Download EST 2054 Answers

EST 2054 - Electrical Service Technician
Answer Schedule
Notes:
1.
(1 mark) means that the preceding statement/answer earns 1 mark.
2.
This schedule sets out the accepted answers to the examination questions. A marker can
exercise their discretion and decide on the overall accuracy of any answer that is
presented in the candidate’s own words.
3.
Symbols and terms - alternatives
Power
W or P
Voltage
V or E or U
Phase
Active
Question 1
(a)
(b)
(c)
(d)
(e)
(f)
Marks
Reference
(i)
No
(1 mark)
(ii)
The minimum insulation resistance
value must be at least 1 MΩ
(1 mark)
(i)
Limited ingress of dust permitted
(no harmful deposit).
(1 mark)
AS/NZS 3000:
Table G1a
(ii)
Protected against strong jets of
water. Limited ingress permitted.
(1 mark)
AS/NZS 3000:
Table G1a
(i)
Opens the starter control circuit
when one phase is lost.
(1 mark)
(ii)
Prevents motor from starting if two
phases on the supply are reversed.
(1 mark)
(i)
Means that the conductor or fittings
are covered with insulation in such
a manner that a person may safely
handle them when they are live.
(1 mark)
ESR 4
(ii)
Means effectively connected to the
general mass of earth.
(1 mark)
ESR 4
●
Open circuited centrifugal switch
(1 mark)
●
Open start winding
(1 mark)
6kA The maximum prospective short
circuit current the breaker can
safely open under fault conditions.
16A Is the maximum current that can
pass through the MCB without
tripping it.
Marking notes
(1 mark)
(1 mark)
EST 2054 ANSWERS – 11 MAY 2013
1
Question 1
Marks
(g)
●
●
Length
Cross-sectional area of conductors
(2 marks)
(h)
(i)
No
(½ mark)
(ii)
The resistance stays constant
regardless of the voltage applied
(i)
One element is open circuited
(1 mark)
(ii)
Only one element is working.
(1 mark)
(i)
(j)
Any
●
●
●
●
TWO of:
A mechanical overload
A reduced supply voltage
The loss of one phase
Excessive bearing wear
Reference
Marking notes
(1½ marks)
(2 marks)
EST 2054 ANSWERS – 11 MAY 2013
2
Question 2
(a)
Marks
(i)
Any
●
●
●
●
ONE of:
A DOL starter
A Primary resistance starter
An auto-transformer starter
An electronic soft starter
(ii)
Any ONE of:
●
A single-phase, split-phase
motor
●
A single-phase, capacitor-start
motor
Stop
Marking notes
(1 mark)
(b)
Fuse
Reference
(1 mark)
Thermal
overload
contact
Start
P
If
a
correct
230V circuit is
shown,
then
the first two
and last bullet
points
are
incorrect
Hold-in
contact
P
Coil
Correct supply
●
Fuses protect entire circuit
●
Stop button correctly connected
(½ mark)
●
Start button correctly connected
(½ mark)
●
Hold-in
contacts
connected
Coil correctly connected
(½ mark)
●
●
●
(c)
(½ mark)
●
●
●
●
(1 mark)
correctly
(½ mark)
Thermal overload auxiliary contact
correctly connected
Working circuit
(½ mark)
The mechanical overload causes
excess current in the motor
windings.
The temperature increases in the
motor windings.
The
thermistor
detects
the
temperature increase and opens
the contact in the control circuit at
a pre-set temperature level.
(1 mark)
(1 mark)
(1 mark)
(1 mark)
EST 2054 ANSWERS – 11 MAY 2013
3
Question 3
Marks
(a)
(1 mark)
(b)
(i)
AS/NZS 3760
(ii)
In-service safety inspection
testing of electrical equipment
(i)
An ohmmeter
(1 mark)
(ii)
Test between the earth pin of the
plug and the frame of the appliance
(1 mark)
and
(1 mark)
Any ONE of:
●
●
Insulation resistance test
(½ mark)
Insulation resistance tester
(½ mark)
500V d.c.
