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SCHEMATIC READING

LEARNING OBJECTIVES

Upon completing this chapter, you should be able to:

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

SCHEMATIC READING

This chapter is divided into three subtopicss - (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.

CABLE-MARKING SYSTEMS

Two typical cable-marking systems you are likely to see are the (1) shipboard and (2) test equipment cable-marking systems.

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.

Q.1 Why must cables and wires be identified?
Q.2 Where would you find the wire identification system for a specific piece of equipment?
Q.3 What does the cable number identify?