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Here is the "Electrician's Mate 3 - Navy Training Courses"
(NAVPERS 10548) in its entirety (or will be eventually). It should provide one of
the Internet's best resources for people seeking a basic electricity course - complete
with examples worked out. See
copyright.
See Table of Contents.
¶ U.S. GOVERNMENT PRINTING OFFICE;
1949
CHAPTER 16
BLUEPRINT READING AND SKETCHING
INTRODUCTION
Electrical wiring drawings or blueprints are maps which show you' the location and circuit connections of
every piece of electrical equipment aboard ship. Blueprints properly used are an invaluable aid "trouble
shooting", in other words, in isolating faults in an electrical circuit. This is undoubtedly the most important
work of the naval electrician. You should therefore study the training course Use of Blueprints (NavPers
10621) to get a basic understanding of how blueprints are made and used. Then read tills chapter and you will know
all the information that goes into Navy wiring blueprints and how to use it.
Mechanical drawing in the
form of sketching frequently is used by the electrician in the event some electrical part is to be constructed in
one of the ship's shops. A correctly made drawing will give a complete pictorial description of the part and
therefore aid greatly in its construction. For this reason a brief review of what you learned in Use of
Blueprints, and a few suggestions as to the layout of simple mechanical drawings, are included in this
chapter.
PRODUCTION, CARE, AND FILING OF BLUEPRINTS
Blueprints are made from drawings in much the same manner that photographs are made from negatives. The
negative for the blueprint is known as a TRACING. It is made by placing a sheet of special white, semi-transparent
paper on cloth over the working drawing. Everything on the drawing is traced on the tracing cloth with black
waterproof ink or a special black pencil. Some drawings are made directly on the tracing material in pencil, then
traced with ink or the special black pencil. This short cut saves time and material and is satisfactory for most
jobs.
To produce a blueprint the tracing is placed on a pane of clear glass mounted in a special frame. The
tracing is covered with a sheet of chemically coated, light-sensitive blueprint paper. A padded back is secured
behind the blueprint paper to keep the two sheets together. The front of the frame is then exposed to a strong
light, which projects through the tracing onto the coated side of the blueprint paper.
After proper amount
of exposure, the print is removed and washed in clear water to remove the unexposed chemical. The exposed portions
of the print paper turn a deep blue during the washing. The lines will be white.
Blueprints are not always
blue. They may be white, brown, black, gray, or other colors. The difference lies in the kinds of light-sensitive
chemical on the paper, and in the development processes required for that chemical. But the process of making the
print is the same - you project a light through the tracing onto the light-sensitive paper.
Blueprints are
valuable permanent records and if properly cared for can be used many times. Listed below are a few simple rules
for getting the best results from your blueprints.
KEEP them OUT OF STRONG SUNLIGHT, as they may fade.
Do NOT ALLOW them TO GET WET or grease smudged.
Do not pencil or crayon notations without proper authority. If you should get instructions TO MARK A BLUEPRINT,
USE A YELLOW PENCIL. Black pencil marks are hard to see on a colored background.
Frequently used blueprints
should be glued to a sheet of cardboard. Cover the face with a coating of clear shellac.
FILING OF BLUEPRINTS
Blueprints are filed in the log room. The bulk of the electrical equipment aboard ship is provided by the
Bureau of Ships and is shown on Bureau of Ships drawings. The Bureau of Ships system of designating and filing
blueprints is desc6bed in the next few paragraphs. Turret and mount electrical installations are furnished by the
Bureau of Ordnance and are shown on BuOrd drawings. The system of designating and filing BuOrd drawings is
described following the BuShips system.
For BuShips drawings, all filing will be separated into letter groups.
The prints an electrician will work with will be filed in the "S" group, covering Ship Materials. There are 94
separate divisions in the "S" group. A power distribution blueprint would be in group S-62, a lighting
distribution print would be in group S-64. To locate the print you desire refer to the Na'l1J Filing A1anual to
determine the division of the "S" group your circuit would be classified under and then look in the files for that
division of the group.
Each print of a circuit or piece of equipment installed by a Navy yard will have an index, group, and file
number on it. Figure 148 shows a typical index group and file marking of a BuShips blueprint. The letters on the
left denote the type of ship and the number of the ship in that class.
RF Cafe -
Electrician's Mate 3 - Navy Training Courses, NAVPERS10548 - Figure 148. - A blueprint index group and file
number.
Figure 148. - A blueprint index group and file number.
In the center of the box is the circuit classification. The right hand numbers are the file numbers of the group
indicated at center.
