TABLE 11-18. 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 Structure Screw or Bolt and Nut Plate Lock-Nut Washer A Washer B Washer C Aluminum Cadmium Cadmium Cadmium None Cadmium Alloys Plated Steel Plated Steel Plated Steel or Plated Steel or Aluminum Aluminum Magnesium Cadmium Cadmium Magnesium None or Cadmium Alloys Plated Steel Plated Steel Alloy Magnesium Plated Steel or Alloy Aluminum Steel, Cadmium Cadmium Cadmium Cadmium Cadmium Cadmium Plated Plated Steel Plated Steel Plated Steel Plated Steel Plated Steel or Aluminum Steel, Corrosion Corrosion Cadmium Corrosion Cadmium Cadmium Resisting Resisting Steel Plated Steel Resisting Steel Plated Steel Plated Steel or or Cadmium Aluminum Plated Steel Tinned Copper Terminal and Jumper Aluminum Cadmium Cadmium Cadmium Aluminum? Cadmium Alloy Plated Steel Plated Steel Plated Steel Alloy Plated Steel Magnesium Alloy!
Steel, Cadmium Cadmium Cadmium Cadmium None Cadmium Plated Plated Steel Plated Steel Plated Steel Plated Steel Steel, Corrosion Corrosion Cadmium Corrosion None Cadmium Resisting Resisting Steel Plated Steel Resisting Steel Plated Steel or Cadmium Plated Steel I Avoid connecting copper to magnesium.
2 Use washers having a conductive finished treated to prevent corrosion, suggest AN960JD10L.
Par 11-189 Page 11-87
FIGURE 11-20. COPPER JUMPER CONNECTOR TO TUBULAR STRUCTURE CAD. PL. STEEL AN 735 CLAMP SCREW COPPER
TERMINAL
ALUMINUM
CYLINDRICAL WASHERS
SURFACE CAD. PL. STEEL
LOCKWASHER CAD. PL. STEEL
LOCK NUT FIGURE 11-21. BONDING CONDUIT TO STRUCTURE CAD. PL. STEEL SCREW AN 735 CLAMP WASHE ALUMINU
STRUCTURE
- ALUMINUM
ALUMINUM ALLOY WASHER
OR CORROSION- RESISTING STEEL CAD. PL. STEEL
CONDUIT LOCKWASHER CAD. PL. STEEL
LOCKNUT FIGURE 11-22. ALUMINUM JUMPER CONNECTION TO TUBULAR STRUCTURE CAD. PL. STEEL SCREW AN 735 CLAMP
ALUMINUM WASHER
BARE ALUMINU
TERMINA
TLINDRICA URFACI ALUMINUM WASHER LOCKNUT CAD. PL. STEEL LOCKWASHER CAD. PL. STEEL
d. Bonding Jumper Attachment. The use of solder to attach bonding jumpers should be avoided. Tubular members should be bonded by means of clamps to which the jumper is attached. Proper choice of clamp material should minimize the probability of corrosion.
e. Ground Return Connection. When bonding jumpers carry substantial ground return current, the current rating of the jumper should be determined to be adequate and that a negligible voltage drop is produced.
Par 11-189 Page 11-88
Par 11-190 Page 11-89
11-190. CREEPAGE DISTANCE. Care should be used in the selection of electrical components to ensure that electrical clearance and creepage distance along surfaces between adjacent terminals, at different potentials, and between these terminals and adjacent ground surfaces are adequate for the voltages involved.
11-191. FUEL SYSTEMS. Small metallic objects within an aircraft fuel tank that are not part of the tank structure, should be electrically bonded to the structure so as to dissipate static charges that may otherwise accumulate on these objects. A practical bonding design would use a flexible braided jumper wire or riveted bracket. In such situations, a DC resistance of 1 ohm or less should indicate an adequate connection. Care should be taken, in designing such connections, to avoid creating continuous current paths that could allow lightning or power fault currents to pass through connections not designed to tolerate these higher amplitude currents without arcing. Simulated static charge, lightning, or fault current tests may be necessary to establish or verify specific designs. All other fuel system components, such as fuel line (line to line) access doors, fuel line supports, structural parts, fuel outlets, or brackets should have an electromechanical (bonding strap) secure connector that ensures 1 ohm or less resistance to the structure. Advisory Circular (AC) 20-53, Protection of Aircraft Fuel Systems Against Vapor Ignition Caused by Lightning, and associate manual DOT/FAA/CT-83/3, provide detailed information on necessary precautions.
