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CHAPTER 12

ELECTRICAL CONDUCTORS

INTRODUCTION

Many factors determine the type of electricalconductor to be used to connect components. Someof these factors are the physical size of the conductor,the type of material used for the conductor, and theelectrical characteristics of the insulation. Other fac-tors that can determine the choice of a conductor arethe weight, the cost, and the environment where theconductor is to be used.

CONDUCTOR SIZES

To compare theconductor with that ofmust be established. A

resistance and size of oneanother, a standard or unitconvenient unit of measure-

ment for the diameter of a conductor is the mil (0.001or one-thousandth of an inch). A convenient unit ofconductor length is the foot. The standard unit ofsize in most cases is the mil-foot. A wire will have aunit size if it has a diameter of 1 mil and a length of1 foot.

Square Mil

The square mil is a unit of measurement usedto determine the cross-sectional area of a square orrectangular conductor (Figure 12-1 views A and B).

A square mil is the area of a square whose sides areeach 1 mil. To obtain the cross-sectional area of anysquare conductor, multiply the dimensions of anyside of the conductor by itself. For example, with asquare conductor with a side dimension of 3 mils,multiply 3 mils by itself (3 mils x 3 mils). This gives across-sectional area of 9 square mils.

To determine the cross-sectional area of arectangular conductor, multiply the length timesthe width of the end face of the conductor (in mils).For example, if one side of the rectangular cross-sectional area is 6 mils and the other side is 3 mils,nultiply 6 mils x 3 mils. The cross-sectional area is

18 square mils.

The following is another example of how todetermine the cross-sectional area of a rectangularconductor. Assume a bus bar is 3/8 inch thick and4 inches wide. The 3/8 inch expressed in decimalform is .375 inch. Since 1 mil equals .001 inch, thethickness of the conductor is 375 mils. The width is4 inches. Since there are 1,000 mils per inch, thewidth is 4,000 mils.

To determine the cross-sectional area, multiplythe length by the width, or 375 mils x 4,000 mils. Thearea (A) equals 1,500,00 square mils.

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Circular Mil Solution:

The circular mil is the standard unit of measureof the cross-sectional area of a wire. This unit ofmeasurement is found in American and English wiretables. The diameter of a round conductor used toconduct electricity may be only a fraction of an inch.Therefore, it is convenient to express this fraction inmils to avoid using decimals. For example, thediameter of a wire is expressed as 25 mils instead of0.025 inch, A circular mil is the area of a circle whosediameter is 1 mil, as shown in Figure 12-2 view B. Thearea in circular mils of a round conductor is obtainedby squaring the diameter, which is measured in mils.Thus a wire having a diameter of 25 mils has an areaof 252 or 625 circular mils.

To determine the number of square mils in thesame conductor, apply the conventional formula fordetermining the area o a circle (area [A] = pi xradius squared = pi x r2. In this formula, A is theunknown. It equals the cross-sectional area in squaremils. Pi is the constant 3.1416. Letter r is the radiusof the circle, or half the diameter. Through substitu-tion A = 3.1416 (12.5)2. Therefore, 3.1416 x 156.25= 490.625 square mils. The cross-sectional area ofthe wire has been shown to have 625 circular mils,while it has only 490.625 square mils. Therefore, acircular mil represents a smaller unit of area than thesquare mil. If a wire has a cross-sectional diameterof 1 mil, by definition he circular mil area (CMA) isA = D2,or A = 12, or A = 1 circular mil. Todetermine thes are mil area of the same wire, theform a A = pir2 is applied. Therefore, A = 3.1416x (.5)2. When the formula is carried forward, A =3.1416 x .25, or A = .7854 square mils. From this, itcan be concluded that 1 circular mil equals .7854square mil. This becomes important when squareconductors (Figure 12-2 view A) and round conduc-tors (view B) are compared. View C shows the com-parison. When the square mil area is given, dividethe area by 0.7854 to determine the circular mil area.When the circular mil area is given, multiply the areaby 0.7854 to determine the square mil area.

Example: The American wire gauge (AWG)No. 12 wire has a diameter of 80.81 mils:

a. What is the area in circular mils?

b. What is the area in square mils?

a. A = D2 = (80.81)2 = 6,530 circular mils.

b. A = 0.7854 x 6,530 = 5,128.7 square mils.

A wire in its usual form is a slender rod orfilament of drawn metal. In larger sizes, wire is dif-ficult to handle. To increase flexibility, it is stranded.Strands are usually single wires twisted together insufficient numbers to make up the necessary cross-sectional area of the cable. The total area in circularmils is determined by multiplying the area in circularmils of one strand by the number of strands in thecable.

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Circular Mil-Foot

A circular mil-foot is a unit of volume(Figure 12-3). It is a unit conductor 1 foot in lengthwith across-sectional area of 1 circular mil. Becauseit is considered a unit conductor, the circular mil-footis useful in making comparisons between wires thatare made of different metals. For example, a basis ofcomparison of the resistivity (to be discussed later)of various substances may be made by determiningthe resistance of a circular mil-foot of each of thesubstances.

