Soldering

Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-34

Unclassified

2.3 SOLDERING The following information will aid you in learning basic soldering skills. It should enable you to solder wires to electrical connectors, splices, and terminal lugs that we have discussed earlier in the chapter. Special skills and schooling are required for the soldering techniques used in printed circuit boards and microminiature component repair. 2.3.1 Soldering Process Cleanliness is essential for efficient, effective soldering. Solder will not adhere to dirty, greasy, or oxidized surfaces. Heated metals tend to oxidize rapidly. This is the reason the oxides, scale, and dirt must be removed by chemical or mechanical means. Grease or oil films can be removed with a suitable solvent. Connections to be soldered should be cleaned just prior to the actual soldering operation.

Items to be soldered should normally be "tinned" before making a mechanical connection. Tinning is the coating of the material to be soldered with a light coat of solder. When the surface has been properly cleaned, a thin, even coating of flux should be placed over the surface to be tinned. This will prevent oxidation while the part is being heated to soldering temperature. Rosin-core solder is usually preferred in electrical work. However, a separate rosin flux may be used instead. Separate rosin flux is frequently used when wires in cable fabrication are tinned.

Q21. Why must items to be soldered be cleaned just prior to the soldering process? 2.3.2 Tinning Copper Wire and Cable Wires to be soldered to connectors should be stripped so that when the wire is placed in the barrel; there will be a gap of approximately 1/32 inch between the end of the barrel and the end of the insulation. This is done to prevent burning the insulation during the soldering process and to allow the wire to flex easier at a stress point. Before copper wires are soldered to connectors, the ends exposed by stripping are tinned to hold the strands solidly together. The tinning operation is satisfactory when the ends and sides of the wire strands are fused together with a coat of solder. Do not tin wires that are to be crimped to solderless terminals or splices.

Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-35

Unclassified

Copper wires are usually tinned by dipping them into flux (view A of figure 2-25) and then into a solder bath (pot) (view B of the figure). In the field, copper wires can be tinned with a soldering iron and rosin-core solder. Tin the conductor for about half its exposed length. Tinning or solder on the wire above the barrel causes the wire to be stiff at the point where flexing takes place. This will result in the wire breaking. The flux used in tinning copper wire is a mixture of denatured alcohol and freshly ground rosin. This type of flux may be mixed just prior to use. A premixed paste flux may also be used. The solder used for terminal lugs, splices, and connectors is a mixture of 60- percent tin and 40-percent lead. Maintain the temperature of the solder bath (pot) between 450 and 500º F. This keeps the solder in a liquid state. Skim the surface of the solder pot, as necessary, with a metal spoon or blade. This keeps the solder clean and free from oxides, dirt, and so forth.

Figure 2-25 Dip-tinning In a solder pot Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-36

Unclassified

Dip-tin wires smaller than No. 8 in groups of 8 or 10. Dip-tin wires size No. 8 and larger individually. The procedure for dip-tinning is as follows: 1. Prepare the flux and solder as previously described. 2. Make sure the exposed end of the wire is clean and free from oil, grease, and dirt. Strands should be straight and parallel. Dirty wire should be re-stripped. 3. Grasp the wire firmly and dip it into the prepared flux to a depth of about 1/8 inch (see view A of figure 2-25). 4. Remove the wire and shake off the excess flux.

5. Immediately dip the wire into molten solder. Dip only half of the stripped conductor length into the solder (see view B of figure 2-25). 6. Turn the wire slowly in the solder bath until the wire is well tinned. Watch the solder fuse to the wire. Do not keep the wire in the bath longer than necessary. 7. Remove the excess solder by wiping the tinned conductor on a cloth. WARNING Do not shake off excess solder. It can cause serious burns if it contacts your skin. It can also cause short circuits in exposed electrical equipment that may be in the immediate area of the tinning operation.

CAUTION Use only rosin flux or rosin-core solder for tinning copper wires to be used in electrical and electronics systems. Corrosive flux will cause damage. During the tinning operation, do not melt, scorch, or burn the insulation. Q22. What does "tinning" mean in relationship to soldering? Q23. Why should wire be stripped 1/32 inch longer than the depth of the solder barrel? Q24. How much of the stripped length of a conductor should be tinned? Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-37

Unclassified

2.3.3 Alternative Dip-Tinning Procedure If an electrically heated solder pot is not available, a small number of wires can be tinned using the following procedure (see figure 2-26): 1. Cut off the beveled section of the tip of a discarded soldering iron tip. 2. Drill a hole (1/4- to 3/8-inch diameter) in the round part of the tip about two-thirds through. 3. Heat the iron and melt the rosin-core solder into the hole. 4. Tin the wires by dipping them into the molten solder one at a time. 5. Keep adding fresh rosin-core solder as the flux burns away.

