NEETS Module 4 − Introduction to Electrical Conductors, Wiring
Techniques, and Schematic Reading
3−21, 4−1, 4−11, Index
and Direct Current
||Alternating Current and Transformers
||Circuit Protection, Control, and Measurement
||Electrical Conductors, Wiring Techniques,
and Schematic Reading
||Generators and Motors
||Electronic Emission, Tubes, and Power Supplies
||Solid-State Devices and Power Supplies
||Wave-Generation and Wave-Shaping Circuits
||Wave Propagation, Transmission Lines, and
||Introduction to Number Systems and Logic Circuits
||- Introduction to Microelectronics
||Principles of Synchros, Servos, and Gyros
||Introduction to Test Equipment
||Radio-Frequency Communications Principles
||The Technician's Handbook, Master Glossary
||Test Methods and Practices
||Introduction to Digital Computers
||Introduction to Fiber Optics
|Note: Navy Electricity and Electronics Training
Series (NEETS) content is U.S. Navy property in the public domain.
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
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.
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.
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.
Two typical cable-marking systems you are likely to see are the (1) shipboard
and (2) test equipment
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.
Figure 3-1. - Cable tag.
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.
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?
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.
Figure 3-2. - Test equipment cable marking.
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.
Wire-marking systems are used to identify wires in aircraft, shipboard electronic
power tool and appliance cables.
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.
Figure 3-3. - Aircraft wire marking.
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.
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?
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
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):
Figure 3-4. - Designating conductor marking between unlike terminals.
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.
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.
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 appliance 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?
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.
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.
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.
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
Figure 3-7. - Isometric 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.
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.
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.
Figure 3-9. - Single-line diagram.
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
Q9. What types of diagrams are the most convenient from which
to learn the basic Functions of a circuit?
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.