Re-take - Useful Information for 2394 :

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Q/As 2394 .

Which of the following is the minimum short circuit test current for a low résistance ohmmeter .

50mA
100mA
200mA
300mA

This is the requirements for the test instrument , as identified in BS-7671 Regulation 612.2.1. & GN-3 .

 

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Q/As 2394 .

A continuity test is to be carried out and the instrument has been confirmed as being in calibration and undamaged , which of the following is the remaining check that needs to be carried out to confirm the instrument is suitable to use .

it is set to 230V a.c.
The battery is in a satisfactory condition
The leads comply with GS-38
it is set to read high values of résistance

The condition of the battery is the remaining check to be made on the test instrument to confirm it is suitable for use . Where the test voltage is ≤ 50V a.c. the requirement for GS-38 compliant leads is not necessary , providing the maximum short circuit is unlikely to cause a high energy flashover , The maximum current for this test is ≤ 200mA , therefore GS-38 compliant leads are nut required

 

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Q/As 2394 .

Which of the following factors directly affects the conductor résistance of a cable .

a) Insulation and CSA
b) Length and CSA
c) Length and Insulation
d) Load current and CSA

of the four options given , ( b ) is the only one in which both components will directly affect the conductor résistance , Load current will only have an indirect effect on conductor résistance by raising the conductor temperature .

 

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Q/As 2394 .

Two identical cables are connected in parallel , Which of the following describes the effect on the combined conductor résistance compared to the single cable .

Doubled
Quartered
Halved
No effect

The two cables will have the same résistance , which when connected in parallel will result in their combined résistance being half that of one single cable .

 

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Q/As 2394 .

Which of the following factors affect the insulation résistance of a cable .

Conductor cross-sectional area
(b) Cable length
Installation method
Load current .

of the four options given ( b ) is the only one which will have an effect on the insulation résistance of the cable .

 

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Q/As 2394 .

Four identical circuits are connected to a distribution board , Which of the following describes the effect on the combined insulation résistance at the ( DB ) when compared to that of a single circuit .

Doubled
Quartered
Halved
No effect

When a number of circuits are connected at a distribution board the cables are connected in parallel and so insulation résistance will be lower . in this case there are four identical cable connected in parallel and so the combined insulation résistance will be a quarter of the insulation résistance of a single cable . if the cables' insulation résistances are extremely high then this effect may not be registered by the test instrument , as the overall insulation résistance of the combined circuits may be above the upper limit of the test instrument .

 

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Q/As 2394 .

A test for continuity of circuit protective conductors is carried out at every point on a circuit , Which of the following describes the purpose of this test .

To confirm correct polarity
To confirm the conductors are the correct CSA
To determine the ( R1 + R2 ) value for the circuit
(d) To confirm exposed conductive parts are connected to the MET .

of the four options given , is the only one which identifies the purpose of the test . The other three may be determined as a result of the test ,
depending on the method used , but are not the purpose of carrying out the test .

 

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Q/As 2394 .

Which of the following correctly describes the relationship between prospective fault current and the fault current rating of a BS-EN-60898-1 circuit breaker .

( Ipƒ ) ≥ ( Icn )
( Ipƒ ) ≤ ( Icn )
( Ipƒ ) ≤ ( In )
( Ipƒ ) ≥ ( In )

The ( Icn ) of the circuit breaker is the maximum current the circuit breaker can safely disconnect . although it may then no longer be serviceable . to meet the requirements this value must be equal to or higher than the maximum fault current which may occur .

 

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Question 2394 :

What is faster that Usain Bolt , My fingers typing . Gentlemen please hit the thank you button at your own leisure

 

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Q/As 2394 .

Which of the following is not a method for determining prospective earth fault current at the origin of an installation

Enquiry to the DNO
Direct measurement
Calculation using measured ( Ze ) and the supply voltage .
(d) Calculation using measured ( Zs ) and the supply voltage .

prospective fault current is measured to determine the maximum fault current which may occur , Any impedance measurement taken at the end of a circuit will be higher than that at the origin of the circuit , As a result the value obtained from the calculation in ( d ) is not going to produce the maximum value .

 

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Gentlemen am Not downloading this for fun . Your Arse is on the line here . ( Time & Money ) Forewarned is forearmed

On your own Head 2394 / 5

Take Heed .. from C&Gs .. " Warning "

Answer that describes dangerous techniques and a heavy penalty will be applied to answers that describe invalid procedures

The installations being inspected and tested are generally energised , unless information is given to the contrary . ◄◄◄
As a result the need to isolate in order to carry out certain tests must be included in the test process . The description would generally need to include :

the need to obtain permission , to safety isolate and lock off and to retain the key .
A description of the actual safe isolation process would only need to be provided where expressly asked for in the Question .

This qualification relates to the periodic inspection of electrical installations and so encompasses the preparation , client discussion and the inspection , testing and reporting process , The testing process will include the need to confirm that test results are compliant with the requirements of BS-7671: Candidates will also need to identify non-compliances and award appropriate classification codes , Candidates will also be expected to identify the safety and practical aspects of periodic inspection .

Inspection:
The inspection process is a vital part of the periodic inspection process , many conditions may be identified during the inspection which would not be revealed by testing alone . Candidates are expected to be aware of the areas to be inspected , the actual items to be checked and the human senses to be Used whilst inspecting those items , Recording the outcome for each inspection item is also a requirement of the reporting process .

Candidates should be aware that the Schedule of inspections for the periodic inspection of installations provided in BS-7671: & GN-3 , together with the ( Examples of items requiring inspection given in BS-7671: , Appendix 6 ) provides detailed information on the items of inspection for these installations , Candidates should become familiar with the items they are to consider , inspect and record and this will greatly improve both their understanding of the inspection process and their success in any related questions .

