NUE 032
CIRCUIT DEVELOPMENT

Operation of a contactor
1.See page 5 and 6 of your work book

AC Magnetic Cores page 6-7
1. Initial high current flows due to low resistance and low inductive
reactance of the coil
2. Riveted steel laminations
3. Laminated core in order to reduce eddy currents
4. Accurate grinding of fixed amd moving parts
5. Shading rings or Frager windings to eliminate “chattering’

Coil, Main contacts and Auxiliary
Contacts page 7
1. The Coil produces the magnetic flux required to attract the moving
armature of the electromagnet.
2. Main Contacts: These are designed to make and break the current in
the power circuit
3. Auxiliary contacts: provide hold in and sequence interlocking as well
as signalling
5. Instantaneous normally open (N/O) conducting when the coil is
energised
6. Instantaneous normally closed (N/C) contacts conducting when coil is
de-energised
7. Instantaneous C/O (change over) contacts

Contactor Selection page 10
1.The type of voltage
2.The load characteristics (full load)
3.The duty requirement (utilisation)
4.Standards required by customer
5.Operating conditions like , temperature,
altitude and environment.

AC APPLICATION page 11
1.Category AC1 – Applies to all types of AC load
with a power factor not less than .95
2.Category AC 2 – Applies to starting, plugging
(reverse current braking) or inching of slip-ring
motors
3.Category AC3 – Applies to squirrel cage
motors with breaking during normal running
4.Category AC4 – Covers applications with
starting , plugging or inching of squirrel cage
motors.

DC Application page 12
1. Category DC1 – This applies to all dc loads where the
time constant (L/R) is less than or equal to 1 ms.
2. Category DC2 – This applies to the breaking of shunt
motors whilst running.
3. Category DC3 – This applies to staring, plugging and
inching of shunt motors.
4. Category DC4 – This concerns Series motors, with
breaking while running.
5. Catergory DC5 – This category applies to the starting,
reverse current breaking and inching of series motors.

Contactor Contact Identification
page 13
1 3 5 A1 13
2 4 6 14
A1

Auxiliary Contacts
1 3 5 A1 21
2 4 6 22
A1

Auxiliary Contacts
1 3 5 A1 13 21
2 4 6 14 22
A1

Contactor Coil page 14
K Normally open
power contacts
Normally open
auxiliary contacts
Normally closed Normally closed
power contacts auxiliarycontacts

Timer Block and Overloads page 15
57 65 95 97
66 96
58 98

Factors leading to Contact
Deterioration page 16
1.Mains voltage
2.Voltage drop in the control circuit
3.Vibration
4.Transient mains failure
5.Consequences

Timers page 21
Symbol for ON DELAY timer ON and OFF Delay timer coil
coil
K K
Symbol for OFF Delay timer
coil
Timed Contacts Normally open
K

SYMBOLS (SEE EXTRA SHEET)
1.COPY SYMBOLS

Limit Switches page 25
Normally open Normally closed Change over

Push Buttons page 29
1.Normally open Start Button
Normally closed Stop Button

Relay Circuits and Drawing
Conventions see page 32
1.Schematic diagrams conventions
1. Power flow is from Left to Right
2. Logic flow is from top to bottom
3. All circuits are drawn in the de-energised state
4. All contacts operate in a clockwise direction
5. All coils/lamps/power consuming devices vertically line up on the
left hand side of the drawing
6. Joins have dots on them
7. Wires that cross without joining don’t have dots on them
8. Joins are not right on the hinge of the contacts
9. Contacts can be drawn mirror image, as long as the above
conventions are followed.

1. Must Do’s for Converting Wiring Diagrams to
Schematic Diagrams
1. If wire numbers are not given, put them in.
2. Determine the function of the circuit. (e.g. Star-Delta Motor starter)
3. If Possible, determine the general form of that type of circuit (e.g.
from memory text)
4. Do all sketches in pencil. This facilitates later correction
5. Once he power section is drawn, draw two “power rails” down, one
each side of the page, from their relevant starting points, for the
“Control section”
6. Beginning from the beginning of one of these power trails,
preferably near the Start/Stop station, determine he circuit.
7. Mark off each wiring diagram wire as it is done with either a high
lighter, or pencil.
8. Redraw the circuit, a number of times if necessary, until it is correct,
and follows the accepted conventions for schematic diagrams.

S2
S1
K
13 14
K
13 14
K

S2
S1
K
13 14
K
H1
13 14
K

S1 S2
K
13 14
K
13 14
K

Circuit diagrams from Workbook
page 33
1.When converting horizontal format to vertical
format remember Power flow and sequence.
S1 K
S2
K
K H1

1. Convert the wiring diagram on page 34 to a circuit diagram.
1. Draw in the power circuit (blue lines)
2. Extand the power rails down the page
3. Draw in the control circuit (black lines)
OL
F1
K
F2
S2
S1
K
OL
K
A N

Remote Stop Starts page 51
S1 S3
S2
K1
K
S4
K
13 14
All stop buttons are connected in series while start buttons are
connected in parrallel

Interlocking page 53
S1 S2
K1
K
13
K 14
S3
S4
K K 1
13 K1 14

Interlocking page 53
S1 S2
K1
K
13
K 14
S3
S4
K K 1
13 K1 14

Jogging Circuit page 61
S2
S1
K
13 14
K

S2
S1
K
13 14
K

S2
S1
K
13 14
K
jog

Explanation of Circuits
K F1
S2
S1
K
13
K 14

Fault Finding