Answers to SPARKS Magazine – September Issue 2014

© Sparks Magazine 1

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


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?

Question 2: State the precaution / s that need to be considered before isolating any electrical circuit, groups of circuits or electrical equipment?

Question 3: Briefly explain the recommended procedure for isolating a circuit or groups of electrical circuits.

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.

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.

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.


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.

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.

The means of isolation may be:

• Circuit - breaker • Fuse • Plug and socket, • Switch – disconnector • Isolator


Question 5: Write a method statement for the safe isolation procedure from the point of securely isolating the circuit.

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

• 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


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


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

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

Excess metal can be removed with a flat file

A file is used to remove excess metal using a physical action.


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


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

Task 4: How can file teeth become damaged?

Task 5: Explain how a file can be cleaned and any precautions that must be taken

Task 6: Suggest three safety observations to be adopted when using files

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.

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.

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.

• 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


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

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.

• Alterations and additions to existing electrical installations. • Replacement of equipment but not distribution boards or consumers control

units.

A copy of the certificate must be retained by:

• The contractor (copy) • The person ordering the work/s. (original)


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


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. Description of minor works installation of a fused-‐connection unit to existing ring final circuit 2. Location / Address 243 Widecombe Place, Belchester DN0 4EX 3. Date minor works completed 1st April 2014 4. 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____________


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 single-phase a.c. circuits.

Task 1: Identify the correct name for each of the instruments identified in the circuit diagram below:

L

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:

1

2 3

By obtaining measurements for current, voltage and power in the inductive circuit the power factor (pf), of the circuit can be calculated, the formula is: pf = W or pf = true power VA apparent power


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.

PAGE 27 – Test Your Knowledge – Match The Definition

Question Number

Answer letter

Check

1 D 2 H 3 J 4 F 5 I 6 E 7 A 8 G 9 C

10 B

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 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?

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.

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?

Ca from Table F1 is 0.96

Ca from Table F1 is 0.92

Cg from Table F3 is 0.73

(Note the final number of installed circuits will be 7)


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?

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. cross-sectional-area), is needed?

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?

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?

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

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

Use table F4 (i), Column 2 (i.e. Reference method A and single-phase circuits)

Current rating of this cable is 151A

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


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?

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


Note: Table F6 provides current carrying capacity and voltage drop data in a single table

Use table F6, Column 1 for cross-sectional-area and Column 8 for 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.


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?

Final note: Always check your selection of data and your calculations

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.


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 Which one of the following is a Transmission voltage?

Answer

a 230V

b 400V

c 11kV

d 400kV X

No 2 The public electricity supply is generated at a frequency of Answer

a 60Hz

b 50Hz X

c 25Hz

d 15Hz

No 3 A ring – main is the correct definition for Answer

a A public power supply generated at a power station

b The connection of local sub-stations distributing electricity to customers

X

c The connection of 13A socket-outlets around a building

d The electricity distribution system in a large commercial premises


No 4 A three-phase and neutral supply can be abbreviated Answer

a TPNS

b ATPN

c PNS

d TPN X

No 5 The domestic electricity supply system that requires the customer to provide an earth electrode is known as a

Answer

a TN system

b TT system X

c TNS system

d TN-C-S system

No 6 Electrical energy is measured by a Answer

a kWh meter X

b Watt meter

c Ammeter

d Voltmeter


No 7 The correct sequence of electrical equipment at the supply intake location of a domestic residence is

Answer

a Service fuse, CCU, energy meter

b Energy meter, CCU, service fuse

c CCU, energy meter, service fuse

d Service fuse, energy meter, CCU X

No 8 The abbreviation MET is which one of the following? Answer

a Main earthing terminal X

b Main electrode terminal

c Multiple earth terminal

d Multiple electrode termination

No 9 The generation of electricity is based on the principle of

Answer

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 X


No 10 The correct symbol for electrical mains supply intake is Answer

a

b

c

X

d

Pass 60% or 6/10


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 electro-technical 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

Answer

a 2.75m X

b 2.55m

c 2.00m

d 1.75m

No 2 Which one of the following does not provide overload protection?

