of the table on the diagonal line which is numbered 20 amperes; (4) Follow this line until the pointer intersects the diagonal line marked "curve 2;" and (5) Drop pointer straight downward to the bottom of the chart and we are between the number 16 and 18. As the results are again between sizes, select the larger No. 16 wire. This is the smallest size wire acceptable for carrying 20-ampere current in a single wire in free air without overheating.
f. Compare the wire sizes selected. Use & cable no smaller than No. 8 in order to satisfy requirement (a) and no smaller than a No. 16 in order to satisfy requirement (b). Since we must meet both requirements, select the larger No. 8.
g. In this particular instance, the voltagedrop requirement was more critical because it required a larger size than the heat-dissipation requirement. This is usually true when a relatively light current is carried over a relatively long distance. However, when a short wire and/or a heavy current is required, the heatdissipation capabilities of the wire may become the critical factor and may dictate the size of the wire to be used.
h. The tabulation referenced in paragraph 442a shows several values of voltage drop which is allowable for various systems and conditions when selecting wire for use from the bus to the equipment. Additionally, the voltage drop permissible in wires from the generator to the bus and from the battery to the bus will vary with the regulated voltage of the system i.e., nominal 14 V., 28 V., 116 V., etc.
445. SPLICES IN ELECTRIC WIRE, Splicing of electric wire should be kept to a minimum and avoided entirelv in locations subiect to extreme AC 43.13-1A 1972 dle may be spliced provided the completed splice is located so it can be periodically inspected. Stagger splices (see figure 11.8) so the bundle does not become excessively enlarged.
Many types of aircraft splice connectors are available for use when splicing individual wires. Use of the self-insulated splice connector is preferred; however, a noninsulated splice connector may be used provided the splice is covered with plastic sleeving which is secured at both ends. Solder splices may be used; however, they are particularly brittle and not recommended.
446. OPEN WIRING. Electric wiring is often installed in aircraft without special enclosing means. This practice is known as open wiring and offers the advantages of ease of maintenance and reduced weight.
a. Wire Bundles. To simplify maintenance and to minimize the damage that may result from a single fault, limit the number of wires in the run. Shielded wire, ignition wire, and wires which are not protected by a circuit breaker or fuse usually are routed separately. Avoid bending radii less than 10 times the outer diameter of the bundle to prevent excessive stresses on the wire insulation.
b. Insulating Tubing. Soft insulating tubing (spaghetti) cannot be considered as mechanical protection against external abrasion of wire, since at best it provides only a delaying action.
Use conduit or ducting when mechanical protection is needed.
c. Clamping of Wire Bundles. Use clamps lined with nonmetallic material to support the wire bundle along the run. Tying may be used between clamps, but should not be considered as a substitute for adequate clamping. Adhe-
AC 43.13-1A Page 167 1972 therefore are not acceptable as a clamping means.
d. Separation from Flammable Fluid Lines. An arcing fault between an electric wire and a MS 21919 metallic flammable fluid line may puncture the CABLE CLAMP line and result in a serious fire. Consequently, EQUIVALENT OR make every effort to avoid this hazard by physical separation of the wire from lines or equipment containing oil, fuel, hydraulic fluid, or alcohol. When separation is impractical, locate the electric wire above the flammable fluid line and securely clamp to the structure. In no case, should a wire be supported by a flammable CLEARANCE fluid line. 14" MINIMUM
447. HEAT PRECAUTIONS. Separate wires from high temperature equipment, such as resistors, exhaust stacks, heating ducts, etc., to prevent insulation breakdown. Insulate wires that must run through hot areas with a high temperature ANGLE BRACKET WITH insulation material such as asbestos, fiberglas, TWO POINT FASTENING or teflon. Avoid high temperature areas when using cables having soft plastic insulation such as polyethylene because these materials are FIGURE 11.9--Cable clamp at bulkhead hole.
subject to deterioration and deformation at elevated temperatures. Many coaxial cables have this type of insulation. - WIRES LESS THAN 1/d
INCH FROM HOLE EDGE
448. PROTECTION AGAINST CHAFING. Protect wire and wire groups against chafing or abrasion as damaged insulation may result in short circuits, malfunctions, or inoperative equip- GROMMET ment. Support wire bundles using MS-21919 cable clamps as indicated in figure 11.9. When clamped in position, if there is less than 1/4- inch clearance between a bulkhead cutout and the wire bundle, install a suitable grommet as indicated in figure 11.10. The grommet may be cut at 45° angle to facilitate installation provided it is cemented in place and the slot is lo-
however, the following basic principles should be practiced:
o. Make sure all cutting tools used for stripping are sharp.
b. When using special wire stripping tools, adjust the tool to avoid nicking, cutting, or otherwise damaging the strands.
c. Damage to wires should not exceed the limits specified in figure 11.11.
