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To interpret shipboard electrical prints, you need to recognize the graphic symbols for electrical diagrams and the electrical wiring equipment symbols for ships as shown in Graphic Symbols for Electrical and Electronic Diagrams, ANSI Y32.2, and Electrical Wiring Equipment Symbols for Ships' Plans, Part 2, MIL-STD-15-2. Appendix 2 contains the common symbols from these standards. In addition, you must also be familiar with the shipboard system of numbering electrical units and marking electrical cables as described in the following paragraphs.

Numbering Electrical Units

All similar units in the ship comprise a group, and each group is assigned a separate series of consecutive numbers beginning with 1. Numbering begins with units in the lowest, foremost starboard compartment and continues with the next compartment to port if it contains familiar units; otherwise it continues to the next aft compartment on the same level.

Proceeding from starboard to port and from forward to aft, the numbering procedure continues until all similar units on the same level have been numbered. It then continues on the next upper level and so on until all similar units on all levels have been numbered. Within each compartment, the numbering of similar units proceeds from starboard to port, forward to aft, and from a lower to a higher level. Within a given compartment, then, the numbering of similar units follows the same rule; that is, LOWER takes precedence over UPPER, FORWARD over AFT, and STARBOARD over PORT.

Electrical distribution panels, control panels, and so forth, are given identification numbers made up of three numbers separated by hyphens. The first number identifies the vertical level by deck or platform number at which the unit is normally accessible. Decks of Navy ships are numbered by using the main deck as the starting point as described in Basic Military Requirements, NAVEDTRA 12043. The numeral 1 is used for the main deck, and each successive deck above is numbered 01, 02, 03, and so on, and each successive deck below the main deck is numbered 2, 3, 4, and so on.

The second number identifies the longitudinal location of the unit by frame number. The third number identifies the transverse location by the assignment of consecutive odd numbers for centerline and starboard locations and consecutive even numbers for port locations. The numeral 1 identifies the lowest centerline (or centermost, starboard) component. Consecutive odd numbers are assigned components as they would be observed first as being above, and then outboard, of the preceding component. Consecutive even numbers similarly identify components on the portside. For example, a distribution panel with the identification number, 1-142-2, will be located on the main deck at frame 142, and will be the first distribution panel on the port side of the centerline at this frame on the main deck.

Main switchboards or switchgear groups supplied directly from ship's service generators are designated 1S, 2S, and so on. Switchboards supplied directly by emergency generators are designated 1E, 2E, and so on. Switchboards for special frequencies (other than the frequency of the ship's service system) have ac generators designated 1SF, 2SF, and so on.

Sections of a switchgear group other than the generator section are designated by an additional suffix letter starting with the letter A and proceeding in alphabetical order from left to right (viewing the front of the switchgear group). Some large ships are equipped with a system of distribution called zone control. In a zone control system, the ship is divided into areas generally coinciding with the fire zones prescribed by the ship's damage control plan.

Electrical power is distributed within each zone from load center switchboards located within the zone. Load center switchboards and miscellaneous switchboards on ships with zone control distribution are given identification numbers, the first digit of which indicates the zone and the second digit the number of the switchboard within the zone as determined by the general rules for numbering electrical units discussed previously.

Cable Marking

Metal tags embossed with the cable designations are used to identify all permanently installed shipboard electrical cables. These tags (fig. 6-1) are placed on cables as close as practical to each point of connection on both sides of decks, bulkheads, and other barriers. They identify the cables for maintenance and replacement. Navy ships use two systems of cable marking; the old system on pre-1949 ships, and the new system on those built since 1949. We will explain both systems in the following paragraphs.

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