( How to not screw UP ) ... Read the related Questions

Confirmation of compliance ; of the installation with the requirements of BS-7671: forms part of the periodic inspection process , The source document generally identifies that all testing is carried out at an ambient temperature of ( 20ºC ) This means that test values will not be at normal operating temperature and so this must be considered and where necessary compensated for .

 

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Younger viewers . making you Aware , The answers are always in front of you . BS-7671:2011: & GN-3

Question Test Sheet
This paper relates to a " Closed book Exam " & therefore candidates should attempt the exam paper with no study-notes or text books .

Q) Minor Electrical Installation Work Certificate does not require a record of :
recap ; R/P.393. Your Q .

System earthing arrangements ... Part 2 : Installation details .
Departures , if any BS-7671:2008: ... Part 1 : Description of minor works
Method of fault protection ... Part 2 : Installation details .
Prospective fault current .

 

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Younger viewers . Just knocked up this for an Example . Stretching it

A New installation is protected against faults by ( ADS ) When inspecting this method of protection , which of the following is not a essential check .

Your Q . Protective Conductors

a) Earthing conductor .
b) Circuit protective conductor(s)
c) Main protective bonding conductor(s)
d) Fire barriers

R/P.27 . Earthing Conductor is defined as “ A protective conductor connecting the Main Earthing Terminal of an installation to an earth electrode or to other means of earthing”

Protective conductors for Earthing are known as Circuit Protective Conductors (CPCs)
R/P.27 . Earthing : Connection of the exposed-conductive-parts of an installation to the main earthing terminal of that installation .

R/P.27 . Equipotential bonding is defined as: “ Electrical connection maintaining various exposed-conductive-parts and extraneous-conductive-parts at substantially the same potential ”

543.2.1. Types of Protective conductor .
A protective conductor may consist of one or more of the following :
(i) single - core cable
(ii) conductor in a cable .

542.4.1. In every installation a main earthing terminal shall be provided to connect the following to the ( Earthing conductor )
(i) The circuit protective conductor(s)
(ii) The protective bonding conductor(s)

recap ; R/P37 . Fig 2.1.

1 , 2 , 3 , 4 , Protective conductors .
Circuit protective conductor(s)
Main protective bonding conductor(s)
Earthing Conductor
4 .. Where required .

 

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Principles , practices & Legislation for the periodic inspection of electrical installation . 2395-302 .

Written Examination

in this paper you will often be asked to provide longer answers for questions that ask you to " describe " or " explain " These are often related to inspection and / or test procedures and you are required to demonstrate your knowledge of the inspection and / or test process . ( 10 )

example ;
Describe , in detail , the procedure for carrying out a test to confirm , the continuity of the main protective bonding conductor connected to the water installation pipework .

there are a number of pointers in the question , The answer is worth 10 marks and the question asks for " detail " so a full description is required .

As this examination only considers periodic inspection , you can determine that the installation is energised , you would always need to confirm that it is safe to isolate the installation or circuit and state that safe isolation is carried out . On occasions the question may state that the permission to isolate has been given or safe isolation has been carried out

Such questions may also be preceded by a number of auxiliary questions relating to the actions required before or after the test concerned , in such cases these items would not need to be repeated in the procedure .

There is no such indication for this question and so the requirements must be included and so you will need to include obtaining permission and the isolation procedure in your description .

Option 1 ;
The answer could be provided as a description of the process in a " story " format , as in the following .

" " story format "
I would obtain permission from the client to isolate the installation , carry out safe isolation of the whole installation , lock off and retain the ( unique key ) I would then disconnect one end of the main protective bonding conductor . I would select a low-résistance ohmmeter , check condition and function , select a suitable long test lead and ( null the test leads ) , I would connect one test lead to the disconnected main protective bonding conductor and the other lead to the far end of the conductor , Test and record the results , I would then reconnect the main protective bonding conductor before reenergising the supply "

This answer and similar variations are perfectly acceptable and you would obtain the marks for the question , however , it does rely on the procedure being written down correctly the first time without missing any steps , it involves a considerable amount of writing and it is often difficult to spot any errors during the examination when you read back through your answer .

Option 2 ;
The answer can be structured as a set of bullet points .
• Obtain permission to isolate the supply
• Safety isolate , lock off and retain the key . PS unique key
• Disconnect the main protective bonding conductor at one end
• Select a low-résistance ohmmeter , check condition and function
• Select a suitable long test lead
• Null the test leads
• Connect the test leads to the disconnected bonding conductor and the far end .
• Test and record the result
• Reconnect the main protective bonding conductor before reenergising the supply

There is plenty of space to write down your answer . so you can leave a space between each bullet point , giving you the opportunity to add an additional line in later if you have missed a step in the process , you can also read through your answer much quicker and identify any omissions

Additional bullet points may be added at the end if you find you have missed out some information providing they identify when the action is carried out . for example if you find you have omitted to null the test leads the final bullet point could be added as ;

• Before carrying out the test the test leads should be nulled .

The second option , with the use of the bullets points , is generally quicker to complete , less prone to errors or omissions and clearly demonstrates your understanding of the test process , you can try both methods to find out which best suits you , however , Option 2 is strongly recommended .

it is important to recognise the need to carry out testing in a way that does not put yourself or anyone else at risk , also the test must be carried out in such a manner that produces valid results . No marks will be awarded for an answer that describes dangerous techniques and a heavy penalty will be applied to answers that describe invalid procedures .

 

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What will be asked of You . 2394

Be able to test electrical installations prior to them being placed into service

You are required to be able to :
Select the test instrument(s) and their accessories for tests to include :

Continuity .
Insulation résistance .
Polarity .
Earth electrode résistance .
Earth fault loop impedance .
Prospective fault current .
RCD operation .
Phase sequence .
Functional testing .

