectricConnector
3. Terminology
MS3180 Cover, Protective, Electrical Connector Plug,
Bayonet Coupling for MIL-C-26482 Connectors
3.1 Definitions:
MS3181Cover,Protective,ElectricalConnectorReceptacle,
3.1.1 abrasion resistance, n—ability of a material to resist
Bayonet Coupling for MIL-C-26482 Connectors
intrinsic property deterioration as a result of physical abrasion.
MS3416Backshells, Straight, for Electrical Connectors
3.1.2 adhesive, n—compound that adheres or bonds two
MS3440Connectors, Receptacle, Electric Series 2, Narrow
items together.
Flange Mount, Bayonet Coupling, Solder Pin Contact
3.1.2.1 Discussion—Adhesives may come from either natu-
Class H
ral or synthetic sources.
MS3443Connectors, Receptacle, Electric, Series 2, Solder
3.1.3 Airworthiness Directive (AD), n—regulationissuedby
Flange Mount, Bayonet Coupling, Solder Pin Contact
the Federal Aviation Administration (FAA) that applies to
Class H
aircraft, aircraft engines, propellers, or appliances when an
MS3450Connectors,Receptacle,Electrical,WallMounting,
unsafe condition exists and that condition is likely to exist or
Rear Release, Crimp Contact, AN Type
develop in other products of the same type design.
MS3451 Connectors Receptacle, Electrical, Cable
3.1.4 ampere (A), n—basic unit of current flow; 1 A is the
Connecting, Rear Release, Crimp Contact, AN Type
amount of current that flows when a difference of potential of
MS3452Connector, Receptacle, Electric, Box Mounting,
1Visappliedtoacircuitwitharesistanceofone;1coulomb/s.
Rear Release, Crimp Contact, AN Type
MS3456Connectors, Plug, Electrical, Rear Release, Crimp
3.1.5 antenna, n—device designed to radiate or intercept
Contact, AN Type
electromagnetic waves.
MS3459Connector, Plug, Electrical, Self-Locking, Cou-
3.1.6 appliance,n—anyinstrument,mechanism,equipment,
pling Nut, Rear Release, Crimp Contact, AN Type
part, apparatus, appurtenance, or accessory, including commu-
MS3470Connectors, Receptacle, Electric, Series 2, Single
nications equipment, that is used or intended to be used in
HoleMount,BayonetCoupling,SolderPinContact,Class
operating or controlling an aircraft in flight; is installed in or
H
attached to the aircraft; and is not part of an airframe, engine,
MS3471Connector, Receptacle, Electric, Series 2, Crimp
or propeller.
Type,CableConnecting,BayonetCoupling,ClassesA,L,
3.1.7 arc fault circuit breaker (AFCB), n—containscircuitry
S, and W
tocausecircuitbreakertoopenwhenarcingfaultsaredetected.
MS3472Connector, Receptacle, Electric, Series 2, Crimp
Type, Wide Flange Mounting, Bayonet Coupling, Classes 3.1.8 arc resistance (noncarbon tracking), n—measure of
the ability of a material to resist physical penetration by an
A, L, S, and W
MS3475 Connector, Plug Electric, RFI Shielded, Series 2, electrical arc.
Crimp Type, Bayonet Coupling, Classes L, S, and W
3.1.9 avionics, n—science and technology of electronics as
MS3476Connector, Plug Electric, Series 2, Crimp Type,
applied to aviation.
Bayonet Coupling, Classes A, L, S, and W
3.1.10 bond, n—adhesion of one surface to another with or
MS25437Terminal-Lug
without the use of an adhesive as a bonding agent.
MS35489Grommet
3.1.11 bonding, v—general term applied to the process of
MS90387 Tool, Hand,Adjustable for Plastic and Metal Tie
electrically connecting two or more conductive objects.
