NEETS MODULE 4-ELECTRICAL CONDUCTORS, WIRING TECHNIQUES, AND SCHEMATIC READING

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

1-1 UNCLASSIFIED 1 ELECTRICAL CONDUCTORS LEARNING OBJECTIVES

Upon completing this chapter, you should be able to:

1. Recall the definitions of unit size, mil-foot, square mil, and circular mil and the mathematical equations and calculations for each. 2. Define specific resistance and recall the three factors used to calculate it in ohms. 3. Describe the proper use of the American Wire Gauge when making wire measurements. 4. Recall the factors required in selecting proper size wire. 5. State the advantages and disadvantages of copper or aluminum as conductors. 6. Define insulation resistance and dielectric strength including how the dielectric strength of an insulator is determined. 7. Identify the safety precautions to be taken when working with insulating materials. 8. Recall the most common insulators used for extremely high voltages. 9. State the type of conductor protection normally used for shipboard wiring. 10. Recall the design and use of coaxial cable.

1.1 INTRODUCTION TO ELECTRICAL CONDUCTORS In the previous modules of this training series, you have learned about various circuit components. These components provide the majority of the operating characteristics of any electrical circuit. They are useless, however, if they are not connected together. Conductors are the means used to tie these components together.

Many factors determine the type of electrical conductor used to connect components. Some of these factors are the physical size of the conductor, its composition, and its electrical characteristics. Other factors that can determine the choice of a conductor are the weight, the cost, and the environment where the conductor will be used.

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

1-2 UNCLASSIFIED 1.2 CONDUCTOR SIZES To compare the resistance and size of one conductor with that of another, we need to establish a standard or unit size. A convenient unit of measurement of the diameter of a conductor is the mil (0.001, or one-thousandth of an inch). A convenient unit of conductor length is the foot. The standard unit of size in most cases is the MIL-FOOT. A wire will have a unit size if it has a diameter of 1 mil and a length of 1 foot.

1.2.1 Square Mil The square mil is a unit of measurement used to determine the cross-sectional area of a square or rectangular conductor (views A and B of figure 1-1). A square mil is defined as the area of a square, the sides of which are each 1 mil. To obtain the cross-sectional area of a square conductor, multiply the dimension of any side of the square by itself. For example, assume that you have a square conductor with a side dimension of 3 mils. Multiply 3 mils by itself (3 mils ⋅ 3 mils). This gives you a cross-sectional area of 9 square mils.

Figure 1-1 Cross-sectional areas of conductors

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

1-3 UNCLASSIFIED Q1. State the reason for the establishment of a "unit size" for conductors. Q2. Calculate the diameter in MILS of a conductor that has a diameter of 0.375 inch. Q3. Define a mil-foot. To determine the cross-sectional area of a rectangular conductor, multiply the length times the width of the end face of the conductor (side is expressed in mils). For example, assume that one side of the rectangular cross-sectional area is 6 mils and the other side is 3 mils. Multiply 6 mils ⋅ 3 mils, which equals 18 square mils. Here is another example. Assume that a conductor is 3/8 inch thick and 4 inches wide. The 3/8 inch can be expressed in decimal form as 0.375 inch. Since 1 mil equals 0.001 inch, the thickness of the conductor will be 0.001 ⋅ 0.375, or 375 mils. Since the width is 4 inches and there are 1,000 mils per inch, the width will be 4 ⋅ 1,000, or 4,000 mils. To determine the cross- sectional area, multiply the length by the width; or 375 mils ⋅ 4,000 mils. The area will be 1,500,000 square mils.

Q4. Define a square mil as it relates to a square conductor.

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

1-4 UNCLASSIFIED 1.2.2 CIRCULAR MIL The circular mil is the standard unit of measurement of a round wire cross-sectional area (view C of figure 1-1). This unit of measurement is found in American and English wire tables. The diameter of a round conductor (wire) used to conduct electricity may be only a fraction of an inch. Therefore, it is convenient to express this diameter in mils to avoid using decimals. For example, the diameter of a wire is expressed as 25 mils instead of 0.025 inch. A circular mil is the area of a circle having a diameter of 1 mil, as shown in view B of figure 1-2. The area in circular mils of a round conductor is obtained by squaring the diameter, measured in mils. Thus, a wire having a diameter of 25 mils has an area of 25 2, or 625 circular mils. To determine the number of square mils in the same conductor, apply the conventional formula for determining the area of a circle (A = πr2). In this formula, A (area) is the unknown and is equal to the cross-sectional area in square mils, π is the constant 3.14, and r is the radius of the circle, or half the diameter (D). Through substitution, A = 3.14, and (12.5)2; therefore, 3.14 ⋅ 156.25 = 490.625 square mils. The cross-sectional area of the wire has 625 circular mils but only 490.625 square mils. Therefore, a circular mil represents a smaller unit of area than the square mil.

Figure 1-2 A comparison of circular and square mils

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

1-5 UNCLASSIFIED If a wire has a cross-sectional diameter of 1 mil, by definition, the circular mil area (CMA) is A = D2, or A = 12, or A = 1 circular mil. To determine the square mil area of the same wire, apply the formula A = πr2; therefore, A = 3.14 x (.5)2 (.5 representing half the diameter). When A = 3.14 x 25, A = .7854 square mil. From this, it can be concluded that 1 circular mil is equal to .7854 square mil. This becomes important when square (view A of figure 1-2) and round (view B) conductors are compared as in view C of figure 1-2.

When the square mil area is given, divide the area by 0.7854 to determine the circular mil area, or CMA. When the CMA is given, multiply the area by 0.7854 to determine the square mil area. For example,

Problem: A 12-gauge wire has a diameter of 80.81 mils. What is (1) its area in circular mils and (2) its area in square mils?

Solution:

(1) A = D 2 = 80.812 = 6,530 circular mils (2) A = 0.7854 x 6,530 = 5,128.7 square mils

Problem: A rectangular conductor is 1.5 inches wide and 0.25 inch thick. What is (1) its area in square mils and (2) in circular mils? What size of round conductor is necessary to carry the same current as the rectangular bar?

Solution:

(1) 1.5 inches = 1.5 inches x 1,000 mils per inch = 1,500 mils

0.25 inch = 0.25 inch x 1,000 mils per inch = 250 mils

A = 1,500 x 250 = 375,000 square mils

(2) To carry the same current, the cross-sectional area of the round conductor must be equal. There are more circular mils than square mils in this area. Therefore,

A = 375,000 0.7854 = 477,000 circular mils

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

1-6 UNCLASSIFIED A wire in its usual form is a single slender rod or filament of drawn metal. In large sizes, wire becomes difficult to handle. To increase its flexibility, it is stranded. Strands are usually single wires twisted together in sufficient numbers to make up the necessary cross-sectional area of the cable. The total area of stranded wire in circular mils is determined by multiplying the area in circular mils of one strand by the number of strands in the cable.

Q5. Define a circular mil. Q6. What is the circular mil area of a 19-strand conductor if each strand is 0.004 inch? 1.2.3 Circular-Mil-Foot A circular-mil-foot (figure 1-3) is a unit of volume. It is a unit conductor 1foot in length and has a cross-sectional area of 1 circular mil. Because it is a unit conductor, the circular-mil-foot is useful in making comparisons between wires consisting of different metals. For example, a basis of comparison of the RESISTIVITY (to be discussed shortly) of various substances may be made by determining the resistance of a circular- mil-foot of each of the substances.

In working with square or rectangular conductors, such as ammeter shunts and bus bars, you may sometimes find it more convenient to use a different unit volume. A bus bar is a heavy copper strap or bar used to connect several circuits together. Bus bars are used when a large current capacity is required. Unit volume may be measured as the centimeter cube. Specific resistance, therefore, becomes the resistance offered by a cube- shaped conductor 1centimeter in length and 1 square centimeter in cross-sectional area. The unit of volume to be used is given in tables of specific resistances.

Figure 1-3 Circular-mil-foot

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

1-7 UNCLASSIFIED 1.3 SPECIFIC RESISTANCE OR RESISTIVITY Specific resistance, or resistivity, is the resistance in ohms offered by a unit volume (the circular-mil-foot or the centimeter cube) of a substance to the flow of electric current. Resistivity is the reciprocal of conductivity. A substance that has a high resistivity will have a low conductivity, and vice versa. Thus, the specific resistance of a substance is the resistance of a unit volume of that substance.

Many tables of specific resistance are based on the resistance in ohms of a volume of a substance 1 foot in length and 1 circular mil in cross-sectional area. The temperature at which the resistance measurement is made is also specified. If you know the kind of metal a conductor is made of, you can obtain the specific resistance of the metal from a table. The specific resistances of some common substances are given in table 1-1.

Table 1-1 Specific Resistances of Common Substances Substance Specific resistance at 20°C Centimeter cube (microhoms) Circular-mil-foot (ohms) Silver 1.629 9.8 Copper (drawn) 1.724 10.37 Gold 2.44 14.7 Aluminum 2.828 17.02 Carbon (amorphous) 3.8 to 4.1 ............................................ Tungsten 5.51 33.2 Brass 7.0 42.1 Steel (soft) 15.9 95.8 Nichrome 109.0 660.0

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

1-8 UNCLASSIFIED The resistance of a conductor of a uniform cross section varies directly as the product of the length and the specific resistance of the conductor, and inversely as the cross- sectional area of the conductor. Therefore, you can calculate the resistance of a conductor if you know the length, cross-sectional area, and specific resistance of the substance. Expressed as an equation, the "R" (resistance in ohms) of a conductor is

R = 𝜌 L A

Where:

ρ = (Greek rho) the specific resistance in ohms per circular-mil-foot (refer to table 1-1)

L = length in feet

A = the cross-sectional area in circular mils

Problem:

What is the resistance of 1,000 feet of copper wire having a cross-sectional area of 10,400 circular mils (No. 10 wire) at a temperature of 20º C?

Solution:

The specific resistance of copper (table 1-1) is 10.37 ohms. Substituting the known values in the preceding equation, the resistance, R, is determined as

Given:

ρ = 10.37 ohms

L = 1,000 ft

A = 10,400 circular mils

Solution:

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

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

1-9 UNCLASSIFIED If R, ρ, and A are known, the length (L) can be determined by a simple mathematical transposition. This has many valuable applications. For example, when locating a ground in a telephone line, you will use special test equipment. This equipment operates on the principle that the resistance of a line varies directly with its length. Thus, the distance between the test point and a fault can be computed accurately.