Carry out tests in accordance with BS-7671: & GN-3 .
to include :
Continuity including
□ main protective bonding conductors'
□ circuit protective conductors'
□ ring final circuits
□ insulation résistance
□ polarity
□ external earth fault loop impedance (Ze)
□ system earth fault loop impedance (Zs) ... ( Z impedance , s system ) Zs
□ prospective fault current
□ RCD operation including additional protection
□ phase sequence
□ functional testing

Confirm compliance by verifying test results

Complete appropriate documentation in accordance with the BS-7671: GN-3 , including :
• Electrical Inspections Certificate
• Schedule of Inspections
• Schedule of Test results

Be able to commission electrotechnical systems and equipment .

You are required to be able to :
□ Clarify the commissioning procedures with relevant persons .
□ Carry out the commissioning of circuits , accessories and equipment to confirm functionality .

 

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2395-01 . Understand what is being asked of You . ( 1 )

Outcome 1 , Understand the requirements for completing the safe isolation of electrical circuits and installation
You are require to be able :
□ State : the requirements of the Electricity at Work Regulations for the safe inspection of electrical systems and equipment
□ State : specify the appropriate procedure for completing safe isolation
□ State : the reasons for carrying out safe isolation
□ State : the implications of not carrying out safe isolation
□ Identify : the Health & Safety requirements which apply when inspecting , testing and commissioning electrical installations and circuits

Outcome 2 , Understand the requirements for inspection , testing and recording the condition of electrical installations
You are require to be able :
□ State : the purpose of periodic inspection of electrical installations
□ State : the requirements of periodic inspection
□ Identify : the relevant documents associated with the inspection & testing and condition reporting of an electrical installation

Outcome 3 , Understand the requirements for completing the periodic inspection of electrical installations
You are require to be able :
□ Select : appropriate items to be checked during the inspection process
□ Identify : the human senses which can be used during the inspection process
□ State : how the senses can be used during the inspection process
□ Specify the requirements for the inspection of electrical installations in service

Outcome 4 , Understand the difference between periodic inspection and initial verification
You are require to be able :
□ State : the reasons for requiring a periodic inspection as identified in GN-3
□ State : the need to determine the Extent & Limitations of a periodic inspection with the client and interested third parties before work begins
□ Explain : the application of sampling when carrying out periodic inspection & testing to include:

• Factors which determine the extent of sampling
• Situations where sampling may not be appropriate
• Identify the need to record agreements with the client and third parties on the condition report
• Explain the reasons why testing may be undertaken in a different order to that identified in BS-7671: for initial verification
• Identify the considerations which need to be made during a periodic inspection to ensure the safety of the persons & livestock on the premises
• State the purpose of the observations and classification codes in regards to :
□ the observations to be recorded
□ appropriate recommendations to be made

• State the action to be taken if a dangerous situation is identified during the periodic inspection as identified in BS-7671: & GN-3
• Explain the action required by the inspector when the Extent & Limitations agreed may not be achieved on site
• Explain the difference between defects and non-compliances
• Explain why fault finding and remedial work does not form part of the periodic inspection process

Outcome 5 , Understand the requirements for safe testing of electrical installations which have been placed in service
You are require to be able :
□ State : the tests to be carried out during the periodic inspection of an electrical installation in accordance with the BS-7671: & GN-3
□ Identify : the appropriate instrument for each test to be carried out in terms of :
• Checks to confirm the instrument is fit for purpose
• Identifying the right scale / settings of the instrument appropriate to the test to be carried out
□ Specify the requirements for the safe use of instruments to be used for testing and commissioning , to include :
• Checks required to prove that test instruments and leads are safe and functioning correctly
• The need for instruments to be regularly checked and calibrated

 

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2395-01 . (2)

Outcome 6 , Understand the requirements for testing before circuits are energised
You are require to be able :
□ State : why it is necessary to verify the continuity , to include :
• protective bonding conductors
• circuit protective conductors
• ring final circuit conductors

□ State : the methods for verifying the continuity , to include :
• protective conductors
• ring final circuit conductors
□ Explain : the factors that affect conductors résistance values
□ Specify : the procedures for completing insulation résistance testing
□ State : the effects on insulation résistance values that the following can have :
• Cables connected in parallel
• Variations in cable length
□ Explain : why it is necessary to verify polarity
□ State : the procedures for verifying polarity

Outcome 7 , Understand the requirements for testing energised installations
You are require to be able :
□ State : the method of measuring earth electrode résistance to include :
• installations forming part of a TT system
• Generators and transformers

□ Describe : common earth fault loop paths
□ State : the methods for verifying protection by automatic disconnection of supply
□ Identify : the requirements for the measurement of prospective fault current
□ Specify : the methods for determining prospective fault current
□ Verify : the suitability of protective devices for prospective fault current
□ Specify : the methods for testing the operation of residual current devices
□ State : the reasons for verifying phase sequence
□ State : the methods used to verify phase sequence
□ Describe : the methods used to verify voltage drop
□ State : the cause of voltage drop in an electrical installation
□ Determine : voltage drop
□ State : the need for functional testing
□ Identify : items which require functional testing
□ State : the appropriate procedures for dealing with clients during the periodic inspection process

Outcome 8 , Understand and Interpret test rests
You are require to be able :
□ Explain : why it is necessary to confirm whether test results comply with standard values
□ Analyse test results to determine action to be taken

Outcome 9 , Understand the requirements for the completion of electrical installation condition reports and associated documentation
You are require to be able :
□ Explain : the purpose of an electrical installation condition report
□ State : the information that must be contained within an electrical installation condition report
□ Explain : the requirements for the recording and retention of completed electrical installation condition reports , in accordance with BS-7671:

Outcome 10 , Be able to confirm safety of system and equipment prior to completion of inspection and testing
You are require to be able :
□ Carry out safe isolation procedures in accordance with regulatory requirements
□ Comply with the hearth and safety requirements of themselves and others within the work location during the periodic process
□ Check the safety of electrical systems prior to the commencement of inspection and testing .