FIGURE 11.11.-Allowable nicked or broken strands.
Wire size Nicked or broken strands Copper AN #22-#12 None #10 2 #8 -#4 14 #2 -#0 12 Aluminum All Sizes None NoTE: Longitudinal scratches in copper wire are not considered cause for rejection or rework.
450. TERMINALS, Terminals are attached to the ends of electric wires to facilitate connection of the wires to terminal strips or items of equipment. The tensile strength of the wire to terminal joint should be at least equivalent to the tensile strength of the wire itself, and its resistance negligible relative to the normal resistance of the wire. Terminals specifically designed for use with the standard sizes of aircraft wire are available through normal supply channels. Haphazard choice of commercial terminals may lead to overheated joints, vibration tailures, and corrosion difficulties.
a. Solder Terminals. For most applications, soldered terminals have been replaced by solderless terminals. The solder process has dis- AC 43.13-1A 1972 solder and become more susceptible to breakage due to vibration.
(5) The wire insulation may be charred during the soldering process.
b. Solderless Terminals. The terminal manufacturer will normally provide a special crimping or swaging tool for joining the solderless terminal to the electric wire. Aluminum wire presents special difficulty in that each individual strand is insulated by an oxide coating.
This oxide coating must be broken down in the crimping process and some method employed to prevent its reforming. In all cases, follow the terminal manufacturer's instructions when installing solderless terminals.
451. ATTACHMENT OF TERMINALS TO STUDS.
Electrical equipment malfunction has frequently been traced to poor terminal connections at terminal boards. Loose, dirty, or corroded contact surfaces will produce localized heating which may ignite nearby combustible materials or overheat adjacent wire insulation to the smoking point.
452. BONDING JUMPER INSTALLATIONS. Make bonding jumpers as short as practicable, and install in such manner that the resistance of each connection does not exceed .003 ohm. The jumper must not interfere with the operation of movable aircraft elements, such as surface controls, nor should normal movement of these elements result in damage to the bonding
a. Bonding Connections. To assure a lowresistance connection, remove nonconducting finishes; such as paint and anodizing films, from the attachment surface to be contacted by the bonding terminal. Do not ground electric wirina dirantle to mamacium nasta
AC 43.13-1A Page 189 1972 FIGURE 11.12.--Stud bonding or grounding to flat surface.
SCREW OR BOLT WASHER A
LOCKWASHER E
• STRUCTURE
WASHER B WASHER C
PLAIN NUT
WASHER D
TERMINAL (LIMIT TO 4) LOCKNUT
LOCKWASHER F Aluminum Terminal and Jumper Struoture Sorew or Bolt and Look nut Plain Washer Woeher Washer C&D Look washer Look washer Aluminum Alloya Cad. Plated Cad. Aluminam Aluminum Cad. Cad.
Steel Plated Alloy Alloy Plated Plated Steel Steel Steel Magnesium Cad. Plated Cad. Magnesium Magnesium Cad. Cad.
Alloye Steel Plated Alloy Alloy Plated Plated Steel Steel Steel Steel, Cadmium Cad. Plated Cad. None None Cad. Cad.
Plated Steel Plated Plated Plated Steel Steel Steel Steel, Corrosion Corrosion Cad. None None Cor. Cad.
Resisting Resisting Plated Resist Plated Steel ¡ Steel Steel Steel Tinned Copper Terminal and Jumper Aluminum Alloys Cad. Plated Cad. Aluminum Aluminum Cad. Cad. Cad.
Rtaal Dlarat A 1100 Platad plate Platad
Page 190 AC 43.13-1A 1973 FIGURE 11.18.-Plate nut bonding or grounding to flat surface.
