Download Answers to SPARKS Magazine – September Issue 2014

 ANSWERS TO SPARKS MAG SEPTEMBER 2014 ISSUE
PAGE 4–5 Spot The Mistake
1. CPC damaged
2. Hole should not be more than 1mm
3. Conduit kinked
4. Same as 2
5. Terminal screw into cable insulation
6. Set too big. Should just clear obstruction
7. Same as 5
8. CPC damaged
9. Set too big. Cables from switches appear to be a little short
1 © Sparks Magazine PAGE 10-12 Safe Isolation of Power Supplies
Question 1:
List the HSE recommended test equipment that will be needed before safe isolation
can be carried out?
The Health & Safety Executive (HSE) Guidance Note, GS38, identifies the electrical test
equipment recommended for use by electricians.
The recommendation is to use purpose built voltage test instruments compliant with the
guidance given in GS38. The use of non-contact voltage indicators (voltage sticks),
multi-meters and neon screwdrivers, should not be used.
To ensure the correct working of the test instrument it should be ‘proved’ to be working
on a known live source or proprietary proving unit before and after use.
Question 2:
State the precaution / s that need to be considered before isolating any electrical
circuit, groups of circuits or electrical equipment?
The precautions to be taken before work is carried out on low voltage electrical
equipment or circuits, is that:
• The correct point of isolation is identified
• That permission is granted for the isolation of the power supply
Note:
Checks must be made that the circuit / circuits can be isolated and that no harm can be
done by isolating, and subsequently reinstating the power supply. This procedure
should involve talking to the customer or supervisor and agreeing that isolation can be
undertaken.
Question 3:
Briefly explain the recommended procedure for isolating a circuit or groups of
electrical circuits.
After checking that isolation can be made it is essential that the supply cannot
inadvertently be reinstated. A padlock or suitable locking device can be used for this
purpose. Caution notices will also be required at the point(s) of isolation.
In the event that more than one person will be working on the isolated circuit or
equipment it is advisable that each person has a unique padlock and key that they can
use to ensure security of the point of isolation until all personnel have completed their
work. A multi-lock device can be used into which a number of padlocks can be inserted.
2 © Sparks Magazine The basic principle of safe isolation is that the point of isolation is under the control of
the person who is carrying out the work on the isolated conductors.
Question 4:
Identify all of the possible means of isolation for a final circuit.
The means of isolation may be:
•
•
•
•
•
Circuit - breaker
Fuse
Plug and socket,
Switch – disconnector
Isolator
All personnel involved in work on electrical systems and equipment must be
competent and, where necessary, be suitably instructed on safe systems of work.
Personnel should be provided with written instructions, and have access to,
appropriate locking-off devices, warning notices, a voltage detector and proving unit.
Permit – to – Work:
The permit-to-work system must be applied to work on high voltage (HV) systems
that have been made ‘dead’ and for certain low voltage (LV) work such as the case
when more than one person will be working on the isolated circuit
A Permit is a statement that a circuit or item of equipment has been safely isolated
and it is therefore safe for work to commence.
Note:
Permits should not be used for live working as this can cause confusion and possible
danger. Further information regarding permits, are given in the HSE document
HSG85.
In some situations it may be necessary to provide a Method Statement detailing the
activities that are to take place, including safe isolation.
3 © Sparks Magazine Question 5: Write a method statement for the safe isolation procedure from the
point of securely isolating the circuit.
•
All relevant points of isolation will be identified and locked off using a
padlock and unique key.
Note 1: The key will be kept by the person carrying out the work.
Note 2: In the case of several personnel working on the isolated circuits,
etc. a multi-lock hasp will be used to prevent access to the isolation device
until such time that all personnel have completed their work and removed
their padlocks from the hasp.
•
The approved voltage tester must be checked against a known power
supply or proving unit.
•
Access to the point at which proving –dead is to be carried will now need
to be made, i.e. the isolator or other point of isolation
•
Tests will need to be made between the live parts and / or live parts to
earth for the circuit / s to be worked on. If safe then continue procedure
otherwise seek advice from the supervisor.
•
On completion of testing at the point of isolation, re-prove the voltage
tester with the known source or proving unit
•
Commence work if safe to do so
Information:
Most leading agencies provide step-by-step guidance for carrying out safe-isolation.