Q7. Define specific resistance. Q8. List the three factors used to calculate resistance of a particular conductor in ohms. 1.3.1 Wire Sizes The most common method for measuring wire size in the Navy is by using the American Wire Gauge (AWG). An exception is aircraft wiring, which varies slightly in size and flexibility from AWG standards. For information concerning aircraft wire sizes, refer to the proper publications for specific aircraft. Only AWG wire sizes are used in the following discussion.

Wire is manufactured in sizes numbered according to the AWG tables. The various wires (solid or stranded) and the material they are made from (copper, aluminum, and so forth) are published by the National Bureau of Standards. An AWG table for copper wire is shown at table 1-2. The wire diameters become smaller as the gauge numbers become larger. Numbers are rounded off for convenience but are accurate for practical application. The largest wire size shown in the table is 0000 (read "4 naught"), and the smallest is number 40. Larger and smaller sizes are manufactured, but are not commonly used by the Navy. AWG tables show the diameter in mils, circular mil area, and area in square inches of AWG wire sizes. They also show the resistance (ohms) per thousand feet and per mile of wire sizes at specific temperatures. The last column shows the weight of the wire per thousand feet. An example of the use of table 1-2 is as follows.

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

1-10 UNCLASSIFIED

Table 1-2 Standard Solid Copper (American Wire Gauge)

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

1-11 UNCLASSIFIED Problem:

You are required to run 2,000 feet of AWG 20 solid copper wire for a new piece of equipment. The temperature where the wire is to be run is 25º C (77º F). How much resistance will the wire offer to current flow?

Solution:

Under the gauge number column, find size AWG 20. Now read across the columns until you reach the "ohms per 1,000 feet for 25º C (77º F)" column. You will find that the wire will offer 10.4 ohms of resistance to current flow. Since we are using 2,000 feet of wire, multiply by 2.

10.4 ohms x 2 = 20.8 ohms

An American Standard Wire Gauge (figure 1-4) is used to measure wires ranging in size from number 0 to number 36. To use this gauge, insert the wire to be measured into the smallest slot that will just accommodate the bare wire. The gauge number on that slot indicates the wire size. The front part of the slot has parallel sides, and this is where the wire measurement is taken. It should not be confused with the larger semicircular opening at the rear of the slot. The rear opening simply permits the free movement of the wire all the way through the slot.

Figure 1-4 Wire gauge

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

1-12 UNCLASSIFIED Q9. Using table 1-2, determine the resistance of 1,500 feet of AWG 20 wire at 25º C. Q10. When using an American Standard Wire Gauge to determine the size of a wire, where should you place the wire in the gauge to get the correct measurement? 1.3.2 Stranded Wires and Cables A wire is a single slender rod or filament of drawn metal. This definition restricts the term to what would ordinarily be understood as "solid wire." The word "slender" is used because the length of a wire is usually large when compared to its diameter. If a wire is covered with insulation, it is an insulated wire. Although the term "wire" properly refers to the metal, it also includes the insulation.

A conductor is a wire suitable for carrying an electric current.

A stranded conductor is a conductor composed of a group of wires or of any combination of groups of wires. The wires in a stranded conductor are usually twisted together and not insulated from each other.

A cable is either a stranded conductor (single-conductor cable) or a combination of conductors insulated from one another (multiple-conductor cable). The term "cable" is a general one and usually applies only to the larger sizes of conductors. A small cable is more often called a stranded wire or cord (such as that used for an iron or a lamp cord). Cables may be bare or insulated. Insulated cables may be sheathed (covered) with lead, or protective armor. Figure 1-5 shows different types of wire and cable used in the Navy.

Figure 1-5 Conductors

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

1-13 UNCLASSIFIED Conductors are stranded mainly to increase their flexibility. The wire strands in cables are arranged in the following order:

The first layer of strands around the center conductor is made up of six conductors. The second layer is made up of 12 additional conductors. The third layer is made up of 18 additional conductors, and so on. Thus, standard cables are composed of 7, 19, and 37 strands, in continuing fixed increments. The overall flexibility can be increased by further stranding of the individual strands.

Figure 1-6 shows a typical cross section of a 37-strand cable. It also shows how the total circular-mil cross-sectional area of a stranded cable is determined.

Figure 1-6 Stranded conductor

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

1-14 UNCLASSIFIED 1.4 SELECTION OF WIRE SIZE Several factors must be considered in selecting the size of wire to be used for transmitting and distributing electric power. These factors will be discussed throughout this section. Military specifications cover the installation of wiring in aircraft, ships, and electrical/electronic equipment. These specifications describe the technical requirements for material purchased from manufacturers by the Department of Defense. An important reason for having these specifications is to ensure uniformity of sizes to reduce the danger of fires caused by the improper selection of wire sizes. Wires can carry only a limited amount of current safely. If the current flowing through a wire exceeds the current-carrying capacity of the wire, excess heat is generated. This heat may be great enough to burn off the insulation around the wire and start a fire.

1.5 FACTORS GOVERNING THE CURRENT RATING The current rating of a cable or wire indicates the current capacity that the wire or cable can safely carry continuously. If this limit, or current rating, is exceeded for a length of time, the heat generated may burn the insulation. The current rating of a wire is used to determine what size is needed for a given load, or current drain.

The factors that determine the current rating of a wire are the conductor size, the location of the wire in a circuit, the type of insulation, and the safe current rating. Another factor that will be discussed later in this chapter is the material the wire is made of. As you have already seen, these factors also affect the resistance in ohms of a wire-carrying current.

1.5.1 Conductor Size An increase in the diameter, or cross section, of a wire conductor decreases its resistance and increases its capacity to carry current. An increase in the specific resistance of a conductor increases its resistance and decreases its capacity to carry current.

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

1-15 UNCLASSIFIED 1.5.2 Wire Location The location of a wire in a circuit determines the temperature under which it operates. A wire may be located in a conduit or laced with other wires in a cable. Because it is confined, the wire operates at a higher temperature than if it were open to the free air. The higher the temperature under which a wire is operating, the greater will be its resistance. Its capacity to carry current is also lowered. Note that, in each case, the resistance of a wire determines its current-carrying capacity. The greater the resistance, the more power it dissipates in the form of heat energy.

Conductors may also be installed in locations where the ambient (surrounding) temperature is relatively high. When this is the case, the heat generated by external sources is an important part of the total conductor heating. This heating factor will be explained further when we discuss temperature coefficient. We must understand how external heating influences how much current a conductor can carry. Each case has its own specific limitations. The maximum allowable operating temperature of insulated conductors is specified in tables. It varies with the type of conductor insulation being used.

1.5.3 Insulation The insulation of a wire does not affect the resistance of the wire. Resistance does, however, determine how much heat is needed to burn the insulation. As current flows through an insulated conductor, the limit of current that the conductor can withstand depends on how hot the conductor can get before it burns the insulation. Different types of insulation will burn at different temperatures. Therefore, the type of insulation used is the third factor that determines the current rating of a conductor. For instance, rubber insulation will begin deteriorating at relatively low temperatures, whereas varnished cloth insulation retains its insulating properties at higher temperatures. Other types of insulation are fluorinated ethylene propylene (FEP), silicone rubber, or extruded polytetrafluoroethylene. They are effective at still higher temperatures.

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

1-16 UNCLASSIFIED 1.5.4 Safe Current Ratings The National Board of Fire Underwriters prepares tables showing the safe current ratings for sizes and types of conductors covered with various types of insulation. The allowable current-carrying capacities of single copper conductors in free air at a maximum room temperature of 30º C (86º F) are given in table 1-3. At ambient temperatures greater than 30º C, these conductors would have less current-carrying capacity.

Table 1-3 Temperature Ratings and Current-Carrying Capacities (in Amperes) of Some Single Copper Conductors at Ambient Temperatures of 30°C Size Moisture Resistant Rubber or Thermoplastic Varnished Cambric or Heat Resistant Thermoplastic Silicone Rubber or Fluorinated Ethylene Propylene (FEP) Polytetra- Fluoroethylene 0000 300 385 510 850 000 260 330 430 725 00 225 285 370 605 0 195 245 325 545 1 165 210 280 450 2 140 180 240 390 3 120 155 210 335 4 105 135 180 285 6 80 100 135 210 8 55 70 100 115 10 40 55 75 110 12 25 40 55 80 14 20 30 45 60

Q11. List the four factors you should use to select wire for a specified current rating. Q12. What are three types of nonmetallic insulating materials that can be used in a high- temperature environments? Q13. State why it is important for you to consider the ambient (surrounding) temperature of a conductor when selecting wire size.

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

1-17 UNCLASSIFIED 1.6 COPPER-VERSUS-ALUMINUM CONDUCTORS Although silver is the best conductor, its cost limits its use to special circuits. Silver is used where a substance with high conductivity or low resistivity is needed.

The two most commonly used conductors are copper and aluminum. Each has positive and negative characteristics that affect its use under varying circumstances. A comparison of some of the characteristics of copper and aluminum is given in table 1-4.

Table 1-4 Comparative Characteristics of Copper and Aluminum CHARACTERISTICS COPPER ALUMINUM Tensile strength (lb/in2) 55,000 25,000 Tensile strength for same conductivity (lb) 55,000 40,000 Weight for same conductivity (lb) 100 48 Cross section for same conductivity (C.M.) 100 160 Specific resistance (Ω/mil ft)

Copper has a higher conductivity than aluminum. It is more ductile (can be drawn out). Copper has relatively high tensile strength (the greatest stress a substance can bear along its length without tearing apart). It can also be easily soldered. However, copper is more expensive and heavier than aluminum.

Although aluminum has only about 60 percent of the conductivity of copper, its lightness makes long spans possible. Its relatively large diameter for a given conductivity reduces corona. Corona is the discharge of electricity from the wire when it has a high potential. The discharge is greater when smaller diameter wire is used than when larger diameter wire is used. However, the relatively large size of aluminum for a given conductance does not permit the economical use of an insulation covering.

Q14. State two advantages of using aluminum wire for carrying electricity over long distances. Q15. State four advantages of copper over aluminum as a conductor.

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

1-18 UNCLASSIFIED 1.6.1 Temperature Coefficient The resistance of pure metals, such as silver, copper, and aluminum, increases as the temperature increases. However, the resistance of some alloys, such as constantan and manganin, changes very little as the temperature changes. Measuring instruments use these alloys because the resistance of the circuits must remain constant to get accurate measurements.