The index group and file markings of figure 148 indicate that this blueprint is from
the heavy cruiser Wichita, it is a lighting distribution print, and it is to be filed a2 #25 in the S-64 group of
files.
Bureau of Ordnance electrical drawings cover the electrical equipment and' wiring inside a turret
or mount and are identified primarily by the serial number of the drawing. The drawing title also tells the mount
or turret the equipment is part of, so to find the drawing for a piece of electrical equipment in a mount or
turret, you must know the BuOrd designation for that mount or turret. You find this out from the Gunner's Mate,
who can also provide you with the ordnance drawings, which are kept in the gunnery officer's office.
FUNDAMENTALS OF DRAFTING
Before you can thoroughly understand a blueprint and be able to sketch a drawing of your own, you must first
know the types of lines used. Figure 149 illustrates the different lines.
RF Cafe - Electrician's Mate 3 - Navy Training Courses, NAVPERS10548 - Figure 149. -
Types of lines in making drawings.
Figure 149. - Types of lines in making drawings.
The VISIBLE OBJECT lines represents visible edges, the outline of the object. If a surface is hidden from
sight but needs to be shown in some manner, use an INVISIBLE OBJECT line. This line will show the location and
extent of the hidden surface, and by rendering it broken, will- indicate that the surface represented is not from
this view. Visible and invisible object lines are used in figure 150.
Whenever the object drawn is
symmetrical about a common center, such as a shaft, a hole drilled in a casting, or any other circular object
(that is just alike on both sides of the center) a CENTER LINE is used to indicate the axis of the hole or shaft.
It is made of alternate dashes and single dots. Center lines should be drawn lightly. If a hole in an object is to
be indicated, horizontal and vertical center lines both should be shown.
DIMENSION LINES are light lines having arrowheads at their ends. They are used to show the dimensions of
the object. EXTENSION LINES are extensions of object lines. They indicate the limits of a dimension. The OBJECT
LINES of a drawing, full or broken, always are heavier than the center, extension and dimension lines. Object
lines are described as being number 1 lines in weight and all others number 2 in weight. The use of these lines is
illustrated in figure 151.
SYMBOLS
When a draftsman makes an electrical wiring diagram, he uses electrical abbreviations or symbols instead of
drawing each piece of electrical equipment in detail.- Unfortunately an identical piece of equipment may be
represented by an entirely different symbol by different draftsmen. Therefore, a single set of standard symbols
are difficult to prepare, but listed here are a few of the more common ones.
Actually there are two
complete lists of symbols - ELEMENTARY and SCHEMATIC. The ELEMENTARY SYMBOLS, shown in figure 150, are used on
wiring diagrams that SHOW each conductor and all the CONNECTIONS in the circuit. These symbols are more detailed
than the schematic symbols. SCHEMATIC SYMBOLS, some of which are shown in figure 154, are used to SHOW the
LOCATION and general layout of the circuit. The types of drawings in which the different types of symbols are used
are discussed in the later paragraphs on WIRING DRAWINGS.
Notice that no elementary symbols specify
watertightness while schematic symbols do. On the schematic list the symbols showing watertightness have a double
line. W. T. is the abbreviation for watertight. N. W. T. indicates that the piece of equipment represented is not
watertight.
RF Cafe - Electrician's Mate 3 - Navy Training Courses, NAVPERS10548
- Figure 150. - Electrical symbols.
Figure 150. - Electrical symbols.
ORTHOGRAPHICS
A drawing is a plan, sometimes a specification. Drawing' is a means of expression, and consequently is a form
of language. It is far better to give a machinist's mate a drawing of a sleeve bearing that you wish to have made
than to give him an oral description of the bearing.
The clearest method of representing an object is by
showing it in ORTHOGRAPHIC views. Orthographic comes from the word "ortho," which means at right angles to. An
orthographic view, therefore, is any drawing that shows true size and shape of one surface of an object when that
surface is at right angles or perpendicular to your line of vision.
RF Cafe -
Electrician's Mate 3 - Navy Training Courses, NAVPERS10548 - Figure 151. - Views of a block.
Figure 151. - Views of a block.
You may make as many orthographic views as the object has sides. If the object drawn has an irregular shape,
that is all its sides are different then the drawing will contain a view for each side. Seldom are more than two
or three views necessary to give a complete picture of an object. In all cases a correctly made orthographic
drawing contains as many views as necessary to give a complete description of an object. Figure 151 is an
orthographic drawing of a block. Six orthographic views of this object could be drawn. Careful inspection of the
object will reveal that the top and bottom are identical, and that there is no difference between the front and
black side, or right and left ends. Therefore, as shown in figure 151, only three views are necessary.
