Re-take - Useful Information for 2394 :

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On rate mode . O.S.G. refer to

The value can be used to [ determine the earth fault loop impedance ] ( Zs ) of the circuit to verify compliance with the loop impedance requirements of BS-7671: see 10.3.6.

10.3.6. Earth fault loop impedance :
612.9. The earth fault loop impedance ( Zs ) is required to be determined for the furthest point of each circuit . it may be determined by :
► direct measure of ( Zs ) or
► direct measure of ( Ze ) at the origin and adding ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) measured during the continuity test ( 10.3.1. & 10.3.2. ) [ Zs = Ze + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) ] or
► Adding ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) measured during the continuity tests to the value of ( Ze ) declared by the distributor ( see 1.1. (iv) & 1.3. (iv)

The effectiveness of the distributors earth must be confirmed by a test . etc

What lets us down badly is not understanding the very basics . it's all in books

 

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Please read the Q )

re-cap Inspection & testing .. my point is ( drawings )

Answer
disconnect conductors at a suitable point on the circuit

5 c) Describe how the continuity of the ring-final-circuit test is to be carried out on Circuit 9 once the circuit has been safely insulated and secured .

Step 1
• Test the conductor end-to-end loop résistance
• Record results r[SUP]1[/SUP] , r[SUP]N[/SUP] , r[SUP]2[/SUP]

Step 2 ... Interconnect line of outgoing leg with neutral of incoming leg and line of incoming leg with neutral of outgoing leg .

Step 3 ... Interconnect line of outgoing leg with cpc of incoming leg and line of incoming leg with cpc of outgoing leg
• Test line to cpc at each socket-outlet
• Record highest value as R[SUP]1[/SUP] + R[SUP]2[/SUP]
• Reinstate the circuit

-&- are saying don't waffle on , time is precious in Exams .

Comments ...
Answering these types of questions using bullet point is clear and easy way to see that no part are missed out and that the test is complete .

A drawing may be used in place of the interconnection statements such as :


GN-3 P/37 refer Figure 2.2b . Figure 2.2c . connector block etc

Step 1
cross connect line and neutral ... drawing may be used in Exams

This may be easer that writing the connection descriptions in full . There is no set sequence for step 2 & 3 but all three steps must be detailed in order to score well on this question

Tip : Failure to identify that at each step test are carried out at each socket-outlet will lose several marks .

 

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612.2.2. Continuity : Test be made to verify the continuity of ( each-conductor )
Continuity of ring final circuit conductors including circuit-protective-conductor(s) of every ring-final-circuit must be verified .

if the conductors are the same size
if the protective conductor has a reduced CSA , the résistance of the protective loop will be proportionally higher than that of the line , neutral loop

O.S.G. 10.3.2. / 612.2.2. Three step test is required to Verify the continuity of : ( Step 3 )

Step 3 10.3.2 (iii)
Line-conductors & circuit-protective-conductors ( CPC ) crossed connected .
The résistance between line & earth is then measured again at each outlet , The highest value recorded represents the maximum ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) of the circuit and can be used to determine the earth-loop-impedance ( Zs ) of the circuit .

This test also verifies the polarity at each socket-outlet

 

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Main earthing terminals
MET testing . R/P160

the regulations have stated the facts
As called for in Regulations 542.4.1. & 542.4.2. as MET is required for every installation .

One of the principal purposes of the MET is to provide for disconnection of the earthing-conductor from circuit-protective-conductors and bonding-conductors , So that the external line to earth loop impedance ( Ze ) can be measured .

542.4. Main earthing Terminals or Bars

542.4.2
The means of disconnection must involve the use of a tool .. can be ( Bars / Spanner or Terminals / Screwdriver ) may be provided in the form of a disconnectable link , (( with any connections' to MET providing reliability & continuity ))

Protective Conductor(s)

Including :
Earthing conductor(s)
Circuit-protective-conductor(s)
Main-protective-conductor(s)
Supplementary-protective-bonding-conductor(s) where required

 

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R/P 53 . 411.3.1.2. Protective equipotential bonding

Where an installation is contained in more than one separate building , Regulation 411.3.1.2. calls for a MET .. ( & equipotential bonding ) for each building

411.3.1.2 In each installation :
Main protective bonding conductor(s) shall connect to the main earthing terminal extraneous-conductive-parts including the following :

i) Water installation pipes
ii) Gas installation pipes
iii) Other installation pipework & ducting
iv) Central heating and air conditions systems
v) Exposed metallic structural parts of the building

 

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System earth fault loop impedance ( Zs ) s)) system ..