Down Straps
3.1.11.1 Discussion—In aircraft, the purpose of bonding
QQ-S-571 Solder, Electronic (96 to 485 Deg C)
(except as applied to individual connections in the wiring and
2.7 Other Standards:
grounding systems) is to provide conductive paths for electric
RTCA DO-160Environmental Conditions and Test Proce-
currents. This is accomplished by providing suitable low-
dures for Airborne Equipment
impedanceconnectionsjoiningconductiveaircraftcomponents
EIA 471Symbol & Label for Electrostatic Sensitive De-
and the aircraft structure. Another purpose of bonding is to
vices
6 8
.Available from RTCA, Inc., 1828 L St., NW, Suite 805, Washington, DC Available from National Electrical Manufacturers Association (NEMA), 1300
20036. N. 17th St., Suite 1752, Rosslyn, VA 22209, http://www.nema.org.
7 9
Available from Electronic Industries Alliance (EIA), 2500 Wilson Blvd., Available from ICAO, Document Sales Unit, 999 University St., Montreal,
Arlington, VA 22201, http://www.eia.org Quebec H3C 5H7, Canada.
F2639−18
ensure the safe passage of current caused by lightning or static 3.1.29 dielectric strength, n—maximum electric field that a
electricity through the aircraft structure. material can withstand without failure of its electrical insula-
tion properties.
3.1.12 bundle, n—wire bundle consists of a quantity of
wiresfastenedorsecuredtogetherandalltravelinginthesame 3.1.30 discontinuity, n—interruption in the normal physical
direction. structure or configuration of a part such as a crack, lap, seam,
inclusion, or porosity.
3.1.13 bus or bus bar, n—solidcopperstripstocarrycurrent
3.1.31 drip loop, n—bundle installation method used to
between primary and secondary circuits; also used as jumpers.
prevent water or other fluid contaminants from running down
3.1.14 cable (electrical), n—assembly of one or more con-
the wiring into a connector.
ductors within an enveloping protective sheath so constructed
as to permit use of conductors separately or in a group. 3.1.32 electrical wiring interconnection system (EWIS),
n—any wire, wiring device, or combination of these, including
3.1.15 calibration,n—setofoperations,performedinaccor-
termination devices, installed in any area of the aircraft for the
dance with a definite document procedure, that compares the
purpose of transmitting electrical energy between two or more
measurements performed by an instrument or standard, for the
intended termination points.
purpose of detecting and reporting, or eliminating by
3.1.33 electricity, n—one of the fundamental quantities in
adjustment, errors in the instrument tested.
nature consisting of elementary particles, electrons, and pro-
3.1.16 certification, n—implies that a certificate is in exis-
tonsthataremanifestedasaforceofattractionorrepulsionand
tence that certifies or states a qualification.
also in work that can be performed when electrons are caused
3.1.17 circuit, n—closed path or mesh of closed paths
to move; a material agency that, when in motion, exhibits
usually including a source of electromotive force (EMF).
magnetic, chemical, and thermal effects and when at rest is
3.1.18 circuit breaker, n—protective device for opening a
accompanied by an interplay of forces between associated
circuitautomaticallywhenexcessivecurrentisflowingthrough
localities in which it is present.
it.
3.1.34 electromagnet, n—temporary magnet that is magne-
3.1.19 conductor, n—wire or other material suitable for
tized by sending current through a coil of wire wound around
conducting electricity.
an iron core.
3.1.20 conduit, n—rigid metallic or nonmetallic casing or a
3.1.35 electromagnetic/radio frequency interference (EMI/
flexible metallic casing covered with a woven braid or syn-
RFI), n—frequency spectrum of electromagnetic radiation
thetic rubber used to encase electrical cables.
extending from subsonic frequency to X-rays.
