Module 4 - Introduction to Electrical Conductors, Wiring Techniques,
and Schematic Reading
Navy Electricity and Electronics Training Series (NEETS)
Chapter 3:  Pages 3-11 through 3-20

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,
 
 

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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.
 
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?
 
 

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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.

 
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
 
 

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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.
 
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.
 

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.
 
 

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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?
 

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.
 
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.
 
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
 
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.
 
 

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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.
 
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.

 
!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.
 
 

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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.

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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.
 

 
Electrical Diagrams - Examples of electrical diagrams you will be required to "read" (interpret) and their uses are as follows:
 

 
Pictorial Diagram - 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.
 
 

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NEETS Table of Contents

• Introduction to Matter, Energy, and Direct Current
• Introduction 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
• Modulation Principles
• Introduction to Number Systems and Logic Circuits
• Introduction to Microelectronics
• Principles of Synchros, Servos, and Gyros
• Introduction to Test Equipment
• Radio-Frequency Communications Principles
• Radar Principles
• The Technician's Handbook, Master Glossary
• Test Methods and Practices
• Introduction to Digital Computers
• Magnetic Recording
• Introduction to Fiber Optics