(½ mark)
The appliance is not connected to
the supply
10,000Ω or more
(½ mark)
Earth leakage test
(½ mark)
Any ONE of:
*
Earth leakage tester
*
Clip-on ammeter
The appliance is live
(½ mark)
(1 mark)
(1 mark)
(1 mark)
5 mA or less
(d)
Marking notes
(1 mark)
(iii) 1Ω or less
(c)
Reference
Any TWO of:
●
They are effectively anchored.
●
The inner cores are not exposed or
twisted;
●
The external sheaths are not cut,
abraded, twisted, or damaged to
such an extent that the insulation
of the inner cores is visible
●
Unprotected
conductors
or
insulation tape are not in evidence.
(2 marks)
EST 2054 ANSWERS – 11 MAY 2013
AS/NZS 3760
2.3.2
4
Question 4
Marks
(a)
The supply and/or the appliance would
be short-circuited.
(2 marks)
(b)
A 0 volt reading will be obtained which
can lead to the false conclusion that the
circuit is de-energised.
(2 marks)
(c)
Class I
Class II
(2 marks)
(d)
●
●
●
●
6 months
12 months
Ensure the correct instrument for
the conditions is used.
Inspect instrument, clips, leads and
probes to ensure they are in good
condition.
Ensure correct range is selected on
the instrument.
Ensure
leads
are
correctly
connected.
Reference
Marking notes
AS/NZS 3760:
2001: Table 2
2003: Table 2
(4 marks)
EST 2054 ANSWERS – 11 MAY 2013
5
Question 5
(a)
Marks
Reference
Marking notes
(i)
Phase
Centrifugal switch
Run winding
Start winding
Neutral
●
●
●
●
(ii)
Any
●
●
●
Correctly
connected
start
winding
Correctly
connected
centrifugal switch
Correctly
connected
run
winding
Working circuit
ONE of:
External starting relay
Solid state current relay
Timer
(iii) Any ONE of:
●
Reverse the connections of the
start winding.
●
Reverse the connections of the
run winding.
(b)
Power
I
=
=
=
=
=
(c)
(1 mark)
(1 mark)
(1 mark)
(1 mark)
(1 mark)
(1 mark)
(½ mark)
(½ mark)
(½ mark)
746 x 0.45
335.7W
P
V
335.7
230
1.46A
(½ mark)
(1 mark)
It has a higher starting torque.
(1 mark)
EST 2054 ANSWERS – 11 MAY 2013
6
Question 6
(a)
(i)
(ii)
I
●
Marks
=
P
V
(½ mark)
=
2000
230
(½ mark)
=
8.69A
(1 marks)
Three
Reference
Marking notes
(½ mark)
Any ONE of:
●
●
(b)
Brown
active
(½ mark)
Light blue
neutral
(½ mark)
Green/yellow
earth
(½ mark)
Red
active
Black
neutral
Green
earth
(i)
An ohmmeter
(ii)
Any ONE of:
●
●
(1 mark)
Method 1
Turn the three-heat switch to
the “high” position.
(1 mark)
Measure the resistance
between active and neutral at
the plug
(1 mark)
Method 2
Disconnect the elements.
Measure the resistance of each
element in turn
●
Method 3
Turn the three-heat switch to
the “low” position.
Measure the resistance
between active and neutral at
the plug
(iii) ●
Method 1
R
=
V2
P
(½ mark)
=
230 x 230
2000
(½ mark)
=
26.45Ω
(1 mark)
is the expected resistance
of the elements in the
(1 mark)
EST 2054 ANSWERS – 11 MAY 2013
7
Question 6
Marks
Reference
Marking notes
“high” position
●
Method 2
R
=
V2
P
=
230 x 230
1000
=
52.9Ω
is the expected resistance
of each element
●
Method 3
R
=
V2
P
=
230 x 230
1000
=
52.9Ω
105.8Ω is the expected
resistance
with
the
elements in series.
EST 2054 ANSWERS – 11 MAY 2013
8
Question 7
Marks
The maximum current a fuse can carry
continuously without operating.