 

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2395-01 . (3)

Outcome 11 , Be able to carry out inspection of electrical installations
You are require to be able :
□ Identify : a safe system of work appropriate to the work activity
□ Carry : out a periodic inspection of an electrical installation in accordance with the requirements of BS-7671: & GN-3
□ Complete a condition Report Inspection Schedule in accordance with the requirements of BS-7671: & GN-3

Outcome 12 , Be able to test electrical installations in service
You are require to be able
□ Select the test instruments and their accessories for tests to include :
• continuity
• insulation résistance
• polarity
• earth electrode résistance
• earth fault loop impedance
• prospective fault current
• RCD operation
• phase sequence
• functional testing

□ Carry : out tests in accordance with BS-7671: & GN-3 to include :
• continuity including
º main protective bonding conductors
º circuit protective conductors
º ring final circuits
• Insulation résistance
• polarity
• earth fault loop impedance ( Ze )
• system earth fault loop impedance ( Zs )
• prospective fault current
• RCD operation including additional protection
• phase sequence
• functional testing
• additional protection
• verification of voltage drop

□ Compare test results with standard requirements and previous test results

Outcome 13 , Produce a condition report with recorded observations and classifications
You are require to be able
□ Use information to determine defects and non-compliances to include :
• dwellings
• other premises
□ Complete Electrical Installation Condition Report and associated documents
□ Handover of the condition report to the client with appropriate information and guidance regarding actions to be taken

 

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Putting your answers on paper

it is important to remember when you are answering the questions that the examiners cannot ;

• ask you further questions to establish your understanding , they can only award marks for the information you provide .
• assume what you mean or know , they can only interpret the information they are given in your answers .


Test instruments should be calibrated in accordance with the manufacturer's instructions to ensure accurate test results , in addition to calibration which of the flowing should be carried out and recorded .

□ Regular confirmation of the instruments compliance with BS-7671:
□ Extension of the instrument warranty period
□ Regular instrument accuracy checks
□ Closed circuit voltage checks .

Regular instruments accuracy checks are required to ensure the instrument continues to provide accuracy results , as identified in GN-3 , 4.2. if regular checks are not carried out it may result in the need to re-inspect and test earlier installations , once an instrument defect is identified

Which of the following is the maximum voltage above which test leads must comply with the requirements of GS-38
□ 25V a.c.
□ 25V d.c.
□ 50V a.c.
□ 50V d.c.

Where the test voltages are ≤ 50V a.c. the requirement for GS-38 compliant leads is not necessary where the short circuit fault current is unliky to cause a high energy flashover , test current for this test is ≥ 200mA

Which of the following requirements form GS-38 applies to test equipment which requires more than one test lead .
□ The leads must be at least 1m in length
□ The leads must have a CSA of at least 1.5mm[SUP]2[/SUP]
□ The leads must be colour coded for identification ... is the only one of the listed items described in GS-38
□ The leads must be permanently attached to the instrument .

 

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Remember , What grades . Pass or Fail .

Which of the following instrument must be used to measure the earth electrode résistance for a standby generator .... ◄►( PS keep this in mind )
□ Earth fault loop impedance
□ Insulation résistance tester
□ Low résistance ohmmeter
□ Earth electrode résistance tester .. PS , I no off two Electricians' that got this on 2394.

There is no return path for the current when testing the earth electrode for a transformer or generator , Therefore the test must be undertaken using an Earth electrode résistance tester and not an earth fault loop impedance tester . The other options are not suitable .

Which of the following is not a method used to determine that automatic disconnection of supply for a final circuit is achieved .
□ Direct measurement of ( Zs ) at the furthest point on the circuit
□ Adding the measured value of ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) the ( Ze ) found by enquiry
□ Adding the measured value ( Ze ) and the measured value of ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) for the circuit
□ Measuring the prospective fault current at the furthest point on the circuit

Prospective fault current is measured to determine the maximum fault current which may occur at the point where protective devices are installed to ensure they are able to safely disconnect the fault current. Any measurement taken at the end of a circuit will be lower than that at the origin of the circuit and so not the maximum value

The purpose of the measurement of prospective fault current at the origin of an electrical installation is to determine whether
□ The required disconnection time is met
□ The earth fault loop path can withstand the fault current
□ The protective device can safely disconnect the maximum fault current
□ Supplementary earth fault path are required

Prospective fault current is measured to determine the maximum fault current which may occur at the point where the protective device is installed to ensure the device is able to safely disconnect the fault current

Which of the following is not a method for determining prospective earth fault current at the origin of an instrument
□ Enquiry to the DNO
□ Direct measurement
□ Calculation using measured ( Ze ) and the supply voltage
□ Calculation using measured ( Zs ) and the supply voltage

Prospective fault current is measured to determine the maximum fault current which may occur , Any impedance measurement taken at the end of a circuit will be higher than that at the origin of the circuit , As a result the value obtained from the calculation in ( d ) is not going to produce the maximum value

 

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Yes this Question has been asked on 2394:
PS . there are still in the Regulations BS-3036 fuse

S1A devices are 1KA. in sizes 5 ,15 , 20 , 30 , 45 , & 60A
S2A devices are 2kA. in sizes 5 ,15 , 20 , 30 , 45 , 60 & 100A
S4A devices are 4kA. in sizes 30, 45, 60 & 100A

Q ) Which of the following protective device is never suitable for determining prospective earth fault current at the origin of an installation
□ BS-3036 fuse
□ BS-88-3 fuse
□ BS-88-2 fuse
□ BS-EN-60898-1 circuit breaker .. 6kA / 10kA .

The maximum breaking capacity of a BS-3036 fuse is 4kA , so it is not a suitable protective device where the fault current is 10kA .

• Note : that the devices are available in three types relating to short-circuit capacity, i.e. 1, 2 & 4kA.

