Diagrams - Elsevier

CHAPTER 1
Diagrams
This is an area often overlooked or even ignored. The IEE Wiring
Regulations require that ‘diagrams, charts, tables or equivalent
forms of information are made available’ to the installer and
inspector and tester.
BS EN 60617 SYMBOLS
BS EN 60617 gives the graphical symbols that should be used in
all electrical/electronic diagrams or drawings. Since the symbols
fall in line with the International Electrotechnical Commission
(IEC) document 617, it should be possible to interpret non-UK
diagrams. Samples of the symbols used in this book are shown in
Figure 1.1.
Kind of current and voltage
Direct current
Mechanical controls
Mechanical coupling
Earth and frame connections
Alternating current
Positive polarity
Negative polarity
FIGURE 1.1
Earth or ground,
general symbol
Frame, chassis
BS EN 60617 Symbols.
1
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2 Wiring Systems and Fault Finding For Installation Electricians
Lamps and signalling devices
Lighting
Lighting outlet position,
shown with wiring
Signal lamp,
general symbol
Lighting outlet on wall,
shown with wiring
running to the left
Signal lamp,
flashing type
Lamp, general symbol
Indicator,
electromechanical
Luminaire, fluorescent,
general symbol
With three fluorescent
tubes
Bell
Single-stroke bell
5
With five fluorescent
tubes
Projector, general
symbol
Buzzer
Spotlight
Push-button with
restricted access
(glass cover, etc.)
Floodlight
Emergency lighting
luminaire on special
circuit
Time switch
Self-contained
emergency lighting
luminaire
Miscellaneous
Antenna
Distribution centre,
shown with five
conduits
Fan, shown with wiring
Intercommunication
instrument
Water heater, shown
with wiring
FIGURE 1.1
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Diagrams 3
Architectural and topographical installation plans and diagrams
Switches
Socket outlets
Socket outlet (power),
general symbol
Switch, general symbol
Switch with pilot light
3
Three outlets shown:
two forms
Switch, two pole
Two-way switch,
single pole
With single-pole switch
Intermediate switch
Socket outlet (power)
with isolating
transformer, for
example shaver outlet
Socket outlet
(telecommunications),
general symbol
Designations are used to distinguish different
types of outlets:
Dimmer
Pull-cord switch,
single pole
Push-button
Push-button with
indicator lamp
FM Frequency
TP Telephone
modulation
M Microphone
Loudspeaker TV Television
TX Telex
FIGURE 1.1
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4 Wiring Systems and Fault Finding For Installation Electricians
Switchgear, control gear and protective devices
Contacts
All-or-nothing relays
Coil of a slow-releasing
relay
Make contact, normally
open: also general
symbol for a switch
Break contact
Coil of a slow-operating
relay
Change-over contact,
break before make
Coil of a relay
unaffected by
alternating current
Break contact with
spring return
Coil of an alternating
current relay
Push-button switch
(non-locking)
Coil of a mechanically
latched relay
Contactor, normally
open: three forms
Actuating device of
a thermal relay
Fuse and fuse switches
Fuse, general symbol
Fuse with the supply
side indicated
Contactor, normally
closed: three forms
Fuse switch
Fuse disconnector
Circuit breaker:
two forms
1
2
Change-over contact,
make before break
1
2
Make contact,
early to close
1
Break contact,
late to open
3 4
Make contact with
spring return
FIGURE 1.1
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Other forms for contacts and switches
Dotted lines denote alternative switch position
2
2
1
3
2
3
1
2
1
1
2
1
3
4
1
4
3
2
1 2
2
3 4
(Continued)
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Diagrams 5
DIAGRAMS
The four most commonly used diagrams are the block diagram,
interconnection diagram, the circuit or schematic diagram and the
wiring or connection diagram.
Block diagrams
These diagrams indicate, by means of block symbols with suitable
notes, the general way in which a system functions. They do not
show detailed connections (Figure 1.2a and b).
Personal
attack
button
Alarm
control
panel
Alarm
sounder
Sensors
infrareds
magnetic, etc.
(a)
Incoming
supply
Supply
authority
cut-out
Consumer
unit
Final
circuits
(b)
FIGURE 1.2
installation.
Meter
(a) Security system, (b) Intake arrangement for domestic
Interconnection diagrams
In this case, items of equipment may be shown in block form but
with details of how the items are connected together (Figure 1.3).
