two-, T for three-, and F for four-conductor cables. The
number following this letter denotes the wire’s circular
mil area in thousands. For example, the cable supplying
distribution box symbol 615 (fig. 6-2) is marked
(2-38-1)-L-Al-T-g. This marking identifies a three-con-
ductor, 9000-circular mil, 120-volt, ship’s service sub-
main lighting cable supplied from panel 2-38-1. Note
that you would need the isometric wiring diagram for
the main deck and above to follow the complete run of
this cable. This print would show lighting main
2(38-l)-lL-A-T-30 supplying a distribution box some-
where on the main deck (or above), and submain cable
(2-38-l)-IL-Al-T-9 coming from this distribution box
to supply distribution box symbol 615 on the second
platform, frame 19 starboard.
Remember, the isometric wiring diagram shows
only the general location of the various cables and
fixtures. Their exact location is shown on the wiring
plan discussed briefly in the next paragraphs.
Wiring Deck Plan
The wiring deck plan is the actual installation dia-
gram for the deck or decks shown and is used chiefly in
ship construction. It helps the shipyard electrician lay
out his or her work for a number of cables without
referring to individual isometric wiring diagrams. The
plan includes a bill of material that lists all materials and
equipment necessary to complete installation for the
deck or decks concerned. Equipment and materials
except cables are identified by a symbol number both
on the drawing and in the bill of material.
Wiring deck plans are drawn to scale (usually 1/4
inch to the foot), and they show the exact location of
all fixtures. One blueprint usually shows from 150 to
200 feet of space on one deck only. Electrical wiring
equipment symbols from MIL-STD-15-2 are used to
represent fixtures just as they do in the isometric
wiring diagram.
Elementary Wiring Diagram
These diagrams show in detail each conductor,
terminal, and connection in a circuit. They are used to
check for proper connections in circuit or to make the
initial hookup.
In interior communication (IC) circuits, for
example, the lugs on the wires in each connection are
stamped with conductor markings. The elementary
wiring diagrams show these conductor markings
alongside each conductor and how they connect in the
circuit. Elementary wiring diagrams usually do not
show the location of connection boxes, panels, and so
on; therefore, they are not drawn to any scale.
Electrical System Diagrams
Navy ships have electrical systems that include
many types of electrical devices and components.
These devices and components may be located in the
same section or at various locations throughout the
ship. The electrical diagrams and drawings necessary
to operate and maintain these systems are found in the
ship’s electrical blueprints and in drawings and
diagrams in NAVSHIPS’ and manufacturers’
technical manuals.
BLOCK DIAGRAM.—These diagrams of
electrical systems show major units of the system in
block form. They are used with text material to present
a general description of the system and its functions.
Figure 6-3 shows a block diagram of the electrical
steering system for a large ship. Look at the diagram
along with the information in the following
paragraphs to understand the function of the overall
system.
The steering gear system (fig. 6-3) consists of two
similar synchro-controlled electrohydraulic systems;
one for each rudder (port and starboard). They are
separate systems, but they are normally controlled by
the same steering wheel (helm) and they move both port
and starboard rudders in unison. Each port and star-
board system has two 100 hp main motors driving a
variable-stroke pump through reduction gears. Each
also has two 5-hp servo pump motors interconnected
electrically with the main pump motors so both operate
simultaneously. During normal operation, one main
pump motor and one servo pump motor are used with
the other units on standby. If the normal power supply
fails, both port and starboard transfer switchboards may
be transferred to an emergency 450-volt supply.
The steering system may be operated from any one
of three steering stations located in the pilothouse, at
a secondary conn, and on the open bridge. A
transmitter selector switch in the IC room is used to
assign steering control to any of the three. To transfer
steering control from the pilothouse to the open bridge
station, the selector switch in the IC room must be in
the pilothouse position. Duplicate power and control
cables (port and starboard) run from a cable selector
in the IC room to port and starboard cable selector
switches in the steering gear room. From these
switches, power and control cables connect to receiver
selector switches. These selector switches allow
selection of the appropriate synchro receiver for the
system in operation.
6-5