In working with square or rectangular conduc-tors, such as ammeter shunts and bus bars, it issometimes more convenient to use a different unitvolume. Bus bars are to be used when a large currentcapacity is required. Accordingly, unit volume mayalso be measured as the centimeter cube. Specificresistance, therefore, becomes the resistance offered

by a cube-shaped conductor 1 centimeter in lengthand 1 square centimeter in cross-sectional area. Theunit volume to be used is given in tables of specificresistances.

SPECIFIC RESISTANCE OR RESISTIVITY

Specific resistance, or resistivity, is the resis-tance in ohms offered by a unit volume (the circularmil-foot or the centimeter cube) of a substance to theflow of electric current. Resistivity is the reciprocalof conductivity. A substance that has a high resis-tivity will have a low conductivity and vice versa.

Thus, the specific resistance of a substance isthe resistance of a unit volume of that substance.Many tables of specific resistance are based on theresistance in ohms of a volume of a substance 1 footin length and 1 circular mil in cross-sectional area. Ifthe kind of metal of which a conductor is made isknown, the specific resistance of the metal may beobtained from one of these tables. These tables alsospecific the temperature at which the resistance mea-surement is made. Table 12-1 gives the specificresistance of some common substances.

The resistance of a conductor of a uniformcross section varies directly as the product of thelength and the specific resistance of the conductorand inversely as the cross-sectional area of theconductor. Therefore, the resistance of a conduc-tor may be calculated if the length, cross-sectional

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area, and specific resistance of the substance isknown. Expressed as an equation, the resistance (R)in ohms of a conductor is —

R = p LA

Where: p (Greek rho) = the specific resis-tance in ohms per circular mil-foot (refer toTable 12-1)

L = the length in feetA = the cross-sectional area in circular mils

Example: What is the resistance of 1,000 feetof copper wire having a cross-sectional area of 10,400circular mils (No. 10 AWG wire) at a temperature of20C?

Given

p = 10.37 ohms/circular mil-footL = 1,000 feetA = 10,400 circular mils

Solution:

R = p L = 10.37 (1,000) = 1 ohm (approximately)A 10,400

RELATIONSHIP BETWEEN WIRE SIZES

Wires are manufactured in sizes numberedaccording to a table known as the American wiregauge (AWG). The National Bureau of Standardspublishes tables for various conductors either solidor stranded and the material they are made from,such as copper or aluminum. Table 12-2 is oneexample of such a table. The wire diameters becomesmaller as the gauge numbers become larger. (Numb-ers are rounded off for convenience but are accu-rate for practical application.) The largest wire inTable 12-2 is 0000, and the smallest is number 22.Larger and smaller sizes are manufactured but arenot commonly used by the Army. The tables showthe diameter, circular mil area, and area in squareinches of the different AWG wire sizes. It alsoshows the resistance per thousand feet of thevarious wire sizes at 25C.

STRANDED WIRES AND CABLES

A wire is a slender rod or filament of drawnmetal. The definition restricts the term to whatwould ordinarily be understood as solid wire. Theword “slender” is used because the length of a wireis usually’ large in comparison with the diameter. Ifa wire is covered by insulation, it is called an insu-lated wire. Although wire properly refers to themetal, it is generally understood to include theinsulation.

A conductor is a wire suitable for carrying anelectric current. A stranded conductor is com-posed of a group of wires or of any combination ofgroups of wires. The wires in a stranded conductorare usually twisted together and not insulated fromeach other.

A cable is either a stranded conductor (a singleconductor cable) or a combination of conductorsinsulated from one another (multiple conductorcable). The term “cable” is a general one, and inpractice, it usually applies only to larger sizes ofconductors. A small cable is more often called astranded wire. The insulated cables may be sheathed(covered) with lead or protective armor.

Figure 12-4 shows some of the different typesof wire and cable used in the military.

Conductors are stranded mainly to increasetheir flexibility. The wire strands in cables arearranged in the following order. The first layer ofstrands around the center conductor are made of 6conductors. The second layer is made up of 12 con-ductors. The third layer is made up of 18 conductors,and so on. Thus, standard cables are composed of 7,19, and 37 strands, in continuing fixed increments.

The overall flexibility may be increased by fur-ther stranding of the individual strands. All Armymarine electrical wires and cables will be of thestranded type. The excessive vibration of a vesselprohibits solid conductor wires.

Figure 12-5 shows a typical cross section of a37-strand cable. It also shows how the total cir-cular mil cross-sectional area of a stranded cableis determined.

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SELECTION OF WIRE SIZE

Several factors must be considered in select-ing the size wire to be used for transmitting anddistributing electric power. There are militaryspecifications that cover the installation of wiring ofships and electrical/electronic equipment. Thesespecifications describe the technical requirementsfor material which is to be purchased from manufac-turers by the Department of Defense. One impor-tant reason for these specifications is to reduce thedanger of fires caused by the improper selection ofwire sizes. Wires can carry only a limited amount ofcurrent safely. If the current flowing through a wireexceeds the current-carrying capacity of the wire,excess heat is generated. This heat may be greatenough to burn off the insulation around the wire andcontinue to do much greater damage by starting afire.