In table 1-1, the resistance of a circular-mil-foot of wire (the specific resistance) is given at a specific temperature, 20º C in this case. It is necessary to establish a standard temperature. As we stated earlier, the resistance of pure metals increases with an increase in temperature. Therefore, a true basis of comparison cannot be made unless the resistances of all the substances being compared are measured at the same temperature. The amount of increase in the resistance of a 1-ohm sample of the conductor per degree rise in temperature above 0º C is called the temperature coefficient of resistance. For copper, the value is approximately 0.00427 ohm.

A length of copper wire having a resistance of 50 ohms at an initial temperature of 0º C will have an increase in resistance of 50 x 0.00427, or 0.214 ohms. This applies to the entire length of wire and for each degree of temperature rise above 0º C. A 20º C increase in resistance is approximately 20 x 0.214, or 4.28 ohms. The total resistance at 20º C is 50 + 4.28, or 54.28 ohms.

Q16. Define the temperature coefficient of resistance. Q17. What happens to the resistance of copper when it is heated?

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

1-19 UNCLASSIFIED 1.7 CONDUCTOR INSULATION To be useful and safe, electric current must be forced to flow only where it is needed. It must be "channeled" from the power source to a useful load. In general, current-carrying conductors must not be allowed to come in contact with one another, their supporting hardware, or personnel working near them.

To accomplish this, conductors are coated or wrapped with various materials. These materials have such a high resistance that they are, for all practical purposes, nonconductors. Nonconductors are generally referred to as "insulators" or "insulating material."

Only the necessary minimum amount of insulation is applied to any particular type of conductor designed to do a particular job. This is done because of several factors. The expense, stiffening effect, and a variety of physical and electrical conditions under which the conductors are operated must be taken into account. Therefore, there are a variety of insulated conductors available to meet the requirements of any job.

Two fundamental properties of insulating materials (that is, rubber, glass, asbestos, or plastic) are insulation resistance and dielectric strength. These are two entirely different and distinct properties.

1.7.1 Insulation Resistance Insulation resistance is the resistance to current leakage through the insulation materials. Insulation resistance can be measured with a megger without damaging the insulation. Information so obtained is a useful guide in appraising the general condition of insulation. Clean, dry insulation having cracks or other faults may show a high value of insulation resistance but would not be suitable for use.

1.7.2 Dielectric Strength Dielectric strength is the ability of an insulator to withstand potential difference. It is usually expressed in terms of the voltage at which the insulation fails because of the electrostatic stress. Maximum dielectric strength values can be measured only by raising the voltage of a TEST SAMPLE until the insulation breaks down.

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1-20 UNCLASSIFIED Q18. Compare the resistance of a conductor to that of an insulator. Q19. State two fundamental properties of insulating materials. Q20. Define insulation resistance. Q21. Define dielectric strength. Q22. How is the dielectric strength of an insulator determined?

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1-21 UNCLASSIFIED 1.7.3 Types of Insulation The insulating materials discussed in the next paragraphs are commonly used in Navy electrical and electronic equipment.

1.7.3.1 Rubber One of the most common types of insulation is rubber. The voltage that may be applied to a rubber-covered conductor is dependent on the thickness and the quality of the rubber covering. Other factors being equal, the thicker the insulation, the higher may be the applied voltage. Rubber insulation is normally used for low- or medium-range voltage. Figure 1-7 shows two types of rubber-covered wire. One is a two-conductor cable in which each stranded conductor is covered with rubber insulation; the other is a single, solid conductor. In each case, the rubber serves the same purpose: to confine the current to its conductor.

Referring to the enlarged cross-sectional view in figure 1-7, note that a thin coating of tin separates the copper conductor from the rubber insulation. If the thin coating of tin were not used, a chemical action would take place and the rubber would become soft and gummy where it makes contact with the copper. When small, solid, or stranded conductors are used, a winding of cotton threads is applied between the conductors and the rubber insulation. Figure 1-7 Rubber insulation

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1-22 UNCLASSIFIED CODE-GRADED RUBBER - Code-graded rubber is the standard that the National Electrical Code (NEC) has adopted as the minimum requirements for rubber insulation as specified by Underwriters' Laboratories. In this code system, the letter R indicates the use of a rubber insulator. Type R signifies that the wire is rubber coated.

The NEC codes Type RH and Type RHH signify a rubber heat-resistant compound. Type RW signifies a rubber moisture-resistant compound. A Type RHW signifies a rubber heat- and moisture-resistant compound. Type RHW is approved for use in wet or dry locations at a maximum conductor temperature of 75º C. Neoprene, a low-voltage compound, is the one exception to Type RHW. Although not a rubber compound, neoprene meets the requirements of Underwriters' Laboratories and was designated Type RHW.

LATEX RUBBER - Latex rubber is a high-grade compound consisting of 90 percent unmilled grainless rubber. There are two designations for this type of insulation: Type RUH and Type RUW. Type RUH (rubber unmilled heat-resistant) is used in dry locations when the conductor temperature does not exceed 75º C. Type RUW (rubber unmilled moisture-resistant) is used in wet locations when the conductor does not exceed 60º C.

SILICONE - Silicone is a rubber compound that does not carry the "R" designator for many of its applications. An example of this is Type SA (silicone-asbestos). In Type SA, the insulator around the conductor is silicone rubber, but the outer covering must consist of heavy glass, asbestos-glass, or asbestos braiding treated with a heat, flame, and moisture-resistant compound.

Q23. What is the purpose of coating a copper conductor with tin when rubber insulation is used?

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1-23 UNCLASSIFIED 1.7.3.2 Plastics Plastic is one of the more commonly used types of insulating material for electrical conductors. It has good insulating, flexibility, and moisture-resistant qualities. Although there are many types of plastic insulating materials, thermoplastic is one of the most common. With the use of thermoplastic, the conductor temperature can be higher than with some other types of insulating materials without damage to the insulating quality of the material. Plastic insulation is normally used for low- or medium-range voltage.

The designators used with thermoplastics are much like those used with rubber insulators. The following letters are used when dealing with NEC type designators for thermoplastics:

Letter Designates T Thermoplastic H Heat-Resistant W Moisture-resistant A Asbestos N Outer nylon jacket M Oil-resistant

For example, a NEC designator of Type THWN would indicate thermoplastic heat- and moisture-resistant with an outer nylon jacket.

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1-24 UNCLASSIFIED 1.7.3.3 Varnished Cambric Varnished cambric insulation can withstand much higher temperatures than rubber insulation. Varnished cambric is cotton cloth that has been coated with an insulating varnish. Figure 1-8 shows a cable covered with varnished cambric insulation. The varnished cambric is in tape form and is wound around the conductor in layers. An oily compound is applied between each layer of the tape to prevent water from seeping through the insulation. It also acts as a lubricant between the layers of tape, so they will slide over each other when the cable is bent.

Cambric insulation is used on extremely high-voltage conductors used in substations and powerhouses. It is also used in other locations subjected to high temperatures. In addition, it is used on the coils and leads of high-voltage generators. Transformer leads also use this insulation because it is unaffected by oils or grease and has high dielectric strength. Varnished cambric and paper insulation for cables are the two types of insulating materials most widely used at voltages above 15,000 volts. Such cable is always lead covered to keep out moisture.

Figure 1-8 Varnished cambric insulation

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1-25 UNCLASSIFIED 1.7.3.4 Extruded Polytetrafluoroethylene Extruded polytetrafluoroethylene is a high-temperature insulation used extensively in aircraft and equipment installations. It will not burn, but will vaporize when subjected to intense heat. Conductors for high temperatures use a nickel coating rather than tin or silver to prevent oxidation. Nickel-coated wire is more difficult to solder, but makes satisfactory connections with proper soldering techniques.

WARNING

Avoid breathing the vapors from extruded polytetrafluoroethylene insulation when it is heated. Symptoms of overexposure are dizziness or headaches. These symptoms disappear upon exposure to fresh air.

Q24. What safety precaution should you take when working with extruded polytetrafluoroethylene insulated wiring? 1.7.3.5 Fluorinated Ethylene Propylene (FEP) FEP has properties similar to extruded polytetrafluoroethylene, but will melt at soldering temperatures. It is rated at 200º C and is, therefore, considered a high-temperature insulation. There are no known toxic vapors from FEP. Common-sense practice, however, requires that you provide adequate ventilation during any soldering operation.

1.7.3.6 Asbestos Asbestos insulation was used extensively in the past for high-temperature insulation. Today, it is seldom used by the Navy. Many naval ships and aircraft, however, still contain asbestos-insulated wiring. Aboard ship, this is particularly true in galley and laundry equipment. The reason for discontinuing the use of asbestos as an insulator is that breathing asbestos fibers can produce severe lung damage. It can render you disabled or cause fatal fibrosis of the lungs. Asbestos is also a factor in the development of cancer in the gastrointestinal tract. Safety precautions concerning asbestos will be covered in more detail at the end of chapter 3.

WARNING

Avoid inhalation of asbestos fibers. Asbestos fibers have been found to cause severe lung damage (asbestosis) and cancer of the gastrointestinal tract. Follow Navy safety precautions when working with all asbestos products.

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1-26 UNCLASSIFIED One type of asbestos-covered wire is shown in figure 1-9. It consists of stranded copper conductors covered with felted asbestos. The wire is, in turn, covered with asbestos braid. This type of wire is used in motion-picture projectors, arc lamps, spotlights, heating element leads, and so forth.

Another type of asbestos-covered cable is shown in figure 1-10. It is combination of asbestos and varnished cambric. This type of insulation serves as leads for motors and transformers that sometimes must operate in hot, damp locations. The varnished cambric covers the inner layer of felted asbestos. This prevents moisture from reaching the innermost layer of asbestos. Asbestos loses its insulating properties when it becomes wet. It will, in fact, become a conductor. Varnished cambric prevents this from happening because it resists moisture. Although this insulation will withstand some moisture, it should not be used on conductors that may at times be partially immersed in water. Under those circumstances, the insulation must be protected with an outer lead sheath.

Figure 1-9 Asbestos Insulation Figure 1-10 Asbestos and varnished cambric insulation

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1-27 UNCLASSIFIED The NEC has designators for eight types of asbestos wire. The designators and a description of each are listed below.

Type A Nonimpregnated asbestos without an asbestos braid Type AA Nonimpregnated asbestos with an outer asbestos braid or glass Type AI Impregnated asbestos without an asbestos braid Type AIA Impregnated asbestos with an outer asbestos braid or glass Type AVA Asbestos, varnish-cambric insulation with an outer asbestos braid or glass Type AVL Asbestos, varnish-cambric insulation with an outer asbestos braid covered with a lead sheath Type AVB Asbestos, varnish-cambric insulation with an outer flame-retardant cotton braid Type SA Silicone rubber insulated with outer heavy glass, asbestos-glass, or asbestos braid

Q25. State the reasons that the Navy is getting away from the use of asbestos insulation. Q26. State what happens to the insulating characteristics of asbestos when it gets wet.

