Download ET 36 Answers

ET 36 - Electrician Theory Examination Marking 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
Reference
Question 1
Marking notes
Marks
(a)
Any TWO of:
(2 marks)
An MEN switchboard:
●
Has an MEN link between the neutral
and earth busbars
●
Has a connection to earth via an
earthing lead to an earth electrode
●
Is electrically closest to the point of
supply
●
Can supply to another MEN switchboard
(b)
They have a constant rotating magnetic field
(2 marks)
(c)
Any TWO of:
(2 marks)
(d)
(e)
●
Reducing starting current
●
Reducing voltage surges
●
Limiting mechanical shock
(i)
0.01 MΩ minimum
(1 mark)
(ii)
1Ω maximum
(1 mark)
Any TWO of:
(2 marks)
●
Capacity of the supply source
●
Transformer impedance.
●
Circuit impedance
●
Length of cable route between the
transformer and the main switchboard
ET 36 ANSWERS – 11 SEPTEMBER 2010
1
Reference
Question 1
Marking notes
Marks
(f)
When current is flowing there is an internal
volt drop due to the impedance of the
windings.
(g)
(i)
No effect
(1 mark)
(ii)
Any ONE of
(1 mark)
(h)
P
●
110 V
●
63.5V
=
V2
(2 marks)
R
=
240 x 240
24
P
=
2400W
=
V2
(½ mark)
R
=
230 x 230
(½ mark)
24
(i)
(j)
=
2204.17W
(½ mark)
=
2400 – 2204.17 = 195.83
(½ mark)
●
Under fault conditions the earthing of
the metal frame keeps the frame of
appliance at earth potential.
(1 mark)
●
This ensures the operation of protective
devices
(1 mark)
(i)
1MΩ
(1 mark)
(ii)
5mA
(1 mark)
ET 36 ANSWERS – 11 SEPTEMBER 2010
2
Reference
Question 2
Marking notes
Marks
(a)
Each fitting has a 1 amp fuse, the circuit is
protected by a 16A MCB.
(1 mark)
(b)
(i)
It protects the whole of the circuit.
(1 mark)
(ii)
●
Short-circuit
●
Overload.
(c)
(d)
(i)
It protects Fitting A
(ii)
●
Short-circuit
●
Overload.
(1 mark)
(1 mark)
(1 mark)
(i)
It protects the whole of the circuit.
(1 mark)
(ii)
Any earth fault on the circuit.
(1 mark)
(e)
The MCB
(f)
Any TWO of:
(1 mark)
(2 marks)
●
The MCB would operate disconnecting
all the lights in the circuit.
●
The wiring and components in Fitting B
may have a much lower current rating.
●
The MCB may not trip and cause a
shock hazard due to a faulty fitting.
ET 36 ANSWERS – 11 SEPTEMBER 2010
3
Reference
Question 3
Marking notes
Marks
(a)
(b)
(c)
●
Use an ohmmeter.
●
Test between the cable ends.
resistance indicates a winding.
A low
(1 mark)
●
Each winding must have the same
resistance.
(1 mark)
●
Use an insulation resistance tester
(½ mark)
●
Use a test voltage of 500V d.c
(½ mark)
●
Test between
windings.
three
(1 mark)
●
Test between each of the three
windings and the motor framework
(1 mark)
●
Each test result must be not less than
1 Megohm.
(1 mark)
each
(1 mark)
of
the
Any THREE of:
(3 marks)
●
Protective
earthing
continuity test.
conductor
●
Visual test.
●
Polarity test.
●
Check the integrity of the terminations
ET 36 ANSWERS – 11 SEPTEMBER 2010
4
Reference
Question 4
Marking notes
Marks
(a)
(i)
Ifault =
230
(½ mark)
(7 + 0.5)
=
Itotal =
=
(ii)
30.66A
(½ mark)
Ifault + Iload = 30.66 + 25
(½ mark)
55.66A
(1 mark)
The 30A fuses have a fusing factor (gG
Utilisation Category) of 1.5
Fusing current = 1.5 x 30 = 45 A
(½ mark)
Total current is 55.66A, which is more
than the fusing current of 45A
(½ mark)
The fuse will operate.
(b)
(i)
Ifault =
(1 mark)
230
(½ mark)
(7 + 12)
=
Itotal =
=
(ii)
12.1A
(½ mark)
Ifault + Iload = 12.1 + 25
(½ mark)
37.1A
(1 mark)
Total current is 37.1A, which is less
than the fusing current of 45A
(½ mark)
The fuse will not operate
(½ mark)
or
The fuse may take a long time to
operate.
(iii) Vd across Earth conductor equals shock
voltage
VdE =
IxR
=
12.1 x 12
=
145.2 V
(½ mark)
(½ mark)
Electric shock hazard of 145.2V frame
to earth exists
(1 mark)
ET 36 ANSWERS – 11 SEPTEMBER 2010
5
Reference
Question 5
Marking notes
Marks
(a)
Red line
L1
L2
White line
L3
Blue line
Neutral
bar
Earth Bar
C
D
B
A
Socket-outlet
E
Earth fault
Class 1 heater
(b)
●
Accurate fault loop drawn
(2 marks)
(i)
Between points A and B
(1 mark)
(ii)
Between points C and D
(1 mark)
(iii) Between points D and E
(1 mark)
ET 36 ANSWERS – 11 SEPTEMBER 2010
6
Reference
Question 5
Marking notes
Marks
(c)
Iload =
W
(½ mark)
V
=
2000
(½ mark)
230
IF
=
8.7 A
=
230
(1 mark)
(½ mark)
(0.5 + 0.67 + 60)
IT
=
3.76A
(1 mark)
=
IL + IF
(½ mark)
=
8.7 + 3.76
=
12.46A
(1 mark)
ET 36 ANSWERS – 11 SEPTEMBER 2010
7
Reference
Question 6
Marking notes
Marks
(a)
(b)
●
Polarity
●
Earth Continuity
●
Earth Loop Impedance
●
RCD Test
(i)
Any ONE of:
(ii)
(2 marks)
●
Earth loop impedance test
●
RCD test
●
Polarity test
(1 mark) The question is not
specific
enough
to
indicate which of the
tests should be carried
out.