Figure 2-26 Alternate dip-tinning method Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-38

Unclassified

2.3.4 Procedure for Tinning Copper Wire with a Soldering Iron In the field, wires smaller than size No. 10 can be tinned with a soldering iron and rosin- core solder as follows (see figure 2-27): 1. Select a soldering iron with the correct heat capacity for the wire size (see table 2-3). Make sure that the iron is clean and well tinned. Table 2-3 Approximate Soldering Iron Size for Tinning Wire Size (AWG) Soldering Iron Size (Heat Capacity) #20 - #16 65 Watts #14 & #12 100 Watts #10 & #8 20 Watts 2. Start by holding the iron tip and solder together on the wire until the solder begins to flow.

3. Move the soldering iron to the opposite side of the wire and tin half of the exposed length of the conductor. The tinned surfaces to be joined should be shaped, fitted, and then mechanically joined to make a good mechanical and electrical contact. The parts must be held still. Any motion between the parts while the solder is cooling usually results in a poor solder connection, commonly called a "fractured solder" joint. Q25. What causes a "fractured solder" joint? Figure 2-27 Tinning wire with a soldering iron Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-39

Unclassified

2.3.5 Soldering Tools Many types of soldering tools are in use today. Some of the more common types are the soldering iron, soldering gun, resistance soldering set, and pencil iron. The following discussion will provide you with a working knowledge of these tools. 2.3.5.1 Soldering Irons Some common types of hand soldering irons are shown in figure 2-28. All high-quality soldering irons operate in the temperature range of 500 to 600º F. Even the 25-watt midget irons produce this temperature. The important difference in iron sizes is not temperature, but thermal inertia. Thermal inertia is the capacity of the iron to generate and maintain a satisfactory soldering temperature while giving up heat to the joint to be soldered. Although it is not practical to solder large conductors with the 25-watt iron, this iron is quite suitable for replacing a half-watt resistor in an electronic circuit or soldering a miniature connector. One advantage of using a small iron for small work is that it is light and easy to handle and has a small tip that is easily used in close places. Even though its temperature is high enough, a midget iron does not have the thermal inertia to solder large conductors.

Figure 2-28 Types of hand soldering Irons Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-40

Unclassified

A well-designed iron is self-regulating. The resistance of its element increases with rising temperature. This limits the flow of current. Some common tip shapes of the soldering irons in use in the Navy are shown in figure 2-29. Figure 2-29 Soldering iron tip shapes Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-41

Unclassified

An iron should be tinned (the application of solder to the tip after the iron is heated) prior to soldering a component in a circuit. After extended use of an iron, the tip tends to become pitted due to oxidation. Pitting indicates the need for retinning. The tip is retinned after first filing the tip until it is smooth (see figure 2-30). Q26. Define thermal inertia. Q27. Why are small-wattage soldering irons not used to solder large conductors? Q28. State why a well-designed soldering iron is self-regulating. Q29. What should be done to a soldering iron tip that is pitted?

Figure 2-30 Reconditioning pitted soldering iron tip Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-42

Unclassified

2.3.5.2 Soldering Gun The soldering gun (figure 2-31) has gained great popularity in recent years because it heats and cools rapidly. It is especially well adapted to maintenance and troubleshooting work where only a small part of the technician's time is spent actually soldering. A transformer in the soldering gun supplies approximately 1 volt at high current to a loop of copper, which acts as the soldering tip. It heats to soldering temperature in 3 to 5 seconds. However, it may overheat to the point of incandescence if left on over 30 seconds. This should be avoided because excess heat will burn the insulation off the wiring. The gun is operated by a finger switch. The gun heats only while the switch is pressed.

Since the gun normally operates only for short periods at a time, it is comparatively easy to keep clean and well tinned. Short operating time allows little oxidation to form. Because the tip is made of pure copper, it is likely to pit, due to the dissolving action of the solder. Figure 2-31 Soldering gun Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-43

Unclassified

The gun or iron should always be kept tinned to permit proper heat transfer to the connection to be soldered. Tinning also helps control the heat to prevent solder buildup on the tip. This control reduces the chance of the solder spilling over to nearby components and causing short circuits. Maintaining the proper tinning on the iron or gun, however, may be made easier by tinning with silver solder (a composition of silver, copper, and zinc). The temperature at which the bond is formed between the copper tip and the silver solder is much higher than with lead-tin solder. This tends to decrease the pitting action of the solder on the copper tip.