Out but not gone . ?? ... BS-3036 fuse

O.S.G. P/72 .
Regulation 533.1.1.3 of BS-7671:2008 refer
states that a fuse shall preferably be of the cartridge type but this does not preclude the use and installation of semi-enclosed fuses. Where a semi- enclosed fuse is selected, the carrier shall be fitted with an element in accordance with the manufacturer’s instructions,

533.1.1.3 permits the fitting of a single element of tinned copper wire of the appropriate diameter specified in Table 53.1 P/140

Terminology
Those fuses referred to as " rewirable fuses " are correctly termed semi enclosed fuses as they are partially enclosed within the fuse-carrier.

semi-enclosed fuse ... BS-3036 fuse
a fuse in which the fuse element is neither in free air ( other than the air in any external containing case not forming part of the fuse ) nor totally enclosed

Rated breaking capacity
BS-3036 defines breaking capacity as: breaking-capacity rating a prospective current stated by the manufacturer to be the greatest

BS 3036 are suitable in certain applications only.
BS 3036 semi-enclosed fuses cannot be relied upon to operate within 4 hours at 1.45 times the nominal current of the fuse element.
Correct protection can be obtained by modifying the normal condition ( In ≤ Iz ) such that the fuse rating does not exceed 1.45 ÷ 2 = 0.725 times the rating of the circuit conductor

For this reason, larger cables may need to be selected where overload protection is provided by semi-enclosed fuses than when it is provided by a cartridge fuse or fuses or circuit-breaker ( Appendix 4 of BS 7671 and Guidance Note 6 give further guidance ). 2008

Fault Current Protection . from my old 16th Edition notes .

The purpose of fault current protection is to disconnect the supply speedily and restrict damage and danger as far as possible .
All parts of an installation must be protected against the highest ( pƒc ) that can be anticipated at any particular point in the system The ( pƒc ) is at is highest at the intake position and will decrease ( or attenuate ) through the installation as the résistance of cables is added to the fault part .

Short Circuit Rating : Under short-circuit conditions there will be a considerable current surge . This is the ( pƒc ) .. for a standard 100A supply the ( PFC ) often quoted by DNO is 16 000A ( kA ) The value is never as high as that .

much depends upon the arrangement of the supply network and the distance from the substation

Rated short-circuit capacity ( Icn ) of the circuit breaker conforming to BS-EN-60898-1 is the value of the ultimate short circuit breaking capacity assigned by the manufacture .

circuit breaker also has a corresponding " in-service " short circuit breaking capacity ( Ics ) which is either equal to , or lower than , the rated short circuit capacity ( Icn )

Conveniently , ( Icn & Ics ) are the same value for circuit breakers conforming to BS-EN-60898 having an ultimate short-circuit capacity of ( 6kA ) or Less .

 

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Useful junk .

Overcurrent protective device . BS-EN-60898-1
it is only the rated short circuit capacity ( Icn ) that is marked on the circuit breaker 6000A (kA)

Younger members . ( Maximum )
Regulations : specify various maximum disconnection times for different types of circuit(s) for TN - TT - systems

41.3. ( Maximum ) disconnection times
Final circuits not exceeding 32A .. TN - 0.4s .. TT - 0.2s
Final circuits exceeding 32A & for distribution circuits .. TN - 5s .. TT - 1s

from table 41.1. the above values are applicable for a nominal voltage 120V < Uo ≤ 230V

Circuit breaker BS-EN-60898-1 has the characteristics such that it will disconnect the supply in less than 0.1s providing that the maximum earth fault loop impedance permitted by BS-7671: for the circuit being protected is not exceeded .

( PFC ) of an earth fault depends on the maximum earth fault loop impedance at the point of a fault .
if that impedance is lower than the maximum permitted value in Table 41.3. Chapter 41 ... ( Protection against Electric Shock ) disconnection of the supply will occur in less than 0.1s , circuit breaker conforms to BS-EN-60898-1

 

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2394:
Putting your answers on paper . Due to the time constraints of the exam , do not waste time by copying out the question .
Facts . The markings of your answers does not include any penalties or additional marks for spelling or grammar .

Useful junk .

Overcurrent protective device .
circuit breakers conforming BS-EN-60898-1 is deemed to comply . but there is a need to take account of the increase in temperature and résistance of circuit conductors as a result of overcurrets .

Regulation reminds us . Circuit loop impedance . 612.9. Earth fault loop impedance

Circuit loop impedance given in regulations cover this condition and should not be exceeded where the conductor's are at their normal operating temperature . Regulation reminds us ; if the conductors are at a different temperature when tested , which is usually around ( 20ºC ) the reading should be adjusted accordingly .

This requirement often presents a problem for the person carrying out tests . who is unlikely to be certain of the normal operating temperature . Where this is the case , it is safe to assume the maximum permissible operating temperature of the cable which , in the case of ( thermoplastic PVC ) insulated cables , is ( 70ºC )

2394 : derived for typical test condition's .. View for thought's

Most of your answers are in BS-7671:2011: & GN-3 .

 

[amberleaf]

.. 2014 .

100mA BS-EN-61008-1 RCD is installed in a TT installation to provide fault protection , Which of the following identifies the maximum test current to be applied and the maximum disconnection time at that test current when testing the RCD
□ 100mA & 200mA
□ 100mA & 300mA
□ 500mA & 200mA
□ 500mA & 300mA

The RCD is provided for fault protection and not additional protection and the ( 1 x I∆n ) is the maximum test current that needs to be applied , As this is a BS-EN-61008-1 device the maximum disconnection time is 300mS .