HOW TO MAKE A DRAWING
Following is a list of the general. steps to help you in sketching an orthographic drawing. Practice on simple
objects first, then try the more difficult.
Study the object and decide the combination of views that
will give the best description.
Block in outline views, in proper arrangement, with light construction
lines.
Build up the detail of each view, such as representing all invisible edges with broken lines.
Give each view its proper name and dimensions.
Check drawing for any possible errors.
Darken all object lines and erase construction lines which have no further purpose
to the drawing.
To satisfy step 1, bear in mind that an orthographic drawing needs only as many views as necessary to give a
complete picture of an object. All orthographic drawings should have the views presented in their proper relation.
That is, don't put end views on top, and bottom views on top. Referring to figure 151, you can see that all
horizontal measurements on both the front and top views are equal. This is the reason they are drawn IN LINE with
each other. The vertical measurements of the front and' end views sometimes are different and the arrangement of
the views is not always the same, but the same RELATIVE POSITION of the views in regard to each other always IS
THE SAME.
The scale of a drawing refers to the size of the drawing in relation to actual size of the
object. Thus when a drawing is made on a scale of 1 inch equals 1 foot, the size of the drawing is one twelfth of
the size of the object drawn. Before beginning any drawing determine the scale to be used and make a note of it on
the drawing.
ISOMETRICS
Often it is desirable to give a "picture drawing" in conjunction with an orthographic sketch so one may gain
an idea of the general shape and size of an object. This type of drawing is called PERSPECTIVE.
A
perspective drawing is to show an object exactly as it appears to your eye. A perspective drawing would show the
same outline that would appear in a photograph.
Your eye as well as the photograph and perspective drawing tell you things that aren't exactly true. Just
recall the last time you looked down a straight stretch of railroad track. Your eyes told you that the tracks came
together at a distant point. You knew the tracks were parallel so you didn't believe your eyes. The camera records
this deception and since the perspective drawing gives exactly what is seen to the eye, it also registers a lie.
The isometric drawing is similar to the perspective, but all parallel edges are drawn truly parallel. All its
lines representing horizontal and vertical lines on an object have true length. Vertical lines are shown in a
vertical position, but lines representing horizontal edges are drawn at an angle of 30° with the true horizontal.
Vertical lines and lines representing horizontals are known as isometric lines. The picture at the top of figure
151 is an isometric drawing.
Isometrics cannot be used alone for complicated parts or structures, but may
be used as an aid in clarifying the accurate orthographic drawings. Remember that no lines except the isometric
lines of an isometric drawing can be relied upon for true measurements.
SHIP COMPARTMENTATION AND EQUIPMENT MARKING
The different parts of a ship are named so you can talk about a certain part enabling another person to know
exactly what you are talking about.
Knowing how the different decks are numbered, how the compartments are
labeled, and how electrical equipment is numbered will enable you to work more readily from a wiring blueprint.
There are two types of decks, COMPLETE DECKS and PARTIAL DECKS. A complete deck is a deck running the full length
of the ship and a partial deck is a deck running only part of the length of the ship. Decks are named and numbered
according to their location above or below the main deck. The MAIN DECK is the topmost complete deck.
A partial deck that is one deck level above the main deck at the bow is called the FORECASTLE DECK; at the
stern, POOP DECK; amidships, UPPER DECK. A partial deck above the main, upper, forecastle, or poop deck and not
extending to the side of the ship is called a SUPERSTRUCTURE DECK.
A complete deck below the main deck is called the SECOND DECK. Where there are two or more complete decks
below the main deck, they are called .the SECOND DECK, THIRD DECK, FOURTH DECK, etc. A partial deck between two
full decks where vertical height permits is called a HALF DECK. A partial deck below the lowest complete deck is
called a PLATFORM. Where there are two or more partial decks below the lowest complete deck, the one immediately
below the lowest complete deck is called the FIRST PLATFORM, the next is called the SECOND PLATFORM, and so on.
The space below the lowest platform is referred to as the HOLD. The deck at the bottom of the hold is the HOLD
DECK.
Decks are numbered using the main deck as a reference level. The main deck is number 1 deck level.
The next deck below the main deck,' regardless of its name, is number 2 deck level; the second deck below the main
deck is number 3 deck level, and so on down to the hold deck.
