AC 43.13-1A Page 201 1972 Section 6. CONDUITS
497. GENERAL, Conduit is available in metallic and nonmetallic materials and in both rigid and flexible form. Primarily, its purpose is for mechanical protection of the wire within, although some radio interference shielding may be provided.
498. SIZE OF CONDUIT, When selecting conduit size for a specific wire bundle application, it ia common practice to allow for ease in maintenance and possible future circuit expansion by specifying the conduit inner diameter about 25 percent larger than the maximum diameter of the wire bundle. The nominal diameter of rigid metallic conduit is the O.D. Therefore, to obtain the I.D., subtract twice the tube wall thickness.
499. CONDUIT FITTINGS, From the abrasion standpoint, conduit is vulnerable at its ends.
Affix suitable fittings to conduit ends in such manner that a smooth surface comes in contact with wire within. When fittings are not used, flare the end of the conduit to prevent wire insulation damage. Support the conduit using clamps along the conduit run.
as much a8 80 percent of the tube area. Minimum acceptable tube bend radii for rigid conduit is shown in figure 11.24. Kinked or wrinkled bends in rigid conduits are not considered acceptable. Tubing bends that have been flattened into an ellipse and the minor diameter is less than 75 percent of the nominal tubing diameter is not considered satisfactory because the tube area will have been reduced at least 10 percent. Carefully deburr tubing that has been formed and cut to final length to prevent wire insulation damage. When installing replacement tube sections with fittings at both ends, exercise care to eliminate mechanical strain.
502. FLEXIBLE CONDUIT. Flexible aluminum conduit conforming to Specification MIL-C-6186 is available in two types; Type I, Bare Flexible Conduit, and Type II, Rubber Covered Flexible Conduit. Flexible brass conduit conforming to Specification MIL-C-7981 is available and normally used instead of flexible aluminum where necessary to minimize radio interference. Flexible conduit may be used where it is impractical to use rigid conduit such as areas that have
500. CONDUIT INSTALLATION. Many of the past troubles with conduit can be avoided by proper Nominal Minimum bond attention to the following details: 1408 O.D. rodil (inches)
a. Do not locate conduit where passengers or maintenance personnel might use it as a handhold or footstep.
b. Provide drainholes at the lowest point in a conduit run. Drilling burrs should be carefully removed.
c. Support conduit to prevent chafing against structure and to avoid stressing its end fittings.
301. RIGID CONDUIT. Repair conduit sections that have been damaged to preclude injury to the wires or wire bundle which may consume FIoURE 11.24.-Bend radii for rigid condult.
Chap 11 Par 497
Pergo 202 motion between conduit ends or where complex bends are necessary. The use of transparent adhesive tape is recommended when cutting flexible tubing with a hacksaw to minimize fraying of the braid. Center the tape over the eut reference mark and saw through the tape.
AC 43.73-TA 1972 After cutting the flexible conduit, remove the transparent tape, trim the frayed ends of the braid, remove burrs from inside the conduit, and install coupling nut and ferrule. Minimum acceptable bending radii for flexible conduit is shown in fgure 11.25.
FIGURE 11.25.-Minimum bending radii for flexible aluminum or brass conduit.
Nominal I.D. Minimum bending of conduit radise ineido (Imohes) (Imoice)
393.-513. RESERVED.
Per 502 Chap 11
AC 43.13-1А Page 203 1972 Section 7. ROUTING, TYING, LACING, AND CLAMPING
514. GENERAL. Route and support aircrait wiring and conduits to prevent relative movement within the aircraft and provide protection against chafing between wires or other objects.
Provide extra protection where wires or wire bundles may be subjected to rough handling.
Soft insulation tubing is not regarded as satisfactory mechanical protection against abrasion or considered a substitute for proper clamping or tying. Secure all wiring so it is electrically and mechanically sound and neat in appearance.
515. WIRE BEND RADII. A wire bundle consists of a quantity of wires fastened or secured together-all traveling in the same direction.