Earth fault loop impedance ( Ze ) e )) external to the installation .
The external earth fault loop impedance ( Ze ) is one of the supply characteristics to be recorded can only be measured by testing at the origin of the installation .

R/P 390 ( EIC ) supply characteristics . External loop impedance ( Ze [SUP]2[/SUP] ) by enquiry of by measurement . ( direct-measurement )
R/P 397 ( EICR ) supply characteristics . External loop impedance ( Ze [SUP]2[/SUP] ) by enquiry of by measurement . ( direct-measurement )

R/P 31 . Origin of an electrical installation . The position at which electrical energy is delivered to an electrical installation .
R/P 32 . Origin of temporary electrical installation . Point on the permanent installation or other source of supply from which electrical energy is delivered to the temporary electrical installation . refer GN-3 P/53 Zs = Zdb + ( R[SUP]1[/SUP] +R[SUP]2 [/SUP])

Direct measurement : -&-s
This indicates that a test is required and the results are not to be established by using a calculation . for example , where you are asked to describe the direct measurement of earth fault loop impedance , then a description of the test procedure is required , Describing an R[SUP]1[/SUP] +R[SUP]2 [/SUP]test and then stating how to determine the value by calculation using Zs = Ze + ( R[SUP]1[/SUP] +R[SUP]2 [/SUP]) will result in on marks being awarded for the answer

2394 : -&-s Q) Which of the following is not a method for determining prospective-earth-fault-current at the origin of an installation ?
A) Calculation using the measured Zs and the supply voltage .

( Ipƒ ) 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 is not going to produce the maximum value .

 

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• O.S.G. Table 11 - 2.5mm[SUP]2[/SUP] / 1.5mm[SUP]2[/SUP] cable has a résistance of 19.51mΩ per metre
The résistance of 54 metres is : 54 x 19.51 / 1000 = 1.05Ω , 1.05 ÷ 4 0.26Ω

R[SUP]1 [/SUP]+ R[SUP]2 [/SUP]for the circuit is 0.26Ω
Zs = Ze + R[SUP]1 [/SUP]+ R[SUP]2 [/SUP]0.24Ω + 0.26 = 0.5Ω

• An installation has seven circuits . Circuit 1 . 4 . 6 have insulation résistance of greater than 200MΩ
Circuit 2 .3 . 5. & 7 . have résistance values of 50 . 80 . 60 . 50 , Calculate the total résistance of the circuit .

1 ÷ 50 = 0.02 , 1 ÷ 80 = 0.0125 , 1 ÷ 60 = 0.016666666 , 1 ÷ 50 = 0.02 :- 0.02 + 0.0125 + 0.016666666 + 0.02 = 0.069
1/50 + 1/80 + 1/60 + 1/50 = 0.069 .. R = 1 ÷ 0.069 = ****Ω

 

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( little rs & Big Rs )
You will not be the first to fall short at understanding the little rs & big Rs
R/P 402 : Schedule of test results . Ring final circuit continuity ( Little rs 10 , 11 , 12 )
Big Rs , Continuity Ω ( R[SUP]1 [/SUP]+ R[SUP]2 [/SUP]) 13* , * Where there are no spurs connected to a ring final circuit this value is also the ( R[SUP]1 [/SUP]+ R[SUP]2 [/SUP]) of the circuit

( Little rs 10 , 11 , 12 ) r[SUP]1[/SUP] , r[SUP]N [/SUP], r[SUP]2[/SUP] , are the end-to-end ring final circuit readings
R[SUP]1[/SUP] ) is the maximum résistance of the line-conductor for a circuit .
R[SUP]2[/SUP] ) is the maximum résistance of the circuit-protective-conductor for a circuit
( R[SUP]1 [/SUP]+ R[SUP]2 [/SUP]) is the test reading value of the two-resistances added together
( R[SUP]1 [/SUP]+ R[SUP]N [/SUP]) is done to help confirm polarity so does not need recording

Note : that spurs from the ring-final-circuit will give higher readings

 

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At random . Q/As word for word .

2394 & 2395 Inspection & Testing
Section B :
Remember that the answers to the following questions must relate to the scenario contained in the Source Document .