Overheating small or delicate wiring can easily occur when a soldering gun is used. For most jobs, even the LOW position of the trigger overheats the gun after 10 seconds. With practice, the heat can be controlled by pulsing the gun on and off with its trigger. The HIGH position is used only for fast heating and for soldering heavy connections. When a soldering iron or gun is used, heating and cooling cycles tend to loosen the nuts or screws that hold the replaceable tips. When the nut on a gun becomes loose, the resistance of the tip connection increases. The temperature of the connection is increased, thus reducing the heat at the tip. Continued loosening may eventually cause an open circuit. Therefore, check and tighten the nut or screw, as needed.

CAUTION Soldering guns should never be used to solder electronic components, such as resistors, capacitors, and transistors, because the heat generated can destroy the components. They should be used only on terminals, splices, and connectors (not the miniature type). Q30. What happens if a soldering gun switch is pressed for periods longer than 30 seconds? Q31. What causes the nuts or screws that hold the tips on soldering irons and guns to loosen? Q32. A soldering gun should NOT be used on what components? Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-44

Unclassified

2.3.5.3 Resistance Soldering Set A time-controlled resistance soldering set (figure 2-32) is now used at many maintenance activities. The set consists of a transformer that supplies 3 or 6 volts at a high current to stainless steel or carbon tips. The transformer is turned ON by a foot switch and OFF by an electronic timer. The timer can be adjusted for as long as 3 seconds soldering time. This set is especially useful for soldering cables to plugs and similar connectors; even the smallest types. In use, the double-tip probes of the soldering unit are adjusted to straddle the connector cup (connector barrel) to be soldered. One pulse of current heats it for tinning. After the wire is inserted, a second pulse of current solders the connection and completes the job.

Since the soldering tips are hot only during the brief period of actual soldering, burning of wire insulation and melting of connector inserts are greatly reduced. The greatest difficulty with this device is keeping the probe tips free of rosin and corrosion. A cleaning block is mounted on the transformer case for this purpose. Some technicians prefer fine sandpaper for cleaning the double tips. Figure 2-32 Resistance soldering set Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-45

Unclassified

CAUTION Do not use steel wool for cleaning tips. It is dangerous when used around electrical equipment because the strands can fall into the equipment and cause short circuits. Q33. What is an advantage of using a resistance soldering iron when soldering wire to a connector? Q34. Why is steel wool NEVER used as an abrasive to clean soldering tools? 2.3.5.4 Pencil Iron and Special Tips An almost indispensable item is the pencil-type soldering iron with an assortment of tips (figure 2-33). Miniature soldering irons have a wattage rating of less than 40 watts. They are easy to use, and are recommended for soldering small components, such as miniature connectors.

Figure 2-33 Pencil iron with special tips Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-46

Unclassified

One type of pencil iron is equipped with several different tips that range from one-fourth to one-half inch in size (diameter) and are of various shapes. This feature makes it adaptable to a variety of jobs. Unlike most tips that are held in place by setscrews, these tips have threads and screw into the barrel. This feature provides excellent contact with the heating element, thus improving heat transfer efficiency. "Antiseize" compound is generally applied to the threads of the tip each time a tip is installed into the iron. This allows the tip to be easily removed when another is to be inserted.

A special feature of this iron is the soldering pot that screws in like a tip and holds about a thimbleful of solder. It is useful for tinning the ends of a large number of wires. The interchangeable tips are of various sizes and shapes for specific uses. Extra tips can be obtained and shaped to serve special purposes. The thread-in units are useful in soldering small items. Another advantage of the pencil soldering iron is that it can be used as an improvised light source to inspect the completed work. Simply remove the soldering tip and insert a 120-volt, 6-watt, type 6S6 lamp bulb into the socket.