It will be helpful to explore the guidance by looking at web sites. The HSE provide
comprehensive information regarding electricity at work and the precautions that
need to be taken when working on or near live conductors. See www.hse.gov.uk
4 © Sparks Magazine PAGE 16 – Matching Units and Symbols
1
G
2
D
3
J
4
A
5
B
6
I
7
E
8
C
9
F
10
H
PAGE 17 – Matching Units and Symbols
1–
C
2–
E
3–
F
4–
H
5-
G
6-
B
7-
A
8-
D
9-
J
10 - I
5 © Sparks Magazine PAGE 22-23 – Hand Tools
Worksheet #2 (Covering Outcome 5 sub-section 3 of Unit 305 ‘Understand the practices and
procedures for the preparation and installation of wiring systems and electro-technical equipment in
buildings, structures and the environment’ (Level 3 NVQ Diploma in Installing Electro-Technical
Systems and Equipment 2357-13 / 91)
Hand tools:
The electrician will need to use, and look after, a range of hand tools in order to carry-out
his/her duties. Apart from the generally accepted hand-tools such and pliers, screwdrivers
and stripping knife, an electrician will also need a hacksaw, engineers square and a range of
files.
The following tasks all refer to files, the various types available and the care needed to
ensure they last you a long time.
Files:
Task 1: Describe the purpose of a file
A file is used to remove excess metal using a physical action.
If for example the cut edge of a section of steel trunking is uneven a flat file can be used to
remove unwanted metal and thereby make the edge level or straight.
Trunking not cut
straight
6 Excess metal can be
removed with a flat file
© Sparks Magazine Types of file:
Task 2: Identify each of the following files
Single-cut flat file Double-cut or cross-cut Three-corner or
triangular Round or Rat tail Square Half-round 7 © Sparks Magazine The cutting ‘teeth’ of a file can be formed in various ways:
Rough or Bastard files have very course teeth that are cut across each other and are
designed to remove large quantities of material.
Second cut files have teeth cut one way only and are designed to cut equal layers of
material with the result the finish is generally smoother than that of the rough cut file.
A smooth file will have teeth cut at a smaller depth than the other files mentioned
above, the resulting cut is a smooth fine finish to the work-piece
•
•
•
Care of files:
Task 3: State how a file may be damaged
The metal used to make a file is very hard but can easily be broken. Excessive
pressure, twisting or levering the file is likely to result in it snapping.
Task 4: How can file teeth become damaged?
File teeth can easily be damaged by knocking one file against another or against a
hard metal surface such as a vice. It is possible to damage teeth by ‘attacking; the
work in a rough or violent manner.
Task 5: Explain how a file can be cleaned and any precautions that must be taken
When a file becomes clogged with metal particles, (swarf), the surface will appear
shinny. It is a good idea to clean out the swarf using a file – card or stiff wire brush.
Always wear eye protection when performing this task as small metal particles can
fly-up into your eyes.
Task 6: Suggest three safety observations to be adopted when using files
8 •
Never us a file without a handle, if the file jambs on the forward stroke the
tang is liable to push into your wrist.
•
If a handle comes off it is best to fit a new one, if this is not possible then
reuse the old handle but follow the same procedure as fitting a new one, i.e.
het the tang to red-hot and then push the tang into the handle until it is deep
enough to hide 50% of the tang.
•
Never use a broken file you will not be able to perform the job well
© Sparks Magazine Final note:
Always discard used files sensibly, if possible recycle the metal.
PAGE 24-25 Electric Certification
(Covering Outcome 5 of Unit 307 ‘Understand principles, practices and legislation for the inspection,
testing, commissioning and certification of electro-technical systems and equipment in buildings,
structures and the environment’ (Level 3 NVQ Diploma in Installing Electro-Technical Systems and
Equipment 2357-13 / 91)
The Minor Electrical Installation Works Certificate:
Task 1:
State the purpose of the Minor Electrical Installation Works Certificate
•
•
Alterations and additions to existing electrical installations.
Replacement of equipment but not distribution boards or consumers control
units.
The ‘certificate’ is a single sided A4 pro-forma on which all the necessary details relating to
the minor electrical installation work are stated.
Task 2:
State two persons that need to retain copies of the Minor Electrical Installation Works
Certificate when work has been completed.
A copy of the certificate must be retained by:
9 •
•
The contractor (copy)
The person ordering the work/s. (original)
© Sparks Magazine Task 3:
The following task requires you to study the installation details and complete a copy of the
attached Minor Electrical Installation Works Certificate
INSTALLATION DETAILS SET 1:
You have installed a fused-connection unit, (fused spur) on an existing 32A rated ring-final
circuit at ABC stores, 243 Widecombe Place, Belchester, DN0 4EX on 1st April 2014. The
original ring circuit was installed five years ago and looks in good condition as does the rest
of the electrical installation in the store. The supply system is TN-S and fault protection is by
ADS. The existing ring circuit is protected by a 32A Type B circuit-breaker to BS EN60898
and additional protection is provided by a 30mA RCD, the addition of the fused-connection
unit will not compromise the current rating of the existing ring-final circuit. No previous test
results are available to compare with the test results obtained when the addition was
completed. The ‘new’ test results are all within the expected range. Continuity of circuit
protective conductor and main protective bonding conductor is 0.1Ω and 0.5Ω respectively;
insulation resistance between all conductors is +200MΩ; polarity was confirmed; earth fault
loop impedance is 1.10Ω and the RCD reaction time test proved satisfactory with the I∆n at
25mS.
