NEETS Module 4—Introduction to Electrical Conductors, Wiring Techniques, and Schematic Reading
Pages i - ix
, 1-1 to 1-10
1-11 to 1-20
, 1-21 to 1-28
2-1 to 2-10
,2-11 to 2-20
2-21 to 2-30
, 2-31 to 2-40
2-41 to 2-53
, 3-1 to 3-10
3-11 to 3-20
, 3-21 to 3-24
to 4-10, 4-11 to 4-18, Index
Figure 3-10—Schematic diagram.
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.
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.
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?
If the fuse shown on the schematic (figure 3-10) opens, what lights will operate?
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.
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.
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. TERMINAL DIAGRAM
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
Figure 3-12.—Terminal diagrams.
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.
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?
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.
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
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
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
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. ASBESTOS
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
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
· 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.
!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.
· 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.
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
· Do NOT hold the test probe when circuits over 300 volts are tested.
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
· 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. Portable Electric
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.
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?
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
—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.
—Examples of electrical diagrams you will be required to "read"
(interpret) and their uses are as follows:
—Shows a picture or sketch of the various components of a system and
the wiring between the components. This diagram is used to identify the components of a system.
Introduction to Matter, Energy, and Direct Current,
to Alternating Current and Transformers, Introduction to Circuit Protection,
Control, and Measurement
, Introduction to Electrical Conductors, Wiring Techniques,
and Schematic Reading
, Introduction to Generators and Motors
Introduction to Electronic Emission, Tubes, and Power Supplies,
Introduction to Solid-State Devices and Power Supplies
Introduction to Amplifiers, Introduction to
Wave-Generation and Wave-Shaping Circuits
, Introduction to Wave Propagation, Transmission
Lines, and Antennas
, Microwave Principles,
, Introduction to Number Systems and Logic Circuits, Introduction
to Microelectronics, Principles of Synchros, Servos, and Gyros
Introduction to Test Equipment
, Radar Principles,
The Technician's Handbook,
Master Glossary, Test Methods and Practices,
Introduction to Digital Computers,
Magnetic Recording, Introduction to Fiber Optics