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FACTORS AFFECTING THE CURRENTRATING

The current rating of a cable or wire indicatesthe current capacity that the wire or cable can safelycarry continuously. If this limit, or current rating, isexceeded for a length of time, the heat generated maybum the insulation. The current rating of a wire isused to determine what size is needed for a givenelectrical load.

The following factors determine the currentrating of a wire:

The conductor size.

The material of whichmade.

the conductor is

The location of the wire.

The type of insulation used.

Ambient temperature.

Some of these factors affect the resistance of awire carrying current.

An increase in the diameter or cross section ofa conductor decreases its resistance and increases itscapability to carry current. An increase in thespecific resistance of a conductor increases its resis-tance and decreases its capacity to carry current.

The location of a conductor determines thetemperature under which it operates. A cable maybe located in a row of other cables (banked) or placedalongside other cables in one of two rows (double-banked). Therefore, it operates at a higher tempera-ture than if it is open to the free air. The higher thetemperature under which a wire is operating, thegreater its resistance. Its capacity to carry current isalso lowered. In each case, the resistance of a wiredetermines its current-carrying capacity. Thegreater the resistance, the more power it dissipatesin the form of heat energy. Electrical conductorsmay also be installed in locations where the ambienttemperature is relatively high. When this is the case,the heat generated by external sources constitutes anappreciable part of the total conductor heating. Thiswill be explained further under Temperature Coeffi-cient. Due allowances must be made for the in-fluence of external heating on the allowableconductor current. Each case has its own specificlimitations. Table 12-3 gives the maximum current-carrying capacity for distribution cable. Table 12-4shows control cable ampacities. Table 12-5 specifiesthe maximum allowable operating temperature ofinsulated conductors. It varies with the type of con-ductor insulation being used.

The insulation of a wire does not affect itsresistance. It does, however, determine how muchheat is needed to burn the insulation. The limit ofcurrent that an insulated conductor can withstanddepends on how hot the conductor can get before itburns the insulation. Different types of insulationwill burn at different temperatures. Therefore, thetype of insulation used is a factor that determines thecurrent rating of a conductor. Polyvinyl chloride(PVC) insulation will begin to deteriorate at relativelylow temperatures. Silicon rubber retains its insulat-ing properties at much higher temperatures.

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COPPER VERSUS ALUMINUM CONDUCTORS

Although silver is the best conductor, its costlimits its use to special circuits. It is used where asubstance with high conductivity or low resistivity isneeded.

Copper has high conductivity. It is more duc-tile (can be drawn out). It has relatively high tensilestrength (the greatest stress a substance can bearalong its length without tearing apart). It can alsobe easily soldered. US Army vessels use only softannealed copper wire. The copper conductor istinned or alloy-coated to ensure compatibility withinsulation.

TEMPERATURE COEFFICIENT

The resistance of pure metals, such as silver,copper, and aluminum, increases as the temperatureincreases. The resistance of some alloys, such asconstantan and manganin, changes very little as thetemperature changes. Measuring instruments usethese alloys because the resistance of the circuitsmust remain constant to achieve accurate measure-ments. The amount of increase in the resistance of al-ohm sample of the conductor per degree rise intemperature above 0C is called the temperature coef-ficient of resistance. For copper, the value is about0.00427 ohm. This and more is taken into accountwhen designing the electrical distribution system ofthe vessel. A wire is not just any wire. There is areason and a purpose for the entire electrical system.The only changes in the electrical system should befor expedient repairs and approved modifications.Do not modify electrical systems without properauthority.

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CONDUCTOR INSULATION

To be useful and safe, electric current must beforced to flow only where it is needed. It must bechanneled from the power source to a useful load. Ingeneral, current-carrying conductors must not beallowed to come in contact with one another, theirsupporting hardware, or personnel working nearthem. To accomplish this, conductors are coated orwrapped with various materials. These materialshave such a high resistance that they are, for allpurposes, nonconductors. They are generallyreferred to as insulators or insulating material.

Only the necessary minimum of insulation isapplied to any particular type of conductor designedto do a particular job. This is done because of severalfactors. The expense, stiffening effect, and variety ofphysical and electrical conditions under which theconductors are operated must be considered.Therefore, a wide variety of insulated conductors isavailable to meet the requirements of any job.

Two fundamental properties of insulatingmaterials, such as rubber, glass, asbestos, and plas-tic, are insulation resistance and dielectric strength.These are two entirely different and distinctproperties.

Insulation resistance is the resistance to currentleakage through the insulation materials. Insula-tion resistance can be measured by means of a meg-ger without damaging the insulation. Informationso obtained serves as a useful guide in appraisingthe general condition of the insulation. Clean, dryinsulation having cracks or other faults may show ahigh resistance but would not be suitable for use.Megger testing does not damage the cable. This isone form of nondestructive testing.

Dielectric strength is the ability of the insula-tion to withstand potential difference. It is usuallyexpressed in terms of the voltage at which the insula-tion fails because of the electrostatic stress. Maxi-mum dielectric strength values can be measured onlyby raising the voltage of a test sample until the insula-tion breaks down. When the dielectric strength istested, the cable insulation is damaged. This is anexample of destructive testing.