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6 Wiring Systems and Fault Finding For Installation Electricians
1.0 mm2 twin
with cpc cable
0.5 mm2 circular
twin flex
Ceiling
rose
Two-way
switch
FIGURE 1.3
1.0 mm2 3-core
with cpc cable
Lampholder
Two-way
switch
Two-way lighting system.
Circuit or schematic diagrams
These diagrams show how a system works, and need to pay no
attention to the actual geographical layout of components or
parts of components in that system. For example, a pair of contacts which form part of, say, a timer may appear in a different and
quite remote part of the diagram than the timer operating coil that
actuates them. In this case some form of cross-reference scheme is
needed (e.g. T for the timer coil and T1, T2, T3, etc. for the associated contacts).
It is usual for the sequence of events occurring in a system to be
shown on a circuit diagram from left to right or from top to bottom. For example, in Figure 1.4, nothing can operate until the
main switch is closed, at which time the signal lamp comes on via
the closed contacts of the push-button. When the push is operated
the lamp goes out and the bell is energized via the push-button’s
top pair of contacts.
Wiring or connection diagrams
Here the diagrams show how a circuit is to be actually wired.
Whenever possible, especially in the case of control panels, they
should show components in their correct geographical locations.
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Diagrams 7
Main
switch
Push-button
Battery
Lamp
Single-stroke
bell
FIGURE 1.4
The wiring between terminals may be shown individually on simple diagrams, but with complicated systems such wiring is shown
in the form of thick lines with the terminating ends entering and
leaving just as if the wiring were arranged in looms. Clearly, Figure
1.5a and b are the wiring diagrams associated with the circuit
shown in Figure 1.4. Although Figure 1.5a would be simple to wire
without reference to the circuit diagram, Figure 1.5b would present
a problem as it is shown if Figure 1.4 were not available.
In either case an alphanumeric (A1, GY56, f7, etc.) reference system is highly desirable, not only for ease of initial wiring, but also
for fault location or the addition of circuitry at a later date. Both
circuit and wiring diagrams should be cross-referenced with such a
system (Figure 1.6a–c).
Note how, in Figure 1.6c, each termination is referenced with the
destination of the conductor connected to it. Also note how much
more easily a circuit diagram makes the interpretation of the circuits function.
CIRCUIT CONVENTION
It is probably sensible at this point to introduce the reader to
circuit convention. This is simply a way of ensuring that circuit
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8 Wiring Systems and Fault Finding For Installation Electricians
Lamp
Push-button
Bell
Main switch
Battery
(a)
Lamp
Bell
Push-button
Battery
Main switch
(b)
FIGURE 1.5
diagrams are more easily interpreted, and is achieved by drawing
such diagrams in a de-energized state known as normal.
Hence, if we take a new motor starter out of its box, all of the
coils, timers, overloads and contacts are said to be in their normal
position. Figure 1.7a–d (see page 10) illustrate this convention as
applied to relays and contactors.
Note that, provided diagrams follow this accepted convention, it
is unnecessary to label contacts normally open (N/O) or normally
closed (N/C).
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Diagrams 9
Push (P)
Switch (SW)
1
2
1
2
3
4
B
1
Battery (B)
Singlestroke
bell
(SS)
Lamp (L)
B
2
(a)
L
4
2 1
P
3
SS
2
1
2
1
SW
B
(b)
L
SS
1
2
P
43
P1
21
B
SS P4
L2
SW1
B
(c)
FIGURE 1.6
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L2
B
B
P2
B
1
L1
P3
SS SW2
P1
2
SW
Schematic and wiring diagrams.
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10 Wiring Systems and Fault Finding For Installation Electricians
Relay coil,
general
Relay coil,
AC
Contactor or
relay coil
Relay coil,
general
C
(a)
N/O N/C N/O N/C
N/O N/C N/O
or
Supply
Common C
Supply
RA
RA1 N/O
(b)
C
C
RB
N/O N/O
(c)
FIGURE 1.7
RA2 N/C
RB1
(d)
Contactor and relay conventions.
CONSTRUCTING AND INTERPRETING
CIRCUIT DIAGRAMS
In order to construct or interpret a circuit/schematic diagram of the
controls of a particular system, it is necessary to understand, in broad
principles, how the system functions. A logical approach is needed,
and it may take the novice some while before all ‘clicks’ into place.
Here is an example to consider.
Electronic valet
You work hard every day and return home late every evening.
