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SECTION 9-3
INSTALLING CABLE STRAPS AND HANGERS
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1. UTILIZATION OF SPARES.
When the electronic installation worker needs to run a cable for a new installation, he should find out if there
are spare cables in existing wireways,
and spare stuffing tubes in bulkheads.
If no spares are available in wireways,
it will be necessary to make up additional straps and hangers.
2. METHOD OF MAKING STRAPS.
The material used in making straps is
strap steel, 3/4 inches x 3/32 inches for
overhead spans up to 6 inches wide. For
all vertical runs, horizontal runs and
overhead spans over 6 inches wide, use
3/4 inches x 1/8 inches steel.
Straps must fit the cables snugly to
avoid chafing and vibration that would
eventually damage the cables, so the
straps must be accurately formed. This
cannot be done easily on the job; it requires the use of shop equipment designed for convenience in forming straps
to any desired shape. This equipment
consists of a set of short, steel rods,
in sizes corresponding to the diameters
of all commonly used cables, and a
clamping mechanism for holding any desired grouping of these rods.
The strap is clamped, at one end, to
the rods and is formed to the shape of
the rods by use of a hammer and drive
bar. (See Figure 9-11).
Holes are then punched or drilled to
clear a 5/16 inch -18 machine screw at
appropriate locations. It is important
to file all sharp edges from the straps
and to remove any burrs from the
drilled or punched holes.
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Prior to mounting the cable straps, a
protective coating, such as zinc plating,
to give a good metal to metal contact between armor and cable strap, should be
given the straps in order to comply with
radio noise interference reduction requirements.
3. MOUNTING CABLE STRAPS.
Cable straps are supported by means
of pads, studs, and hangers. Pads are
round pieces of steel, usually 9/16 inch
in diameter by 3/8 inch thick, drilled and
tapped for ANS, right hand, 5/16 inch- 18
threads with class 2 fit. They are welded
to the ship's structure so that the cable
straps can be screwed in place. Installing pads is easiest when they are
drilled and tapped and secured to the cable
strap. Spot weld or tack the pads and
then remove the cable strap before welding the pad entirely to prevent damage to
the strap.
Pads or studs may be used on bulkheads not subject to condensation or
moisture. Hangers are used where condensation occurs or where the bulkhead
is insulated. Where aluminum bulkheads
or overheads are encountered, drilling
and riveting or bolting may be necessary
to secure the hangers or straps.
No attempt will be made here to outline all the procedures to be followed for
all the various conditions one encounters.
These are found in BuShips 9-S-3980-L
Alt. 27. Some of the more commonly
encountered conditions are shown in Figure 9-2 to Figure 9-7.
Studs, attached to the ship by the stud
welding process (Fig. 9-8) may be used
to support cable straps. Studs are a
type of headless machine bolt welded to
steel bulkhead or overhead.
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9-20
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FIGURE 9-2
METHODS OF SUPPORTING SINGLE CABLES
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9-21
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FIGURE 3
METHODS OF SUPPORTING CABLES |
9-22
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FIGURE 9-4
METHOD OF SUPPORTING A SINGLE ROW OF CABLES
ON STEEL DECKS AND W.T. BULKHEADS
FIGURE 9-5
METHOD OF SUPPORTING MULTIPLE ROWS OF
CABLES ON STEEL DECKS
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9-23
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FIGURE 9-6
METHOD OF SUPPORTING TWO ROWS
OF CABLES ON STEEL BULKHEADS
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9-24
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FIGURE 9-7
METHOD OF SUPPORTING TWO ROWS OF CABLES ON STEEL
BULKHEADS HAVING INSULATION
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9-25
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Figure 9-8
STUD SECURED BY THE WELDING PROCESS
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9-26
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They are available in sizes 1/4 inch,
5/16 inch and 3/8 inch. Hexagonal nuts
and lock washers are used with them.
Another type of stud known as the collar
stud has a shoulder, which allows the
securing nut to be turned down to the
shoulder thus giving a spacing between
the cable and the bulkhead or overhead.
Before mounting cable straps, make a
thorough inspection of all spaces the cable
will go through. Avoid obstructions, hot
objects, and unventilated spaces if practicable. Locate places where watertight bulkheads must be drilled and mark
the location for drillers, allowing space
for the welder to work all around stuffing
tubes. Inspect both sides of a bulkhead
before drilling to check clearance and
avoid damage.