Wire bundles may consist of two or more groups of wires. It is often advantageous to have a number of wire groups individually tied within the wire bundle for ease of identity at a later date, as shown in figure 11.26. To improve the appearance and to minimize the possibility of insulation abrasion, comb wire groups and bundles so the wires lie parallel to each other. A combing tool similar to that shown in figure 11.27 may be made from any suitable insulating material, taking care to assure all edges are rounded to protect the wire insulation. Bends in wire groups or bundles should not be less than 10 times the outside diameter of the wire group or bundle. However, a bend 8 times the diameter is acceptable to facilitate connections to terminal strips,
BUNDLE TIE GROUP TIE BUNDLE TIE
- 118- "APPROX. 3" FIGURE 11.27.-Comb for straightening wires in bundles.
provided the wire group or bundle is supported at each end of the bend.
516. SLACK. Normally, wire groups or bundles should not exceed 1/2 inch deflection between support points, as shown in figure 11.28. This measurement may be exceeded provided there is no possibility of the wire group or bundle touching a surface which may cause abrasion.
o. Provide sufficient slack at each end to:
(1) Permit replacement of terminals;
(2) Prevent mechanical strain on wires;
(3) Permit shifting of equipment for maintenance purposes.
517. ROUTING WIRES. In the process of accom- FIGURE 11.26.-Group and bundle ties. plishing an aircraft repair, it is often neces- Chap 11 Par 514
Page 204 AC 43.12-14 1972 1/2 INCH MAXIMUM
WITH NORMAL HAND PRESSURE FIGURE 11.28.-Slack between supports.
sary or desirable to reroute a group or bundle of wire. When it is necessary to deviate from the routing used by the manufacturer, consider the following:
o. Chafing. Protect wires or wire groups against chafing or abrasion where contact with other wires or sharp surfaces would damage the insulation. When a wire bundle passes through a hole in a bulkhead, support as shown in figure 11.9. Insert a grommet if a wire passes within 1/4 inch of the hole edge, as shown in figure 11.10.
b. Protection Against Battery Acids, Solvents, and Fluids. It is not advisable to route wires below & battery or closer than 6 inches from the bilge of the fuselage. Protect wires that will be exposed to damage from fluids by an outer sleeving of plastic tubing, as shown in figure 11.29. Extend the plastic tubing well beyond the area of exposure and provide a 1/8- inch drainhole at the lowest point. Assure the wire insulation is not damaged when cutting the hole in the plastic. Frequently inspect wires exposed to battery acid or fluids and replace when the insulation jacket shows signs of discoloration or saturation by fluids.
c. Protection in Wheel Wells and Landing Gear Areas. Wires located on landing gear and in the wheel well area can be exposed to many hazardous conditions if not suitably protected. Encase all wiring attached to a landing gear or located in the wheel well areas in conduit or protect by sleeves of flexible tubing and secure to prevent relative movement. Where wire bun- Par 517 DRAINAGE HOLE 1/8 INCH DIAMETER AT LOWEST POINT IN TUBING. MAKE THE
HOLE AFTER INSTALLATION IS COMPLETE
AND LOWEST POINT IS FIRMLY ESTABLISHED FIGURE 11.28.-Drainage hole in low point of tubing.
des pass fiex points, there should be no strain on attachments or excessive slack when parts are fully extended or retracted. Inspect the wiring and protective tubing frequently and replace at the first sign of wear.
d. Protection Against Personnel and Cargo. Install wiring so the structure affords protection against its use as a handhold and damage from cargo. Where the structure does not afford adequate protection, use conduit or provide a suitable mechanical guard.
e. Protection Against High Temperature. Wire insulation deteriorates rapidly when subjected Chap 11
AC 43.13-1A 1972 to high temperatures. Insulate wires that must be run through hot areas with a material such as asbestos, fiberglass or equivalent high temperature-resistant product. Wherever possible, keep wires separated from high-temperature equipment; and when replacing wires, do not use low-temperature insulated wires to replace high-temperature insulated wires.
f. Wiring Precoutions. Maintain a minimum clearance of 8 inches from any control cable.