When you come in you look forward to a smooth scotch, a
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Diagrams 11
sit down and then a relaxing soak in a hot bath. If you were
acquainted with electrical control systems you could arrange for
these little luxuries to be automated as shown in Figure 1.8.
T2
TC1
KS
1
3
2
DD1
FS
T1
Supply
FIGURE 1.8
TC
T
DD
BFU
Electronic valet.
The system components are as follows:
TC
KS
T
DD
Typical 24h time clock: TC1 is set to close at 2100 h.
Key switch operated by front door key: momentary action, contacts open
when key is removed.
Timer which can be set to close and open contacts T1 and T2 as required.
Drinks dispenser with a sprung platform on which the glass sits. When
energized, DD will dispense a drink into the glass.
When the glass is removed, the platform springs up closing contacts 1 and
3 on DD1.
DD1 Changeover contacts associated with DD.
FS Normally closed float switch, which opens when the correct bath water
level is reached.
BFU (bath filling unit): electrically operated hot water valve.
Let us now follow the system through:
1. At 9.00 pm or 2100 h the N/O contact TC1 on the time
clock TC closes, giving supply to one side of the key switch
and to the timer contact T1.
2. You arrive home and open the door with the key, which
closes the N/O spring-return contacts on KS, thus
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12 Wiring Systems and Fault Finding For Installation Electricians
3.
4.
5.
6.
7.
energizing the timer T. The drinks dispenser DD is also
energized via its own N/C contacts DD1 (1 and 2).
The timer T (now energized) instantly causes its own N/O
contacts T1 to close, allowing supply to be maintained to
T and DD via T1 (this is called a ‘hold-on’ circuit) when the
key is removed from the key switch KS. N/O timer contacts
T2 are set to close in say, 10 min. By the time you reach the
lounge DD has poured your scotch.
When you remove the glass from the dispenser, DD1
contacts 1 and 2 open, and 1 and 3 close, de-energizing the
dispenser and putting a supply to one side of the 10 min
timed contacts T2.
You can now sit down, relax and enjoy your drink, knowing
that shortly, contacts T2 will close and energize the bath
filling unit BFU via the N/C float switch FS.
When the bath level is correct, the float switch FS
opens and de-energizes BFU. You can now enjoy your
bath.
One hour, say, after arriving home, the timer T will have
completed its full cycle and reset, opening T1 and T2 and
thus restoring the whole system to normal.
This system is, of course, very crude. It will work but needs some
refinement. What if you arrive home early – surely you need not
stay dirty and thirsty? How do you take a bath during the day without using the door key and having a drink? What about the bath
water temperature? And so on. If you have already begun to think
along these lines and can come up with simple solutions, then circuit/schematic diagrams should present no real problems to you.
Quiz controller
Here is another system to consider. Can you draw a circuit/schematic diagram for it? (A solution is given at the end of the book.)
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Diagrams 13
The system function is as follows:
1. Three contestants take part in a quiz show. Each has a
push-to-make button and an indicator lamp.
2. The quizmaster has a reset button that returns the system
to normal.
3. When a contestant pushes his/her button, the corresponding
lamp is lit and stays lit. The other contestants’ lamps will
not light.
4. The items of equipment are: a source of supply; a reset button
(push-to-break); three push-to-make buttons; three relays
each with 1 N/O and 2 N/C contacts and three signal lamps.
The resulting diagram is a good illustration of the use of an alphanumeric system to show relay coils remote from their associated
contacts.
HEATING AND VENTILATION SYSTEM
Figure 1.9 is part of a much larger schematic of the controls for the
heating and ventilation system in a large hotel.
From the diagram it is relatively simple to trace the series of events
that occur in this section of the system.
Clearly, there are four pumps: two boiler pumps and two variable
temperature pumps. One of each of these pairs is a standby in the
event of failure of the other; this will become clear as we interpret
the scheme.
There is a controller (similar to the programmer of a central heating system) which receives inputs from two temperature sensors
and operates an actuator valve and a time switch. There are two
sets of linked, three-position switches and direct-on-line threephase starters with single-phase coils S1/4, S2/4, S3/4 and S4/4 for
the pumps. There is also run and trip indication for each pump.
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5
6
7
Actuator
1
2
MB
valve MV1 3
FIGURE 1.9
R8
2
24 V AC
1 Plant time
2 switch
3 interlock
12
13
Terminal
strip
R9/1
6
7
16
17
18
19
9
8
10
11
R8/2
Off
2
1
Off
2
1
1
O/L
O/L
O/L
O/L
0.37 F
R9
Heating and ventilation schematic diagram.