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1-28 UNCLASSIFIED 1.7.3.7 Paper Paper has little insulation value alone. However, when impregnated with a high grade of mineral oil, it serves as a satisfactory insulation for extremely high-voltage cables. The oil has a high dielectric strength, and tends to prevent breakdown of the paper insulation. The paper must be thoroughly saturated with the oil. The thin paper tape is wrapped in many layers around the conductors, and then soaked with oil.

The three-conductor cable shown in figure 1-11 consists of paper insulation on each conductor. It has a spirally wrapped nonmagnetic metallic tape over the insulation. The space between conductors is filled with a suitable spacer to round out the cable. Another nonmagnetic metal tape is used to secure the entire cable. Over this, a lead sheath is applied. This type of cable is used on voltages from 10,000 volts to 35,000 volts.

Q27. What are the most common insulators used for extremely high voltages?

Figure 1-11 Paper-insulated power cables

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1-29 UNCLASSIFIED 1.7.3.8 Silk and Cotton In certain types of circuits (for example, communications circuits), a large number of conductors are needed, perhaps as many as several hundred. Figure 1-12 shows a cable containing many conductors. Each is insulated from the others by silk and cotton thread. Because the insulation in this type of cable is not subjected to high voltage, the use of thin layers of silk and cotton is satisfactory.

Silk and cotton insulation keeps the size of the cable small enough to be handled easily. The silk and cotton threads are wrapped around the individual conductors in reverse directions. The covering is then impregnated with a special wax compound.

Figure 1-12 Silk and cotton Insulation

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1-30 UNCLASSIFIED 1.7.3.9 Enamel The wire used on the coils of meters, relays, small transformers, motor windings, and so forth, is called magnet wire. This wire is insulated with an enamel coating. The enamel is a synthetic compound of cellulose acetate (wood pulp and magnesium). In the manufacturing process, the bare wire is passed through a solution of hot enamel and then cooled. This process is repeated until the wire acquires from 6 to 10 coatings. Thickness for thickness, enamel has higher dielectric strength than rubber. It is not practical for large wires because of the expense and because the insulation is readily fractured when large wires are bent.

Figure 1-13 shows an enamel-coated wire. Enamel is the thinnest insulating coating that can be applied to wires. Hence, enamel-insulated magnet wire makes smaller coils. Enameled wire is sometimes covered with one or more layers of cotton to protect the enamel from nicks, cuts, or abrasions.

Q28. What is the common name for enamel-insulated wire?

Figure 1-13 Enamel Insulation

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1-31 UNCLASSIFIED 1.7.3.10 Mineral Insulated Mineral-insulated (MI) cable was developed to meet the needs of a noncombustible, high heat-resistant, and water-resistant cable. MI cable has from one to seven electrical conductors. These conductors are insulated in a highly compressed mineral, normally magnesium oxide, and sealed in a liquid-tight, gastight metallic tube, normally made of seamless copper (figure 1-14).

Figure 1-14 Two-conductor mineral-insulated (MI) cable

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1-32 UNCLASSIFIED 1.8 CONDUCTOR PROTECTION Wires and cables are generally subject to abuse. The type and amount of abuse depends on how and where they are installed and the manner in which they are used. Cables buried directly in the ground must resist moisture, chemical action, and abrasion. Wires installed in buildings must be protected against mechanical injury and overloading. Wires strung on crossarms on poles must be kept far enough apart so that the wires do not touch. Snow, ice, and strong winds make it necessary to use conductors having high tensile strength and substantial frame structures.

Generally, except for overhead transmission lines, wires or cables are protected by some form of covering. The covering may be some type of insulator like rubber or plastic. Over this, additional layers of fibrous braid or tape may be used and then covered with a finish or saturated with a protective coating. If the wire or cable is installed where it is likely to receive rough treatment, a metallic coat should be added.

The materials used to make up the protection for a wire or cable are grouped into one of two categories: nonmetallic or metallic.

Q29. If a cable is installed where it receives rough treatment, what should be added? 1.8.1 Nonmetallic Protection The category of nonmetallic protective coverings is divided into three areas. These areas are (1) according to the material used as the covering, (2) according to the saturant in which the covering was impregnated, and (3) according to the external finish on the wire or cable. These three areas reflect three different methods of protecting the wire or cable. These methods allow some wire or cable to be classified under more than one category. Most of the time, however, the wire or cable will be classified based upon the material used as the covering regardless of whether or not a saturant or finish is applied. Many types of nonmetallic materials are used to protect wires and cables. Fibrous braid is by far the most common and will be discussed first.

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1-33 UNCLASSIFIED 1.8.1.1 Fibrous Braid Fibrous braid is used extensively as a protective covering for cables. This braid is woven over the insulation to form a continuous covering without joints (figure 1-15). The braid is generally saturated with asphalt, paint, or varnish to give added protection against moisture, flame, weathering, oil, or acid. Additionally, the outside braid is often given a finish of stearin pitch and mica flakes, paint, wax, lacquer, or varnish depending on the environment where the cable is to be used.

The most common type of fibrous braid is woven from light, standard, or heavy cotton yarn. Cotton yarn comes in different colors, which allows color-coding of the individual conductors. Cotton will not withstand all the possible environments in which a cable may be laid. Other materials currently being used to make fibrous braid are glazed cotton, seine twine or hawser cord, hemp, paper and cotton, jute, asbestos, silk, rayon, and fibrous glass. The choice of which material to use depends on the strength needed in the cable as well as how resistant it must be to its environment.

Figure 1-15 Fibrous braid covering

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1-34 UNCLASSIFIED 1.8.1.2 Fibrous Tape Fibrous tape coverings are frequently used as a part of the protective covering of cables. The material of tape coverings is made into the tape before application to the cable. The material in yarns for braid covering is woven into fabric during the application to the cable. When tape covering is used, it is wrapped helically around the cable with each turn overlapping the previous turn.

The most common types of fibrous tape are rubber-filled cloth tape and a combination of cotton cloth and rubber. Except for duct tape, tape covering is never used as the outer covering on a cable. Tape coverings are used directly over the insulation of individual conductors and for the inner covering over the assembled conductors of a multi- conductor cable. Frequently, tape coverings are used under the sheath of a lead-sheathed cable. Duct tape, which is made of heavy canvas webbing saturated with an asphalt compound, is often used over a lead-sheathed cable for protection against corrosion and mechanical injury.

Q30. How many categories of nonmetallic protective coverings are there? Q31. What is the most common type of nonmetallic material used to protect wires and cables? Q32. What are the most common types of fibrous tape? 1.8.1.3 Woven Covers Woven covers, commonly called loom, are used when exceptional abrasion-resistant qualities are required. These covers are composed of thick, heavy, long-fibered cotton yarns woven around the cable in a circular loom, much like that used on a fire hose. They are not braids, although braid covering are also woven; they are designated differently.

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1-35 UNCLASSIFIED 1.8.1.4 Rubber and Synthetic Coverings Rubber and synthetic coverings are not standardized. Different manufactures have their own special compounds designated by individual trade names. These compounds are different from the rubber compounds used to insulate cable. These compounds have been perfected not for insulation qualities but for resistance to abrasion, moisture, oil, gasoline, acids, earth solutions, and alkalies. None of these coverings will provide protection against all types of exposure. Each covering has its own particular limitations and qualifications.

1.8.1.5 Jute and Asphalt Coverings Jute and asphalt coverings are commonly used as a cushion between cable insulation and metallic armor. Frequently, they are also used as a corrosive-resistant covering over a lead sheath or metallic armor. Jute and asphalt coverings consist of asphalt-impregnated jute yarn heli-wrapped around the cable or of alternate layers of asphalt-impregnated jute yarn. These coverings serve as a weatherproofing.

1.8.1.6 Unspun Felted Cotton Unspun felted cotton is commonly used only in special classes of service. It is made as a solid felted covering for a cable.

Q33. What materials are commonly used as cushions between cable insulation and metallic armor?

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1-36 UNCLASSIFIED 1.8.2 Metallic Protection Metallic protection is of two types: sheath or armor. As with all wires and cables, the type of protection needed will depend on the environment where the wire or cable will be used.

1.8.2.1 Metallic Sheath Cables or wires that are continually subjected to water must be protected by a watertight cover. This watertight cover is either a continuous metal jacket or a rubber sheath molded around the cable.

Figure 1-16 is an example of a lead-sheathed (jacketed) cable used in power work. This cable is a standard three-conductor type. Each conductor is insulated and then wrapped in a layer of rubberized tape. The conductors are twisted together, and rope or fillers are added to form a round core. Over this is wrapped a second layer of tape called a serving. Finally, a lead sheath is molded around the cable.

Lead-sheathed cable is one of three types currently being used: alloy lead, pure lead, and reinforced lead. An alloy-lead sheath is much like a pure lead sheath but is manufactured with 2-percent tin. This alloy is more resistant to gouging and abrasion during and after installation. Reinforced lead sheath is used mainly for oil-filled cables where high internal pressures can be expected. Reinforced lead sheath consists of a double lead sheath. A thin tape of hard-drawn copper, bronze, or other elastic metal (preferably nonmagnetic) is wrapped around the inner sheath. This tape gives considerable additional strength and elasticity to the sheath, but must be protected from corrosion. For this reason, a second lead sheath is applied over the tape.

Figure 1-16 Lead-sheathed cable

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1-37 UNCLASSIFIED 1.8.2.2 Metallic Armor Metallic armor provides a tough protective covering for wires and cables. The type, thickness, and kind of metal used to make the armor depend on three factors: (1) the use of the conductors, (2) the environment where the conductors are to be used, and (3) the amount of rough treatment that is expected.

Figure 1-17 shows three examples of metallic armor cable: wire braid, steel tape, and wire armor.

WIRE-BRAID ARMOR - Wire-braid armor (view A of figure 1-17 ), also known as basket-weave armor, is used when light and flexible protection is needed. Wire braid is constructed much like fibrous braid. The metal is woven directly over the cable as the outer covering. The metal used in this braid is galvanized steel, bronze, copper, or aluminum. Wire-braid armor is mainly for shipboard use.