Mark the location of hangers, pads, or
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studs used in the cable run for welder.
If the surface over which the cable is
to run is insulated, cut away the
insulation where the hangers or studs are to
be welded, allowing just enough space
for the welder to work. If studs are used,
it is necessary to grind the steel surfaces to a bright finish before welding.
Hanger spacing should not exceed 16
inches center to center. After all the
hangers and clamps are in place, the
cable is run as described in "Installation in Wireways". When running cables
across beams, and in order to avoid obstructions and preserve alignment of
the cable run, make use of cable supports
(Figure 9-9) and extended cable hangers .
When going through decks, a kickpipe
(Figure 9-10) will usually be necessary
to protect the cable from damage.
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9-27
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FIGURE 9-9
METHOD OF SUPPORTING CABLE USING CHANNEL |
9-28
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FIGURE 9-10
TYPICAL KICKPIPE ASSEMBLY
CABLE SUPPORTS |
9-29
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FIGURE 9-11
CABLE STRAP FORMATION |
9-30
SECTION 9-4
INSTALLATION IN WIREWAYS
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1. INTRODUCTION.
Because cable runs should be as direct
as possible, wireways should be planned
before the development of deck wiring
plans. While this is mainly a function
of the design section, some considerations in planning are presented to acquaint
the installation worker with some of the
problems involved. The plan for wireways should provide for:
a. Protection from battle damage
b. Circuit trunking
c. Protection from excessive heat
d. Protection from excessive
moisture
e. Protection in hazardous locations
f. Minimum interference with
machinery removal
g. Spare wireway area for future
expansion
h. Cables to guns and directors
i. Cables away from the magnetic
compasses
The greater part of cable installation
in wireways is usually done while a ship
is still on the ways, with no equipment
aboard. This work is handled by the
electrical group. However, an understanding of installation methods and
practices will benefit the electronic
installation men when equipment is added
or short runs must be made.
Tools and material necessary for the
average cable run are as follows:
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Wrench (adjustable, open-end,
for stuffing-tube gland nuts)
Black 1 inch friction tape, packing material (see section on
stuffing tubes)
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Plastic sealer, hacksaw, knife,
diagonal cutters, screw driver,
side cutters, armor strippers,
lacing cord and shuttle.
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A spin-tite wrench and box wrench
are very useful in tightening down the
5/16 inch - 18 hex machine screw used
with pads. Round head machine screws
may also be used.
2. HANDLING CABLE.
a. BENDING. - In handling cable,
both before and during installation, care
should be taken to avoid abrasion and
crushing, or sharp bends made without
the aid of a mandrel. Such bends are
most likely to occur when a cable is
taken off a reel or unwound from a coil.
Sharp "kinks", if pulled on, can ruin that
section of cable by causing internal
damage to insulation. All bends should
be made with a radius no less than the
minimum given in the table.
Where cables spread out to enter bulkhead stuffing tubes, the bends should be
given a generous sweep to allow for
flexibility at this point. Sufficient flexibility should exist to allow for deflection of the bulkhead without subjecting
the cables to destructive tension or
shearing. Run enough excess cable to
permit repairs to be made at cable ends
and to avoid cable renewals.
b. LOW TEMPERATURES. - Cables
become stiff at temperatures below
35°F and must be handled extra carefully to avoid cracking or rupturing the
sheath or the insulation.
Any compartment in which cables are
being installed should be heated and the
cables should be handled only when their
temperature is above freezing.
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9-31
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If cable must be installed in a compartment at 35°F. or below, stow the cable
first in a compartment heated to at least
50°F. but not over 120°F. , and leave it
there until it is warm enough so that installation in the cold compartment can
be completed before the cable cools down.
Cable installations can be made successfully, at or slightly below 35°F. by
handling the cable very carefully. While
pulling the cable into the wireways, the
radius of bend should be no shorter than
absolutely necessary.
The part of the cable where a bend is
to be made in putting it into its final
position should be heated with a portable,
warm-air blower. The bend should not
have a radius less than the minimum
given in the cable bend data tables.