11-192. ELECTRIC SHOCK PREVENTION BONDING. Electric shock to personnel should be prevented by providing a low-resistance path of 1/100 ohm or less between structure and metallic conduits or equipment. The allowable ground resistance should be such that the electric potential of the conduit or equipment housing does not reach a dangerous value under probable fault conditions. The current carrying capacity of all elements of the ground circuit should be such that, under the fault condition, no sparking, fusion, or dangerous heating will occur. Metallic supports usually provide adequate bonding if metal-to-metal contact is maintained.
11-193. LIGHTNING PROTECTION BONDING. Electrical bonding is frequently required for lightning protection of aircraft and systems, especially to facilitate safe conduction of lightning currents through the airframe. Most of this bonding is achieved through normal airframe riveted or bolted joints but some externally mounted parts, such as control surfaces, engine nacelles, and antennas, may require additional bonding provisions. Generally, the adequacy of lightning current bonds depends on materials, cross-sections, physical configurations, tightness, and surface finishes. Care should be taken to minimize structural resistance, so as to control structural voltage rises to levels compatible with system protection design. This may require that metal surfaces be added to composite structures, or that tinned copper overbraid, conduits, or cable trays be provided for interconnecting wire harnesses within composite airframes. Also, care must be taken to prevent hazardous lightning currents from entering the airframe via flight control cables, push rods, or other conducting objects that extend to airframe extremities. This may require that these conductors be electrically bonded to the airframe, or that electrical insulators be used to interrupt lightning currents. For additional information on lightning protection measures, refer to DOT/FAA/TC-22/11. Report DOT/FAA/CT 86/8, April 1987, Determination of Electrical Properties of Grounding, Bonding and Fastening Techniques for Composite Materials, may provide additional information for composite materials.
Par 11-193 Page 11-90
a. Control Surface Lightning Protection Bonding. Control surface bonding is intended to prevent the burning of hinges on a surface that receives a lightning strike; thus causing possible loss of control. To accomplish this bonding, control surfaces and flaps should have at least one 6,500 circular mil area copper (e.g., 7 by 37 AWG size 36 strands) jumper across each hinge. In any case, not less than two 6,500 circular mil jumpers should be used on each control surface. The installation location of these jumpers should be carefully chosen to provide a low-impedance shunt for lightning current across the hinge to the structure. When jumpers may be subjected to arcing, substantially larger wire sizes of 40,000 circular mils or a larger cross-section are required to provide protection against multiple strikes. Sharp bends and loops in such jumpers can create susceptibility to breakage when subjected to the inductive forces created by lightning current, and should be avoided.
b. Control Cable Lightning Protection Bonding. To prevent damage to the control system or injury to flight personnel due to lightning strike, cables and levers coming from each control surface should be protected by one or more bonding jumpers located as close to the control surface as possible. Metal pulleys are considered a satisfactory ground for control cables.
11-194. LIGHTNING PROTECTION FOR ANTENNAS AND AIR DATA PROBES.
Antenna and air data probes that are mounted on exterior surfaces within lightning strike zones should be provided with a means to safely transfer lightning currents to the airframe, and to prevent hazardous surges from being conducted into the airframe via antenna cables or wire harnesses. Usually, the antenna mounting bolts provide adequate lightning current paths. Surge protectors built into antennas or installed in coaxial antenna cables or probe wire harnesses will fulfill these requirements. Candidate designs should be verified by simulated lightning tests in accordance with RTCA DO-160G.