The main water service is bonded with 10mm 2 single-sheathed earth cable
10 © Sparks Magazine MINOR ELECTRICAL INSTALLATION WORKS CERTIFCIATE To be used for minor electrical installation work that does not include new circuits. PART 1: Description of minor works 1.
2.
3.
4.
Description of minor works installation of a fused-­‐connection unit to existing ring final circuit Location / Address 243 Widecombe Place, Belchester DN0 4EX Date minor works completed 1st April 2014 Details of departures, if any from BS7671:2008 None PART 2: Installation details 1. System earthing arrangement TN-­‐C-­‐S TN-­‐S 
 TT 2. Method of fault protection ADS 3. Protective device for the modified circuit Type __32A_CB_ Rating __Type B___ Comments on existing installation, including adequacy of earthing and bonding arrangements General appearance of the electrical installation seems to be in good condition PART 3: Essential tests Earth continuity satisfactory 
Insulation resistance: Line / neutral ________+200________MΩ Line / earth __________+200________MΩ Neutral / earth_______ +200 _______ MΩ Earth loop impedance____1.10______Ω Polarity satisfactory 
RCD operation (if applicable). Rated residual operating current I∆n__30_mA operating time of _25__ms at I∆n PART 4: Declaration I /we CERTIFY that the said works do not impair the safety of the existing installation, that the said works have been designed, constructed , inspected and tested in accordance with BS7671:2008, amended to __2011____, and that the said works, to the best of my/our knowledge and belief, at the time of my/our inspection complies with BS7671 except as detailed in Part 1 above. Name:___________your name __________ For and on behalf of _your company_____ Address___your company address _______ Signature: ___________XXX _____________ Position: ______Electrician ______________ Date: _________today’s date____________ 11 © Sparks Magazine PAGE 26 Connecting Electrical Measuring Instruments
(Covering Unit 309 Outcome 7 ‘Understand how different electrical properties can affect electrical
circuits, systems and equipment’. (Level 3 NVQ Diploma in Installing Electro-Technical Systems and
Equipment 2357-13 / 91)
Understanding the type and use of various electrical test instruments is important
because incorrect connection can seriously damage the instrument, the circuit in
which it is connected and could pose a danger to the operator.
The following tasks relate to the measuring or determination of power in singlephase a.c. circuits.
Task 1:
Identify the correct name for each of the instruments identified in the circuit diagram
below:
L
2 3 1 N
Key: 1 – Voltmeter
2 – Ammeter
3 – Wattmeter
Task 2:
State the purpose in measuring the electrical quantities at the points shown in the
circuit:
By obtaining measurements for current, voltage and power in the inductive circuit the power factor (pf), of the circuit can b e calculated, the formula is: pf = W or pf = true power VA apparent power 12 © Sparks Magazine Task 3:
Calculate the power rating (W) of an inductive load if the power factor is 0.85, the
current is 50A and the voltage is 230V.
pf = true power pf = W therefore W = pf x V x A apparent power VA W = 0.85 x 230 x 50 W = 9775 watts or 9.78kW (rounded up) PAGE 27 – Test Your Knowledge – Match The Definition
13 Question
Number
Answer
letter
1
2
3
4
5
6
7
8
9
10
D
H
J
F
I
E
A
G
C
B
Check

© Sparks Magazine PAGE 28-30 – Selecting Data using the IET On-Site Guide
Selecting data using the IET On-Site Guide
(Covering Outcome 3 of Unit 304 (or EAL equivalent) ‘Understand principles for selecting cables and
circuit protective devices’ (Level 3 NVQ Diploma in Installing Electro-Technical Systems and
Equipment 2357-13 / 91)
The following tasks will require reference to Appendix F of the IET On-Site Guide:
BS7671:2008 +A1 2011.
The main objective of this exercise is to locate and use technical information in preparation
for and in the calculation of suitable circuit cable sizes.
Questions: For each answer indicate the Table reference and column that is
applicable
1) A 90°C thermosetting PVC insulated cable is to be installed in an ambient temperature of
35°C, what is the rating factor for this cable?