3. GROUPING CABLES.
When grouping cables in wire-ways,
arrange those types and sizes of cable
that can be bent on the shortest radius on
the inner side of the cable group, allowing the cables that cannot be bent as
sharply to be placed on the outside of the
group (Figure 9-12). Avoid grouping
together cables which will result in building up of electrical disturbances or interfere with the proper functioning of the
electrical circuits involved. All shipboard circuits may be classified as either
low level, medium high level, or high
level for the purposes of grouping.
Low level circuits are those circuits
which normally carry small levels of
useful signal (1000 microvolts or less),
such as transducer lead-ins.
Medium high level circuits are those
which normally carry useful signals in
the order of several volts or less such
as audio amplifiers.
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High level circuits are those which
normally carry high levels of power such
as ships service power supply.
All low level circuits should be physically removed as far as practicable from high
level circuits.
EXAMPLE: Radar pulse cables are causing serious interference trouble on low
level cables, such as sonar cables to the
transducer. Separation of these circuits
is essential to the proper operation of the
sonar system.
4. LAYING CABLE IN WIREWAYS.
From the reels, cables should be "walked
in" cable runs. Only the manual efforts
of the installation crew are used to pull
cables. Under no circumstances should
block and tackle, chain falls, or other
mechanical devices be used to pull cables
taut.
The sag between hangers should be the
same for large and small cables and
should be maintained uniform between all
hangers in the run. Such sag should not
exceed one inch.
Temporary cable straps, made oversize
without cable outline, are useful in arranging cables neatly as work along a wireway proceeds. They are installed at
positions ahead of those being worked
upon and support the cables loosely. Soft
baling wire may be used to support cables
in hangers temporarily, especially at
bends. Permanent straps are installed
after the cables are properly arranged
with regard to break-offs and separation
into two or more wireways. After the
cables are located in the wireway, tighten
the straps so that they hold the cable but
are not so tight as to cause deformation
of cables or to prevent lengthwise movement of the cables.
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9-32
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FIGURE 9-12
ARRANGING CABLES IN WIREWAYS |
9-33
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5. PASSING THROUGH BULKHEADS.
a. NWT BULKHEADS. - Where cables
pass through non-watertight bulkheads
or beams that are 1/4 inch thick or over,
no stuffing tubes are used, but the clearance holes should be drilled slightly
larger than the cable and the edges of
the holes rounded off to prevent chafing
of the leads. Where non-watertight
beams or bulkheads are under 1/4 inch
in thickness, standard or special bushings
as shown in Figure 9-13A, 13B, and
13C should be used. On all non-watertight bulkheads, where sharp bends occur
in the cables immediately after passing
through such holes, standard or special
bushings are used.
b. WT BULKHEADS. - When cables
pass through W T bulkheads they will
feed through W T stuffing tubes. The
usual practice is to stuff and pack the
tubes as they are encountered along the
cable run. Avoid using a screw driver
for packing as this may damage threads
and insulation. A tool similar to the
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packing stick described in section on tools
is recommended. Proper packing
methods are described in the section on
stuffing tubes.
6. APPLIANCE ENTRANCES.
Where cables enter into vertically installed NWT appliances, avoid entering
the appliance from the top. Water
should not accumulate in NWT appliances,
but condensation can run down a cable
entering at the top and cause a failure.
If possible enter at the bottom or side.
When an entrance at the bottom is made,
take care that the cable end is taped and
sealed to prevent the entrance of moisture
into the interior of the cable (Figure 9-14).
Commercial cable clamps (Figure 9-15)
(Greenfield Connectors) are widely used
where cables enter NWT appliances.
These are discussed in the chapter on
stuffing tubes.
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19-34
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FIGURE 9-13A
METHODS CF RUNNNG CABLES
THROUGH N.W.T. BULKHEADS
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9-35
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FIGURE 9-13B
METHODS OF RUNNING CABLES
THROUGH N.W.T. BULHEADS
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9-36
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FIGURE 9-131C
METHODS OF RUNNING CABLES
THROUGH N.W.T. BULKHEADS
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9-37
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FIGURE 9-14
METHODS OF MAKING UP CABLE ENDS
CABLE ENTERING BOTTOM OF ENCLOSURE
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9-38
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FIGURE 9-15
CABLE CLAMPS-COMMERCIAL TYPE
FORMED SHEET STEEL
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9-39
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