The first deck above the main deck is 01 deck level, the second deck above the main deck is 02 deck level
and so on to the topmost deck of the ship.
A half deck takes the number of the deck directly below it. A
letter "H" precedes this number to denote a half deck. A half deck located between the main and second decks would
be numbered "H2".
As an example of how decks are numbered, consider a ship having a superstructure deck, an upper deck, a main,
second, and third deck, a first and second platform, and a hold deck. In addition to these decks there is a half
deck between the second and third decks. These decks will be numbered as follows:
| Superstructure deck ...... |
02 |
Third deck ................ |
3 |
| Upper deck .................... |
01 |
First platform ........... |
4 |
| Main deck ...................... |
1 |
Second platform ...... |
5 |
| Second deck .................. |
2 |
Hold deck ................. |
6 |
| Half deck ....................... |
H3 |
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COMPARTMENTS
Transverse bulkheads across the ship cut naval vessels into 3 or 4 main sections. These sections are labeled
A, B, 0, and D, from fore to aft. In a three-section ship, SECTION A extends from the bow to the first transverse
bulkhead of the engineering section. SECTION B includes the space from first bulkhead to the after bulkhead of the
engineering section. SECTION C comprises the remaining section aft.
In a four-section ship, the machinery
or engineering space is divided into two parts, sections Band 0, with SECTION D comprising the remaining spaces
aft. While the ship is considered as having only three or four main sections, that does not mean that there are
only two or three transverse bulkheads. There are, many others, all adding to the structure of the vessel and
contributing to its compartmentation and watertight integrity.
Compartments aboard ship are given letters
and numbers denoting the location and use of the compartment. The following compartment marking is an example:
A-201-L
| A |
2 |
01 |
L |
Section of
Ship |
Deck Level |
Position of Compartment in the Section |
Use of Compartment |
Taking the letters and numbers from left to right the first letter indicates the section of the ship the
compartment is located in. The first number tells us the deck level. The two numbers following the deck level tell
us whether the compartment is located on the port or starboard side of the ship and also give us the position of
the compartment fore and aft in the section.
Port side compartments have even numbers, starboard compartments odd numbers. The first compartment forward on
the port side of a general section in the ship is given the number 02, the next compartment aft of it on the port
side 04, etc. All numbers in each section begin at the forward end of that section.
The letter at the right
gives the use of the compartment. The list below is an explanation of the code -
A Storerooms.
B Gun and torpedo battery compartments.
C Ship control and fire control compartments.
E Machinery compartments.
F Fuel compartments.
LUB Lubricating oil storage compartments.
GAS Gasoline compartments.
L Living compartments.
M Ammunition storage compartments.
T Trunks and hatches.
V Void compartments.
W Water compartments.
All
compartments and spaces that are bounded completely by watertight, oiltight, airtight, or fumetight structures
have their own individual markings. Where a watertight compartment located below the, weather deck is divided into
two or more airtight or fumetight spaces by air tight or fume tight bulkheads, the appropriate number is assigned
the watertight compartment and each airtight or fumetight subdivision within the compartment is designated by the
addition of a suffix to this number. Thus if watertight compartment
A-312-L contains fumetight or airtight longitudinal (fore and aft) bulkheads, the space to starboard of this
bulkhead is designated as A-312-1L and the space to port as A-312-2L.
A half deck compartment has the letter H directly before the deck level.
Here are some examples:
B-301-E
| B |
3 |
01 |
E |
| Amidships Section |
Third deck |
Forward compartment
Starboard side |
Machinery compartment |
B-0102-E
| B |
01 |
02 |
C |
| Amidships Section |
One deck above the main deck |
Forward compartment
Port side |
Ship control or fire control compartment |
RF Cafe - Electrician's Mate 3 - Navy Training Courses, NAVPERS10548 - Figure 152. -
Deck and comportment numbering system.
Figure 152. - Deck and comportment numbering system.
Compartments such as pump rooms, auxiliary machinery rooms, engine and fire rooms generally extend upwards
through two or more decks. These are numbered from forward to aft in order. Their numbers are prefixed by the
section letter. For example, a pump room forward might extend two decks, in which case its number would be A-I;
the next compartment, extending two or more decks, would be the fire room which would be B-2, followed by the
engine room, B-3. Should there be a similar place aft, it might be called C-4. The numbers follow in order, the
letters changing according to the section in which the compartment is located. The numbering system for decks and
compartments is illustrated in figure 152.