Figure 1-17 Metallic armor cable

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1-38 UNCLASSIFIED STEEL TAPE - A second type of metallic armor is steel tape. Steel tape covering (view B of figure 1-17) is wrapped around the cable and then covered with a serving of jute. There are two types of steel tape armor. The first is called interlocking armor. Interlocking armor is applied by wrapping the tape around the cable so that each turn is overlapped by the next and is locked in place. The second type is flat-band armor. Flat- band armor consists of two layers of steel tape. The first layer is wrapped around the cable but is not overlapped. The second layer is then wrapped around the cable covering the area that was not covered by the first layer.

WIRE ARMOR - Wire armor is a layer of wound metal wire wrapped around the cable. Wire armor is usually made of galvanized steel and can be used over a lead sheath (see view C of figure 1-17). It can be used with the sheath as a buried cable where moisture is a concern, or without the sheath (view D of figure 1-17) when used in buildings.

Q34. What are the two types of metallic protection? Q35. What are the three types of lead-sheathed cables? Q36. What are the three examples of metallic armor cable that were discussed?

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1-39 UNCLASSIFIED 1.9 COAXIAL CABLE Coaxial cable (figure 1-18) is defined as two concentric wires, cylindrical in shape, separated by a dielectric of some type. One wire is the center conductor and the other is the outer conductor. These conductors are covered by a protective jacket. The protective jacket is then covered by an outer protective armor.

Coaxial cables are used as transmission lines and are constructed to provide protection against outside signal interference.

Figure 1-18 Coaxial cable

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1-40 UNCLASSIFIED 1.10 SUMMARY In this chapter you learned that conductors are the means for tying the various components of an electrical or electronic system together. Many factors determine the type of conductor to be used in a specific application. In order for you to compare the different types and sizes of conductors, we discussed the following factors:

Unit Size - The unit size of a conductor is the mil-foot. A mil-foot is a circular conductor 1foot long with a diameter of 1 mil (0.001 inch, or one-thousandth of an inch).

Conductor Sizes - The square mil and the circular mil are the units of measure used to determine the cross-sectional area of electrical conductors. The square mil, as it relates to a square conductor, is the cross-sectional area of a square conductor that has a side of 1 mil. The circular mil is the cross-sectional area of a circular conductor having a diameter of 1 mil. The circular mil area (CMA) of a conductor is computed by squaring the diameter of the circular conductor is mils. Thus, a wire having a diameter of 4 mils (0.004 inch) has a CMA of 4 2, or 16 circular mils. If the conductor is stranded, the CMA for a strand is computed, and the CMA for the conductor is computed by multiplying the CMA of the strand by the number of strands. The relationship of the square mil to the circular mil is determined by comparing the square mil area of a circular conductor having a diameter of 1 mil (A = πr 2) to the circular mil area of the same conductor (D2). Therefore, there is 0.7854 square mil to 1 circular mil. There are more circular mils than square mils in a given area.

Specific Resistance - The specific resistance of a substance is the resistance in ohms offered by a unit volume (the circular-mil-foot) to the flow of electric current. The three factors that are used to calculate the specific resistance of a particular conductor are (1) its length, (2) its cross-sectional area, and (3) the specific resistance of a unit volume of the substance from which the conductor is made. The specific resistance for various sizes and lengths of standard solid copper wire can be determined by the use of tables.

Wire Gauge - A wire gauge is used to determine the American Standard Wire Gauge size of conductors. The measurement of a bare conductor is taken in the slot, not in the circular area at the bottom of the slot.

Selection of Wire Size - Four factors must be considered in selecting the proper wire size for a particular electrical circuit. These factors are (1) conductor size, (2) the material it's made of, (3) the location of the wire in the circuit, and (4) the type of insulation used. Some of the types of insulation used in a high-temperature environment are FEP, extruded polytetrafluoroethylene, and silicone rubber. The ambient (surrounding) temperature of a conductor is an important part of total conductor heating.

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1-41 UNCLASSIFIED Copper-versus-Aluminum Conductors - The two most common metals used for electrical conductors are copper and aluminum. Some advantages of copper over aluminum as a conductor are that copper has higher conductivity, is more ductile, has a higher tensile strength, and can be easily soldered. Two advantages of aluminum wire for carrying electricity over long distances are its lightness and it reduces corona (the discharge of electricity from a wire at high potential).

Temperature Coefficient of Resistance - The temperature coefficient of resistance is the amount of increase in the resistance of a 1-ohm sample of a conductor per degree of temperature rise above 0º C. The resistance of copper and other pure metals increases with an increase in temperature.

Conductor Insulation - Insulators have a resistance that is so great that, for all practical purposes, they are nonconductors. Two fundamental properties of insulating materials are (1) insulation resistance and (2) the resistance to current leakage through the insulation. Dielectric strength is the ability of the insulation material to withstand potential difference. The dielectric strength of an insulator is determined by raising the voltage on a test sample until it breaks down.

Insulating Materials - Some common insulating materials have properties and safety precautions that should be remembered. These are:

• The purpose of coating a copper conductor with tin when rubber insulation is used is to prevent the insulation from deteriorating due to chemical action. • When extruded polytetrafluoroethylene insulation is heated, caution should be observed not to breathe the vapors. • The most commonly used insulating materials for extremely high-voltage conductors are varnished cambric and oil-impregnated paper. • Magnet wire is the common name for enamel-insulated wire used in meters, relays, small transformers, motor windings, and so forth. • The Navy is getting away from using asbestos insulation because asbestos fibers can cause lung disease and/or cancer. • Asbestos insulation becomes a conductor when it gets wet.

Conductor Protection - There are several types of conductor protection in use. The type commonly used aboard Navy ships is wire-braid armor.

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1-42 UNCLASSIFIED ANSWERS TO QUESTIONS Q1. THROUGH Q36.

A1. To allow comparisons between conductors of different sizes and resistance.

A2. 375 mils (move the decimal three places to the right).

A3. A circular conductor with a diameter of 1 mil and a length of 1 foot.

A4. The cross-sectional area of a square conductor with a side of 1 mil.

A5. The cross-sectional area of a circular conductor with a diameter of 1 mil.

A6. Circular mil area (CMA) = D 2 (in mils) × number of strands0.0004 inch = 4 mils (CMA) = 4 2 ×19 (strands)(CMA) = 16 × 19 = 304 mils.

A7. The resistance of a unit volume of a substance.

A8. Length, cross-sectional area, and specific resistance of a unit volume of the substance from which the conductor is made.

A9. 1,000 ft = 10.4 ohms1,500 ft = 1.5 × 0.4 = 15.6 ohms

A10. In the parallel walled slot not the circular area.

A11. Conductor size, the material it is made of the location of the wire in a circuit, and the type of insulation used.

A12. FEP, extruded polytetrafluoroethylene, and silicone rubber.

A13. The heat surrounding the conductor is an important part of total conductor heating.

A14. It is light and reduces corona.

A15. It has higher conductivity, it is more ductile, it has relatively high tensile strength, and it can be easily soldered.

A16. The amount of increase in the resistance of a 1-ohm sample of the conductor per degree of temperature rise above 0º C

A17. It increases.

A18. Conductors have a very low resistance and insulators have a resistance that is so great that, for all practical purposes, they are nonconductors.

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1-43 UNCLASSIFIED A19. Insulation resistance and dielectric strength.

A20. The resistance to current leakage through the insulation.

A21. The ability of the insulation material to withstand potential difference.

A22. By raising the voltage on a test sample until it breaks down.

A23. To prevent the rubber insulation from deteriorating due to chemical action.

A24. Avoid breathing the vapors when the insulation is heated.

A25. Breathing asbestos fibers can cause lung disease and/or cancer

A26. It will become a conductor.

A27. Varnished cambric and oil-impregnated paper.

A28. Magnet wire.

A29. Metallic coat.

A30. Three.

A31. Fibrous Braid.

A32. Rubber-filled cloth tape and a combination of cotton cloth and rubber.

A33. Jute and Asphalt coverings.

A34. Sheath and armor

A35. Alloy lead, pure lead, and reinforced lead.

A36. Wire braid, steel tape, and wire armor

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3-1 UNCLASSIFIED 3 SCHEMATIC READING LEARNING OBJECTIVES

Upon completing this chapter, you should be able to:

1. Recognize the marking system for cables to include shipboard and test equipment systems. 2. Recognize the marking system for wire to include aircraft and shipboard electronic equipment systems. 3. Recall the seven types of electrical diagrams and the functional design of each. 4. Recall basic safety practices and precautions for working around electrical and electronic systems.

3.1 INTRODUCTION TO SCHEMATIC READING This chapter is divided into three subtopics.(1) cable and wire-marling systems, (2) electrical and electronic diagrams, and (3) safety precautions. First, we will discuss the systems used for marking cables and wires. We will then explain each of the types of diagrams you will encounter when troubleshooting, testing, repairing, or learning about circuit or system operation. Finally, we will briefly discuss safety practices relating to working around electrical and electronic systems.

3.2 CABLE- AND WIRE-MARKING SYSTEMS Cables and wires are marked to give the technician a means of tracing them when troubleshooting and repairing electrical and electronic systems.

Numerous cable- and wire-marking systems are used in ships, aircraft, and equipment throughout the Navy. A few of these systems are briefly discussed here to acquaint you with how marking systems are used. For a specific system or equipment, you should refer to tile applicable technical manual.

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3-2 UNCLASSIFIED 3.2.1 Cable-Marking Systems Two typical cable-marking systems you are likely to see are the (1) shipboard and (2) test equipment cable-marking systems.

3.2.1.1 Shipboard Cable-Marking Systems Metal tags embossed with the cable markings are used to identify all permanently installed shipboard electrical cables. These cable tags (figure 3-1) are placed on cables close to each point of connection, and on both sides of decks, bulkheads, and other barriers to identify the cables. The markings on the cable tags identify cables for maintenance and circuit repairs. The tags show (1) the SERVICE LETTER, which identifies a particular electrical system, (2) the CIRCUIT LETTER or LETTERS, which identify a specific circuit within a particular system, and (3) the CABLE NUMBER, which identifies an individual cable in a specific circuit.

In figure 3-1, note that the cable is marked "C-MB144." The letter C denotes the service; in this case, the IC (interior communication) system. The letters MB denote the circuit; in this case, the engine-order circuit. The number 144 denotes cable number 144 of the MB circuit.

Figure 3-1 Cable tag

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3-3 UNCLASSIFIED Q1. Why must cables and wires be identified? Q2. Where would you find the wire identification system for a specific piece of equipment? Q3. What does the cable number identify? 3.2.1.2 Test Equipment Cable-Marking Systems View A of figure 3-2 shows apiece of test equipment that is used to check out electrical or electronic equipment or a system. It also shows the cables that are used to hook the tester to the equipment. The cables have metal or plastic tags at each end showing the cable number and the connector number.