A maximum disconnection time of 200mS applies to some older RCDs manufactured to a British Standard , but not to BS-EN-61008-1 device(s)

Older RCDs .. BS - only .. 200mS
BS-EN-61008-1 .. 300mS

A 30mA BS-EN-61009-1 RCBO is installed on a socket-outlet circuit to provide additional protection , Which of the following identifies the maximum test current to be applied and the maximum disconnection time at that test current .
□ 30mA & 300mA
□ 30mA & 200mA
□ 150mA & 300mA
□ 150mA & 40mS

You're Q . 5 x 30mA = 150mA

The RCBO is provided for additional protection and the ( 5 x I∆n ) is the maximum fault current that needs to be applied . As this device is providing additional protection , the maximum disconnection time is ( 40mS ) as required by BS-7671: Regulation 414.1.1.

 

[amberleaf]

Younger members . in collage
please tell you classmates about this forum . I have did everything but sit your Exam 2394. Amberleaf

 

[amberleaf]

Which of the following is not a suitable method of confirming phase sequence , Read the Question carefully under Exam conditions

□ Measurement using a rotating disc type instrument
□ Measurement using an indicator type instrument
□ Measurement using an approved voltage indicator
□ Checking polarity and connections throughout the installation

the method of determining phase sequence are given in GN-3 , An approved voltage indicator cannot be used to determine phase sequence .

GN-3 . P/57 . PS what can be used . Phase sequence testing . take your Q from above ▲ ▲ ▲
• rotating disc type . Yeah
• indicator lamp type . Yeah

 

[amberleaf]

let's stretch it out a bit .

Q) The purpose of a functional test on an RCD carried out quarterly , using the integral test button , is to confirm

□ The correct functioning of the RCD in the event of a fault
□ That the operation of the RCD complies with BS-7671:
□ That the RCD operates in the event of a short circuit
□ The correct mechanical operation of the RCD mechanism

Operating the RCD test button will only confirm the mechanical operation of the RCD

GN-3 . P/59 . Integral test device .
612.13.1. An Integral test device is incorporated in each RCD , This device enables the functioning of the mechanical parts of the RCD to be verified by pressing the button marked ( T ) or Test

GN-3 . points out some down falls . to watch for . As an Inspector . !! ( Have you Verify )
• The continuity of the earthing conductor or the associated circuit protective conductors Ps RCDs Earth fault . etc
• Any earth electrode or other means of earthing
• Any other part of the associated installation earthing
• The sensitivity of the device .

Point to Remember , Yes we all use Multifunction testers nowadays .

GN-3 P/58 . Operation of residual current devices . 411.4.5.
for each of the tests , readings should be taken on both positive and negative half-cycles and the longer operating time recorded

Point to note : The RCD test button will only operate the RCD if it is energized

 

[amberleaf]

A test is carried out on the interlock for switching an alternative power supply , Which of the following is the type of test being undertaken
□ Functional
□ Continuity
□ Load
□ Installation

This test confirms the operation of the interlocking device and is therefore a , Your Q . Functional test .

 

[amberleaf]

Q) Following a test of earth fault loop impedanc4e ( Zs ) the following results are compared with the values given in BS-7671: Which of the following describes the purpose of the comparison

□ To confirm correct test method are used
□ To confirm conductor csa is suitable for the circuit
□ To determine whether disconnection times will be achieved under earth fault conditions
□ To determine whether the protective devices will operate under short circuit conditions

The operation of a protective device under earth fault conditions relies upon a sufficiently large current flowing , from Ohms Law the supply voltage and impedance of the system will determine the fault current . The ( Zs ) value is the variable and can therefore be used to determine whether disconnection will be achieved within the required time .

 

[amberleaf]

Q) Checking that the measured test results meet the required values will enable the inspector to confirm that the electrical installation is :
□ Correctly installed
□ Safe to be in service
□ Compliant with BS-5266
□ Never going to be dangerous

Providing the test result obtained during the inspection & testing meet the requirements of BS-7671: and the design requirements , the installation will be suitable for use .

 

[amberleaf]

( 1 ) Inspection & Testing 2394 & 2395

Section B - All questions carry equal marks , Answer all three questions . show all calculations

Questions 4 to 6 all refer to the enclosed scenario , see source document . Ensure you read this scenario before attempting these questions

4 a) The loop length for the office ring final circuit is 60m and all the socket-outlets are connected directly into the ring , Determine , showing all calculations

i) the expected ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) value ... 7 marks

ii) the expected measured ( Zs ) value ... 4 marks

b ) When measuring ( Zs ) for the toilet lighting circuit the circuit breaker operates .
State why the circuit breaker tripped during the earth fault loop impedance test ... 4 marks

5) The circuit for the tree phase saw bench is installed to the local isolator for the saw.
a) A test of earth fault loop impedance is to be carried out on the saw circuit .

i) State the test instrument to be used . ... 2 marks
ii) State the document that specifies the requirements for the test leads ... 2 marks
iii) Describe , in detail , how the test would be carried out . .. 6 marks

b) i) Determine , using the information in Figures 1 and 2 , the expected ( Zs ) value for the circuit . Show all calculations .. 3 marks

ii) Explain , in detail , why the measured value for this circuit is lower than the value calculated in b) i) above .. 2 marks

6 ) Describe , with the aid of a fully labelled diagram , the earth fault loop path for the outside lighting circuit . .. 15 marks

 

[amberleaf]

( 2 )

Section B -
Remember that the answers to the following questions must relate to the scenario contained in the Source Document .

