MIL-DTL-24784 / 21B (SH)
1.
Unit power and grounding FCD. Unit power and grounding FCDs shall show the
generation and distribution of power to all assemblies within the unit. All cable,
connector, and pin numbers shall be shown except those listed on sheet 1 as unused.
Cabinet-mounted parts shall be shown in schematic form. All power supplies and
regulators that are packaged as complete assemblies shall be shown in symbolic form.
Lowest level replaceable assemblies shall not be further detailed in detailed FCD form.
Since a power and grounding FCD is a schematic diagram rather than a wiring diagram,
it does not show routing of wires, but it shall show the continuities that exist. Several
types of circuit returns may exist in the system: (1) ground, (2) chassis or frame
connection, and (3) common connections. Each of these grounds shall be shown by
using symbols where it shall simplify the FCD (see figure 21-29).
a)
Prime power inputs shall be shown on the left of the FCD and signal flow shall be
left-to-right. Grounds shall be shown by using the symbols illustrated in IEEE 315.
The layout of circuit parts shall follow a logical arrangement and be consistent with
other unit-oriented power and grounding diagrams; for example, primary AC
distribution, power control and indication, interlocks, gate monitoring and gate
distribution. Also, unnecessary long lines shall be shortened to conserve space. The
hardware boundaries can be distorted where necessary, to preserve smooth signal
flow. Crossed lines and "doglegs" shall be kept to a minimum.
b) Each relay and switch element or contact set shall be identified. If the switch is a
front panel control, and it is accessible during normal equipment operation, the
nomenclature of the switch exactly as it appears on the front panel shall be placed
adjacent to the switch symbol. When multisection switches or relays have more than
one element or contact set, the sets or elements shall be identified individually but
with some alpha- numeric relationship. It is desirable to align the contact sets if
possible, but not at the expense of disturbing functional flow. Relays and switches
will not necessarily have their contact sets in the same functional area; often they
will function in different circuits. When this occurs, the various sets of contacts and
actuating elements shall be connected by a dashed line (if on different FCD sheets,
sheet and zone references shall be used to connect the dashed line) to illustrate
mechanical linkage. Spare contact sets of switches and relays shall not be shown on
the body of the diagram.
3.5.1.3.1 Requirements for preparing FCDs. A clear and complete referencing system is
required for use on FCDs because of the interrelationship between FBDs and FCDs, and the
interconnection between sheets of FCDs. The referencing system shall include all or a portion of
the following reference information:
a.
Signal names.
1.
Major or important signal paths on an FCD shall be identified by descriptive signal
names. All signal lines that interface between FCD sheets shall be identified by
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