View B of figure 3-2 shows the method of connecting the tester to the piece of equipment to be tested. (For a specific tester, the technical manual supplied with the tester shows the method of connection.) The tester shown has four cables. These are numbered W1, W2, W3, and W4. Each cable has two connectors (plugs), one on each end, that are numbered P1 and P2. The cable tag on one end of the cable reads W1-P1, and the other end reads W1 -P2. As shown in the figure, W1-P1 is connected to the receptacle J1 on the tester. W1-P2 is then connected to receptacle J1 on the equipment to be tested. The same procedure is followed for connecting the remaining three cables. The hookup is then complete.

The shipboard and the test equipment cable markings just discussed are only two of many cable-marking systems you may encounter. There are too many systems to attempt to discuss them all. As stated earlier, you should study an equipment or installation technical manual before attempting repairs or connections.

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3-4 UNCLASSIFIED

Figure 3-2 Test equipment cable marking

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3-5 UNCLASSIFIED 3.2.2 Wire-Marking Systems Wire-marking systems are used to identify wires in aircraft, shipboard electronic equipment, and power tool and appliance cables.

3.2.2.1 Aircraft Wire-Marking Systems All aircraft wiring is identified on wiring diagrams exactly as the wire is marked in the aircraft. Each wire is coded by a combination of letters and numbers (figure 3-3) imprinted on the wire at prescribed intervals along the wire run.

Look at figure 3-3. The circuit function letter (P in this example) identifies the basic function of the circuit concerned. The letter P indicates that the wire is in the dc power distribution system of the aircraft. The wire number, 215, indicates that it is the 215th wire in the dc distribution system. The wire segment letter (A) identifies the position of each wire segment of the circuit. The wire segments are lettered in alphabetical sequence and change each time the wire passes through a terminal or connector. For example, after the wire passes through the first terminal or connector, the segment letter A, as in this instance, would change to B.

Figure 3-3 Aircraft wire marking

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3-6 UNCLASSIFIED The wire size number (4) is the AN wire size. AN wire sizes have more strands for flexibility and are slightly different in circular mil area than AWG (American Wire Gauge) wire sizes. The current-carrying capacity of each is almost the same. The last letter (N) is the ground or phase letter. The letter N identifies any wire that completes the circuit to the ground network of the aircraft.

In a 3-phase ac power distribution system, a phase letter (A, B, or C) is used as the last letter of the wire marking. If aluminum wire is used as the conductor, ALUMINUM or ALUM will be added as a suffix to the wire identification code.

Q4. If a wire passes through a connector what portion of the aircraft wire identification number changes? 3.2.2.2 Shipboard Electronic Equipment Wire-Marking Systems The following explanation is an example of the type of conductor marking used in shipboard electronic equipment. These conductors may be contained in cables within the equipment. Cables within equipment are usually numbered by the manufacturer. These numbers will be found in the technical manual for the equipment. If the cables connect equipment between compartments on a ship, they will be marked by the shipboard cable- numbering system previously described.

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3-7 UNCLASSIFIED On the conductor lead, at the end near the point of connection to a terminal post, spaghetti sleeving is used as a marking material and an insulator. The sleeving is marked with identifying numbers and letters and then slid over the conductor. The marking on the sleeving identifies the conductor connections both "to" and "from" by giving the following information (figure 3-4):

The terminal "from"

The terminal board "to"

The terminal "to"

These designations on the sleeving are separated by a dash. The order of the markings is such that the first set of numbers and letters reading from left to right is the designation corresponding to the terminal "from" which the conductor runs. Following this is the number of the terminal board "to" which the conductor runs. ("TB" is omitted when the sleeve is marked.) The third designation is the terminal "to" which the conductor runs.

Figure 3-4 Designating conductor marking between unlike terminals

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

3-8 UNCLASSIFIED For example, as shown in figure 3-4, the conductor is attached to terminal 2A of terminal board 101 (terminal "from" 2A on the spaghetti sleeving). The next designation on the sleeving is 401, indicating it is going "to" terminal board 401. The last designation is 7B, indicating it is attached "to" terminal 7B of TB 401. The spaghetti marking on the other end of the conductor is read the same way. The conductor is going "from" terminal 7B on terminal board 401 "to" terminal 2A on terminal board 101.

On occasion, it may be necessary to run conductors to units that have no terminal board numbers; for example, a junction box. In this case, an easily recognizable abbreviation may be used in place of the terminal board number on the spaghetti sleeving. The designation "JB2" indicates that the conductor is connected to junction box No. 2. A conductor to junction box No. 2 of a piece of equipment would be identified as shown in figure 3-5. In the same manner, a plug would be identified as "P." This P number would be substituted for the terminal board number marking on the sleeving.

Figure 3-5 Marking of conductors running to a junction box

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

3-9 UNCLASSIFIED 3.3 POWER TOOL AND APPLIANCE MARKING SYSTEMS As with the wire- and cable-numbering systems discussed so far, there are many color- coding systems used in electrical and electronic applications. The color-coding system discussed here is the one used to code conductors for power tools and appliances.

An electrical power tool or appliance is required to have a three-wire cable. The conductors in the cable are color-coded black, white, and green. At shore bases or civilian facilities, one side of the electrical input is grounded. The grounded side is called the "common," and is color-coded white. The other side of the input is called the "line," or hot side, and is color coded "black". The green conductor is connected to ground and to the frame of the applicance or tool.

Aboard ship, neither side is grounded; therefore, both sides are considered the "fine," or both are hot. The black or the white conductor may be connected to either line, since there is no difference. The green conductor is connected to ground. Ground aboard ship is the ship's hull.

The purpose of the ground wire (green) is to prevent an electrical shock to the operator in case there is an electrical short to the frame of the appliance or tool.

Q5. What markings are found on spaghetti sleeving? Q6. What is the purpose of the green conductor in a power tool or electrical appliance cable?

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

3-10 UNCLASSIFIED 3.4 ELECTRICAL DIAGRAMS It is absolutely essential that personnel in the electrical or electronic ratings be able to "read" (interpret) various types of electrical diagrams. Personnel working in these ratings commonly refer to all electrical diagrams as "schematics." This term is not correct, however. A schematic is a specific type of diagram with characteristics of its own and with a specific purpose. Each of the various diagrams discussed in this chapter has a specific purpose and distinguishing features that set it apart from the others. The diagrams discussed may be used for the following purposes:

• To learn a specific system operation • To locate the components of a system • To identify the components of a system • To trace a circuit • The troubleshoot equipment • The repair equipment.

When you have completed this subject, you should be able to recognize the relationship between the various diagrams, their distinguishing features, and the purpose of each type of diagram. A continuing reference to the figures in the text should help you understand the subject matter more clearly.

We will use a simplified drawing of the electrical system of an automobile to explain the various electrical diagrams and how to "read" them.

3.4.1 Pictorial Diagram The simplest of all diagrams is the pictorial diagram. It shows a picture or sketch of the various components of a specific system and the wiring between these components. This simplified diagram provides the means to readily identify the components of a system, even if you are not familiar with their physical appearance. This type of diagram shows the various components without regard to their physical location, how the wiring is marked, or how the wiring is routed. It does, however, show you the sequence in which the components are connected.

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

3-11 UNCLASSIFIED Figure 3-6 is a pictorial diagram of an automobile starting and ignition system. If you are not already familiar with the components of this system, study the diagram. You should then be able to recognize the physical appearance of each component and its interconnections with the other components of the system.

Figure 3-6 Pictorial diagram of automotive starter and ignition systems

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

3-12 UNCLASSIFIED 3.4.2 Isometric Diagram The purpose of an isometric diagram is to assist you in locating a component within a system. If you do not know where to look for a component, the isometric diagram is of considerable value to you. This type of diagram shows you the outline of a ship, airplane, or piece of equipment. Within the outline are drawn the various components of a system in their respective locations. The isometric diagram also shows the interconnecting cable runs between these components.

Figure 3-7 is an isometric diagram of portions of the same automobile starting and lighting systems discussed in the pictorial diagram (figure 3-6). The battery, starter, and other components can now be seen, each in its actual location within the automobile.

Figure 3-7 Isometric diagram

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

3-13 UNCLASSIFIED 3.4.3 Block Diagram A block diagram is used primarily to present a general description of a system and its functions. This type of diagram is generally used in conjunction with text material. A block diagram shows the major components of a system and the interconnections of these components. All components are shown in block form, and each block is labeled for identification purposes.

The block diagram shown in figure 3-8 is an illustration of an automobile's electrical power, starting, and ignition systems. It must be emphasized that the following explanation is primarily for the purpose of assisting you in learning to "read" or interpret a block diagram. The explanation of the functions of the automobile power, starting, and ignition systems is of secondary importance. By tracing from component to component in the block diagram and following the explanation, you are given a general description of the system functions. In addition, you should be able to understand the arrangement of the components in a block diagram.

Figure 3-8 Block diagram

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

3-14 UNCLASSIFIED The battery is the initial source of power for the starter and ignition systems. The starter is turned by power from the battery when the ignition switch is turned to the START position. Power is also supplied, through the ignition switch, to the coil. From the coil, power is supplied to the distributor and finally to the spark plugs for ignition.

Once the engine is running, the starter is no longer required. The running engine acts as the prime mover for the alternator. (This is accomplished through a belt and pulley system attached to the engine's crankshaft.) The alternator now takes over as the power supplier for the ignition system. It supplies power through the ignition switch to the coil, from the coil to the distributor, and finally from the distributor to the spark plugs. At the same time, the alternator supplies power back through the voltage regulator to the battery for charging purposes. This completes the cycle until the engine is shut down and started again.

Note that the engine is not shown in the block diagram as the prime mover for the alternator. The engine is a mechanical rather than an electrical function. The illustrated block diagram is of the electrical system only. There are block diagrams that show strictly mechanical components or both mechanical and electrical components.

3.4.4 Single-Line Diagram The single-line diagram is used basically for the same purpose as the block diagram. When used with text material, it gives you a basic understanding of the functions of the components of a system.

There are two major differences between the single-line diagram and the block diagram. The first difference is that the single-line diagram uses symbols, rather than labeled blocks, to represent components. Second, the single-line diagram shows all components in a single line (figure 3-9). There are no interconnections shown for selected components as were shown on the block diagram (for example, alternator to voltage regulator and back to the battery). The single-line diagram is very simplified and should be used primarily to learn (in very broad terms) the function of each of the various components as a part of the total system.