Figure 12-6 shows two types of insulated wire.One is a single, solid conductor. The other is atwo-conductor cable with each stranded conductor

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covered with a rubber-type insulation. In each case,the rubber serves the same purpose: to confide thecurrent to its conductor.

Materials

Marine cable insulation should be one of thefollowing materials:

Polyvinyl chloride (designated T). This isthe most common type of insulation cur-rently used on modern vessels. It is a formof polymerized vinyl compound, resin, orplastic. The maximum conductortemperature that the insulation can handleis 75C. The voltage range is a maximumof 600 volts. The maximum allowableambient temperature is 50C. It is of ther-moplastic construction. This means itbecomes soft when heated and rigid whencooled and cured. Polyvinyl chloride-protected cable provides a nonmetallicrigid sheathed cable. It is commonly calledPVC.

WARNING

This product produces extremelytoxic vapors when ignited. Whenselecting this type of cable, a desig-nation of “LS” (low smoke) indi-cates insulation modificationshave been made to reduce thesetoxic gases.

Ethylene propylene rubber (designatedE). This insulation is thermosetting (notreshapeable). The maximum conductortemperature that the insulation can handleis 90C. The maximum allowable ambienttemperature is 60C. It is normally used forup to 2,000 volts. For special applications,a maximum of 5,000 volts may be used.

Cross-linked polyethylene (designated X).This insulation is thermosetting. The max-imum conductor temperature it can hand-le is 90C. The maximum allowableambient temperature is 60C. It is usedfrom 2,001 to 5,000 volts.

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Mineral (MI) (designated M). This is arefactory material made of magnesiumoxide that is highly compressed to providethe properties needed for insulation. Themaximum conductor temperature that theinsulation can handle is 85C. The ambienttemperature is specified by distinct designonly. Some special applications allow amaximum conductor temperature of 250C.Care must be taken when consideringcable end fittings. See IEEE Standard 45,Table A-21, for ampacity.

Silicon rubber (designated S). The maxi-mum conductor temperature that the in-sulation can handle is 100C. Themaximum allowable ambient temperatureis 70C. It may be used in specific applica-tions up to 5,000 volts.

Impregnated glass, varnished cloth (desig-nated GTV). The outside covering con-sists of a composite wall of glass orvarnished cloth layers. Figure 12-7 showsthe insulation helically wound around thecable. The maximum conductor tempera-ture that the insulation can handle is 100C.The maximum allowable ambienttemperature is 70C.

Moisture-Resistant Jackets

An additional cable identification designationof I will be displayed on all cables with a moisture-resistant jacket. The jacket will be composed of oneof the following:

Thermoplastic type T.

Thermoplastic type T covered with a nyloncoating, which changes the designator totype N.

Thermosetting chlorosulfonatedpolyethylene (type CP).

Separators and Fillers

Separators may be provided inside the insula-tion to allow free stripping of cable conductors.Fillers eliminate air spaces in the cable (Figure 12-8).Marine cables will not permit the passage of wateralong the inside of a cable, nor will they supportconductor oxidation.

Additional insulating coding and specifica-tions may be found in the Recommended Practicefor Electrical Installations on Shipboard, the

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Institute of Electrical and Electronics Engineers,Inc. (IEEE Standard 45).

Enamel Coating

The wire used on the coils of meters, relays,small transformers, motor windings, and so forth iscalled magnetic wire. It is insulated with an enamelcoating. The enamel is a synthetic compound ofcellulose acetate (wood pulp and magnesium). In themanufacturing process, the bare wire is passedthrough a solution of hot enamel and then cooled.This process is repeated until the wire acquires from6 to 10 coatings. Enamel has a higher dielectricstrength than rubber, thickness for thickness. It is notpractical for large wires because of the expense andbecause the insulation is readily fractured when largewires are bent. Do not handle any enamel-coveredconductors in a rough manner. Never set a dis-assembled component down on its enamel-coatedwires.

Figure 12-9 shows an enamel-coated wire.Enamel is the thinnest insulating coating that can beapplied to wires. Hence, enamel-insulated magneticwire makes smaller coils. Enameled wire is some-times covered with one or more layers of cotton toprotect the enamel from nicks, cuts, or abrasions.

CONDUCTOR PROTECTION

Wires and cables are generally subject toabuse. The type and amount of abuse depends onhow and where they are installed and the manner inwhich they are used. Generally, except for overheadtransmission lines, wires or cables are protected bysome form of covering. The covering may be sometype of insulator like rubber or plastic. Over this, anouter covering of fibrous braid may be applied. Ifconditions require, a metallic outer covering may beused. The type of outer covering used depends onhow and where the wire or cable is to be used.

Metallic armor provides a tough protectivecovering for wires or cables. The type, thickness, andkind of metal used to make armor depends on threefactors:

The use of the conductors.

The circumstances under which the con-ductors are to be used.

The amount of rough treatment that isexpected.