Answer

a BS88 HRC fuse

b RCD X

c BS3036 semi-enclosed fuse

d BS1362 cartridge fuse

The maximum height above floor level that the switch shown in figure 1 can be located is


No 3 In which one of the following systems is neutral and protective functions combined in a single conductor throughout?

Answer

a TN-S

b TN-C-S

c TT

d TN-C X

No 4 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

Answer

a 0.34 X

b 1.96

c 1.04

d 1.44

No 5

Answer

a Enclosure not complete and no line conductor

b IP rating compromised and un-protected cable entry X

c Un-protected cable entry and no barrier

d Insufficient circuit breakers and no barrier

Figure 2 shows a metal-clad CCU. The figure indicates two failures to comply with BS7671 requirements, these are:


No 6 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:

Answer

a Ca and Cg X

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

Answer

a Cable c.s.a.

b Location of circuit in respect to the CCU

c Type of cable sheath

d mV/A/m X

No 8 A circuit supplying a distribution board from a supply intake position is called a

Answer

a Secondary mains circuit

b Distribution circuit X

c Sub circuit

d Sub distribution circuit


No 9 A fuse operates on the Answer

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 X

No 10

Answer

a Switch – fuse

b Isolator

c Fuse – switch X

d Functional switch

Pass 60% or 6/10

Figure 3 shows a


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 3m Area = 5 x 3 Area = 15m2 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 = L x W 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 = L x W 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


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 = BIL 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 this is as far as we need to go, so let’s put it to the test B x I

L = F L = = 24 L = 4 so again the rearrangement is correct B x I 2 x 3


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


PAGE 42-43 Preparing for Assessment

Fault Protection

Protective devices

Thermal Thermal

Fuses Circuit Breakers Magnetic

BS3036 – semi-‐enclosed BS EN 60898

BS88 – HRC or HBC RCBO’s – BS EN 61009

BS1362 -‐ Cartridge


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) Continuity of protective conductors including main and supplementary bonding (ii) Continuity of ring – final circuit conductors (iii) 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 …’

• 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.


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?


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 Electricity at Work Regulations 1989 – Regulations is written ‘Act’ o Health & Safety at Work Act 1974 – Act is written ‘Regulations’

Other titles that are often incorrectly stated:

o Electrical Installation Certificate o Schedule of Inspections o Schedule of Test Results o 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


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 linked-

out 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.


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)

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?

a) I = P / V

b) I = V / R

c) I = F / BL

e = Blv

e = 4 x 2.5 x 6

e = 60V


3) State three non - renewable power sources that are likely to be found in the UK today.

4) By using a suitable diagram show the components and connections for a single – tube fluorescent luminaire.

5) List three types of overcurrent protective devices that may be found in a commercial electrical installation

6) Calculate the illumination at point (EA) immediately beneath the light source.

800cd

3.5m

EA

• Coal

• Oil

• Gas

Diagram should indicate:

• Choke • Starter • Tube • PF capacitor

• BS88 fuse • Circuit-breaker • RCBO

EA = I / d²

EA = 800 / 3.5²

EA = 65.3lx


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

8) State the meaning of the following terms: Zs; Ze; R1; R2:

9) Name three starting methods for electric motors.

10) Use a suitable method to determine the angle formed between the perpendicular height and hypotenuse of the triangle shown below.

3m 8m

a) Circuit protective conductor b) Earthing conductor c) Main protective bonding conductor d) Supplementary protective bonding conductor

Zs = earth fault loop impedance

Ze = external section of the earth loop impedance

R1 = Resistance of the line conductor

R2 = Resistance of the cpc

a) Direct – on – line b) Star – Delta c) Wound – Rotor or Rotor resistance

Alternatively: Auto-transformer / Soft-start

Cosine = Adjacent / Hypotenuse

Cos = 3 / 8

Cos = 0.375

To find the angle in degrees, invert or second function cosine 0.375

This gives: 67.9º


PAGE 48 - Reading and Understanding

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!


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’…

Documents

Answers to SPARKS Magazine – September Issue 2014