3.1.35.1 Discussion—Thistermshallnotbeusedinplaceof
3.1.21 contact, n—electrical connectors in a switch,
the term radio frequency interference (RFI). (See radio fre-
solenoid, or relay that controls the flow of current.
quency interference.) Shielding materials for the entire EMI
3.1.22 corrosion resistance, n—abilityofamaterialtoresist
spectrum are not readily available.
intrinsic property deterioration as a result of environment.
3.1.36 electron, n—negativechargethatrevolvesaroundthe
3.1.23 crack, n—partial separation of material caused by
nucleus of an atom; a unit of a negative electrical charge.
vibration, overloading, internal stresses, nicks, defective
3.1.37 electronics,n—generaltermthatdescribesthebranch
assemblies, fatigue, or rapid changes in temperature.
ofelectricalscienceandtechnologythattreatsthebehaviorand
3.1.24 creepage, n—conductionofelectricalcurrentalonga
effects of electron emission and transmission.
surface between two points at different potentials.
3.1.38 expandable sleeving, n—open-weave braided sleev-
3.1.24.1 Discussion—The current’s ability to pass between
ing used to protect wire and cables from abrasion and other
two points increases with higher voltage and when deposits of
hazards (commonly called “Expando”).
moisture or other conductive materials exist on the surfaces.
3.1.39 fill, n—threads in a fabric that run crosswise of the
3.1.25 curing temperature, n—temperature at which a resin
woven material.
or an assembly is subjected to cure the resin.
3.1.40 flame resistance, n—ability of a material to resist
3.1.26 cut-through strength, n—measure of the effort re-
intrinsic property deterioration because of immersion in flame.
quired to sever a material.
3.1.41 fluorinated ethylene propylene (FEP), n—melt-
3.1.27 data, n—information that supports or describes, or
extrudable fluorocarbon resin, very similar in appearance and
both, the original aircraft design, alteration, or repair including
performance to polytetrafluoroethylene (PTFE), but with a
the following: (1) drawings, sketches, and/or photographs; (2)
maximum temperature rating of 200°C.
engineering analysis; (3) engineering orders; and (4) operating
limitations. 3.1.42 flux, n—materials used to prevent, dissolve, or facili-
tate removal of oxides and other undesirable surface sub-
3.1.28 derating, n—technique whereby a part is stressed in
stances.
actualusageatvalueswellbelowthemanufacturer’sratingfor
3.1.42.1 Discussion—Also, the name for magnetic fields.
the part.
3.1.28.1 Discussion—By decreasing mechanical, thermal, 3.1.43 fuse, n—protective device containing a special wire
and electrical stresses, the probability of degradation or cata- that melts when current exceeds the rated value for a definite
strophic failure is lessened. period.
F2639−18
3.1.44 generator, n—device for converting mechanical en- 3.1.64 resistance, n—opposition a device or material offers
ergy into electrical energy. to the flow or current.
3.1.65 resistance to fluids, n—ability of a material to resist
3.1.45 grommet, n—insulatingwasherthatprotectsthesides
of holes through which wires shall pass or a metal or plastic intrinsic property deterioration as a result of fluids.
drain attached to fabric on aircraft.
3.1.66 resistance to notch propagation, n—ability of a
material to resist propagation of breeches.
3.1.46 grounding, v—term usually applied to a particular
form of bonding that is the process of electrically connecting
3.1.67 severe wind and moisture problem (SWAMP) areas,
conductiveobjectstoeitherconductivestructureorsomeother
n—areas such as wheel wells, wing folds, and near wing flaps
conductive return path for the purpose of safely completing
and areas directly exposed to extended weather conditions are
either a normal or fault circuit.
considered SWAMP areas on aircraft.
3.1.47 harness, n—group of cables or wires securely tied as
3.1.68 silicone rubber, n—high-temperature (200°C) plastic
a unit.
insulation that has a substantial silicone content.
3.1.48 heat distortion temperature, n—temperatureatwhich
3.1.69 smoke emission, n—gasesorparticulateemittedfrom
a material begins to alter its intrinsic properties.
a material as a result of combustion.