Ca from Table F1 is 0.96
2) A non-sheathed mineral insulated cable is to be installed in a location where it cannot be
touched and the temperature is expected to reach 40°C, state the rating factor applicable to
this cable.
Ca from Table F1 is 0.92
3) A new multi-core cable is to be supported on a vertical cable tray with 6 other multi-core
cables. What is the rating factor to be applied to the new cable?
Cg from Table F3 is 0.73
(Note the final number of installed
circuits will be 7)
14 © Sparks Magazine 4) A new single-phase circuit is to be installed to method B in an existing steel trunking. The
new circuit is to be installed with 7 other single-phase circuits. What is the rating factor to be
applied to the new circuit?
Cg from Table F3 is 0.52
Note:
1. Reference Method B is enclosed
2. The final number of installed circuits will be 8 in number
3. In practice an assessment will need to be made in respect to the effect the new
circuit is likely to have on the current carrying capacities of the existing circuits
5) A three-phase circuit uses single-core insulated cable enclosed in conduit on a wall. The
cable is expected to carry a current of no more than 55A, what cable size, (i.e. crosssectional-area), is needed?
Use table F4 (i), Column 5 (i.e. for Reference method B and 3-phase circuits)
Nearest current to 55A is 68A, cable size 16mm2
6) A single – phase 70mm2 single core 70°C thermoplastic insulted cable is enclosed in steel
conduit on a thermally insulated wall, what is the maximum current rating for this cable?
Use table F4 (i), Column 2 (i.e. Reference method A and single-phase circuits)
Current rating of this cable is 151A
7) A multi-core cable with thermosetting insulation has a cross-sectional-area of 35mm2 and
supplies a single-phase circuit. What is the voltage drop per ampere per metre, (mV/A/m) for
this cable?
Use table F5 (ii), Column 1 for cross-sectional-area and Column 3 for mV/A/m
Value from column 3 is 1.25 mV/A/m
15 © Sparks Magazine 8) An insulated and sheathed flat cable 10mm2 is to be installed to Method C, i.e. clipped
direct to a surface. What is the maximum current rating of this cable, and the mV/A/m?
Use table F6, Column 1 for cross-sectional-area and Column 8 for mV/A/m
Value from column 8 is 4.4 mV/A/m
Note: Table F6 provides current carrying capacity and voltage drop data in a single table
9) An insulated and sheathed flat cable carries 25A for a length of 50m. If the cable is 6mm2
what is the total voltage drop for this cable?
Use table F6, Column 1 for cross-sectional-area and Column 8 for mV/A/m
Value from column 8 is 7.3 mV/A/m
The total or Actual Voltage Drop (AVD) = mV/A/m x Design current Ib x Length L
1000
AVD = 7.3 x 25 x 50
1000
AVD = 9.125 V
Note: In practice this value must be checked against the allowable voltage drop for the
circuit. Remember the allowable voltage drop will depend on the type of circuit, (see
paragraph 2 in Appendix F sub-section Voltage drop.
16 © Sparks Magazine 10) A single-phase multi-core thermosetting pvc insulated cable is to be installed with 3 other
circuits in a conduit. The conduit is to pass through an area where the ambient temperature
is likely to be 35°C. If the rating of the protective device is 32A what is the tabulated current
rating of the cable when the rating factors are applied?
Use table F1 (i) for Ca. This is 0.96
Use table F3
for Cg. This is 0.65 (i.e. for 4 circuits enclosed)
Total rating factor:
C = Ca x Cg
C = 0.96 x 0.65
C = 0.624
Tabulated current It = In (Note In is the nominal current setting of the protective device)
C
It = 32
0.624
It = 51.3A
From Table F4 (ii) the nearest size cable to 51.3A is 10mm2 rated at 52A.
Note: It will be necessary to confirm the voltage drop of this cable before accepting
10mm2 as being suitable.
Final note: Always check your selection of data and your calculations
17 © Sparks Magazine PAGE 32 – The Principles of Electrical Supply
Practice multiple-choice questions for the principles of electricity supply:
(Covering Outcome 2 of Unit 305/025 ‘Understand and carry out electrical work on domestic plumbing
and heating systems and components’ (Level 3 Domestic Plumbing and Heating City & Guilds 6189)