LOCKWASHER
SCREW OR BOLT WASHER A - LIMITED TO 4
WASHER B
RIVET NUT PLATE Aluminum Terminal and Jumper Struoture Screw or Bolt and Nut plato Rivet Lookwashor Washer & Washer & Aluminum Alloys Cad. Plated Steel Aluminum Alloy Cadmium Cad. plated None Plated Steel steel or alumiaom Magnesium Alloya Cad. Plated Steel Aluminum Alloy Cadmium Cad. plated None or Plated Steel steel or Magnesium aluminum alloy Steel, Cadmium Cad. Plated Steel Cor. Beslet. Steel Cadmium Cad. plated None plated Plated Steel steel or aluminum Steel, Corrosion Corrosion Resist. Cor. Resist. Steel Cadmium Cad. plated Cadmium Resisting Steel or Cad. Plated Steel steel or plated Plated Steel aluminum steel Tinned Copper Terminal and Jumper Aluminum Alloys Cad. Plated Steel Aluminum Alloy Cadmium Cad. plated Aluminam Plated Steal 1 ateal
AC 43.13-1A Page 191 1972 FIGURE 11.14.-Bolt and nut bonding or grounding to flat surface.
- SCREW OR BOLT
WASHER A
WASHER B
LOCKWASHER
TERMINAL LIMITED TO 4
LOCKNUT WASHER C Aluminum Terminal and Jumper Etruoture Bores or Bolt and Hut plate Lookraaher Washer 1 Washer B Washer O Alaminum Alloy Cad. Plated Steel Cad. Plated Steel Cad. plated steel None Cad. plated or aluminum steel or aluminum Magnesium Alloy Cad. Plated Steel Cad. Plated Steel Magnesfum Alloy None or Cad. plated Magnesium steel or
• AllOy aluminum Steel, Oadmium Cad. Plated Steel Cad. Plated Steel Cad. Plated Steel Cadmium Cad. plated plated plated steel or ateel aluminum Steel, Corrosion Corrosion Resiat. Cad. Plated Steel Corrosion Resiat- Cadmium Cad. plated Resisting Steel or Cad. Ing Steel plated steel or plated steel steel aluminum Tinned Copper Terminal and Jumper Aluminum Alloy Cad. Plated Steel Cad. Plated Steel Cad. plated steel Aluminum Cad. plated aline ateol
Page 192 AC 43.12-1A 1972 CAD. PL. STEEL AN 735 CLAMP SCREW COPPER
TERMINAL
ALUMINUM
CYLINDRICAL WASHERS
SURFACE CAD. PL. STEEL
LOCKWASHER CAD. PL. STEEL
LOCKNUT FIGURE 11.15-Copper jumper connecter to tubular structure.
CAD. PL. STEEL SCREW AN 735 CLAMP WASHER ALUMINUM
• STRUCTURE _ ALUMINUM
ALUMINUM ALLOY WASHER OR CORROSION.
RESISTING STEEL CAD. PL. STEEL
CONDUIT LOCKWASHER CAD. PL. STEEL
LOCKNUT FIGURE 11.16.-Bonding condult to structure.
CAD. PL. STEEL SCREW AN 735 CLAMP
ALUMINUM WASHER
ALUMINUM
TERMINAL
AC 43.13-1A 1972 avoided, the choice of jumper and hardware should be such that corrosion is minimized, and the part likely to corrode would be the jumper or associated hardware. Figures 11.12 through 11.17 show the proper hardware combinations for making a bond connection. At locations where finishes are removed, apply a protective finish to the completed connection to prevent subsequent corrosion.
c. Bonding Jumper Attachment. Avoid the use of solder to attach bonding jumpers. Bond tu- Page 193 bular members by means of clamps to which the jumper is attached. Proper choice of clamp material will minimize the probability of corrosion.
d. Ground Return Connection. When bonding jumpers carry substantial ground return current, determine that the current rating of the jumper is adequate, and that a negligible voltage drop is produced.
453.-463. RESERVED.
Page 194 AC 43.13-1А 1972 Section 4. WIRE MARKING
464. WIRE IDENTIFICATION. To facilitate instal- 465. SLEEVE SELECTION FOR IDENTIFICATION.
lation and maintenance, original wire-marking identification is to be retained. The wire identi- a. Flexible vinyl sleeving, either clear or fication marking should consist of a combina- opaque, is satisfactory for general use.
tion of letters and numbers which identify the b. For sleeving exposed to high temperatures wire, the circuit it belongs to, its gauge size, and any other information to relate the wire to (over 400° F.), use materials such as silicone rubber or silicone fiberglas.
a wiring diagram. The preferred method is to stamp the identification marking directly on c. Use nylon sleeving in areas where resistthe wire. Place identification markings at each ance to solvent and synthetic hydraulic fluids end of the wire and at 12- to 15-inch intervals is necessary. The size of identification sleeving along the length of the wire. Wires less than & for the various sizes of wire are shown in inches long need not be stamped. Wire lengths fgure 11.18.