3.1.49 impact strength, n—ability of a material to resist
3.1.70 soldering, v—group of welding processes that pro-
intrinsic property deterioration as a result of physical impact.
ducescoalescenceofmaterialsbyheatingthemtothesoldering
temperature and using a filler metal having a liquidus not
3.1.50 insulator, n—materialthatwillnotconductcurrentto
exceeding 450°C (840°F) and below the solidus of the base
an appreciable degree.
metals and the filler metal is distributed between the closely
3.1.51 integrated circuit, n—small,completecircuitbuiltup
fitted surfaces of the joint by capillary action.
by vacuum deposition and other techniques, usually on a
3.1.71 solenoid, n—tubular coil for the production of a
silicon chip, and mounted in a suitable package.
magnetic field; electromagnet with a core that is able to move
3.1.52 inverter,n—deviceforconvertingdirectcurrent(DC)
in and out.
to alternating current (AC).
3.1.72 special properties unique to the aircraft, n—any
3.1.53 magnetic field, n—spacearoundasourceofmagnetic
characteristic of an aircraft not incorporated in other designs.
flux in which the effects of magnetism can be determined.
3.1.73 swarf, n—term used to describe the metal particles
3.1.54 mechanical strength, n—abilityofamaterialtoresist
generated from drilling and machining operations.
intrinsic property deterioration as a result of physical forces.
3.1.73.1 Discussion—Swarf particles may collect on and
3.1.55 multiconductor cable, n—consists of two or more between wires within a wire bundle.
cables or wires, all of which are encased in an outer covering
3.1.74 switch, n—deviceforopeningorclosinganelectrical
composed of synthetic rubber, fabric, or other material.
circuit.
3.1.56 open circuit, n—incomplete or broken electrical cir-
3.1.75 tape, n—tape or a “narrow fabric” is loosely defined
cuit.
as a material that ranges in width from ⁄4 to 12 in. (0.6 to 30
3.1.57 plastic, n—organic substance of large molecular cm).
weight that is solid in its finished state and, at some stage
3.1.76 thermocouple, n—device to convert heat energy into
during its manufacture or its processing into a finished article,
electrical energy.
can be shaped by flow.
3.1.77 transformer, n—device for raising or lowering AC
3.1.58 polytetrafluoroethylene (PTFE) tape (insulation),
voltage.
n—wrapped around a conductor and layered into a virtually
3.1.78 transmitter, n—electronic system designed to pro-
homogeneous mass.
duce modulated radio frequency (RF) carrier waves to be
3.1.58.1 Discussion—It is used both as a primary insulation
radiated by an antenna; also, an electric device used to collect
against the conductor and as an outer layer or jacket over a
quantitative information at one point and send it to a remote
shield. Maximum temperature rating is 260°C.
indicator electrically.
3.1.59 polyvinylidine fluoride (PVF2), n—fluorocarbon
3.1.79 velocity of propagation (VOP), n—or velocity factor
plastic that, when used in aircraft wire, is invariably radiation
is a parameter that characterizes the speed at which an
cross-linked and used as the outer layer.
electrical or radio signal passes through a medium and ex-
3.1.60 radar (radio detecting and ranging), n—radioequip-
pressedasapercentage,itistheratioofasignal’stransmission
ment that uses reflected pulse signals to locate and determine
speed compared to the speed of light.
the distance to any reflecting object within its range.
3.1.80 volt, n—unit of potential, potential difference, or
3.1.61 rectifier, n—device for converting AC to DC.
electrical pressure.
3.1.62 relay, n—electricallyoperatedremotecontrolswitch.
3.1.81 waveguide, n—hollow,typicallyrectangular,metallic
tube designed to carry electromagnetic energy at extremely
3.1.63 resin, n—vast profusion of natural and increasingly
high frequencies.
synthetic materials used as adhesives, fillers, binders, and
insulation. 3.1.82 wire, n—single, electrically conductive path.