11-195. STATIC-DISCHARGE DEVICE. Means should be provided to bleed accumulated static charges from aircraft prior to ground personnel coming in contact with an aircraft after landing. Normally, there is adequate conductivity in the tires for this, but if not, a static ground should be applied before personnel come into contact with the aircraft. Fuel nozzle grounding receptacles should be installed in accordance with the manufacturer’s specifications. Grounding receptacles should provide a means to eliminate the static-induced voltage that might otherwise cause a spark between a fuel nozzle and fuel tank access covers and inlets. In addition, static discharging wicks are installed on wings and tail surfaces to discharge static changes while in flight.
11-196. CLEANING. In order to ensure proper ground connection conductivity, all paint, primer, anodize coating, grease, and other foreign material must be carefully removed from areas that conduct electricity. On aluminum surfaces, apply chemical surface treatment to the cleaned bare metal surface in accordance with the manufacturer’s instructions within 4–8 hours, depending on ambient moisture/contaminate content.
11-197. HARDWARE ASSEMBLY. Details of bonding connections must be described in maintenance manuals and adhered to carefully when connections are removed or replaced during maintenance operations. In order to avoid corrosion problems and ensure long-term integrity of the electrical connection, hardware used for this purpose must be as defined in these documents or at least be equivalent in material and surface. Installation of fasteners used in bonded or
Par 11-197 Page 11-91 grounded connections should be made in accordance with SAE ARP1870. Threaded fasteners must be torqued to the level required by SAE ARP1928.
11-198.–11-204. [RESERVED.]
Par 11-205 Page 11-92 SECTION 16. WIRE MARKING
11-205. GENERAL. The proper identification of electrical wires and cables with their circuits and voltages is necessary to provide safety of operation, safety to maintenance personnel, and ease of maintenance.
a. 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 CAGE code identifying the wire manufacturer. Existing installed wire that needs replacement can thereby be identified as to its performance capabilities, and the inadvertent use of a lower performance and unsuitable replacement wire avoided.
b. The method of identification should not impair the characteristics of the wiring.
CAUTION: Do not use metallic bands in place of insulating sleeves. Exercise care when marking coaxial or data bus cable, as deforming the cable may change its electrical characteristics.
11-206. WIRE IDENTIFICATION. To facilitate installation and maintenance, original wire-marking identification is to be retained. 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.
11-207. 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.
11-208. PLACEMENT OF IDENTIFICATION MARKINGS. Identification markings should be placed at each end of the wire and at 15-inch maximum intervals along the length of the wire. Wires less than 3 inches long need not be identified. Wires 3 to 7 inches in length should be identified approximately at the center. Added identification marker sleeves should be so located that ties, clamps, or supporting devices need not be removed in order to read the identification. The wire identification code must be printed to read horizontally (from left to right) or vertically (from top to bottom). The two methods of marking wire or cable are as follows:
a. Direct marking is accomplished by printing the cable’s outer covering. (See Figure 11-23.)
Par 11-208 Page 11-93 FIGURE 11-23. SPACING OF PRINTED IDENTIFICATION MARKS (DIRECT MARKING)
b. In direct marking is accomplished by printing a heat-shrinkable sleeve and installing the printed sleeve on the wire or cables outer covering. Indirect-marked wire or cable should be identified with printed sleeves at each end and at intervals not longer than 6 feet. The individual wires inside a cable should be identified within 3 inches of their termination. (See Figure 11-24.)
FIGURE 11-24. SPACING OF PRINTED IDENTIFICATION MARKS (INDIRECT MARKING) 11 -209. TYPES OF WIRE MARKINGS. The preferred method is to mark directly on the wire. A successful requirement qualification should produce markings that meet the marking characteristics specified in SAE AS50881 without causing insulation degradation. Teflon coated wires, shielded wiring, multiconductor cable, and thermocouple wires usually require special sleeves to carry identification marks. There are some wire marking machines in the market that can be used to stamp directly on the type wires mentioned above. Whatever method of marking
Par 11-209 Page 11-94 is used, the marking should be legible and the color should contrast with the wire insulation or sleeve.
a. Extreme care must, therefore, be taken during circuit identification by a hot stamp machine on insulation wall 10 mils or thinner.
b. Alternative identification methods such as “Laser Printing,” “Ink Jet,” and “Dot Matrix” are preferred. When such modern equipment is not available, the use of stamped identification sleeving should be considered on insulation wall thickness of 10 mils or less.