(b)
(i)
Any ONE of:
●
To protect a final circuit
against excessive current flow
under fault conditions.
●
To protect a final subcircuit
from being overloaded
(2 marks)
(ii)
●
To protect a person using the
final subcircuit circuit
From
receiving
a
severe
electric shock under fault
conditions
(1 mark)
(c)
The MCB is under-rated for the final
subcircuit.
(1 mark)
(d)
The HRC fuse is rated too high for the
final subcircuit
(1 mark)
(e)
●
(1 mark)
●
●
It, prevents the fuse element from
bulging out the side of the carrier
and being accessible to touch.
Under overload conditions the heat
produced in the element is confined
to the tunnel area.
Under short-circuit conditions the
arc and molten element is confined
within the fuse carrier and base.
Marking notes
(1 mark)
(a)
●
Reference
(1 mark)
(1 mark)
(1 mark)
EST 2054 ANSWERS – 11 MAY 2013
9
Question 8
(a)
Locating and turning off the correct
MCB on the switchboard.
Attaching a danger tag to the MCB.
(1 mark)
Unscrew the socket outlet or
permanent
connection
unit
–
whichever
is
closest
to
the
switchboard
Testing for isolation using the
prove-test-prove method.
(1 mark)
(½ mark)
●
In the final subcircuit wiring and
fittings
In the plug-in appliance
●
In the fixed-wired appliance
(½ mark)
●
Disconnecting the final subcircuit at
the switchboard
Un-plug the plug-in appliance
(½ mark)
Disconnect
appliance
(½ mark)
●
●
●
(c)
●
●
●
(d)
Reference
Marking notes
The description has to show:
●
(b)
Marks
the
fixed-wired
(1 mark)
(1 mark)
(½ mark)
(½ mark)
Any ONE of:
●
The final subcircuit
*
Insulation resistance tester
(½ mark)
*
500V d.c.
(½ mark)
*
Bridge the phase and neutral
(½ mark)
*
Test between the bridge and
the earth conductor
A test result nearing 0Ω
(½ mark)
*
●
The plug-in appliance
*
Insulation resistance tester
(½ mark)
*
500V d.c.
(½ mark)
*
Bridge the phase and neutral
pins of the plug
Test between the bridge and
the frame of the appliance.
A test result nearing 0Ω
(½ mark)
*
*
●
(1 mark)
(½ mark)
(1 mark)
The fixed-wired appliance
*
Insulation resistance tester
(½ mark)
*
500V d.c.
(½ mark)
*
Bridge the phase and neutral
conductors of the flexible cord
(½ mark)
EST 2054 ANSWERS – 11 MAY 2013
10
Question 8
*
*
Marks
Test between the bridge and
the frame of the appliance.
A test result nearing 0Ω
Reference
Marking notes
(½ mark)
(1 mark)
EST 2054 ANSWERS – 11 MAY 2013
11
Question 9
(a)
(b)
(c)
(d)
(e)
Marks
●
Phase to Phase
=
400V
(½ mark)
●
Phase to Neutral
=
230V
(½ mark)
●
Phase to Earth
=
230V
(½ mark)
●
Neutral to Earth
=
0V
(½ mark)
(i)
A nominal voltage of 230 volts a.c.
between phase and neutral.
(1 mark)
(ii)
Means any voltage exceeding 50
volts a.c. or 120 volts ripple free
d.c. but not exceeding 1000 volts
a.c. or 1500 volts ripple free d.c.
(1 mark)
=
230 – (230 x 5%)
(1 mark)
=
218.5 V
(1 mark)
(i)
50Hz
(1 mark)
(ii)
Any ONE of:
●
230 x 1.414
●
230
0.707
(½ mark)
=
(½ mark)
325V
Any TWO of:
●
Parallel path to the star point at the
distribution transformer
●
Ties the voltage between phase and
earth to 230V (standard low
voltage)
●
Minimises the potential difference
between neutral and earth
●
A low impedance path to earth
under fault conditions
Reference
Marking notes
AS/NZS 3000
3.6.2
(2 marks)
EST 2054 ANSWERS – 11 MAY 2013
12