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

3-15 UNCLASSIFIED

Q7. What type of electrical diagram is used to identify the components of a system? Q8. What type of diagram is used to find the location of a component? Q9. What types of diagrams are the most convenient from which to learn the basic Functions of a circuit? 3.4.5 Schematic Diagram The schematic diagram shows, by means of graphic symbols, the electrical connections and functions of a specific circuit arrangement. The schematic diagram is used to trace the circuit and its functions without regard to the actual physical size, shape, or location of the component devices or parts. The schematic diagram is the most useful of all the diagrams in learning overall system operation.

Figure 3-10 is a schematic diagram of an automobile electrical system. The automobile electrical system uses the frame of the automobile as a conductor. The frame is called the ground side. Figure 3-10 shows all the electrical components grounded on one side. The negative side of the battery is also grounded. Therefore, the frame is the negative conductor of the system. The opposite side of each of the components is connected through switches to the positive side of the battery. For the purpose of teaching schematic reading, we will discuss only the lighting system and engine instruments.

Figure 3-9 Single-line diagram

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

3-16 UNCLASSIFIED

Figure 3-10 Schematic diagram

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

3-17 UNCLASSIFIED The positive side of the 12-volt battery is connected to the starter solenoid, then to terminal B of the voltage regulator, and then down to point (1). (It should be noted that points (1), (2), (3), and so on, normally are not indicated on the schematic. They are shown here only to help you follow the diagram.) Therefore, if no faults are in the system, point (1) has a 12-volt positive potential at all times. This positive potential can be traced through the fuse to the OFF position of the light switch. The dashed line indicates the mechanical linkage of the switch. When the switch is pulled to the first position (park), +12 volts are applied to point (2). It can now be seen that the tail lights (T), the tag light, the side panel lights, and the instrument lights have +12 volts applied. The opposite side of each light is grounded. The instrument panel lights are grounded through the dimming rheostat. This completes the path for current flow from the negative side of the battery, through all the light bulbs (lamps), back to the positive side of the battery. If no faults exist, the lamps will light.

When the light switch is pulled to the next position (on), the bar on the switch contacts the "off," "park," and "on" contacts of the switch. The lights that were illuminated before are still on, and the + 12 volt potential is now applied to the bright (B) side of the headlights through the dimmer switch. Since the headlights are also grounded on one side, there is now a complete path for current flow, and the headlights also light. If the dimmer switch is actuated, the positive potential is switched from the bright filament to the dim filament of the headlights, and the lights dim.

The brake-light switch has +12 volts applied from point (1), directly to the stop lights (not fused). If the brake pedal is pressed, the switch is actuated, and the +12 volts are applied to both stop lights (S). Because one side of each light is tied to ground, there is a path for current flow, and the lights will light. If the dimming rheostat for the instrument lights is turned in the direction that increases the resistance, more voltage is dropped across the rheostat, less across the lights, and the lights will get dimmer.

The +12 volts at point (1) are also supplied to the OFF position of the ignition switch. When the ignition switch is turned on, the +12 volts are felt at point (3). This is a common point to all the engine instruments.

The gas gauge is a galvanometer with the dial graduated according to the amount of fuel in the tank. The gas gauge tank unit is a rheostat mechanically linked to a float in the gas tank. When the tank is full, the float rises to its highest level and positions the movable arm of the rheostat to a position of minimum resistance. This allows maximum current flow through the galvanometer, and the dial rests at the "full" mark on the gas gauge. As fuel is used by the engine, the float lowers, increasing the resistance of the rheostat to ground. This reduces the current through the galvanometer, and the dial shows a lesser amount of fuel.

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

3-18 UNCLASSIFIED The oil-pressure light gets its ground through a normally closed pressure switch. (When no pressure is applied, the switch is closed.) When the engine is started, the oil pressure increases and opens the switch. This turns the light off by removing the ground.

The water-temperature gauge is a galvanometer like the gas gauge, except its dial is graduated in degrees of temperature. The water-temperature element is a thermistor with a negative temperature coefficient. (A thermistor is a semiconductor device whose resistance varies with temperature.) When the engine is cold, the resistance of the thermistor is at a maximum. This reduces the current through the galvanometer, and a low temperature is indicated on the dial. As the water temperature of the engine increases, the resistance of the thermistor decreases. This allows more current to flow from ground through the galvanometer, and the temperature on the dial shows an increase. On the voltage regulator shown, the "T" terminal is grounded anytime the alternator does not have an output. This gives the alternator light a ground and causes it to illuminate.

Q10. What type of diagram is the most useful in learning the overall operation of a system? Q11. Refer to the schematic diagram in figure 3-10. If the ignition switch is placed in the ON position and all the engine instruments operate properly except the gas gauge, where would the fault probably be? Q12. If the fuse shown on the schematic (figure 3-10) opens, what lights will operate?

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

3-19 UNCLASSIFIED 3.4.6 Wiring Diagram A wiring diagram is a detailed diagram of each circuit installation showing all of the wiring, connectors, terminal boards, and electrical or electronic components of the circuit. It also identifies the wires by wire numbers or color coding. Wiring diagrams are necessary to troubleshoot and repair electrical or electronic circuits. The wiring diagram for an automobile is shown in figure 3-11. It shows all the electrical components and that the interconnecting wiring is color coded.

Figure 3-11 Wiring diagram

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

3-20 UNCLASSIFIED You should use the schematic diagram previously discussed to determine where the trouble might be in the circuit when a malfunction occurs. The schematic diagram does not show the terminals, connector points, and so forth, of the circuit. Therefore, you must go to the circuit wiring diagram to determine where to make the voltage or resistance checks in the circuit when troubleshooting. Following is an example of how to use a schematic diagram in conjunction with a wiring diagram to troubleshoot a circuit.

In the discussion of schematic diagrams, you will recall that when the light switch is pulled to the PARK position, the tail lights, side panel lights, tag light, and the instrument lights come on. Now, suppose that when the light switch is pulled to the PARK position all the lights come on, except the tag light. Referring to the schematic diagram (figure 3- 10), you will recall that when the light switch is placed in the PARK position, +12 volts are applied to point (2). If all the lights come on except the tag light, then the fault must be between point (2) and the tag light ground.

On the schematic shown in figure 3-11, you can see that there are numerous connections to point (2). Point (2) on the wiring diagram is actually composed of three different functions: terminal 1 of TB 1 (the head lamp junction block), terminals 1 and 2 of TB2 (the tail lamp junction block), and the "T" terminal of the light switch; all correspond to point (2) on the schematic. The fault here is in the tag light, which normally receives its +12 volts from terminal 1 of TB2.

To use a voltmeter to find the fault, place the positive lead of the voltmeter to the ground terminal of the tag light and the negative lead to the frame. The voltmeter should read zero, because there should be no difference of potential between the two points. If the meter reads a voltage, the ground lead is either open or has a high-resistance connection. If the meter reads zero, as it should, you will have to go to another test point. In this case, place the positive voltmeter lead on the positive terminal of the tail light. If the voltmeter reads +12 volts, the light bulb is probably burned out or the light socket is defective. If the voltmeter reads zero, then the open is between terminal 1 of TB2 and the light.

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

3-21 UNCLASSIFIED 3.4.7 Terminal Diagram A terminal diagram is useful when connecting wires to terminal boards, relays, switches, and other components of a circuit. Figure 3-12 shows two typical terminal diagrams. View A of the figure shows the wire numbers connected to each terminal of a terminal board. View B shows the different color codes of the wires that are connected to a relay.

This has been a brief overview of the use and interpretation of electrical diagrams. The diagrams used were selected because of their simplicity and ease of interpretation. Many diagrams you will encounter are far more complex. Start with the simpler diagrams you will be working with on the job. Your proficiency in using the more complex diagrams will increase with experience and study.

Figure 3-12 Terminal diagrams

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

3-22 UNCLASSIFIED Q13. What type of diagram is the most detailed? Q14. Why must a wiring diagram be used in conjunction with a schematic to troubleshoot a system? Q15. What type of diagram would be most useful for wiring a relay into a circuit? 3.5 SAFETY The Secretary of the Navy, in establishing a Department of the Navy safety program, stressed, "Safety is an inherent responsibility of command...." He further outlined that, "Assignment of safety responsibility at all echelons of command is a basic requirement." This means responsibility right down through the lowest rated personnel in the command. Most noncombat accidents can be prevented if all personnel cooperate in eliminating unsafe conditions and acts. To this end, each individual is responsible for understanding and applying safety rules, standards, and regulations in all activities. Safety consciousness will help prevent personal injury and damage to property.

Some safety precautions applicable to this module deal with fumes from synthetic insulation, breathing asbestos fibers, and working around/with electrical and electronic circuits and portable power tools.

3.5.1 Synthetic Insulation Almost without exception, the fumes from synthetic materials, such as plastics in high- temperature environments, are objectionable from the standpoint of health and safety. Fluoroplastics (FEP and polytetrafluoroethylene) resist decomposition at higher temperature better than most other plastics.

Exposure to fumes when working with fluoroplastics may cause a temporary flu-like condition similar to the metal fume fever (or "foundryman's fever"). These symptoms are commonly called polymer fume fever. They do not ordinarily occur until several hours after exposure, and pass within 36 to 48 hours, even in the absence of treatment.

One of the largest uses of fluoroplastics is as a wire and cable insulation. When insulated wiring is installed, soldering is a routine fabricating procedure, as is the use of a heated element to remove insulation. In neither of these operations do the combined effects of temperature, quantity of resin, and exposure time produce toxic conditions of significance, as long as normal ventilation is maintained.

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

3-23 UNCLASSIFIED Any special practices or precautions that may be required should follow the same common sense rules that apply to all soldering jobs. Prolonged soldering in confined spaces with restricted air circulation will require some ventilation for personal comfort. The same is true for open shop areas where a number of personnel are engaged in soldering or hot-wire stripping. Normal ventilation for personal comfort usually provides adequate safety. However, it is recommended that a small duct fan or "elephant trunk" exhaust be used at the workbench during soldering or wire stripping to carry away any toxic vapors.

3.5.2 Asbestos Although asbestos-free products have been developed, older products containing asbestos materials still exist and continue to be used in the Navy. One such product is asbestos insulation used on wiring in high-temperature areas aboard ships and in aircraft.

Because of the serious health hazards of asbestos exposure, the government has imposed strict occupational health and environmental protection standards for the control of asbestos. These standards must be strictly enforced and followed by all Navy personnel.