Q) Describe how a test is carried out to determine the prospective fault current at the origin of the installation by direct measurement
A) Secure the area around distribution board
Access incoming live terminals
Using a PFC tester ( or EFLI tester set to kA )
Confirm test leads comply with GS-38
Connect to incoming supply side Line & Earth
Measure PEFC
Connect it incoming supply side Line & Neutral
Measure PSCC
Record highest result as the PFC
Reinstate the DB

▼▼▼▼▼ There may be improvement in the 18th Edition here GN-3
C) In the case there have been no previous questions relating to the preparation such as type of instrument etc. and so this information needs to be included in the answer. ◄◄ Your Q )

Tip . Failure to identify that the test leads must comply with GS-38 will lose several marks . It is vital to remember that the earthing and all protective bonding conductors are connected whilst this test is carried out .

( Ipƒ ) 612.11. Prospective fault current
Regulation 612.11. requires that the prospective fault current under both short-circuit and earth-fault conditions be measured , calculated or determined by another method , at the origin and at other relevant point in the installation .

GN-3 . 4.5. Instruments conforming to BS-EN-61557-3 will fulfil the above requirements
These instruments may also offer additional facilities for deriving prospective fault current . The basic measuring principle is generally the same as for earth fault loop impedance testers . ETC . refer

GN-3 4.5. Earth fault loop impedance testers .
These instruments operate by circulating a current from the line conductor into the protective earth , This will raise the potential of the protective earth system

To minimise electric shock hazard . etc This means that the instrument should cut off the test current after 40mS Etc refer

 

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BS-7671:2008:2011: Voltage-drop PS I will not type this out again

612.14. Verification of voltage drop
Where required to verify compliance with Section 525 , the following options may be used .
i) The voltage drop may be evaluated by measuring the circuit impedance .
ii) The voltage drop may be evaluated by calculations , for example , by diagrams or graphs showing maximum cable length v load current for different conductor cross-sectional areas with different percentage voltage drops for specific nominal voltages , conductor temperatures and wiring systems .

Note : Verification of voltage drop is not normally required during initial verification .

Written Examination 2395-302 Read the Qs) Good luck in Exams

Q/As 3 a) i)
Q) Explain the cause of voltage drop within an installation ( 3mk )
A) Volt drop is a product of the conductor resistance and the load current .
Com) The question refers to voltage drop that occurs normally within the installation which is caused by the conductor résistance and the current flowing , Do not confuse this with the causes of excess voltage drop due to poor design or overloading of the circuit

3 a) ii) State the two methods of determining voltage drop ( 2mk )
A) Measurement & Calculation
[h=4]Com ) it is not acceptable to carry out a direct measurement of voltage drop using volt meter(s) The circuit conductors must be at their normal operating temperature , the circuit under full load and there must be no variation in the supply voltage during the test , The methods given are as a result of the measurement of conductor résistance and the reference to charts or tables giving the details of voltage drop . These are not the figures in tables in Appendix 4 of BS-7671: which are generic design details for the calculation of appropriate cable sizes .[/h]
3) b) i) A radial circuit has a load current (Ib) of 28A at 230V ac and has a combined live-conductor résistance of 0.16Ω at 20°C .
Determine the voltage drop for this circuit , Show all calculations' ( 5mk )

A) Voltage drop = ( R[SUP]1[/SUP] + R[SUP]N[/SUP] ) x Ib x 1.2
So Voltage drop = 0.16 x 28 x 1.2 = 5.376V
Com ) The use of the conductor résistance and load current together with the 1.2 multiplier to compensate for the difference in conductor temperature at the time of test and the normal operating temperature of the conductors when maximum résistance and hence maximum voltage drop will occur .

3 b) ii ) if the radial circuit supplies a machine lathe , determine whether the voltage drop in b (i) above complies with BS-7671: ( 5mk )
A) Maximum volt drop - 230V x 5% = 11.5V ......... As 5.376V is equal to or less than 11.5V so complies

Com ) Alternative calculations such as : max voltage drop = 5% V drop = 5.376 ÷ 230 x 100 = 2.3% which is less than 5% So Ok
may be used and will attract the same marks .

(( 5.376 ÷ 230 = 0.023373913 x 100 = 2.3% ))

Tip . It is important to show the calculations because in this type of question where an error is made in the calculation candidates are only penalised once for the error .
The remainder of the answer is marked based upon the incorrect figure produced and , providing the process is correct , marked accordingly , Candidates could have completely the wrong answer for 3 b (i) but based upon their incorrect figure from that calculation achieve full marks for 3 b (ii ) providing their calculation and conclusion is correct .