To remote
indication
panel
(by others)
8
9
3
4
Immersion
detector
D2
Variable
temperature
circuit controls
1
2
Outside
detector
D3
L
N
Controller
(facia)
NL
S4
S3
S2
S1
4
4
4
4
Run
Trip
Run
Trip
Run
Trip
Run
Trip
L2 C
N L3 L1
AF
AF
AF
AF
F
F
F
F
F
F
F
F
10
11
12
7
8
9
4
5
6
1
2
3
1
2
2
Variable
temperature
pumps
Boiler
primary
pumps
Terminal
strip
N:1
N:1
N:1
N:1
1
Diagrams 15
Let us now follow the sequence of events:
1. The selector switches are set to, say, position 1.
2. The temperature sensors operate and the controller actuates
valve MV1. If the 24 V time switch relay R8/2 is energized,
then its N/O contacts R8/2 are closed, giving supply to the
selector switches.
3. Starters S1/4 and S3/4 are energized via their respective
overload (O/L) contacts; the main contacts close and the
pumps start. Auxiliary contacts on the starters energize the
run lamps.
4. If pump 1, say, were to overload, then the N/O O/L contacts
would close, de-energizing S1/4 and shutting down pump 1,
and supply would be transferred to starter S2/4 for pump 2
via the second linked switch. At the same time the trip
lamp would come on and a supply via a diode and control
cable C would be given to relay R9/1, operating its N/O
contacts R9/1 to indicate a pump failure at a remote panel.
The diode prevents back feeds to other trip lamps via the
control cable C from other circuits.
5. The reader will see that the same sequence of events would
take place if the selector switch were in position 2 in the
first place.
RELAY LOGIC
In the last few pages we have investigated the use of relays for control
purposes. Whilst this is perfectly acceptable for small applications,
their use in more complex systems is now being superseded by programmable logic controllers (PLCs). However, before we discuss these
in more detail, it is probably best to begin with a look at relay logic.
We have already discussed circuit convention with regard to N/O
and N/C contacts, and in the world of logic these contacts are
referred to as ‘gates’.
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16 Wiring Systems and Fault Finding For Installation Electricians
AND gates
If several N/O contacts are placed in series with, say, a lamp (Figure
1.10), it will be clear that contacts A and B and C must be closed
in order for the lamp to light. These are known as AND gates.
A
B
Supply
FIGURE 1.10
C
Lamp
AND gates.
OR gates
If we now rewire these contacts in parallel (Figure 1.11), they are
converted to OR gates in that contact A or B or C will operate the
lamp.
A
B
C
Supply
FIGURE 1.11
Lamp
OR gates.
Combined gates
A combination of AND and OR systems is shown in Figure 1.12,
and would be typical of, say, a remote start/stop control circuit for
a motor. A or B or C will only operate the contactor coil if X and Y
and Z are closed.
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Diagrams 17
A
B
C
X
Y
Z
Supply
FIGURE 1.12
C
Contactor
coil
AND/OR gates.
A simplification of any control system may be illustrated by a block
diagram such as shown in Figure 1.13, where the input may be
achieved by the operation of a switch or sensor, the logic by relays,
coils, timers, etc., and the outputs in the form of lamps, heaters,
sounders, contactors, etc.
Input
Logic
Output
FIGURE 1.13
PROGRAMMABLE LOGIC CONTROLLERS
With complex control requirements, the use of electro-mechanical
relays is somewhat cumbersome, and most modern systems employ
PLCs. In basic terms these do no more than relays (i.e. they process
the input information and activate a corresponding output). Their
great advantage, however, is in the use of microelectronics to achieve
the same end. The saving in space and low failure rate (there are no
moving parts) make them very desirable. A typical unit for, say, 20
inputs (I) and 20 outputs (O), referred to as a 40 I/O unit, would
measure approximately 300 mm by 100 mm by 100 mm, and would
also incorporate counters, timers, internal coils, etc.
A PLC is programmed to function in a specified way by the
use of a keyboard and a display screen. The information may be
programmed directly into the PLC, or a chip known as an EPROM
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18 Wiring Systems and Fault Finding For Installation Electricians
may be programmed remotely and then plugged into the PLC. The
programming method uses ‘ladder logic’. This employs certain
symbols, examples of which are shown in Figure 1.14. These symbols appear on the screen as the ladder diagram is built up.