F2639−18
3.2 Definitions of Terms Specific to This Standard: 5. Wire Selection
3.2.1 electrical system, n—as used in this practice, those
5.1 General:
parts of the aircraft that generate, distribute, and use electrical
5.1.1 Wires shall be sized to carry continuous current in
energy, including their support and attachments.
excessofthecircuit-protectivedevicerating,includingitstime
3.3 Acronyms: current characteristics, and to avoid excessive voltage drop.
3.3.1 AC—alternating current Refer to 8.2 for wire-rating methods.
5.1.2 Electrical Wire Rating:
3.3.2 AFM—aircraft flight manual
5.1.2.1 Wires shall be sized so that they: have sufficient
3.3.3 CDO—Certified Design Organization
mechanical strength to allow for service conditions, do not
3.3.4 CFR—Code of Federal Regulations
exceed allowable voltage drop levels, are protected by system
circuit protection devices, and meet circuit current carrying
3.3.5 COMP—composite
requirements.
3.3.6 COTS—commercial off the shelf
5.1.2.2 Mechanical Strength of Wires—If it is desirable to
3.3.7 DC—direct current
use wire sizes smaller than #20, particular attention shall be
3.3.8 EMI—electromagnetic interference
given to the mechanical strength and installation handling of
these wires, for example, vibration, flexing, and termination.
3.3.9 ESD—electrostatic discharge
Consideration shall be given to the use of high-strength alloy
3.3.10 EWIS—electrical wiring interconnection system
conductors in small gage wires to increase mechanical
3.3.11 F—Fahrenheit
strength. As a general practice, wires smaller than size #20
3.3.12 FEP—fluorinated ethylene propylene shall be provided with additional clamps and be grouped with
at least three other wires. They shall also have additional
3.3.13 FMS—Flight Manual Supplement
support at terminations, such as connector grommets, strain
3.3.14 ID—identification
relief clamps, shrinkable sleeving, or telescoping bushings.
3.3.15 NiCad—nickel cadmium
They shall not be used in applications in which they will be
3.3.16 NiMH—nickel metal hydride subjected to excessive vibration, repeated bending, or frequent
disconnection from screw termination.
3.3.17 OD—outside diameter
5.1.2.3 Voltage Drop in Wires—The voltage drop in the
3.3.18 ODA—Organization Designation Authorization
main power wires from the generation source or the battery to
3.3.19 OEM—original equipment manufacturer
the bus shall not exceed 2% of the regulated voltage when the
generator is carrying rated current or the battery is being
3.3.20 PI—polyimide
discharged at the 5-min rate. The tabulation shown in Table 1
3.3.21 RCCB—remote-controlled circuit breaker
defines the maximum acceptable voltage drop in the load
3.3.22 RFI—radio frequency interference
circuits between the bus and the utilization equipment ground.
3.3.23 RFM—Rotorcraft Flight Manual 5.1.2.4 Resistance—Theresistanceofthecurrentreturnpath
through the aircraft structure is generally considered negli-
3.3.24 RFMS—Rotorcraft Flight Manual Supplement
gible. However, this is based on the assumption that adequate
3.3.25 SOF—safety of flight
bondingtothestructureoraspecialelectriccurrentreturnpath
3.3.26 SSPC—solid-state power controller
has been provided that is capable of carrying the required
electric current with a negligible voltage drop. To determine
3.3.27 SWAMP—severe wind and moisture problems
circuit resistance, check the voltage drop across the circuit. If
3.3.28 TFE—tetrafluoroethylene
the voltage drop does not exceed the limit established by the
aircraft or product manufacturer, the resistance value for the
4. Significance and Use
circuit may be considered satisfactory. When checking a
4.1 Design—The design procedures defined in this practice
circuit, the input voltage shall be maintained at a constant
are intended to provide acceptable guidance in the original
value. Tables 2 and 3 show formulas that may be used to
design of electrical systems.
determine electrical resistance in wires and some typical
examples.