No 1
a
230V
b
400V
c
11kV
d
400kV
No 2
The public electricity supply is generated at a frequency of
a
60Hz
b
50Hz
c
25Hz
d
15Hz
No 3
18 Which one of the following is a Transmission voltage?
A ring – main is the correct definition for
a
A public power supply generated at a power station
b
The connection of local sub-stations distributing electricity
to customers
c
The connection of 13A socket-outlets around a building
d
The electricity distribution system in a large commercial
premises
Answer
X
Answer
X
Answer
X
© Sparks Magazine No 4
A three-phase and neutral supply can be abbreviated
a
TPNS
b
ATPN
c
PNS
d
TPN
No 5
The domestic electricity supply system that requires the
customer to provide an earth electrode is known as a
a
TN system
b
TT system
c
TNS system
d
TN-C-S system
No 6
19 Electrical energy is measured by a
a
kWh meter
b
Watt meter
c
Ammeter
d
Voltmeter
Answer
X
Answer
X
Answer
X
© Sparks Magazine No 7
The correct sequence of electrical equipment at the supply
intake location of a domestic residence is
a
Service fuse, CCU, energy meter
b
Energy meter, CCU, service fuse
c
CCU, energy meter, service fuse
d
Service fuse, energy meter, CCU
No 8
The abbreviation MET is which one of the following?
a
Main earthing terminal
b
Main electrode terminal
c
Multiple earth terminal
d
Multiple electrode termination
No 9
20 The generation of electricity is based on the principle of
a
The chemical effect of an electric current
b
The heating effect of electric current
c
Magnetic effect of an electric current
d
Cutting a conductor with a magnetic field
Answer
X
Answer
X
Answer
X
© Sparks Magazine No 10
The correct symbol for electrical mains supply intake is
Answer
a
b
c
X
d
Pass 60% or 6/10
21 © Sparks Magazine PAGE 33-34 Principles of Electrical Supply
Practice multiple-choice questions for the principles of electricity supply:
(Covering Unit 304 ‘Understand the principles of planning and selection for the installation of electrotechnical equipment and systems in buildings, structures and the environment’ (Level 3 NVQ Diploma
in Installing Electro-Technical Systems and Equipment 2357-13 / 91)
No 1
a
2.75m
b
2.55m
c
2.00m
d
1.75m
No 2
22 The maximum height above
floor level that the switch
shown in figure 1 can be
located is
Which one of the following does not provide overload
protection?
a
BS88 HRC fuse
b
RCD
c
BS3036 semi-enclosed fuse
d
BS1362 cartridge fuse
Answer
X
Answer
X
© Sparks Magazine No 3
In which one of the following systems is neutral and
protective functions combined in a single conductor
throughout?
a
TN-S
b
TN-C-S
c
TT
d
TN-C
No 4
0.34
b
1.96
c
1.04
d
1.44
Answer
X
The maximum value of earth fault loop impedance of a
temporary electrical load supplied at a nominal voltage
(Uo) of 55V and protected by a Type B circuit breaker
rated at 32A is
a
No 5
23 Answer
X
Figure 2 shows a metal-clad
CCU. The figure indicates
two failures to comply with
BS7671 requirements, these
are:
a
Enclosure not complete and no line conductor
b
IP rating compromised and un-protected cable entry
c
Un-protected cable entry and no barrier
d
Insufficient circuit breakers and no barrier
Answer
X
© Sparks Magazine No 6
a
Ca and Cg
b
Ca and Ci
c
Cg and Cf
d
Cg, Ci and Cf
No 7
The voltage-drop in a cable is determined from the design
current, length and
a
Cable c.s.a.
b
Location of circuit in respect to the CCU
c
Type of cable sheath
d
mV/A/m
No 8
24 A cable is to be installed together with other circuits in a
steel trunking. The wiring system passes through an area
of high ambient temperature, the rating factors to be
applied are:
A circuit supplying a distribution board from a supply intake
position is called a
a
Secondary mains circuit
b
Distribution circuit
c
Sub circuit
d
Sub distribution circuit
Answer
X
Answer
X
Answer
X
© Sparks Magazine No 9
A fuse operates on the
a
Effect of high temperature
b
Magnetic effect of an electric current
c
Electronic effect of an electric current
d
Thermal effect of an electric current
No 10
Answer
X
Figure 3 shows a
a
Switch – fuse
b
Isolator
c
Fuse – switch
d
Functional switch
Answer
X
Pass 60% or 6/10
25 © Sparks Magazine PAGE 36-37 Pythagoras Theorem
(see separate sheet)
PAGE 38-39 Voltage Drop
(see separate sheet)
PAGE 40-41 Transposing Formulae
Transposing formulae #1:
The manipulating of formulae can be one of the more difficult tasks confronting the
trainee electrician. The mere mention of ‘electrical science’ and the particularly the
word ‘formula’ often results in an immediate negative reaction such as ‘I am no good
at maths’, well, you don’t need to be, once you have mastered the basic rules and
been shown how to proceed step-by-step, the process is generally quite simple.
Consider the following:
a) How do we determine the area of the floor in this room?