MACHINERY MARKINGS
Every piece of electrical equipment is given three numbers as -
3-46-1
| Deck level |
Frame |
Port or Starboard Position |
| 3 |
46 |
1 |
Here again as in the case of compartment marking, a piece of equipment located on a half deck has a
letter H prefixed to the number of the deck level directly below the half deck.
Equipment on the center
line does not have the third letter as it is on neither port or starboard side.
If the equipment is between
frames, it takes the number of the frame forward.
RF Cafe - Electrician's Mate 3 - Navy Training Courses, NAVPERS10548 - Figure 153. - Method of numbering power
panels.
Figure 153. - Method of numbering power panels.
Should there be two or more pieces of equipment located on the same deck, same frame, same side of ship, then
the last number denotes position in regards to the center line. 305
Consider the case as in figure 153 when we have three panels all located on the second deck, frame 81, port
side. The panel nearest the center line has the smallest even number, the next panel outboard has the next higher
even number, and so on outboard.
Figure 153 is an example of how equipment is marked at various locations.
Note that if a piece of equipment straddles a frame it takes the number of the preceding frame. (See panel
(2-72-2)).
TURRET AND MOUNT MACHINERY MARKINGS
Every turret and mount is full of mechanical installations which do special jobs such as elevating the guns,
hoisting powder or projectiles up to the guns, etc. These installations are furnished by the Bureau of Ordnance
and each installation is called an ORDNANCE ASSEMBLY. Each assembly is designated by a name indicating the job it
does, and a "Mark" and "Mod" number indicating a particular design of such an assembly. Thus in the 5-inch single
mounts on carriers of the MIDWAY class (5-inch Gun Mount Mark 39), these are some of the Ordnance Assemblies you
will find: Elevating Gear Mark 15 Mod 0, Projectile Hoist Mark 6 Mod 0, Power Hoist Mark 6 Mod 0.
The motor switches, and other electrical parts associated with each Ordnance Assembly are considered parts of that
assembly. Each of these electrical parts has a name plate which tells you what Ordnance Assembly it is part of.
A complete set of drawings for every Ordnance Assembly is furnished by the Bureau of Ordnance to each ship and is
kept in the Gunnery Officer's Office. These drawings show where each part of the assembly is located and how it is
constructed. So if you want to know where a particular piece of electrical equipment in a mount or turret is
located, or how it is constructed, first find out what Ordnance Assembly it is part of. Then ask the Gunnery
Officer or Chief Gunner's Mate for the folder of drawings on that assembly. Looking through the drawings in this
folder you will find drawings which show the location and construction of the electrical part you are interested
in.
ELEMENTARY WIRING DRAWINGS
All shipboard wiring blueprints fall under the three general headings of ELEMENTARY wiring drawings, ISOMETRIC
wiring drawings, and wiring DECK PLANS.
The ELEMENTARY wiring drawing is, as the name implies, as simple
and detailed as possible. It shows each individual conductor in the circuit and every connection made. It mayor
may not show the connection boxes themselves. In all Interior Communication (IC) circuits the lugs in each
connection box are stamped with the proper lead markings. The elementary wiring diagram shows these lead markings
alongside each lead of the circuit.
In the case of an elementary wiring drawing for a controller the
drawing often shows the relative position of the various components of the controller. Most elementaries, however,
show nothing of the fixtures or cable runs. Because of this, elementaries are not drawn to scale. Elementary
drawings use the elementary type of symbols. An elementary drawing would be used to check proper connections in a
circuit or to make the initial hook-up. Each elementary wiring blueprint contains one circuit only.
ISOMETRIC WIRING DRAWINGS
Each electrical system has its own ISOMETRIC wiring drawing. If the individual system is not too large, it
will be covered by one blueprint. There will be a separate isometric wiring diagram for each IC circuit.
In isometric drawings the decks are arranged in tiers, starting at the bottom with the hold and successively
arranged to the bridges and superstructure. Section and divisional bulkheads are shown as well as the bulkheads
that divide the deck into the main compartments. The center line is marked with frame numbers every five or ten
frames. The outer edge of each deck is drawn with the general outline of the shape of the ship.
All
athwartship lines are shown at an angle of 60° to the center line, and the location of compartments as shown by
the blueprint gives an accurate idea of the deck arrangement, although not in detail. The purpose of distorting
the athwartship lines is to permit the continuous representation of cables passing between decks. Cables running
from one deck to another are drawn as light lines at right angles to the center line.