When this clearance cannot be maintained, install a mechanical guard. When wiring is run parallel to combustible fluid or oxygen lines, maintain as much separation as possible. Locate wires above or on a level with the fluid lines and, wherever possible, maintain a minimum separation of 6 inches. Where the separation is 1/2 inch to 2 inches, install clamps as shown in figure 11.30 to maintain separation.
These clamps are not to be used as a means of supporting the wire bundle. Install additional clamps to support the wire bundle and fasten the clamps to the same structure used to support the fluid line to prevent relative motion.
Maintain a minimum separation of at least 1/2 inch between plumbing lines and any wire.
518. CLAMPING. Support wires and wire bundies using clamps meeting Specification MS-21919. Exercise care to assure the wire is FIGURE 11.80.-Separation of wires from plumbing lines, Chap 11 Page 205 not pinched when installing clamps to support electrical wiring as shown in figures 11.31 through 11.84. Whenever practical, rest the back of the clamp against a structural member. Install clamps in such manner that the electrical wires do not come in contact with other parts of the aircraft when subjected to vibration. Leave sufficient slack between the last clamp and the electrical equipment to prevent strain at the terminal and to minimize adverse effects on shockmounted equipment.
Where wires or wire bundles pass through bulkheads or other structural members, provide a grommet or suitable clamp to prevent abrasion.
519. TIES AND LACING. Ties, lacing, and straps are used to secure wire groups or bundles, to provide ease of maintenance, inspection, and installation. Cord meeting Specification MIL-C-5649 and twine meeting Specification JAM-T-718 are suitable for lacing or tying wires. In lieu of applying ties, straps meeting Specification MS-17821 or MS-17822 may be used in areas where the temperature does not exceed 120° C. or where the wiring can be damaged by operating units if the strap fails.
a. Lacing. Lace wire groups or bundles inside junction boxes or other enclosures. Single cord-lacing method shown in figure 11.35 may be used for wire groups or bundles 1 inch in diameter or less. The recommended knot for starting the single cord-lacing method is a clove hitch secured by a double-looped overhand knot as shown in step "a" of figure 11.85. Use the double cord-lacing method on wire bundles 1 inch in diameter or larger as shown in figure
11.86. When using the double cord-lacing method, employ a bowline on a bight as the starting knot. Reference step "a" of figure
11.36.
b. Tying. Use wire group or bundle ties where the supports for the wire are more than 12 inches apart. A tie consists of a clove hitch around the wire group or bundle secured by a square knot as shown in figure 11.87.
520.-530. RESERVED.
Par 517
Робро 206 AC 42.13-14 1972
DANGEROUS ANGLES MAX. ·50
SAFE ANGLES FIGURE 11.81.-Safe angle for cable clamps.
MS 21919
CABLE CLAMP OR
EQUIVALENT AN 5I5 SCREW AN 960 AN 960
PLAIN WASHER, PLAIN WASHER, AN 9368
LOCKWASHER, AN 935 EXTERNAL TEETH AN 365 NUT, LOCKWASHER, AN 340 NUT SELF-LOCKING SPLIT FIGURE 11.82.-Typical mounting hardware for MS-2019 cable clamps.
Par 519 Chap 11
AC 43.13-1A Page 207 :1972 MS 21919 CABLE CLAMPS
STRUCTUA "ANGLE" MEMBER "Z" MEMBER AN 730
CORRECT CLAMP
ANGLE BRACKET MS 21919
CABLE CLAMP Ot
EQUIVALENT FIGURE 11.84.-Installing cable clamps to tubular structure.
WIRE IS PINCHED IN CLAMP
INCORRECT FIGURE 11.88.-Installing cable clamp to structure.
Par 519 Chap 11
Pao 208 AC 43.13-1A 1973
PULL HERE UNTIL TIGHT
BEFORE FINISHING KNOT
CORD CROSSES
UNDER LOOS STEP • - STARTING KNOT
FINAL KNOT
STARTING KNOT
TIGHTENED
STEP & - INTERMEDIATE HALF HITCHES
FIRST PART OF FINAL STEP c - (PART I) KNOT TIGHTENED TRIM TO 3/8" MIN STEP € - (PART II) FINAL KNOT PIGURE 11.85.- -Single cord lacing.