5m
First we need to know how to determine area
Area = Length x width
Area = 5 x 3
Area = 15m2
3m
If we were not sure which side is length and width, does it actually matter? The
answer of course is NO, which - ever way we multiply the numbers the result is still
going to be 15
Next we need to consider the formula for area and simplify it to:
A=LxW
If we were given the length of one side of the room and the area, is it possible to find
the length of the other side?
Rule 1: When values are multiplied then we can divide and vice versa.
Let’s try this with the problem in (a) and see what happens if we want to find width:
A=LxW
A = L x W If we divide L x W by L then L will divide into itself once and 1 x W = W
L
26 © Sparks Magazine But we cannot simply forget L so we now divide A by L. In other words we divide the
other side of the equals sign.
A = W this is as far as we need to go so let’s re-write what we have like this:
L
W=A
with the figures inserted:
W = 15
answer: W = 3

L
5
If we had made a mistake, then the answer would not have resulted in (3) as we
knew it must be.
Inserting simple numbers into a formula before it is transposed can be a great help.
Try the following:
b) The force acting on a conductor lying at right-angles to a magnetic field is found
from the formula:
F = BI L
Where:
F = force in Newtons (N)
B = magnetic flux density in Tesla (T)
I = current in Amperes (A)
L = length of the conductor in metres (m)
Now, rearrange the formula to find L using the same steps as in (a) above:
Solution: F=BIL Allocate some simple numbers to the original formula, say B = 2, I = 3 and L = 4 F = 2 x 3 x 4 F = 24 Now we have figures for each unit in the formula we can transpose the original formula to find L F = B x I x L divide B x I x L by B x I B x I Now repeat the process on the other side of the equals sign F = L B x I this is as far as we need to go, so let’s put it to the test L = F L = = 24 L = 4  so again the rearrangement is correct
B x I 2 x 3 27 © Sparks Magazine c) The voltage induced into a conductor that is being cut by magnetic flux is found
from:
e = BLv
Where:
e = induced voltage (V)
B= flux density in Tesla (T)
L= Length of conductor affected by flux in metres (m)
v = velocity at which the conductor is cut by flux in metres per second (m/s)
Rearrange the formula to make (v) the subject.
Solution: e = BLv Allocate numbers as in (b) above and then rearrange the formula. The result should be:-­‐ v = e B x L 28 © Sparks Magazine PAGE 42-43 Preparing for Assessment
Fault Protection Protective devices Thermal Circuit Breakers Thermal Fuses Magnetic BS3036 – semi-­‐enclosed BS EN 60898 BS88 – HRC or HBC RCBO’s – BS EN 61009 BS1362 -­‐ Cartridge 29 © Sparks Magazine PAGE 44 – Written Assignment and Exam Advice
Written Assignment & Exam Guidance:
The purpose of the written assignment or examination is to establish your level of
understanding of the subject – questions are not designed to ‘catch-you-out’ or ‘trick’
questions designed to make you fail.
1) Interpreting the question being asked:
The greatest danger is to answer a question to which you know the answer, but is not
actually the question being asked.
Advice: Read the question carefully and make notes either on rough paper or on your
answer book – but be sure to put a line through the notes when you have answered the
question formally.
2) What a question requires you to do:
The wording of a question is important as it directs you to answer in a particular way.
Understanding the meaning of basic terms is therefore essential.
State: simply means exactly that – ‘state’. A short statement not a long winded
paragraph containing structured sentences – this is a waste of time. One word
answers are often all that is required.
E.g. State the first three tests that need to be performed on a newly completed electrical
installation containing ring final circuits:
•
Answer:
(i)
(ii)
(iii)
Continuity of protective conductors including main and supplementary bonding
Continuity of ring – final circuit conductors
Insulation resistance
List: this requires you to produce a list of actions or items. As with the ‘state’
question as described above your answer should be simple, brief and factual.
Note: If the question requires you to ‘list in the correct sequence…’ then that is exactly
what you must do. The ‘state’ question above could easily have been worded ‘List the first
three tests …’
•
•
30 Explain briefly: as suggested this type of question requires you to provide a brief
explanation about something, such as how to perform the R1+R2 test on a circuit.
© Sparks Magazine Note: Do not waffle the examiner will realise that you are ‘beating about the bush’ to avoid
answering the question – probably because you do not know the answer!
•
Explain with the aid of a diagram: again this is exactly what you must do. Your
answer will consist of both diagram, (drawn neatly and labelled as appropriate), and
a written explanation.
Note: If you only provide a written answer or a scruffy sketch then you will not receive full
marks for the answer.