11-210. HOT STAMP MARKING. Due to widespread use of Hot Stamp wire marking, personnel should refer to SAE ARP5369, Guidelines for Wire Identification Marking Using the Hot Stamp Process, for guidance on minimizing insulation damage. Hot Stamp process uses a heated typeface to transfer pigment from a ribbon or foil to the surface of wires or cables. The traditional method imprints hot ink marks onto the wire. Exercise caution when using this method, as it has been shown to damage insulation when incorrectly applied. Typeset characters, similar to that used in printing presses but shaped to the contour of the wire, are heated to the desired temperature. Wire is pulled through a channel directly underneath the characters. The heat of the type set characters transfers the ink from the marking foil onto the wire.
a. Good marking is obt ained only by the proper combination of temperature, pressure, and dwelling. Hot Stamp will mark wire with an outside diameter of 0.038 to 0.25 inches.
b. Before producing hot stamp wire, it must be assured that the marking machine is properly adjusted to provide the best wire marking with the least wire insulation deterioration.
The marking should never create an indent greater than 10 percent of the insulation wall.
CAUTION: The traditional Hot Stamp method is not recommended for use on wire with outside diameters of less than 0.035 inches. (Refer to SAE ARP5369). Stamping dies may cause fracture of the insulation wall and penetration to the conductor of these materials. When various fluids wet these openings in service, arcing and surface tracking damage wire bundles.
Later in service, when various fluids have wet these openings, serious arcing and surface tracking will have damaged wire bundles.
11-211. DOT MATRIX MARKING. The dot matrix marking is imprinted onto the wire or cable very similar to that of a dot matrix computer printer. The wire must go through a cleaning process to make sure it is clean and dry for the ink to adhere. Wires marked with dot matrix equipment require a cure consisting of an UV curing process, which is normally applied by the marking equipment. This cure should normally be complete 16 to 24 hours after marking. Dot matrix makes a legible mark without damaging the insulation. Depending on equipment configuration, dot matrix can mark wire from 0.037- to 0.5-inch outside diameter.
Multiconductor cable can also be marked.
11-212. I NK JET MARKING. This is a “non-impact” marking method wherein ink droplets are electrically charged and then directed onto the moving wire to form the characters. Two basic ink types are available: thermal cure and UV cure.
Par 11-212 Page 11-95
a. Thermal cure inks must generally be heated in an oven for a length of time after marking to obtain their durability. UV cure inks are cured in line much like dot matrix.
b. Ink jet marks the wire on the fly and makes a reasonably durable and legible mark without damaging the insulation. Ink jets normally mark wire from 0.030- to 0.25-inch outside diameter. Multiconductor cable can also be marked.
11-213. LASER MARKING. Of the variety of laser marking machines, UV lasers are proving to be the best. This method marks into the surface of the wire’s insulation without degradation to its performance. One common type of UV laser is referred to as an excimer laser marker. UV laser produces the most durable marks because it marks into the insulation instead of on the surface. However, excimer laser will only mark insulation that contain appropriate percentages of titanium dioxide (TiO2). The wire can be marked on the fly. UV can mark from 0.030- to
0.25-inch outside diameter. The UV laser makes only gray marks and they appear more legible on white or pastel-colored insulation.
11-214. IDENTIFICATION SLEEVES. Flexible sleeving, either clear or opaque, is satisfactory for general use. When color-coded or striped component wire is used as part of a cable, the identification sleeve should specify which color is associated with each wire identification code. Identification sleeves are normally used for identifying the following types of wire or cable:
a. Unjacketed shielded wire.
b. Thermocouple wire identification is normally accomplished by means of identification sleeves. As the thermocouple wire is usually of the duplex type (two insulated wires within the same casing), each wire at the termination point bears the full name of the conductor.