If leads, tabs, or small wires are bent against a board or terminal, slotted tips are provided to simultaneously melt the solder and straighten the leads. If no suitable tip is available for a particular operation, an improvised tip can be made (see figure 2-34). Wrap a length of bare copper wire around one of the regular tips and bend the wire into the proper shape for the purpose. This method also serves to reduce thermal inertia when a larger iron must be used on small components. Figure 2-34 Improvised tip Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-47

Unclassified

Q35. Why should "antiseize" compound be used on the screw-in tips of the pencil iron? Q36. If no suitable tip is available for a particular job, how may one be improvised? 2.3.6 Solder Any discussion of soldering techniques should include an explanation of solder itself. Ordinary soft solder is a fusible alloy consisting chiefly of tin and lead. It is used to join two or more metals at temperatures below their melting point. In addition to tin and lead, soft solders occasionally contain varying amounts of antimony, bismuth, cadmium, or silver. These are added to change the melting point or physical properties of the alloy.

Ordinary table salt has to be heated to 1,488º F before it melts. However, when a little water is added, it dissolves easily at room temperature. The action of molten solder on a metal like copper may be compared to the action of water on salt. The solder bonds the connection by dissolving a small amount of the copper at temperatures quite below its melting point. Thus, the soldering process involves a metal solvent action between the solder and the metal being joined. A solder joint is therefore chemical in nature rather than purely physical. The bond is formed in part by chemical action and part by a physical bond.

The properties of a solder joint are different from those of the original solder. The solder is converted to a new and different alloy through the solvent action. Two metals soldered together behave like one solid metal. It is unlike two metals bolted, wired, or otherwise physically attached. These types of connections are still two pieces of metal. They are not even in direct contact due to an insulating film of oxide on the surfaces of the metals. Temperature change does not affect the solder alloy. It withstands stress and strains without damaging the joint. An unsoldered connection eventually becomes loosened by small movements caused by temperature variations and by the gradual buildup of oxides on the metal surfaces.

Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-48

Unclassified

To understand fully the alloy or solvent action on molten solder, look at the tin-lead fusion diagram shown in figure 2-35. This diagram shows that pure lead (point A) melts at 621º F. Point C shows the lowest melting point of the tin and lead alloy. The alloy at point C consists of 63-percent tin (SN63) and 37-percent lead. This is commonly called 63/37 solder. It has a melting point of 361º F. This type of solder, because of its very low melting point, is used in printed circuit boards and microminiature electronic repair. As you can see from the chart, the melting point of the alloy is lowered when tin is added to lead.

The solder used to solder wires to electrical connectors, splices, and terminal lugs is a combination of 60-percent tin to 40-percent lead (60/40 solder). The melting point of 60/40 solder is 370º F, as shown at point B of the figure. Type 60/40 solder is less expensive than 63/37 solder and is suitable for all general uses. Figure 2-35 Tin-lead fusion diagram Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-49

Unclassified

Q37. What two metals are used to from soft solder? Q38. Define the metal solvent action that takes place when copper conductors are soldered together. Q39. What is the tin-lead alloy percentage of solder used for electrical connectors, splices, and terminal lugs? 2.3.7 Flux As you know, flux is a cleaning agent to remove oxidation during soldering. Heating a metal causes rapid oxidation. Oxidation prevents solder from reacting chemically with a metal. Flux cleans the metal by removing the oxide layer. This operation is shown in figure 2-36. As the iron is moved in the direction shown, the boiling flux floats away the oxide film. The molten solder following the iron then fuses rapidly with the clean surface of the metal.

Figure 2-36 Action of flux Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-50

Unclassified

There are two classes of flux: corrosive and noncorrosive. Zinc chloride, hydrochloric acid, and sal ammoniac are corrosive fluxes. Corrosive flux should NEVER be used in electrical or electronic repair work. Use only rosin fluxes. Any flux remaining in the joint corrodes the connection and creates a defective circuit. Rosin is a noncorrosive flux and is available in paste, liquid, or powder form. 2.3.8 Solvents A solvent is used for cleaning and removing contaminants (oil, grease, dirt, and so forth) from the soldered connection. Solvents must be nonconductive and noncorrosive.

Solvents must be used in a manner that keeps dissolved flux residue from "contact" surfaces, such as those in switches, potentiometers, or connectors. Ethyl and isopropyl alcohol are acceptable solvents. WARNING These cleaning solvents are highly flammable and may give off toxic vapors. Follow Navy safety precautions and take extreme care when using any flammable solvent. Q40. What purpose does flux serve in the soldering process? Q41. What type of flux must be used in all electrical and electronic soldering? Q42. Why are solvents used in the soldering process?

Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-51

Unclassified

2.3.9 Soldering Aids Some type of heat shunt must be used in all soldering operations that involve heat- sensitive components. A typical heat shunt (figure 2-37) permits soldering the leads of component parts without overheating the part itself. The heat shunt should be attached carefully to prevent damage to the leads, terminals, or component parts. The shunt should be clipped to the lead, between the joint and the part being protected. As the joint is heated, the shunt absorbs the excess heat before it can reach the part and cause damage.

A small piece of beeswax may be placed between the protected unit and the heat shunt. When the beeswax begins to melt, the temperature limit has been reached. The heat source should be removed immediately, but the shunt should be left in place. Removing the shunt too soon permits the heat to flow from the melted solder into the component. The shunt should be allowed to remain in place until it cools to room temperature. A clip-on shunt is preferred because it requires positive action for removal. It does not require that the technician maintain pressure to hold it in place. This leaves both hands free to solder the connection.

Figure 2-37 Heat shunt Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-52

Unclassified

Two safety devices are shown in figure 2-38. These devices prevent burns to the operator when the soldering iron is not in use for short periods of time. Q43. What is the purpose of a heat shunt? Figure 2-38 Soldering iron safety devices Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-53

Unclassified

2.3.10 Lacing Conductors Conductors within equipment must be kept in place to present a neat appearance and aid in tracing the conductors when alterations or repairs are required. This is done by LACING the conductors into wire bundles called cables. An example of lacing is shown in figure 2-39. When conductors are properly laced, they support each other and form a neat, single cable. A narrow, flat tape should be used wherever possible for lacing and tying. This tape is not an adhesive type of tape. Round cord may also be used, but its use is not preferred because cord has a tendency to cut into wire insulation. Use cotton, linen, nylon, or glass fiber cord or tape, according to the temperature requirements. Cotton or linen cord or tape must be prewaxed to make it moisture and fungus resistant. Nylon cord or tape may be waxed or unwaxed; glass fiber cord or tape is usually not waxed.

The amount of flat tape or cord required to single lace a group of conductors is about two and one-half times the length of the longest conductor in the group. Twice this amount is required if the conductors are to be double laced. Before lacing, lay the conductors out straight and parallel to each other. Do not twist them together because twisting makes conductor lacing and wire tracing difficult during troubleshooting. Q44. Besides presenting a neat appearance and supporting each other, what is the other purpose for lacing conductors?

Q45. Why is flat tape preferred instead of round cord when wire bundles are laced? Figure 2-39 Conductor lacing Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-54

Unclassified

Q46. What amount of flat tape or round cord is required to single lace a group of conductors? A lacing shuttle on which the cord can be wound keeps the cord from fouling during the lacing operation. A shuttle similar to the one shown in figure 2-40 can easily be made from aluminum, brass, fiber, or plastic scrap. Rough edges of the material used for the shuttle should be filed smooth to prevent injury to the operator and damage to the cord. To fill the shuttle for a single lace, measure the cord, cut it, and wind it on the shuttle. For double lace, proceed as before, except double the length of the cord before you wind it on the shuttle. For double lace, start both ends of the cord or tape on the shuttle in order to leave a loop for starting the lace. This procedure is explained later in the chapter.

Some equipment requires the use of twisted wires. One example is the use of "twisted pairs" for the ac filament leads of certain electron tube amplifiers to minimize radiation of their magnetic field. This prevents an annoying hum in the amplifier output. You should duplicate the original layout when relacing any wiring harness. Lace or tie bundles tightly enough to prevent slipping, but not so tightly that the cord or tape cuts into or deforms the insulation. Be especially careful when lacing or tying coaxial cable. Coaxial cable is a conductor used primarily for radio-frequency transmission. It consists of a center conductor separated from an outer conductor (usually called a shield) by an insulating dielectric. The dielectric maintains a constant capacitance between the two conductors, which is very important in radio transmission.

The dielectric is soft and deforms easily if tied too tightly or with the wrong type of tape. Figure 2-40 Lacing shuttle Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-55

Unclassified

CAUTION Do not use round cord for lacing or tying coaxial cable or bundles that contain coaxial cable. Use only the approved military specification tape to lace or tie coaxial cables or bundles containing coaxial cables. Q47. What is the purpose of a lacing shuttle? Q48. When should wires be twisted prior to lacing? Q49. What precautions should you take when tying bundles containing coaxial cables? 2.3.10.1 Single Lace Single lace can be started with a square knot and at least two marling hitches drawn tightly. Details of the square knot and marling hitch are shown in figure 2-41. Do not confuse the marling hitch with a half hitch. In the marling hitch, the end is passed over and under the strand, as shown in view A of the figure. After forming the marling hitches, draw them tightly against the square knot, as shown in view B. The lace consists of a series of marling hitches evenly spaced at 1/2-inch to 1-inch intervals along the length of the group of conductors, as shown in view C of the figure.