Par 519 Chap 11
Chap 11 Par $31 the weight of pure water. 75° F.
the weight of the electrolyte as compared to electrolyte will freeze at approximately minus the battery electrolyte. The specific gravity is charged and discharged state. However, the hydrometer to determine the specific gravity of ciable chemical change takes place between the
535. CHECKING LEAD-ACID BATTERIES. Use a not as susceptible to freezing because no appreaction. Nickel-cadmium battery electrolyte is the addition of distilled water. constant discharge due to the internal chemical electrolyte is returned to the cell from which it its useful life and replacement should be con- was extracted. When a specific gravity differ- electrolyte is 1.244. Take care to assure the the corrected specific gravity reading of the sidered. Electrolyte level may be adjusted by battery, the battery is approaching the end of ence of 0.050 or more eixsts between cells of a posed to cold temperatures are subject to plate mind that lead-acid batteries are subject to a prevent freeze damage, maintain the specific freezing point of electrolyte for various specific damage due to freezing of the electrolyte. The 533. BATTERY FREEZING. Lead-acid batteries ex- gravity levels is shown in figure 11.38. To gravity at a reasonably high level, bearing in established for battery electrolyte. Therefore, trolyte is 40° F. or 16 points below the norm turer as to the proper charging voltage limits.
reading is 1.260; the temperature of the elec- the recommendations of the battery manufacin figure 11.89. As an example, the hydrometer per cell found satisfactory. In all cases, follow applied to the hydrometer indication as shown construction with values of 1.4 and 1.5 volts readings, a temperature correction should be charging voltage limit varies with design and However, to determine precise specific gravity the case of nickel-cadmium batteries, the about 1.200 when tested by a hydrometer. voltage per cell should not exceed 2.85 volts. In battery will show a specific gravity reading of within the battery. For lead-acid batteries, the battery reads about 1.240 and a 2/3 discharged rate at which energy is absorbed as heat is between 1.275 and 1.300. A 1/3 discharged bient temperature and state of charge) the fully charged when the specific gravity reading cant, since this will determine (for a given amfactured lead-acid batteries are considered number of cells in the battery is also signifi-
534. TEMPERATURE CORRECTION. U.S. manu- tween maximum charging voltage and the Anally battery failure. The relationship be- + 19 - 8 1.100 lyte boiling, rapid deterioration of the cell, and +18 -10 1.125 excessive cell temperatures leading to electro- + 5 -15 1.150 ature or charging voltage limits will result in — 4 -20 1.176 storage batteries beyond their ambient temper- -85 -16 -87 -28 1.200 1.225 532. BATTERY OVERHEAT FAILURE. Operation of —80 -62 -95 -52 -82 -70 1.275 1.250 1.800 ally identified by the material used for the plates.
recommendations. Storage batteries are usu- F. o. tained in accordance with the manufacturer's ЗрeolЛo characteristics and, therefore, should be main- Frease point in aircraft. These batteries possess different pointe. batteries are the two most common types used FIGURE 11.88.-Lead-acid battery electrolyte freezing 531. GENERAL. Lead-acid and nickel-cadmium Section 8. STORAGE BATTERIES 1972 AC 43.13-1А Page 210
Par 519 Chap 11 FIGURE 11.87.-Making ties.
SQUARE KNOT- OVER BUNDLE
CLOVE HITCH & WRAP CORD TWICE FIGURE 11.36.-Double cord lacing.
FINAL KNOT STEP • INTERMEDIATE HALF HITCHES STEP b STARTING KNOT TIGHTENED.
STARTING KNOT - BOWLINE ON A BIGHT STEP a 1972 Page 209 AC 43.13-1A
AC 43.13-1A Page 211 1972 FIGURE 11.89.--Sulfuric acid temperature correction.