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Figure 12-10 shows an armored cable. Basket-weave wire-braid armor is used wherever a light andflexible protection is needed. In the past, this type ofarmor covering has been used almost exclusively on-board ships. Wire braid is still used for special pur-poses in the engineering spaces. The individual wiresthat are woven together to form the braid are madeout of aluminum or bronze. Besides mechanicalprotection, the wire braid also provides a staticshield. This is important in radio work aboard shipto prevent interference from stray magnetic fields.

CAUTION

The armor braid must begrounded directly or indirectly tothe hull

In this situation, grounding does not mean thatcurrent will be carried through the armor braid undernormal conditions. Rather, it means that an electri-cal path will be provided to the hull should an abnor-mal electrical fault cause current to flow in the armor.

For additional information and specifications, referto IEEE Standard 45-1983, Section 20.2, and Codeof Federal Regulations, Title 46, Subpart 111.05-7.

Cables should not be painted. Only whencables carry a potential of 5,000 volts or greater isyellow color-coding permissible.

For general use, polyvinyl chloride-protectedcable is replacing armor cable.

WIRING TECHNIQUES

Wire connections should be made inside theelectrical component or inside watertight feeder,branch, or connection boxes. These boxes aregenerally brass or bronze. Watertight integrity ismaintained by using stuffing tubes and gaskets. Allthe wire ends should be provided with lugs for con-necting to bus terminals or for bolting and insulatingindividual wires together. During the course of nor-mal electrical servicing, splicing wires is notauthorized.

Electrical cables must be continuous betweenthe terminals except as outlined below:

Component subassemblies may be splicedtogether. Splices may not be made to thesubassembly power supply cables orbranch circuits.

Cables may be spliced to extend a cir-cuit when a vessel is receivingauthorized alterations.

An extremely long cable may be spliced toallow its proper and efficient installation asexplained above.

Splicing is authorized for repair ofdamaged cables if the remainder of thecable is in good mechanical and electricalcondition. The cable must be replaced inits entirety at the most opportune time.

When electrical casualty requires expedientrepairs, it is absolutely necessary that the repairs bemade properly. A poor repair can prevent the opera-tion of emergency equipment or develop into a tire.Any electric circuit is only as good as its weakest link.The basic requirement of any splice or connection isthat it is both mechanically and electrically sound.

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Quality workmanship and materials must be used toensure lasting electrical contact, physical strength,and proper insulation. The most common methodsof making splices and connections in electrical cablesare explained below.

Splicing

Splices should be located in an area that iseasily accessible and inspect able. The splice shouldconsist of the following components:

A conductor connector (terminal lugs,splice bolts, or splices) (Figure 12-11).

A replacement jacket for the insulation.

A shunt or suitable conductor to maintainthe electrical continuity between twosevered pieces of the armor braid.

WARNING

Continuity must be maintained be-tween the armor covering and thevessel’s hull at all times.

Removing Insulation

The preferred method of removing insulationis with the use of a wire-stripping tool. The calibrated

hand wire stripper in Figure 12-12 is excellent foreven the most intricate electrical wire work.

Hand Wire Stripper. The procedure for strip-ping wire with the hand wire stripper is as follows:

Confirm the stripper’s operation. Use aspare wire to ensure the conductor is notmarred by the cutting blades of the wirestripper. If the wire strippers have beenused or abused, consult the manufacturer’sinstructions to adjust the depth of the in-sulation cut.

Insert the wire into the exact center of thecorrect cutting slot for the wire size to bestripped (Figure 12-13). Keep the wireperpendicular to the stripper.

Close the handles together until the wire isheld firmly by the jaws of the wire stripper.

Continue to close the handles only until theinsulation starts to separate. Do not usethe stripper to pull the insulation from theconductor.

Remove the wire from the wire stripper.

Gently unwind the insulation so that thenatural lay of the conductors is notdisturbed.

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NOTE: If you are going to solder theconductor, do not touch the conductorwith your hands. The contaminationfrom your hands will start to oxidizethe conductor, and proper tinning andsoldering will become more difficult.

Knife Stripping. This is not recommended be-cause it cuts into the conductor and effectivelyreduces the circular mil area at the fault. Nicks andcuts also reduce the mechanical strength of the con-ductor at a point that is naturally weaker then thesection of cable where it is protected by insulation.

However, the very nature of a vessel requires itto be placed in situations that must be satisfactorilymanaged until a more advantageous time arrives. In

emergencies, the following procedure will keep con-ductor damage to a minimum.

A sharp knife can be used to strip the insulationfrom a conductor. The procedure is much the sameas sharpening a pencil. The knife should be held ata 60-degree angle to the conductor. Use extremecare to avoid cutting into the conductor. This proce-dure produces a taper on the cut insulation(Figure 12-14). Should the connection requiresolder, the tapered insulation will fuse morereadily to the conductor. This fusion increasesmechanical strength at the weak point andprevents the entrance of moisture.

WIRE STRIPPING CAUTIONS

The following minimum precautions are neces-sary when preparing conductors for repair:

Ensure power is off before connecting orremoving wires.

Do not touch any conductor you intend tosolder.

Ensure the wire strippers are held perpen-dicular to the wire.

Make sure the insulation is clean-cut withno frayed or ragged edges. Trim if neces-sary. This is particularly important whenstripping armored cable. If the frayedarmor insulation is allowed to chafe thereplacement insulation at the spliced area,current may accidentally energize the ex-terior armor of the cable. This can bedeadly.