Figure 2-41 Applying single lace Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-56

Unclassified

When dividing conductors to form two or more branches, follow the procedure illustrated in figure 2-42. Bind the conductors with at least six turns between two marling hitches, and continue the lacing along one of the branches, as shown in view A. Start a new lacing along the other branch. To keep the bends in place, form them in the conductors before lacing. Always add an extra marling hitch just prior to a breakout as shown in view B. Figure 2-42 Lacing branches and breakouts Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-57

Unclassified

Double lace should be used on groups of conductors that are 1 inch or larger in total diameter. Either a single lace or a double lace may be used on groups of less than 1 inch. Q50. How is the single lace started? 2.3.10.2 Double Lace Double lace is applied in a manner similar to single lace, except that it is started with a telephone hitch and is double throughout the length of the lacing (figure 2-43). Both double and single lace may be ended by forming a loop from a separate length of cord and using it to pull the end of the lacing back underneath a serving of approximately eight turns (figure 2-44). An alternate method of ending the lacing is illustrated in figure 2-45.

This method can also be used for either single- or double-cord lacing. Another method is by using a marling hitch as a lock stitch (figure 2-46) to prevent slippage. This procedure will also prevent unraveling should a break occur to the lacing. Figure 2-43 Starting double lace Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-58

Unclassified

Figure 2-44 Terminating double lace Figure 2-45 Alternate method of terminating the lace Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-59

Unclassified

The spare conductors of a multiconductor cable should be laced separately, and then tied to active conductors of the cable with a few telephone hitches. When two or more cables enter an enclosure, each cable group should be laced separately. When groups are parallel to each other, they should be bound together at intervals with telephone hitches (figure 2-47). Figure 2-46 Marling hitch as a lock stitch Figure 2-47 Spot tying cable groups Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-60

Unclassified

2.3.10.3 Spot Tying When cable supports are used in equipment as shown in figure 2-48, spot ties are used to secure the conductor groups if the supports are more than 12 inches apart. The spot ties are made by wrapping the cord around the group as shown in figure 2-49. To finish the tie, use a clove hitch followed by a square knot with an extra loop. The free ends of the cord are then trimmed to a minimum of 3/8 inch. Figure 2-48 Use of spot ties Figure 2-49 Making spot ties Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-61

Unclassified

2.3.10.4 Self-Clinching Cable Straps Self-clinching cable straps are adjustable, lightweight, flat nylon straps. They have molded ribs or serrations on the inside surface to grip the wire. They may be used instead of individual cord ties for securing wire groups or bundles quickly. The straps are of two types: a plain cable strap and one that has a flat surface for identifying the cables. CAUTION Do not use nylon cable straps over wire bundles containing coaxial cable. Do not use straps in areas where failure of the strap would allow the strap to fall into movable parts.

Installing self-clinching cable straps is done with a Military Standard hand tool, as shown in figure 2-50. An illustration of the working parts of the tool is shown in figure 2-51. To use the tool, follow the manufacturer's instructions. Figure 2-50 Installing self-clinching cable straps Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-62

Unclassified

WARNING Use proper tools and make sure the strap is cut flush with the eye of the strap. This prevents painful cuts and scratches caused by protruding strap ends. Do not use plastic cable straps in high-temperature areas (above 250º F). Figure 2-51 Military Standard hand tool for self-clinching cable straps Module 4-Electrical Conductors, Wiring Techniques, and Schematic Reading

Unclassified

2-63

Unclassified

2.3.10.5 High-Temperature Pressure-Sensitive Tape Lacing High-temperature, pressure-sensitive tape must be used to tie wire bundles in areas where the temperature may exceed 250º F. Install the tape as follows (figure 2-52): 1. Wrap the tape around the wire bundle three times, with a two-thirds overlap for each turn. 2. Heat-seal the loose tape end with the side of a soldering iron tip. WARNING Insulation tape (including the glass fiber type) is highly flammable and should not be used in a high-temperature environment. Only insulation tape approved for high-temperature operation (suitable for continuous operation at 500º F) should be used in high-temperature environments.

Figure 2-52 Securing wire bundles in high-temperature areas