•
With the aid of a fully labelled diagram: this is slightly different to the previous
requirement. The diagram needs to be drawn accurately, neatly and be ‘fully’
labelled.
Note: When asked to draw something a pencil and a ruler should be used. Always have an
eraser ready to modify the diagram should you make a mistake. (This will not be possible if
you have produced your drawing using ink.).
•
Show all calculations: to obtain the full marks for this type of question you will need
to show a formula, (in it original and transposed format if required), figures inserted
correctly into the formula, an answer with the correct units attached.
E.g. Determine, the value of fault current that is likely to flow, in the event of an earth fault
occurring in a circuit that has a nominal voltage of 230V and a measured Zs of 0.25Ω.
(Show all calculations)
Answer:
•
Zs = Uo / If
therefore
If = Uo / Zs
and
If = 230 / 0.25 = 920A
Describe: This type of question usually is reserved for Section B questions. You will
need to make a judgement of how much detail to go into. This can be done by
looking at the marks allocated – the more marks the more detail needed. And, the
time you have remaining – if you are short of time you will need to work fast, but this
often leads to missing-out important facts.
3) Terminology:
•
Correct terminology: absolutely essential in this examination.
DO - NOT use trade names such as ‘Megger’
Example:
A continuity tester is not an appropriate instrument for carrying out a continuity measurement
of a circuit protective conductor – why?
31 © Sparks Magazine A continuity tester may not be a low-reading ohmmeter but simply an indicator lamp or
buzzer – it will confirm continuity but it does not give you a precise reading of ohms which is
required to be entered onto the Schedule of Test Results.
•
Correct units: these must be stated when describing the required scale of a test
instrument as well as when quoting formula and providing figures in statements and
answers to calculations.
Remember: the following are the most commonly used symbols in questions relating to
testing and must be clearly understood.
Milli: mA or mΩ
Kilo: kA
Mega: MΩ
Amperes: A
Nominal voltage: Uo
•
Correct titles: so often candidates do not use the correct titles for statutory and / or
non-statutory documents, and, pro-forma that is to be used to record the data
collected when conducting an initial inspection or periodic inspection.
Note: The most common errors are:
o
o
Electricity at Work Regulations 1989 – Regulations is written ‘Act’
Health & Safety at Work Act 1974 – Act is written ‘Regulations’
Other titles that are often incorrectly stated:
o
o
o
o
Electrical Installation Certificate
Schedule of Inspections
Schedule of Test Results
Minor Electrical Installation Works Certificate
Further practice examples:
1) Question: Explain briefly what effect the increase in length has on conductor resistance.
(3 marks)
Answer: Conductor resistance increases as the length of the conductor increases.
Alternatively:
Answer: Conductor resistance is directly proportional to conductor length
32 © Sparks Magazine Note: Both answers are correct and do not contain unnecessary information or waffle. Full
marks would be awarded to either answer.
2) Question: State three documents that specifically relate to electrical installations (3
marks)
Answer:
• BS7671: 2008
• Guidance Note 3
• On-Site Guide
3) Question: Describe the procedure for carrying out an insulation resistance test on a
newly installed lighting circuit. (10 marks)
Answer:
•
•
•
•
•
•
•
•
•
•
Prepare the cable for termination at the distribution board
Make sure that any voltage sensitive devices, such as dimmer switches, are linkedout to prevent damage during testing.
Select an insulation resistance test instrument
Check the calibration of the instrument to ensure it is current
Check the condition of the test instrument and leads including the condition of the
batteries
Set the instrument to the MΩ scale at 500V dc.
Connect the instrument leads to the line and cpc at the distribution board.
Test the insulation resistance and record the result obtained
Repeat with the instrument connected to line and neutral and then neutral to cpc –
record all results obtained
The minimum acceptable insulation resistance test is 2.0MΩ but normally expect
more than 200MΩ as this is a new circuit.
Note: This is a question with 10 marks allocated to it and therefore will require a detailed
and structured answer as given above – not just a single sentence.
33 © Sparks Magazine PAGE – 46-47 Answering Written Questions
Answering written questions: The City & Guilds Level 3 2330-07 Units 302 and 303, and
the Level 3 NVQ Diploma Unit 309, requires written assessments to be completed. The
following questions are designed for you to practice answering short answer written
questions.
Remember:
a. Read the question.
b. Try to identify the key words and phrases that direct you to the type of answer that
the examiner is expecting.
c. Where a calculation is required always begin with the formula in its standard format
(before showing any transformation), then insert the figures and finally show the
answer.
d. ‘Sign-post’ your answers. If the question is in two parts, (a) and (b), then indicate that
your answers are for either (a) or (b), do not use any other sign-post such as (i) or (ii)
it is confusing to the assessor / examiner.