Blectrolyte temperature Pointe to de aubtracted or added to speoiflo gravity
• 0. •p. readinge 140 +24 +20 +18 +12 + 8 + 1
- 4
- 8 80 10 -10 -28 -20 -85 —80
536. CHECKING NICKEL-CADMIUM BATTERIES.
The state of charge of a nickel-cadmium battery cannot be determined by measuring the specific gravity of the electrolyte with a hydrometer as the electrolyte specific gravity does not change with the state of charge. The only accurate way to determine the state of charge of a nickel-cadmium battery is by a measured discharge. After the battery has been fully charged and allowed to stand for at least 2 hours, the fluid level may be adjusted, if necessary, using distilled or demineralized water.
Because the fluid level varies with the state of charge, water should never be added while the battery is installed in the aircraft. Overfilling the battery will result in electrolyte spewage during charging. This will cause corrosive effects on the cell links, self discharge of the battery, dilution of the electrolyte density, and possible blockage of the cell vents and eventual cell rupture.
CAUTION Servicing equipment used for lead-acid batteries is not to be used for servicing nickel-cadmium batteries as acid is detrimental to the proper functioning of a nickel-cadmium battery.
Chap 11
537. ELECTROLYTE CORROSION. Electrolyte spillage or leakage may result in serious corrosion of the nearby structure or control elements as both sulfuric acid and potassium hydroxide are actively corrosive. Electrolyte may be spilled during ground servicing, leaked when cell case rupture occurs, or sprayed from cell vents due to excessive charging rates. If the battery is not case enclosed, properly treat structural parts near the battery which may be affected by acid fumes. Treat all case and drain surfaces which have been affected by electrolyte with a solution of sodium bicarbonate (for acid electrolyte) or boric acid, vinegar, or a 8 percent solution of acetic acid for potassium hydroxide electrolyte.
CAUTION Serious burns will result if the electrolyte comes in contact with any part of the body. Use rubber gloves, rubber spron, and proteetive goggles when handling electrolyte. If sulphuric acid is splashed on the body neutralize with a solution of baking soda and water, and shower or flush the affected area with water. For the eyes, use an eye fountain and flush with an abundance of water.
If potassium hydroxide contacts the skin, neutralize with 3 percent acetic acid, vinegar, or lemon Juice, and wash with water.
For the eyes, wash with a weak solution of boric acid or a weak solution of vinegar and flush with water.
538. NOXIOUS FUMES. When charging rates are excessive, the electrolyte may boil to the extent that fumes containing droplets of the electrolyte are emitted through the cell vents. These fumes from lead-acid batteries may become noxious to the crewmembers and passengers; therefore, thoroughly check the venting system. Nickelcadmium batteries will emit gas near the end of the charging process and during overcharge.
The battery vent system in the aircraft should have sufficient air flow to prevent this explosive mixture from accumulating. It is often advantageous to install a jar in the battery vent discharge system serviced with an agent to neutralize the corrosive effect of battery vapora.
539. INSTALLATION PRACTICES.
a. Clean the external surface of the battery prior to installation in the aircraft.
Par 536
b. When replacing lead-acid batteries with nickel-cadmium batteries, neutralize the battery box or compartment and thoroughly flush with clear water and dry. Acid residue can be detrimental to the proper functioning of a nickel-cadmium battery.
c. Check the condition of the vent system.
d. When installing batteries in an aircraft, exercise care to prevent inadvertent shorting of the battery terminals. Serious damage to the aircraft structure can be sustained by the resultant high discharge of electrical energy.
This condition may normally be avoided by insulating the terminal posts during the installation process.
Par 539 AC 43.73-1A 1972
e. Assure the battery holddown devices are secure but not so tight as to exert excessive pressure which may cause the battery to buckle causing internal shorting of the battery.
1. If a quick disconnect type of battery connector which prohibits crossing the battery lead is not employed, assure that the aircraft wiring is connected to the proper battery terminal. Reverse polarity in an electrical system can seriously damage a battery. Assure battery cable connections are tight to prevent arcing or a high resistance connection.
540.-552. RESERVED.
Chap 11