4.2 Alteration—The alteration procedures defined in this
practice are intended to provide acceptable guidance for
modification of general aviation aircraft. Design of any modi-
fication shall follow the practices and processes defined in the
TABLE 1 Tabulation Chart (Allowable Voltage Drop Between Bus
design sections of this practice.
and Utilization Equipment Ground)
4.3 Certification—Certification guidance provided in this
Nominal Allowable Voltage
Intermittent
practice is intended to provide generally accepted procedures
System Drop Continuous
Operation
and processes for certification of original and modified elec- Voltage Operation
trical systems and equipment. Requirements for certification 14 0.5 1
28 1 2
shall be coordinated with the applicable National Aeronautics
115 4 8
Association/Civil Aeronautics Administration (NAA/CAA)
200 7 14
regulatory agency.
F2639−18
TABLE 2 Examples of Determining Required Tin-Plated Copper
5.1.2.8 TodetermineT forwirescarryingahighpercentage
Wire Size and Checking Voltage Drop Using Fig. 1
of their current-carrying capability at elevated temperatures,
Check Calculated
laboratory testing using a load bank and a high-temperature
Run Circuit Wire Size
Voltage Voltage Drop (VD) =
Lengths, Current, from
chamberisrecommended.Suchtestsshallberunatanticipated
Drop (Resistance/ft)
ft amps Chart
worst-caseambienttemperatureandmaximumcurrent-loading
(Length) (Current)
1 107 20 No. 6 VD = (0.000 44 Ω/ft) combinations.
(107)(20) = 0.942
5.1.2.9 Approximate T can be estimated using the follow-
0.5 90 20 No. 4 VD = (0.000 28 Ω/ft)
ing formula:
(90)(20) = 0.504
4 88 20 No. 12 VD = (0.002 02 Ω/ft)
T 5 T 1 T 2 T = I /I (3)
(88)(20) = 3.60 ~ ! ~ !
2 1 R 1 2 max
7 100 20 No. 14 VD = (0.003 06 Ω/ft)
where:
(100)(20) = 6.12
T = ambient temperature,
T = estimated conductor temperature,
TABLE 3 Examples of Determining Maximum Tin-Plated Copper
T = conductor temperature rating,
R
Wire Length and Checking Voltage Drop Using Fig. 1
I = circuit current (A = amps), and
Maximum Check Calculated
I = maximum allowable current (A = amps) at T .
max R
Maximum Circuit
Wire Wire Run Voltage Drop (VD) =
Voltage Current, (1)This formula is quite conservative and will typically
Size Length, (Resistance/ft)
Drop amps
yield somewhat higher estimated temperatures than are likely
ft (Length) (Current)
to be encountered under actual operating conditions.
1 No. 10 20 39 VD = (0.001 26 Ω/ft)
(39)(20)= 0.98
5.1.2.10 Effects of Heat Aging on Wire Insulation—Since
0.5 — 19.5 VD = (0.001 26 Ω/ft)
(19.5)(20) = 0.366
electrical wire may be installed in areas where inspection is
4 — 156 VD = (0.001 26 Ω/ft)
infrequentoverextendedperiodsoftime,itisnecessarytogive
(156)(20) = 3.93
special consideration to heat-aging characteristics in the selec-
7 — 273 VD = (0.001 26 Ω/ft)
(273)(20) = 6.88
tion of wire. Resistance to heat is of primary importance in the
selectionofwireforaircraftuse,asitisthebasicfactorinwire
rating. Where wire may be required to operate at higher
temperatures because of either high ambient temperature,
5.1.2.5 Resistance Calculation Methods—Figs. 1 and 2
high-current loading, or a combination of the two, selection
provide a convenient means of calculating maximum wire
shall be made on the basis of satisfactory performance under
lengthforthegivencircuitcurrent.ValuesinTables2and3are
the most severe operating conditions.