Here are some examples of the use of ladder logic.
Coil
N/O
N/C
Counter
Reset counter
Timer
FIGURE 1.14
Y or R
C
RC
T
Ladder logic.
Motor control
Figure 1.15 illustrates a ladder logic diagram for a motor control
circuit (no PLC involved here). Closing the N/O contacts X0 gives
supply to the motor contactor coil Y0 via N/C stop buttons X1 and
X2. Y0 is held on via its own N/O contact Y0 when X0 is released.
The motor is stopped by releasing either X1 or X2.
X1
X0
X2
Y0
X denotes inputs
Y denotes outputs
Y0
FIGURE 1.15
Packing control
Figure 1.16 shows the basic parts of a packing process. An issuing
machine ejects rubber balls into a delivery tube and thence into
boxes on a turntable. A photoswitch senses each ball as it passes.
Each box holds 10 balls and the turntable carries 10 boxes.
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Diagrams 19
Issuing
machine
Photocell
Box
Turntable
FIGURE 1.16
Clearly, the issuing machine must be halted after the 10th ball,
and time allowed for all balls to reach their box before the turntable revolves to bring another box into place. When the 10th box
has been filled, the system must halt and a warning light must be
energized to indicate that the process for that batch is completed.
When new boxes are in place the system is restarted by operating
an N/C manual reset button.
This system is ideal for control by a PLC with its integral counters
and timers. Figure 1.17 shows an example of the ladder logic for
this system using the following:
X0
X1
Y0
Y1
Y2
C0
C1
T0
T1
RC
Ch01-H8734.indd 19
N/O photocell switch: closes as ball passes.
N/C manual reset button.
Output supply to issuing machine.
Output supply to turntable.
Output supply to warning light.
Internal counter set to 10 with one N/C and two N/O contacts.
Internal counter set to 10 with one N/C and one N/O contacts.
Timer set for 5 s with one N/O contact.
Timer set for 5 s with one N/C contact.
Reset counter: resets counter when supply to it is cut.
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FIGURE 1.17
C1
X1
C0
T0
C0
C0
T1
X0
Ladder logic.
C1
Y2
RC
Supply to warning light: operates when counter 1 reaches 10
Reset for counter 1: resets when X1 is opened
Supply to counter 1 after counter 0 has counted 10 balls:
counter 1 set to 10
Supply to timer 1 via T0
T1
C1
Supply to turntable after timer 0 has timed 5 seconds, and T0 closes
Supply to timer 0 after counter 0 has counted 10 balls
Supply to issuing machine: cuts off after counter 0 has counted
10 balls and again after counter 1 has in effect counted 10 boxes
Reset for counter 0: resets when timer 1 elapses 5 seconds,
and T1 opens
Counting balls: counter 0 set to 10
Y1
T0
Y0
RC
C0
Diagrams 21
Switch
Cord operated switch
Emergency light
Lighting outlet position
Single socket, switched
Wall light outlet position
Double socket, switched
FIGURE 1.18
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Single fluorescent fitting
Fan
Double fluorescent fitting
Water heater
Architectural symbol layout.
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22 Wiring Systems and Fault Finding For Installation Electricians
Fault location
Another major advantage of the use of PLCs for controlling systems is the relative ease of fault location. In the event of system
failure, the keyboard and screen unit is plugged into the PLC and
the condition of the system is displayed in ladder logic on the
screen. Then, for example, any contact that is in the wrong position will show up.
DRAWING EXERCISES
1. Using BS EN 60617 architectural symbols, draw block
diagrams of the following circuits:
(a) A lighting circuit controlled by one switch, protected
by a fuse, and comprising three tungsten filament lamp
points, two double fluorescent luminaires, and one
single fluorescent luminaire.
(b) A lighting circuit controlled by two-way switches,
protected by a fuse, and comprising three floodlights.
(c) A lighting circuit controlled by two-way switches, and
one intermediate switch, protected by a circuit breaker,
and comprising three spotlights. One of the two-way
switches is to be cord operated.
(d) A ring final circuit protected by a circuit breaker, and
comprising six double switched socket outlets and two
single switched socket outlets.
2. Replace the symbols shown in Figure 1.18 with the correct
BS EN 60617 symbols.
Solutions are given at the end of the book.
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