Ensure all insulation is removed from theconductor. Some wires are provided witha transparent layer between the conductorand the insulation. This must be removed.

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WESTERN UNION SPLICE

Figure 12-15 shows the steps to make a WesternUnion splice. First, prepare the wires for splicing.Remove enough insulation to make the splice andthen clean the conductor. Next, bring the wires to acrossed position and make a long twist or bend ineach wire. Then wrap one of the wire ends four orfive times around the straight portion of the wire.Wrap the other end of the wire in a similar manner.Finally, press the ends of the wire down as close aspossible to the straight portion of the wire. Thisprevents the sharp ends from puncturing the tapecovering that is wrapped over the splice.

STAGGERED SPLICES

Joining small, multiconductor cables togetherpresents somewhat of a problem. Each conductormust be spliced and taped. If the splices are con-tiguous to each other, the size of the joint becomeslarge and bulky. A smoother and less bulky joint maybe made by staggering the splices.

Figure 12-16 shows how a two-conductor cableis joined to a similar size cable by means of staggeringthe splices. Take care to ensure that a short wirefrom one side of the cable is connected to a long wirefrom the other side of the cable being spliced. Thenclamp the sharp ends firmly down on the conductor.Figure 12-16 shows a Western Union splice beingstaggered. Each conductor is insulated separately.

SPLICE INSULATION

The splices discussed above are those usuallyinsulated with tape. The tape used to insulate a spliceshould be centered over the splice and should over-lap the existing insulation by at least 2 inches on eachside. The characteristics of rubber, friction, andplastic electrical tape are described below.

Rubber Tape

Latex (rubber) tape is a splicing compound. Itis used where the original insulation was of a rubbercompound. The tape is applied to the splice with alight tension so that each layer presses tightly againstthe one beneath it. This pressure causes the rubbertape to blend into a solid mass. Care must be takento keep the spliced area watertight. Upon comple-tion, insulation similar to the original is restored.

WARNING

Some rubber tapes are made forspecial applications. These typesare semiconducting and will passcurrent that presents a shockhazard. These types of tape arepackaged similar to the latex rub-ber tape. Take care to insulatesplices only with latex rubber in-sulation tape.

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In roll form, a layer of paper or treated cloth isbetween each layer of rubber tape. This layerprevents the latex from fusing while still on the roll.The paper or cloth is peeled off and discarded beforethe tape is applied to the splice.

Apply the rubber splicing tape smoothly andunder tension so that no air exists between the layers.Start the first layer near the middle of the jointinstead of the end. The diameter of the completedinsulated joint should be somewhat greater thanthe overall diameter of the original wire, includingthe insulation.

Friction Tape

Putting rubber over the splice means that theinsulation has been restored to a great degree. It isalso necessary to restore the protective covering.Friction tape is used for this purpose.

WARNING

Some friction tapes may conductelectrical current.

Friction tape is a cotton cloth that has beentreated with a sticky rubber compound. It comes inrolls similar to rubber tape, except that no paper orcloth separator is used. Friction tape is applied torubber; however, it does not stretch.

Start the friction tape slightly back on theoriginal insulation. Wind the tape so each turn over-laps the one before it. Extend the tape over onto theinsulation at the other end of the splice. From thispoint, wind a second layer back along the splice untilthe original starting point is reached. To completethe job, cut the tape and firmly press down the end.

Plastic Electrical Tape

Plastic electric tape has come into wide use inrecent years. It has certain advantages over rubberand friction tape. For example, it withstands highervoltages for a given thickness. Single layers of certainplastic tapes will withstand several thousand voltswithout breaking down. In practice, however, severallayers of tape are used to equal or slightly exceed theoriginal thickness of the insulation. Additional layersof plastic electrical tape add the protection normally

furnished by friction tape. Plastic electrical tapeusually has a certain amount of stretch so that it easilyconforms to the contour of the splice.

TERMINAL LUGS

Since marine cables are stranded, it is neces-sary to use terminal lugs to hold the stranded wirestogether to help fasten the wires to terminal studs(Figure 12-17). This is the preferred method forconnecting wires to terminals or to other wire ends.Generally, distribution system cable connectors willnot use solder. The terminals used in electricalwiring are either of the soldered or crimped type.Terminals used in repair work must be of the size andtype specified on the electrical wiring diagram for theparticular equipment.

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The increased use of crimp on terminals is aresult of the limitations of soldered terminals. Thequality of soldered connections depends mostly onthe operator’s skill. Other factors, such as tempera-ture, flux, cleanliness, oxides, and insulation damagedue to heat, also add to defective connections.

An advantage of crimp on solderless terminallugs is that they require relatively little operator skillto use. Another advantage is that the only toolneeded is the crimping tool. This allows terminallugs to be applied with a minimum of time and effort.The connections are made more rapidly and arecleaner and more uniform in construction. Becauseof the pressures exerted and the material used, thecrimped connection or splice, properly made, is bothmechanically and electrically sound. Figure 12-17shows some of the basic types of terminals. There areseveral variations of these basic types, such as the useof a slot instead of a terminal hole, three- and four-way splice type connectors, and insulation covering.