for tin-plated copper conductor wires. Because the resistance
5.1.2.11 Maximum Operating Temperature—The current
of tin-plated wire is slightly higher than that of nickel or silver
that causes a temperature steady state condition equal to the
plated wire, maximum run lengths determined from these
rated temperature of the wire shall not be exceeded. Rated
charts will be slightly less than the allowable limits for nickel
temperatureofthewiremaybebasedupontheabilityofeither
or silver-plated copper wire and are therefore safe to use. Figs.
the conductor or the insulation to withstand continuous opera-
1 and 2 can be used to derive slightly longer maximum run
tion without degradation.
lengths for silver or nickel-plated wires by multiplying the
5.1.2.12 Single Wire in Free Air—Determining a wiring
maximum run length by the ratio of resistance of tin-plated
system’scurrent-carryingcapacitybeginswithdeterminingthe
wire divided by the resistance of silver or nickel-plated wire.
maximum current that a given-sized wire can carry without
5.1.2.6 As an alternative method or a means of checking
exceeding the allowable temperature difference (wire rating
resultsfromFig.1,continuousflowresistanceforagivenwire
minus ambient °C).The curves are based upon a single copper
size can be read from Table 4 and multiplied by the wire run
wire in free air. (See Figs. 3 and 4.)
length and the circuit current. For intermittent flow, use Fig. 2.
5.1.3 Aircraft service imposes severe environmental condi-
5.1.2.7 Whentheestimatedormeasuredconductortempera-
tion on electrical wire.To ensure satisfactory service, schedule
ture (T ) exceeds 20°C, such as in areas having elevated
wire inspections annually for abrasions, defective insulation,
ambient temperatures or in fully loaded power-feed wires, the
condition of terminations, and potential corrosion. Grounding
maximum allowable run length (L ), must be shortened from
connections for power, distribution equipment, and electro-
L (the 20°C value) using the following formula for copper
magneticshieldingshallbegivenparticularattentiontoensure
conductor wire:
that electrical bonding resistance will not be significantly
254.5°C L
~ !~ !
1 increased by the loosening of connections or by corrosion
L 5 (1)
~234.5°C!~T !
2 during service.
(1)For aluminum conductor wire, the formula is:
5.1.4 Insulation of wires shall be appropriately chosen in
258.1°C L accordance with the environmental characteristics of wire
~ !~ !
L 5 (2)
routing areas. Routing of wires with dissimilar insulation,
~238.1°C!~T !
(2) These formulas use the reciprocal of each material’s withinthesamebundle,isnotrecommended,particularlywhen
resistive temperature coefficient to take into account increased relative motion and abrasion between wires having dissimilar
conductor resistance resulting from operation at elevated insulation can occur. Soft insulating tubing cannot be consid-
temperatures. eredasmechanicalprotectionagainstexternalabrasionofwire
F2639−18
FIG. 1Conductor Chart, Continuous Flow
since, at best, it provides only a delaying action. Conduit or 5.1.5.2 Arc resistance (non-carbon tracking),
ducting shall be used when mechanical protection is needed. 5.1.5.3 Corrosion resistance,
Refer to 9.8 and 10.7 for conduit selection and installation. 5.1.5.4 Cut-through strength,
5.1.5 Insulation Materials—Insulating materials shall be 5.1.5.5 Dielectric strength,
selected for the best combination of characteristics in the 5.1.5.6 Flame resistance,