Any ONE of the following tests:
Earth Loop Impedance
This test has to show
●
Use of an earth loop impedance
tester
(1 mark)
●
Testing
between
the
active
conductor and the protective
earthing conductor on the socket
out let
(1 mark)
●
Impedance low enough to operate
protection
(1 mark)
RCD Test
This test has to show
●
Use of RCD tester
●
Plugging
outlet
●
RCD should operate within 300
mS at the maximum residual
current of 30 mA.
test
into
the
socket
Polarity Test
This test has to show
(c)
(i)
●
Use of voltage tester
●
Testing
between
active
and
neutral; active and earth; and
neutral and earth on the socket
outlet
●
Values of 230V between active
and neutral and active and earth.
0V between neutral and earth.
Any ONE of:
●
Earth Continuity
(1 mark) The question is
specific
enough
ET 36 ANSWERS – 11 SEPTEMBER 2010
not
to
8
Reference
Question 6
Marking notes
Marks
●
(ii)
indicate which of the
tests should be carried
out.
Polarity
Any One of the following tests:
Earth continuity
This test has to show:
●
Use of an ohmmeter
●
Testing between the earth contact
on the plug and the switchboard
earth bar
●
A reading low enough to operate
the protective device.
Polarity
(1 mark)
(1 mark)
(1 mark)
This test has to show:
●
●
●
Use of an ohmmeter
The
phase
conductor
being
switched
The neutral and earth conductors
going to the correct terminals
ET 36 ANSWERS – 11 SEPTEMBER 2010
9
Reference
Question 7
Marking notes
Marks
(a)
Fuse
Start
Stop
O/L
P
Coil
Hold-in
contact
P
Fuse
●
Correctly connected 400V supply
●
Correctly connected start button
●
Correctly connected stop button
(1 mark) If a 230V working circuit
shown
award
(½ mark) is
2½marks
(½ mark)
●
Correctly connected hold-in contact
(½ mark)
●
Correctly connected coil
(½ mark)
●
Correctly connected thermal overload
(½ mark)
●
400V working circuit
(1½ marks)
(b)
Remote start/stop
station
3 core cable
The cable is connected so that:
(c)
●
The remote stop is in series with the
local stop button
(1 mark)
●
The remote start in parallel with the
local start button
(1 mark)
●
Working circuit
(1 mark)
The stop
parallel.
buttons
have
been
wired
in
(2 marks)
ET 36 ANSWERS – 11 SEPTEMBER 2010
10
Reference
Question 8
Marking notes
Marks
(a)
E
N
L
Tripping Device
Test
button
Sensing
coil/toroid
Class I equipment load
●
Correctly connected test circuit and
resistance
(1 mark) Hazardous conditions
●
(1 mark) ●
●
Correctly connected sensing coil/toroid
●
Correctly connected phase, neutral and
earth.
(1 mark)
●
Correctly connected tripping circuit
(1 mark)
●
●
●
●
(b)
It has to be tested to ensure that it is
voltage-dependent (that is, it will not
automatically reset if supply is restored.)
(2 marks)
(c)
Yes
(½ mark)
The RCD detects the imbalance regardless of
A short circuit
No test resistance
in the test circuit.
The socket outlet is
not earthed
The active of the
test button circuit
is connected to the
supply side of the
main contacts
The neutral is not
switched
No
neutral
conductor shown
(½ mark)
ET 36 ANSWERS – 11 SEPTEMBER 2010
11
Reference
Question 8
Marking notes
Marks
the polarity of the supply.
(d)
PRCD
Portable Residual Current Device.
(1 mark)
RCBO
Residual Circuit Breaker
Overcurrent protection
(1 mark)
SRCD
Socket Residual Current Device
with
(1 mark)
ET 36 ANSWERS – 11 SEPTEMBER 2010
12
Reference
Question 9
Marking notes
Marks
(a)
(i)
Hazardous condition:
●
The star point not
earthed
L1
L2
L3
(ii)
●
Correct delta connections
(½ mark)
●
Correct star connections
(½ mark)
●
Star point earthed
(½ mark)
Secondary phase voltage
=
11000
(½ mark)
43.3
=
254 V
(1 mark)
(iii) Secondary line voltage
=
254 x √3
(½ mark)
=
440 Volts
(1 mark)
(iv) Primary line current
=
kVA x 1000
(½ mark)
√3 x VL
=
150000
(½ mark)
√3 x 11000
=
(v)
7.87 A
(1 mark)
Secondary line current
=
150000
(½ mark)
√3 x 440
=
(b)
196.83 A
(1 mark)
Any ONE of:
(2 marks)
●
The iron core is laminated.
●
Special types of alloys are used for the
core
ET 36 ANSWERS – 11 SEPTEMBER 2010
13