Here are a range of short-answer questions for you to practice. Answers are provided.
Questions:
1) Rearrange the following formulae to make current the subject of the formulae:
a) Power = volts x amps, (P = VI)
b) Resistance = volts / amps, (R = V/I)
c) Force = Flux density x current x length, (F=BIL)
a) I = P / V
b) I = V / R
c) I = F / BL
2) A conductor cuts a magnetic flux at right-angles at a rate of 6m / second. If the flux
density is 4T and the length of the conductor is 2.5m what is the value of the induced
e.m.f. in the conductor?
e = Blv
e = 4 x 2.5 x 6
e = 60V
34 © Sparks Magazine 3) State three non - renewable power sources that are likely to be found in the UK
today.
•
Coal
•
Oil
•
Gas
4) By using a suitable diagram show the components and connections for a single –
tube fluorescent luminaire.
Diagram should indicate:
•
•
•
•
Choke
Starter
Tube
PF capacitor
5) List three types of overcurrent protective devices that may be found in a commercial
electrical installation
•
•
•
BS88 fuse
Circuit-breaker
RCBO
6) Calculate the illumination at point (EA) immediately beneath the light source.
EA = I / d²
800cd
EA = 800 / 3.5²
3.5m
EA
35 EA = 65.3lx
© Sparks Magazine 7) State the correct name used to describe the earth in each of the following locations:
a) A final circuit
b) Between the MET and the incoming cable sheath
c) Between the MET and the main water service pipe
d) Between hot and cold metallic water pipes in a bathroom
a)
b)
c)
d)
Circuit protective conductor
Earthing conductor
Main protective bonding conductor
Supplementary protective bonding conductor
8) State the meaning of the following terms: Zs; Ze; R1; R2:
Zs = earth fault loop impedance
Ze = external section of the earth loop impedance
R1 = Resistance of the line conductor
R2 = Resistance of the cpc
9) Name three starting methods for electric motors.
a) Direct – on – line
b) Star – Delta
c) Wound – Rotor or Rotor resistance
Alternatively: Auto-transformer / Soft-start
10) Use a suitable method to determine the angle formed between the perpendicular
height and hypotenuse of the triangle shown below.
Cosine = Adjacent / Hypotenuse
Cos = 3 / 8
Cos = 0.375
3m
8m
To find the angle in degrees, invert or second
function cosine 0.375
This gives: 67.9º
36 © Sparks Magazine PAGE 48 - Reading and Understanding
37 1
How many animals of each species did Moses take aboard the Ark?
None – it was Noah
2
Divide 30 by ½ and add 10 (no calculators)
70
3
Some months in the year have 31 days, some have 30 days, how many have 28?
Every month has a 28th day
4
You go to bed at eight o’clock in the evening and set the alarm clock to go off at
nine in the morning, how many hours sleep would this allow?
You might not sleep at all so how can you say how many hours?
5
If a doctor gave you three tablets and told you to take one every half hour, how
long would they last?
How do you know how long a tablet will last?
6
How many sides does a circle have?
Two – one inside and one outside
7
How far can a dog run into the woods?
Half way then he is running out again
8
Which country has a fourth of July, Britain or America?
Both of course?
9
A man built a house of rectangular construction, each side having a southern
exposure. A bear came wandering by, what colour was the bear?
White – because it is a polar bear at the North pole
10
If you were alone in a deserted house at night and there was a lamp; a fire and a
candle and you only had one match which would you light first?
None of them – the house is deserted!
11
How many birthdays does the average man have?
One actual birthday
12
Why can’t a man living in York be buried west of the Trent?
Because he is living in York – he is not dead!
13
If you have two coins totalling 11 pence and one of the coins is not a 10 pence
piece, what are the two coins?
A 10p piece and a 1p piece - If one of the coins is not 10p then it must be
1p and the other is a 10p
14
How much dirt is there in a 2’x2’x4’ hole?
None it is a hole!
© Sparks Magazine 15
If two monkeys sit in a corner of a room and look at another pair in another corner
and so forth until every pair in a corner looks at another pair, how many monkeys
could say that they were looking at other monkeys?
None of them - as monkey’s do not talk
16
Would it be all right for a man to marry his widows’ sister?
No – because he would be dead.
17
If you drove a bus leaving Croydon with 40 passengers, dropped off seven and
picked up two at Addiscombe, stopped at Sanderstead and picked up ten, went
to Purley, dropped off eight there and picked up five, then drove on to arrive in
London two hours later, what would the drivers name be?
What is your name? It is you because it says ‘If you’…
38 © Sparks Magazine