The exact location
of fixtures and cable runs cannot be satisfactorily arrived at by use of an isometric wiring blueprint because the
locations shown are only approximate. The symbol numbers of the fixtures in the circuit are given and also the
cable numbers and sizes. This aids the electrician in associating each circuit with its elementary wiring drawing.
An isometric wiring diagram for a turret is shown in figure 154. What this diagram means is illustrated in figure
155.
RF Cafe - Electrician's Mate 3 - Navy Training Courses, NAVPERS10548 -
Figure 154. - Isometric wiring diagram for 8-inch turret illumination system.
Figure 154. - Isometric wiring diagram for 8-inch turret illumination system.
RF Cafe - Electrician's Mate 3 - Navy Training Courses, NAVPERS10548 - Figure 155. -
The turret illumination system indicated by the wiring diagram in figure 154.
Figure 155. - The turret illumination system indicated by the wiring diagram in
figure 154.
Elementary and isometric presentations of a circuit often are on the same blueprint. Isometric wiring drawings
never are drawn to anyone set scale. The isometric wiring drawing uses schematic symbols.
A cable,
regardless of number of conductors, is represented on an isometric wiring diagram by a single line, and no attempt
is made to show the proper connections in connection boxes or at fixtures. An isometric type of drawing thus shows
at a glance a rough picture of the entire circuit's layout. Isometric wiring diagrams of lighting and power
circuits usually are used to indicate only the main supply cables, feeders, and their associated equipment.
WIRING DECK PLANS
The WIRING DECK PLAN is a blueprint used chiefly in construction. It enables the Navy Yard electrician to
layout his work for a number of cables without referring to each individual isometric wiring drawing. Wiring deck
plans do not distort the athwartship members, but represent a true plan.
LIGHTING and POWER wiring deck plans
are the actual installation diagrams for the particular deck illustrated. For these systems, the print includes a
bill of material listing all material and equipment required to complete the installation on the deck concerned.
Equipment and materials, except cable, are assigned symbol numbers and are so indicated on the drawing and in the
bill of materials.
Lighting and power circuits, in alternating current work, have indicated at each
single-phase fixture, fitting, or appliance the phase to which it is to be connected, such as: AB PHASE, BC PHASE,
or CA PHASE. Equipment not so indicated is threephase.
INTERIOR COMMUNICATION and similar type wiring deck
plans are informative plans only, and are merely a composite of all like systems. For these systems, a list of
symbols replaces the bill of materials. Symbols and symbol numbers are shown on the plan, but unlike the isometric
the section leads of the cables are not indicated.
Wiring deck plans always are drawn to the scale of 1/4 inch
equals 1 inch. This drawing, therefore, shows an accurate location of all fixtures. The deck plan shows from 150
to 200 feet of deck space on one deck only. A ship 500 feet long at the main deck would require three wiring deck
plan blueprints for each system on the main deck. This type of blueprint, like the isometric, uses schematic
symbols.
On a small ship a wiring deck plan may cover more than one electrical system. One wiring deck
plan may cover the power, lighting, and IC systems.
TROUBLE SHOOTING BY
USE OF BLUEPRINTS
The real value of any knowledge is determined by whether or not a man can use what he knows in practical
application. The proper use of blueprints in isolating electrical troubles pays dividends in many ways. It
eliminates much of the guesswork in locating trouble in a faulty electrical circuit. Blueprints will save many
man-hours spent "sight traveling" a cable along the overhead, down the bulkhead, and through the decks, trying to
arrive at its termination at some questionable point.
As a simple example-in isolating trouble in a
circuit, assume an electrician is taking insulation tests on the IC circuit fed from the IC switchboard. His
"Megger" registers a zero ground on the general alarm circuit. Since he is not familiar with the location of the
various components of this circuit he heads for the log room to draw out the isometric wiring diagrams and
elementary wiring diagram of the "G" circuit. At this time he asks permission to secure the general alarm system
while he locates the fault.
By looking at the isometric of the "G" circuit he locates all the connection
boxes. From here on he starts a progressive bread-down of the circuit. The logical steps would be:
1.
In the first connection box after leaving the switchboard, break all connections.
2. Read each section of
the circuit emanating from the box with the megger.
3. After locating the section grounded, remake all
connections in the box, close the box,
and move along the grounded cable to the next connection box or
fixture.
4. Repeat steps 2 and 3 along the line until the ground is isolated to one individual
fixture or section of cable.
When the work is completed care should be taken that all covers are properly
replaced and secured and the blueprint is again stored in its proper position in the files.
Chapter 16 Quiz
(click
here)
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