4 ) a ) The loop length for the office ring final circuit is 60m and all the socket-outlets are connected directly into the ring , Determine ,
showing all calculations

i) the expected ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) test value .. 7 marks

Answer : r[SUP]1[/SUP] + r[SUP]2 [/SUP] = 60 x ( 7.41 + 12.10 ) 1000 = 1.17Ω .. ( sum in a sum ; 7.41 + 12.10 = 19.51 ; 60 x 19.51 ÷ 1000 = 1.17Ω )
R[SUP]1[/SUP] + R[SUP]2 [/SUP]= 1.17 ÷ 4 = 0.293Ω

There is more than one way to determine this value but any correct method would be given the marks . The use of a temperature correction factor in this calculation is not appropriate because the question asks for an expected " test " value and the Source Document states that testing is to be carried out at ( 20ºC ) which is the same temperature as that which applies to the mΩ/m values in Fig 2

The calculation could have also been laid out as show below ;

r[SUP]1 [/SUP]= 60 x 7.41 / 1000 = 0.445Ω
r[SUP]2 [/SUP] = 60 x 12.10 / 1000 = 0.726Ω
R[SUP]1[/SUP] + R[SUP]2 [/SUP]= 0.445 + 0.726 / 4 = 0.293Ω .... ( sum in a sum ; 0.445 + 0.726 = 1.171 ÷ 4 = 0.29275 . ( 0.293Ω )

4 a) ii) the expected measured ( Zs ) value .. 4 marks
Answer ; Zs = Ze + R[SUP]1[/SUP] + R[SUP]2 [/SUP]= 0.11 + 0.29 = 0.40Ω

C .
The answer to this question is dependent upon the answer given in, a) i) above . it is not normal practice to penalise a candidate twice for the same error. With this in mind , marks would be awarded for the correct formula , correct total , including units .

4 b) When measuring ( Zs ) for the toilet lighting circuit the circuit breaker operates , State why the circuit breaker tripped during the earth fault loop impedance test .. 4 marks

Answer :
The test current may be greater than the instantaneous tripping current of the circuit breaker causing it to operate .

C .
The examiner is looking for any statement that indicates an understanding of what has happened , Reference to an RCD tripping would not gain any marks as the circuit is not protected by an RCD , This information is shown in Figure 1 . in the Source Document .

5) The circuit for the three phase saw bench is installed to the local isolator for the saw .
a) A test of earth fault loop impedance is to be carried out on the saw circuit .
i) State the test instrument to be used ... 2 marks

5 a) ii) State the document that specifies the requirements for the test leads .. 2 marks

Answer : Leads to GS-38 .

5 a ) iii) Describe , in detail , how the test would be carried out .. 6 marks

Answer :
Supply on
Local isolator
• Access live terminals in the local isolator
• At the incoming terminals of the local isolator test
º L1 to isolator earthing terminal
º L2 to isolator earthing terminal
º L3 to isolator earthing terminal
• Close the local isolator cover
• Record highest result

 

[amberleaf]

( 3 )

C .
The structure of the question is intended to help the candidate identify all relevant information .

A list has been used to answer a) iii) because it is easy to write down , easy to check and time efficient . Each statement must include sufficient information to make it clear how the test would be carried out . it is not necessary to include the instrument title and lead requirement as part of this answer as they have already been identified in i) and ii) above

The test is carried out between each line conductor and the isolator earthing terminal . if a candidate described the isolator earthing terminal as " the earthing terminal " earth " or " the cpc " this would also gain the marks.

if the wrong test was described in the answer , such as R[SUP]1[/SUP] + R[SUP]2 [/SUP]test and the results is then added to ( Zs ) then no marks would be awarded . The question specifically asks for an earth fault loop impedance test and not any test method that could be used to determine ( Zs )

Answers that include dangerous procedures would score zero marks .

5 b ) i) Determine , using the information in Figure 1 & 2 , the expected ( Zs ) value for the circuit . Show all calculations ... 3 marks

Answer : Zs = Ze + R[SUP]1[/SUP] + R[SUP]2 [/SUP] = 0.11 + 2 x 7.41 x 15 / 1000 = 0.11 + 0.22 = 0.33Ω

C .
Marks are awarded for each stage of the calculation . Setting out the calculation and showing each step makes it easy for the examiner to follow the process . it also helps the examiner award marks when the answer is not fully correct . Answers that are not clear , do not contain all steps and contain errors are likely to score fewer marks than an answer containing errors but is clearly laid out . This is because in the latter case the examiner can easily identify the correct parts of the calculation.

5 b ) ii) Explain , in detail , why the measured value for this circuit is lower than the value calculated in b) i) above .. 2 marks

Answer : Résistance ( R[SUP]2[/SUP] ) of is reduced due to steel conduit being in parallel with the cpc .

C .
Although the answer is only worth 2 marks , the question does state " in detail " The examiner is looking for a complete answer , Answers such as " parallel paths " will not score 2 marks as this is not in detail .

6 ) Describe , with the aid of a fully labelled diagram , the earth fault loop path for the outside lighting circuit 15 marks .

Answer : Drawing . TN-C-S System Earth Fault .

The fault path is :
from the point of fault
Along the cpc to the MET
from the MET via the earthing conductor to the supplier's PEN terminal
Along the PEN conductor to the supply transformer winding
Through the transformer winding , along the line conductor to the fault

C .
This answer contains both a fully labelled diagram and a description of the path , Providing the diagram is very clear and the path is shown on the diagram , as is the case above , then full marks would be awarded , The description of the path gives additional information for the examiner to consider when awarding marks . it is in the interest of the candidates to give as much information as possible . if an incorrect system is described / drawn then no marks would be awarded . This is also true if the diagram is incomplete and the type of system cannot be determined .

 

[amberleaf]

...................................................................................................................................................................................................................................................

Source Document . ◄ ▼▼▼
Scenario ( Section B - Questions 4 to 6 )

An existing building has been converted into a builders store on the ground floor with the offices above The electrical installation and supply to the building forms part of a 400 / 230V TN-C-S system . ( Ze is 0.11Ω ) and the prospective fault current ( Ipƒ ) is 4.1 kA

All circuits within the store area are wired in ( 70ºC ) thermoplastic single-core cables , with copper conductors , in surface mounted , galvanised steel trunking and conduit .

All circuits in the office area are wired in ( 70ºC ) flat thermoplastic multicore and cpc cable installed in pvc trunking and the ceiling voids .