Figure 12-18 shows how to determine theamount of insulation to remove from the wire.

Solderless terminals may be of the insulatedtype. The barrel of the terminal or splice is enclosedin an insulating material. The insulation is com-pressed along with the terminal barrel when it iscrimped, but it is not damaged in the process(Figure 12-19).

Aluminum Terminals and Splices

Do not use aluminum terminals, connectors, orwires interchangeably with copper wires and connec-tors. Copper and aluminum expand at different ratesand will become loose over a period of time.Electrolysis also takes place. The two dissimilar me-tals and the salt air will create a chemical reactionthat will eat away the materials. Also, never use analuminum crimping tool for compressing copperhardware.

Preinsulated Terminal Lugs

The use of preinsulated terminal lugs andsplices has become the most common method forcopper wire termination and splicing in recent years.It is by far the best and easiest method. Many toolsare used for crimping terminal lugs and splices.

Small diameter copper wires are terminatedwith solderless, preinsulated copper terminal lugs.As Figure 12-20 shows, the insulation is part of theterminal lug. It extends beyond the barrel so that itcovers a portion of the wire insulation. This makesthe use of spaghetti or heat shrink tubing unneces-sary. Preinsulated terminal lugs also have an insula-tion support (a metal reinforced sleeve) beneath theinsulation for extra supporting strength of the wireinsulation. Some preinsulated terminals fit morethan one size of wire. The insulation is color-coded,and the range of wire sizes is marked on the tongue.This identifies the wire sizes that can be terminatedwith each of the terminal lug sizes (Table 12-6).

For crimping small copper terminal lugs, theMS90413 hand crimping tool is used for wire sizes

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AWG 26 to 14. The MS3316 tool is used for wire sizes12 and 10. Figure 12-21 shows these tools. Thesehand crimping tools have a self-locking ratchet thatprevents the tool from opening until the crimp iscompleted. These and other one-cycle compressiontools (as outlined in ANSI/UL 4S6-1975[25]) are thepreferred method of compression.

After completing the compression, visually in-spect the terminal or splice. Check for the followingconditions:

Indent centered on the terminal barrel.

Soldering Tools

Many types of soldering tools are in use today.Some of the more common types are the solderingiron, soldering gun, resistance soldering set, and pen-cil iron. The main concern when selecting a solder-ing tool is the selection of the wattage. Table 12-7provides a guide for determining the correct wattagefor the size wire.

Indent in line with the barrel.

Terminal lug not cracked.

Terminal lug insulation not cracked.

Insulation grip crimped.

SOLDERING

The following discussion on basic solderingskills provides information needed when solderingwires to electrical connectors, splices, and terminals.

Soldering Iron. Figure 12-22 shows some typesof common soldering irons. All high-quality solder-ing irons operate in the temperature range of 500 to600F. Even the little 25-watt midget irons producethis temperature. The important difference in ironsizes is not the temperature, but the wattage. Thewattage, or thermal inertia, is the capacity of the ironto generate and maintain a satisfactory temperaturewhile giving up heat to the joint to be soldered.Although it is not practical to solder large conductorswith a 25-watt iron, this iron is suitable for replacinga half-watt resistor in an electronic circuit or solder-ing a miniature connector. One advantage of using asmall iron for small work is that it is light and easy tohandle and has a small tip which is easily used in closeplaces. Even though its temperature is high enough,it does not have the thermal energy to solder a largeconductor.

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A well-designed iron is self-regulating. Theresistance of its element increases with risingtemperature, thus limiting the flow of current. Figure12-23 shows some tip shapes of the soldering irons incommon use in the Army.

An iron is always tinned prior to soldering acomponent in a circuit. After extended use, the tiptends to become pitted due to oxidation. Pittingindicates the need for retinning, as shown in Figure12-24. Melt a piece of clean solder dipped in rosinflux over the soldering iron tip until all cavities aregone and the tip is completely shiny and silver-coatedFigure 12-25). Use a lint-free paper towel to wipethe solder away. Do not shake the solder off.

The larger soldering irons used exclusively forlarge conductors may require the tip to be filed first.The tip must then be tinned.

Never clean the tip of an iron by dipping it intothe flux container. All this does is contaminate theflux and add impurities to the next soldering project.

Soldering Gun. The soldering gun (Figure12-26) has gained popularity in recent years

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because it heats and cools rapidly. It is especiallywell-adapted to maintenance and troubleshootingwork where only a small part of the technician’s timeis spent soldering.

A transformer in the soldering gun suppliesabout a volt at high current to a loop of copper, whichacts as the soldering tip. It heats to solderingtemperature in 3 to 5 seconds. However, it mayoverheat to the point of incandescence if left on morethan 30 seconds. This should be avoided becauseexcess heat will burn the insulation of the wiring and

damage the soldering gun. The gun is operated by afinger switch. The gun heats only while the switch isdepressed. For most jobs, depress the trigger for nomore than 10 seconds. Regulate the tip temperatureby pulsating the gun on and off with the trigger.