Asbestos is a general term used to describe several fibrous mineral silicates. Major uses of asbestos include asbestos cement products, floor tiles, fireproofing, high-temperature insulation, asbestos cloth, friction materials (such as brake linings and clutch facings), various gasket materials, and miscellaneous other products.

Inhaling asbestos fibers can produce disabling or fatal fibrosis of the lungs. Fibrosis of the lungs (asbestos) comes from inhaling asbestos fibers. Asbestos is a factor in the development of lung cancer as well as cancer of the gastrointestinal tract. It may take 20 to 40 years between initial exposure to asbestos and the appearance of a cancerous condition. Know where asbestos is in your environment and avoid or take precautions to prevent exposure.

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

3-24 UNCLASSIFIED 3.5.3 Electrical or Electronic Circuits and Portable Power Tools When working on electrical or electronic circuits, you must observe certain general precautions. The following is a listing of common sense safety precautions that you must observe at all times:

• Remember that electrical and electronic circuits often have more than one source of power. Take time to study the schematics or wiring diagrams of the entire system to ensure that all power sources are deactivated. • Remove all metal objects from your person. • Use one hand when turning switches on or off. Keep the doors to switch and fuse boxes closed, except when working inside or replacing fuses. • After first making certain that the circuit is dead, use a fuse puller (figure 3-13) to remove cartridge fuses.

Figure 3-13 Fuse puller

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

3-25 UNCLASSIFIED • All supply switches or cutout switches from which power could possibly be fed should be secured in the OFF or OPEN (safety) position and tagged (figure 3-14). The tagging procedures must be done in accordance with the appropriate manual or instruction for your field of training.

Figure 3-14 DANGER tag

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

3-26 UNCLASSIFIED • Keep clothing, hands, and feet dry if possible. When it is necessary to work in wet or damp locations, use a dry platform or wooden stool to sit or stand on, and place a rubber mat or other nonconductive material on top of the wood. Use insulated tools and molded insulated flashlights when you are required to work on exposed parts. In all instances, repairs on energized circuits must not be made with the primary power applied, except in an emergency, and then only after specific approval has been given by your commanding officer. When approval has been obtained to work on equipment with the power applied, keep one hand free at all times (BEHIND YOU OR IN YOUR POCKET). • Never short out, tamper with, or block open an interlock switch. • Keep clear of exposed equipment; when it is necessary to work on it, work with one hand as much as possible. • Avoid reaching into enclosures, except when it is absolutely necessary. When reaching into an enclosure, use rubber blankets to prevent accidental contact with the enclosure. • Make certain that equipment is properly grounded. • Turn off the power before connecting alligator clips to any circuit. • Never use your finger to test a "hot" line. Use approved voltmeters or other voltage-indicating devices.

3.5.3.1 High Voltage Precautions In addition to observing the general precautions just discussed, you must observe the following additional precautions when working with high voltages:

• Do NOT work with high voltage by yourself; have another person (safety observer), qualified in first aid for electrical shock, present at all times. This individual, stationed nearby, should also know the circuits and location of the switches controlling the equipment, and should be given instructions to pull the switch immediately if anything unforeseen happens. • Always be aware of the nearness of high-voltage lines or circuits. Use rubber gloves where applicable and stand on approved rubber matting. Not all so-called rubber mats are good insulators. • Always discharge the high voltage from components or terminals by using a safety probe. • Do NOT hold the test probe when circuits over 300 volts are tested.

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3-27 UNCLASSIFIED 3.5.3.2 Soldering Irons When using a soldering iron, always keep in mind the following precautions and procedures:

• To avoid burns, ALWAYS ASSUME that a soldering iron is hot. • Never rest a heated iron anywhere but on a metal surface or rack provided for this purpose. Faulty action on your part could result in fire, extensive equipment damage, and serious injuries. • Never use an excessive amount of solder, since drippings may cause serious skin or eye burns. • Do not swing an iron to remove excess solder. Bits of hot solder that are removed in this manner can cause serious skin or eye burns. Hot solder may also ignite combustible materials in the work area. • When cleaning an iron, use a cleaning cloth, but DO NOT hold the cleaning cloth in your hand. Always place the cloth on a suitable surface and wipe the iron across it to prevent burning your hand. • Hold small soldering jobs with pliers or a suitable clamping device to avoid burns. Never hold the work in your hand. • Do not use an iron that has a frayed cord or damaged plug. • Do not solder components unless the equipment is disconnected from the power supply circuit. Serious burns or death can result from contact with a high voltage. • After completing the task requiring the use of soldering iron, disconnect the power cord from the receptacle and, when the iron has cooled, stow it in its assigned storage area.

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3-28 UNCLASSIFIED 3.5.3.3 Portable Electric Power Tools Navy specifications for portable electric power tools require that the electric cord of each tool have a distinctively marked ground wire in addition to the conductors for supplying power to the tool. (Double-insulated portable electric tools obtained from sources qualified under the applicable military specification are exempt from this grounding requirement.) The end of the ground wire within the tool must be connected to the metal housing of the tool. The other end must be connected to a positive ground. For this ground connection, specifically designed ground-type plugs and receptacles, which automatically make this connection when the plug is inserted into the receptacle, must be used. These grounded-type receptacles must be installed for all power outlets. When installed, they must be used with the grounded-type plugs to ground portable tools and equipment. If grounded-type receptacles have not yet been installed, they must be installed as soon as possible. Portable tools not provided with the ground-type plug, and miscellaneous portable electric equipment that does not have a cord with a ground conductor and grounded plug, must be given a three-conductor cord with a standard Navy grounded-type plug. The ground wire must be connected to a positive ground.

Care must be exercised in connecting the plugs and cords. The grounding conductor of the cord must be connected to the ground contact of the plug at one end and to the metal equipment housing at the other end. The cord must be arranged so as not to create a tripping hazard. If the conductor connected to the metallic equipment housing is inadvertently connected to a line contact of the plug, a dangerous potential would be placed on the equipment casing. This could result in a fatal shock to the operator. If the cord is pulled loose from the plug, only a qualified electrician is authorized to repair it.

If the grounded-type plugs and receptacles have not been installed in the spaces where a portable tool is to be used, other types of plugs and receptacles may be used only if a separate ground wire is connected between the tool housing and a positive ground. When the tool cord does not include an extra wire for grounding, an additional insulated wire should be connected between the metal housing of the tool and ground. If the tool housing has two or more conducting parts that are not electrically connected, each part must be connected to the ground wire. Connection of the ground wire to the tool housing and to the ground must be by means of screws or bolts. The use of spring clips for either end of the grounding wire is prohibited.

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3-29 UNCLASSIFIED When the ground connection is to be made by means other than a contact in the plug and receptacle, care must be taken to secure a good contact between the ground wire and the metal by scraping away paint from the metal to ensure a clean surface. The ground connection must be made before inserting the power supply connecting plug, and the plug must be pulled out before removing the ground connection. Frequent inspections of each of the connections of a portable electric tool must be made to ensure that the supply cord and its connections within the tool are suitably insulated and that the ground connection is intact.

The safety precautions just discussed are to protect you and your shipmates. Follow safety precautions to the letter. DO NOT TAKE CHANCES. Carelessness could cost you your life.

Q16. What safety precaution must you observe when soldering or hot-wire stripping fluoroplastic-insulated wire? Q17. What must be used to test an activated circuit? Q18. How should excess solder be removed from a hot soldering iron?

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

3-30 UNCLASSIFIED 3.6 SUMMARY In this chapter, we have discussed some typical cable- and wire-marking systems, electrical diagrams, and some basic safety precautions. A brief summary of these subjects follows:

Cable- and Wire-Marking Systems - Cables and wires must be identified to provide the technician with a means of tracing them when troubleshooting and repairing electrical and electronic systems. The cable and wire-marking systems discussed in this chapter are typical systems. The number of systems used throughout the Navy is too numerous to discuss. For the cable or wire identification for a specific piece of equipment, consult the technical manual for that equipment. One wire identification system you will surely come in contact with is the color coding of wires used on electrical power tools and appliances. Remember, the purpose of the green conductor in a power tool or appliance cable is to prevent electrical shock to the operator in case there is an electrical short to the frame of the appliance or tool.

Pictorial Diagram - shows a picture or sketch of the various components of a system and the wiring between the components.

Isometric Diagram - shows the outline of a ship, airplane, or piece of equipment. This diagram shows the components and the cable runs between the components. This diagram is used to locate components in a system.

Block Diagram - shows the components in block form. Block diagrams are used in conjunction with text material. They are used to present a general description of a system and its functions.

Single-Line Diagram - used for essentially the same purpose as the block diagram-to show the basic functions of a circuit.

Schematic Diagram - shows, through graphic symbols, the electrical connections and functions of a specific circuit arrangement. It is used to trace the circuit without regard to the physical size, shape, or location of the component devices or parts. A schematic diagram shows the overall operation of a system. It is used during troubleshooting to identify possible circuit malfunction locations.

Wiring Diagram - is a detailed diagram of each circuit installation showing all wiring, connectors, terminal boards, and the electrical or electronic components of the circuit. It also identifies the wire-by-wire numbers or color coding. This diagram must be used in conjunction with a schematic diagram to troubleshoot a system in order to find the test point for voltage and resistance checks.

Terminal Diagram - is used in connecting wiring to terminal boards, relays, switches, and other components of a circuit.

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

3-31 UNCLASSIFIED Safety - all individuals are responsible for understanding and complying with safety standards and regulations established to prevent injury to themselves and others and damage to property and equipment.

Having safe working habits and adhering to safety precautions protects YOU and YOUR SHIPMATES. Follow safety precautions to the letter. DO NOT TAKE CHANCES. Carelessness could cost you your life.

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

3-32 UNCLASSIFIED ANSWERS TO QUESTIONS Q1. THROUGH Q18.

A1. To provide the technician with a means to trace the wires when troubleshooting and repairing electrical and electronic systems.

A2. In the technical manual for the equipment.

A3. Individual cable in a specific circuit.

A4. Wire segment letter.

A5. The conductor connections both "to" and "from."

A6. To prevent electrical shock to the operator in case there is an electrical short to the frame of the appliance or too.

A7. A pictorial diagram.

A8. An isometric diagram.

A9. Block or single-line diagram.

A10. A schematic diagram.

A11. Between point (3) and the gas gauge tank unit ground.

A12. Only the brake lights.

A13. Wiring diagram.

A14. To find the test points.

A15. Terminal diagram.

A16. Adequate ventilation.

A17. Approved meters or other indicating devices.

A18. By use of a cleaning cloth.