8 to 7 inches should be stamped at the center.
If the outer covering or wire insulation will FIGURE 11.18.-Sizes of identification sleeving.
not stamp easily, insulating tubing may be stamped with the identification mark and in- Wire Size Sleeving Bixe stalled on the wire. Identification sleeves are MIL-W-50в6 MIL- X7-9072 Nominal I.D.
normally used for identifying the following AN No. (inches) types of wire or cable: #24 12 .085
a. Unjacketed shielded wire. #22 #20 10 11 ,095 .106
b. Thermocouple wire. #18 .118 #16 .118
c. Multiconductor cable. #14 7 •148 # 12 .166
d. High temperature wire with insulation #10 4 .208 difficult to mark (such as asbestos, teflon, and #8 #8 2 .268 fiberglas). #6 #6 .380 #4 #4 8/8 Inch .875
(1) Thermocouple wire identification is nor- #2 #2 1/2 inch .500 mally accomplished by means of identification #1 #1 1/2 inch -500 sleeves. As the thermocouple wire is usually of #0 #0 5/8 inch .625 the duplex type (two insulated wires within #00 #00 5/8 inch -625 the same casing), each wire at the termination Doint bears the full name of the conductor #0000 #000 #000 #0000 8/4 Inch 8/4 inch .750 -750
AC 43.13-1A Роде 195 1972
PRESSURE -
SENSITIVE TAPE XYZ15
SLEEVE MARKER
TIED IN PLACE XYZ15 FIGURE 11.10.--Identification of wire bundles and harnesses.
467,-477. RESERVED.
Page 196 AC 49.13-1А 1972 Section 5. CONNECTORS 478, GENERAL PURPOSE CONNECTORS. Connec tors (plugs and receptacles) are used to facilitate maintenance when frequent disconnection is required. Since the wires are soldered to the connector inserts, the joints should be individually installed and the wire bundle firmly supported to avoid damage by vibration. Connectors have been particularly vulnerable to corrosion in the past, due to condensation within the shell. Special connectors with waterproof features have been developed and may be used may be pro to replace nonwaterproof type plugs in areas where moisture causes a connector problem.
Use a replacement connector of the same basic type and design as the connector it replaces.
Connectors that are susceptible to corrosion difficulties may be treated with a chemically inert waterproof jelly. When replacing connector assemblies, use the socket-type insert on that half which is live or "hot" after the connector is disconnected to prevent unintentional grounding.
479. TYPES OF CONNECTORS. Connectors are identified by AN numbers and are divided into types and classes with manufacturer's variations in each type and class. The manufacturer's variations are differences in appearance and in the method of meeting the specification;
however, they do not preclude mating plugs and receptacles of different manufacturers.
There are six basic types of AN connectors used in aircraft which are further broken down into five classes as indicated in figures it is important that the soldered connectors are readily accessible. The back shell is held together by a threaded ring or by screws.
Class C-A pressurized connector with inserts that are not removable. Looks like a Class A connector but the inside sealing arrangement is sometimes different and is used on walls of bulkheads of pressurized equipment.
Class D-Moisture and vibration resisting connector which has a sealing grommet in the back shell. Wires are threaded through tight fitting holes in the grommet, thereby sealing against moisture.
Class K-A fireproof connector used in areas where it is vital that the electric current is not interrupted, even though connector may be exposed to continuous open flame. Wires are crimped to the pin or socket contacts and the shells are made of steel, This class of connectors is normally longer than the other classes of connectors.
480. AN CONNECTOR IDENTIFICATION. Code letters and numbers are marked on the coupling ring or shell to identify the connector. This code provides all the information necessary to obtain the correct replacement for a defective or damaged part. To facilitate ready identification the code found on a typical connector (aa shown in figure 11.22) is explained as follows:
a. The letters AN indicate the connector was made to a onvarnment standard
AC 43.13-1А Page 197 1972 AN 3102 AN 3100 BOX RECEPTACLE WALL RECEPTACLE AN 3101
CABLE RECEPTACLE AN 3106 AN 3106 STRAIGHT PLUG AN 3107 STRAIGHT PLUG
QUICK DISCONNECT PLUG AN 3108 AN 3106
ANGLE PLUG ANGLE PLUG FIGURE 11.20.-AN connectors.