Inspection and testing is to be carried out in an ambient temperature of ( 20ºC )

detail of conductor résistance in mΩ/m at ( 20ºC ) are shown in ( Figure 2 )

( Figure 2 )
Conductor size mm[SUP]2 [/SUP]1.5 ............ Résistance in mΩ/m at ( 20ºC ) 12.10
Conductor size mm[SUP]2 [/SUP]2.5 ............ Résistance in mΩ/m at ( 20ºC ) 7.41
Conductor size mm[SUP]2 [/SUP]10 ............ Résistance in mΩ/m at ( 20ºC ) 1.83

One drawing to come . ► ( Figure 1 ) worst case scenario I'll type it out

 

[amberleaf]

Question 2394 :

What is faster that Usain Bolt , My fingers typing . Gentlemen please hit the thank you button at your own leisure

 

[Richard Burns]

Source document for Section B scenario, the answers to the above questions must relate to this scenario.

 

[amberleaf]

New :

(*1 ) 2394 : Q/As On Paper you're Inspecting & Testing . To prove yourself . As deemed by BS-7671: & GN-3

Answers , & Comments and advice where appropriate .

Section A
1 a) i) State one statutory document to which the inspector may refer whilst carrying out an inspection and test of an electrical installation .. (1/M)

Ans ; The Electricity at Work Regulation 1989 ◄ The Wording The correct meaning . end off

C;
because the question has asked of one answer , only the first answer given by the candidate would be considered , This is because candidates sometimes write down everything they can remember in the hope that one of the answers may be correct .
This is not showing ( KNOWLEDGE or UNDERSTANDING ) ........................ Make a statement

" ► " EaWR " or " EWR " are acceptable , ►►►►► Electricity at Work " ACT " ►►►►► is incorrect

( PS what does Point's make Prizes ) Your Ticket .

1 a) ii) State tow non-statutory publications to which the inspector may refer whilst carrying out an inspection and test of an electrical installation .. ( 2/M )

Ans ; BS-7671:2008(2011) & IET Guidance Note 3 .. ◄ Your Q . The Wording The correct meaning . end off

C;
Because the question has asked for two answers , only the first two answers given by the candidate would be considered , Other Guidance Notes would be acceptable but the MOST relevant is Guidance Note 3 .

The On-Site Guide is a perfectly acceptable alternative answer . ( Note not ◄► O.S.G. & GN-3 ) Full wording at all times .

 

[amberleaf]

(*2 ) 2394 :

1 a) iii) State the title given in ( LAW ) to the inspector whilst carrying out the inspection of an electrical installation ... 1/M

Ans ; Dutyholder

C;
This question refers to the requirements of The Electricity at Work Regulation's and the term " Dutyholder " refers to anyone having a duty of care to other

1 a) iv) State the legal status of the inspector .. 1/M

Ans ; Competent

C;
Regulation 16 of The Electricity at Work Regulation's requires persons to be competent when carrying out any activity on an electrical system where the work may give rise to danger .

1 b) State the scope of the Minor Electrical Installation Works Certificate ... 2/M

Ans ; Alteration or addition to an existing circuit .

C;
A key part of this answer is the reference to " Existing Circuit " An alteration or addition to an existing installation is NOT within the SCOPE of a Minor Electrical Installation Works Certificate ............ 2394 : Take heed

Any description covering the essential points " alteration " or " addition and " existing circuit " would get the marks .

 

[amberleaf]

(*3 ) 2394 : you will get this one . Yeah

2 a ) i) List five items to be inspected on PVC conduct system .. 5/M

Ans ;
• Conduit system overall
• Fixings
• Bends
• Draw-in points
• Joints

2 a) ii) Explain what is being inspected for each of the items identified in a ) i ) above .. 5/M

Ans ;
• Conduit system overall - conduit system is complete
• Fixings - Sufficient saddles fixed correctly
• Bends - Bending radius not too tight and bend not damaged
• Draw-in points - Sufficient number so that cables can be draw in without damage
• Joints - are secure and fit correctly between lengths and at boxes

C;
The question is in ( Two parts ) i) asks for what is to be inspected and ii) requires the candidate to identify precisely the nature of the ( INSPECTION ) Sometimes these ( Two parts ) are combined into one question

it is important for the candidate to state clearly what is being ( INSPECTED ) and what in particular they would be looking for

" Conduit system not damaged " " conduit complies with appropriate British Standard " , " expansion joints fitted where necessary " and " bushes are tight " are all acceptable answers

Any answer relating to cables , cable terminations and conduit capacity would not be acceptable , although the capacity of the conduit could have been addressed by reference to the conduit being the correct size specified by the designer

 

[amberleaf]

(*4 ) 2394 :

3 a ) Explain , in detail , why an earth fault loop impedance test would need to be carried out on ( Existing circuits ) after the changing of a consumer unit within a domestic installation .. 5/M

You're Q here . ▼▼▼ Have you altered any characteristics ; On Paper you're Inspecting & Testing . To prove yourself . As deemed by BS-7671: & GN-3 . PS we are all sing out the same hymn sheet here .

Ans ;

Existing circuit protective devices have been removed and new protective devices have been fitted , The characteristics of the new devices are likely to be different for previous devices , Therefore it must be confirmed that the earth fault loop impedance is low enough so that the required disconnection times will be met .

C;
The question ask for an explanation " in detail " so the description needs to be comprehensive if full marks are to be awarded , Answers that referred to disconnection and re-connection of conductors and the reliability of those connections would score marks

3 b) i) Explain , why the earthing conductor in an installation must be disconnected from the MET when measuring ( Ze ) ... 2/M

Ans ; To remove parallel earth paths so that the intended fault path can be confirmed to be reliable

C;
if the parallel earth paths are not removed during the test then the reliability of the test result is in DOUBT .