Thermocouple conductors are alumel, chromel, iron, constantan, and copper constantan.
c. Coaxial cable should not be hot stamped directly. When marking coaxial cable, care should be taken not to deform the cable as this may change the electrical characteristics of the cable. When cables cannot be printed directly, they should be identified by printing the identification code (and individual wire color, where applicable) on a nonmetallic material placed externally to the outer covering at the terminating end and at each junction or pressure bulkhead. Cables not enclosed in conduit or a common jacket should be identified with printed sleeves at each end and at intervals not longer than 3 feet. Individual wires within a cable should be identified within 3 inches from their termination.
d. Multiconductor cable normally use identification sleeves for identifying unshielded, unjacketed cable.
e. High-temperature wire with insulation is difficult to mark (such as Teflon and fiberglass).
11-215. IDENTIFICATION TAPE. Identification tape can be used in place of sleeving, in most cases (i.e., polyvinyl fluoride).
Par 11-216 Page 11-96
11-216. OPERATING CONDITIONS. For sleeving exposed to high temperatures (over 400 °F), materials such as silicone fiberglass should be used.
11-217. INSTALLATION OF PRINTED SLEEVES. Polyolefin sleeving should be used in areas where resistance to solvent and synthetic hydraulic fluids is necessary. Sleeves may be secured in place with cable ties or by heat shrinking. The identification sleeving for various sizes of wire is shown in Table 11-19.
TABLE 11-19. RECOMMENDED SIZE OF IDENTIFICATION SLEEVING Wire Size Sleeving Size AN AL No. Nominal ID (inches) #24 12 .085 #22 11 .095 #20 10 .106 #18 9 .118 #16 8 .113 #14 7 .148 #12 6 .166 #10 4 .208 #8 #8 2 .263 #6 #6 0 .330 #4 #4 3/8 inch .375 #2 #2 1/2 inch .500 #1 #1 1/2 inch .500 #0 #0 5/8 inch .625 #00 #00 5/8 inch .625 #000 #000 3/4 inch .750 #0000 #0000 3/4 inch .750
11-218. IDENTIFICATION OF WIRE BUNDLES AND HARNESSES. The identification of wire bundles and harnesses is becoming a common practice and may be accomplished by the use of a marked sleeve tied in place or by the use of pressure-sensitive tape as indicated in Figure 11-25.
Par 11-218 Page 11-97 FIGURE 11-25. IDENTIFICATION OF WIRE BUNDLES AND HARNESSES
a. Wires for which identifications are reassigned after installation may be remarked on sleeves at the termination of each wire segment. It may be necessary to re-identify such wires throughout their lengths to facilitate ease of maintenance.
b. For high-density harnessed, shielded, and jacketed multiconductor cables and when using nonsignificant wire identification, color coding or its alphanumeric equivalent may be interchanged within the same harnesses. The alphanumeric equivalent of the color code should be as set forth in MIL-STD-681.
11-219. TERMINAL MARKING SLEEVE AND TAGS. Typical cable markers are flat, nonheat-shrinkable tags. Heat shrinkable marking sleeves are available for marking wires and cables, and should be inserted over the proper wire or cable and heat shrunk using the proper manufacturer recommended heating tool. (See Figures 11-26 and 11-27.)
FIGURE 11-26. STANDARD SLEEVES (135 °C)
Par 11-219 Page 11-98 FIGURE 11-27. INSTALLATION OF HEAT-SHRINKABLE INSULATION SLEEVES
11-220. SLEEVES AND CABLE MARKERS SELECTION. Sleeves and cable markers must be selected by cable size and operating conditions. (See Tables 11-20 through 11-23).
a. Markers are printed using a typewriter with a modified roller. Blank markers on a bandolier are fed into the typewriter, where they are marked in any desired combination of characters. The typed markers, still on bandoliers, are heated in an infrared heating tool that processes the markers for permanency. The typed and heat-treated markers remain on the bandolier until ready for installation.
b. Markers are normally installed using the following procedure:
(1) Select the smallest tie-down strap that will accommodate the outside diameter of the cable. (See Table 11-24.)
(2) Cut the marking plate from the bandolier. (See Figure 11-28.)
(3) Thread the tie-down straps through holes in marking plate and around cable. Thread tip of tie-down strap through slot in head. (See Figure 11-29.) Pull tip until strap is snug around cable.