following categories: 5.1.5.7 Heat distortion temperature,
5.1.5.1 Abrasion resistance, 5.1.5.8 Impact strength,
F2639−18
FIG. 2Conductor Chart, Intermittent Flow
5.1.5.9 Mechanical strength, 5.1.6 Foramorecompleteselectionofinsulatedwires,refer
5.1.5.10 Resistance to fluids, to SAE AS 4372 and SAE AS 4373.
5.1.5.11 Resistance to notch propagation, 5.1.7 Wires are typically categorized as being suitable for
5.1.5.12 Smoke emission, and either “open wiring” or “protected wiring” application.
5.1.5.13 Special properties unique to the aircraft.
5.2 Aircraft Wire Materials:
NOTE 2—See 5.2.10 for additional insulation properties. 5.2.1 Open Airframe Interconnecting Wire:
F2639−18
TABLE 4 Current-Carrying Capacity and Resistance of Copper Wire
Continuous Duty Current (amps)—Wires in Bundles,
A
Max. Resistance Nominal
Groups, Harnesses, or Conduits
Wire
Ω/1000 ft at 20°C Conductor Area
Size Wire Conductor Temperature Rating
B
Tin-Plated Conductor circ.mils
105°C 150°C 200°C
24 2.5 4 5 28.40 475
22 3 5 6 16.20 755
20 4 7 9 9.88 1 216
18 6 9 12 6.23 1 900
16 7 11 14 4.81 2 426
14 10 14 18 3.06 3 831
12 13 19 25 2.02 5 874
10 17 26 32 1.26 9 354
8 38 57 71 0.70 16 983
6 50 76 97 0.44 26 818
4 68 103 133 0.28 42 615
2 95 141 179 0.18 66 500
1 113 166 210 0.15 81 700
0 128 192 243 0.12 104 500
00 147 222 285 0.09 133 000
000 172 262 335 0.07 166 500
0000 204 310 395 0.06 210 900
A
Rating is for 70°C ambient, 33 or more wires in the bundle for sizes 24 through 10, and 9 wires for size 8 and larger, with no more than 20 % of harness current-carrying
capacity being used at an operating altitude of 60 000 ft (18 288 m). For rating of wires under other conditions or configurations, see 8.2.
B
For resistance of silver- or nickel-plated conductors, see wire specifications.
5.2.1.1 Aircraft Wire Materials—Only wire that meets the poor conductor of electricity and inhibits determination of
performance and environmental standards for airborne use wire. Therefore, all aircraft wiring has a coating of tin, silver,
shall be installed in aircraft. or nickel, which has far slower oxidation rates.
5.2.1.2 Open Airframe Interconnecting Wire— 5.2.5 Tin-coated copper is a very common plating material.
Interconnecting wire is used in point-to-point open harnesses, Its ability to be successfully soldered without highly active
normallyintheinteriororpressurizedfuselage,witheachwire fluxesdiminishesrapidlywithtimeaftermanufacture.Itcanbe
providing enough insulation to resist damage from handling used up to the limiting temperature of 150°C.
and service exposure. (See Table 5.) Electrical wiring is often 5.2.6 Silver-Coated Wire is used where temperatures do not
installed in aircraft without special enclosing means. This exceed 200°C (392°F).
practice is known as open wiring and offers the advantages of 5.2.7 Nickel-Coated Wire retains its properties beyond
ease of maintenance and reduced weight. 260°C, but most aircraft wire using such coated strands have
5.2.2 Protected Wiring: insulation systems that cannot exceed that temperature on
5.2.2.1 Protected Wire—Airborne wire that is used within long-term exposure. Soldered terminations of nickel-plated
equipment boxes, or has additional protection, such as an conductor require the use of different solder sleeves or flux
exterior jacket, conduit, tray, or other covering is known as than those used with tin- or silver-plated conductor.
protected wire. (See Table 6.) 5.2.8 Conductor Stranding—Due flight vibration and
5.2.3 Coaxial Cables—Table 7 lists coaxial cables accept- flexing, stranded round conductor wire shall be used to
able for use in aircraft. Use in aircraft of cables not listed in minimize fatigue breakage on smaller gauge wire. Some
Table 7 requires demonstration of their acceptability for the coaxial cables such as RG142 use a solid center conductor
application. although, it is
...