The gun or iron should always be kept tinnedto permit proper heat transfer to the connection tobe soldered. Tinning also provides adequate con-trol of the heat to prevent solder from building upon the tip. This reduces the chance of the solderspilling over to nearby components and causingshort circuits.

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When the soldering gun or iron is used, heatingand cooling cycles tend to loosen the nuts or screwsthat hold the replaceable tips. When the nut on thegun becomes loose, the resistance of the tip in-creases. The temperature of the connection is in-creased and reduces the heat at the tip. Continuedloosening may even cause an open circuit. There-fore, the tip should be tightened before and duringoperations as needed.

CAUTION

Never use soldering guns to soldersolid state electronic components,such as resistors, capacitors,and transistors, because theheat generated can destroy thecomponents.

Solder

Ordinary soft solder is a fusible alloy consistingchiefly of tin and lead. It is used to join together twoor more metals at temperatures below their meltingpoint, A good general solder for electrical work is60/40 solder; 60/40 represents the tin-to-lead ratio(percentage) of the solder. Eutectic solder (63/37) isan ideal solder combination. Eutectic solder goesfrom a solid to a liquid state without entering a mushycondition. The eutectic solder is used in electricaland electronic soldering processes.

Solder comes on rolls. Many times the solderis hollow and contains a rosin or acid core. The rosin

or acid flux cleans and prevents oxidation of thematerials to be soldered. Never use acid core solderin soldering electronic components. Acid core fluxcauses corrosion and leads to shorts or open condi-tions. Avoid acid core solder whenever possiblewhen soldering electrical components. Rosin is theonly acceptable electrical soldering flux.

Soldering Process

Cleanliness is necessary for efficient, effectivesoldering. Solder will not adhere to dirty, greasy, oroxidized surfaces. Heated metals tend to oxidizerapidly, so the oxide must be removed before solder-ing. Remove oxides, scale, and dirt by mechanicalmeans, such as scraping and cutting with an abrasivecloth, or by chemical means. Remove grease or oilfilms with a suitable solvent (alcohol). Clean theconnections to be soldered just before the actualsoldering operation.

Items to be soldered should normally be tinnedbefore making a mechanical connection. Tinning iscoating the material to be soldered with a light coatof solder (Figure 12-27). When the surface has beenproperly cleaned, place a thin, even coating of fluxover the surface to be tinned. This will prevent oxida-tion while the part is being heated to solderingtemperature. Rosin core solder is usually preferredin electrical work. However, a separate rosin fluxmay be used instead. Separate rosin flux is often usedwhen wires in cable fabrication are tinned.

Placing a very thin coating of solder on thecopper conductor is called tinning the wire. This isdone before soldering the conductor to a terminal orother component. First, strip the insulation from thewire. Do not touch the copper conductor with your

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hands or any other oily objects. Apply heat from thesoldering iron under the copper conductor. Thenapply the solder to the top of the copper conductor.

Starting at either the insulation end of the con-ductor or at the bitter end of the conductor, move thesoldering iron as the solder melts and coat the entirelength of the conductor. There is to be a complete,yet very fine solder coating. Every layer of the con-ductor should be easily defined underneath thebright solder coating.

If the tinned lead is to be connected to a shapeddevice, such as a turret or post, then form the tinnedportion to exactly match the shape. Ensure no openspace is between the tinned wire and the point ofconnection. Figure 12-28 shows the exact relation-ship the stripped conductor maintains with the ter-minal post. The insulation is stripped back farenough to be one conductor diameter from the post.The bitter end of the conductor never goes fartheraround the post terminal than its widest point. Thisis the only way to ensure the best current flow.

In earlier years, tinning was not extended to theinsulation because the wire was thought to providebetter performance when it was allowed to flex atthe insulation. However, actual performance isimproved when this weakened portion is not allowedto flex. Proper strength is maintained when thereis a slight fusing between the soldier and the insula-tion. This gives more protection from vibrationand maintains the conductor more steadily in ap-plication. Tinning to the insulation eliminates the

small movement that causes the conductor to breaknear the insulation.

Do not tin wires that are to be crimped tosolderless terminals or splices.

Once the conductor has been tinned, start toprepare the terminal for soldering. Clean all oils andforeign material from the terminal. Remove allremaining solder and any leftover broken conduc-tors. Use a soldering wick to remove old solderexpeditiously. Place the wick on the old solder andthe soldering tool on top of the wick (Figure 12-29).Capillary action draws the old solder off the ter-minals and into the wick. Clean the area with dena-tured alcohol and a white pencil-type typist eraser.

Connect the tinned conductor to the terminalwithout placing your hands on either prepared sur-face. Apply heat and solder. Never apply the solderto the tip of the soldering iron. Always apply solderto the opposite side of the component lead. Thereshould be just enough solder to penetrate and sur-round the terminal and conductor connection.There should not be so much solder that there is abulge at the connection.

If the conductor or terminal is moved while thesolder is solidifying, a cold solder joint will result.This poor joint has a dull, grainy appearance. If thereis any bridging, dimples, or holes, then the joint hasbeen improperly made and must be remade. Aproperly soldered joint will be bright and shiny.

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