GN-3 P/59 2.7.20. Verification of voltage drop . Section 525 .
612.14. Where it may be necessary to verify that voltage drop does not exceed the limits stated in relevant product standards of installed equipment BS-7671 : provides two options to do so , Where no such limits are stated , voltage drop should be such that it does not impair the proper and safe functioning of install equipment .

Voltage drop problems are quite rare but the inspector should be aware that long runs and / or high currents can sometimes cause voltage drop problems .

refer to GN-3 .

 

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Chief Examiners report - Questions relating to voltage drop also caused difficulty for many candidates

Knowledge of BS-7671 and Guidance Note 3
Questions relating to voltage drop also caused difficulty for many candidates. Many candidates were unable to correctly state the cause of voltage drop in a circuit. A large number of the responses indicated that voltage drop only occurred as a result of poor design giving undersized cables and heavy loads as typical answers. A great many failed to identify that voltage drop is the product of conductor resistance and load current.

Candidates were given information related to a particular circuit and asked to determine i) the expected voltage drop and ii) whether this value complies with the requirements of BS-7671. Many candidates failed to make any allowance for the change in conductor temperature when calculating the expected voltage drop. When determining compliance a large number of candidates failed to indicate why their conclusion was compliant or non-compliant.

 

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2395-303 .. Read the Q) carefully

Chief Examiners report -

Very few candidates were able to explain why the sequence of tests for a periodic inspection may be different from that given in BS 7671 for initial verification. The majority of candidates confused this with the limitations agreed for the periodic inspection. Whilst this can affect the tests carried out, some being omitted, it does not affect the sequence of testing.

What's is the difference between :

Periodic inspection .
Initial verification .

1 d ) Explain why the sequence of testing for the periodic inspection may be different to that given in BS-7671: for initial verification

A) The installation has been inspected and tested and placed in service. Periodic inspection verifies the current condition or the safety of the installation and not the confirmation of the safety of the installation before placing in service .

Com) The candidate needs to explain the purpose of the periodic inspection and how this differs from (( Initial Verification ))
All these tests could be carried out at periodic inspection but not necessarily in the same sequence , The answer needs to clarify why this is the case .

GN-3 P/66 3.8 Requirements for inspection and testing .
Extracts
621.2. The requirement of BS-7671: for periodic inspection and testing is for a detailed inspection comprising an examination of the installation without dismantling or with partial dismantling as required , together with the tests of Chapter 61 considered appropriate by the person carrying out the inspection and testing , The scope of the periodic inspection and testing must be decided by a competent person , taking into account the information contained in this section .

3.1. Periodic inspection and testing
621.2. The purpose of periodic inspection and testing is to provide an engineering view on whether or not the installation is in a satisfactory condition where it can continue to be used safely

GN-3 P/67
Extracts : For safety . it is necessary to carry out a visual inspection of the installation before testing or opening enclosures , removing covers etc . So far as is reasonably practicable, the visual inspection must verify that the safety of persons , livestock and property is not endangered

 

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Chief Examiner . has made some comments

2394 / 5
The inspection process is a vital part of the periodic inspection process , many conditions may be indentified 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: and IET 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

 

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Confirmation of compliance

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 20°C :willy_nilly:

This means that test value will not be at normal operating temperature and so this must be considered and where necessary compensated for .

 

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Written Exams . 2395-
Principles , practices and legislation for the periodic inspection of electrical installations ◄◄◄

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 .
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

For 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 ( 10mk )

There are a number of points in this 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. ◄
Description of the process in a " Story format " :30:

" 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 .

 

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Re-cap Describe , in detail , the procedure for carrying out a test to confirm the continuity of the main-protective-bonding-conductor . Etc

Option 2 ◄
The answer can be structured as a set of ( Bullet points ) as follows

- Obtain permission to isolate the supply
- Safety isolate , lock off and retain the key ..................... " lock off and retain the ( 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 results
- 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 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 muck 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

This would then ensure that the appropriate marks are awarded for your answer .

Continues .

 

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Continues . 2394 / 5 ........... Exams , Time is precious Waste it Wisely . PASS :icon_bs:

Re-cap Describe , in detail , the procedure for carrying out a test to confirm the continuity of the main-protective-bonding-conductor . Etc

The second option , with the use of the bullet points , is generally quicker to comply , 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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Just some Facts : Sample Test 2395-302 :mad2:

Principles , practices and legislation for periodic inspection , testing and condition reporting of electrical installations .
Periodic inspection , testing and condition reporting .

You should have the following for this assessment :
non-programmable calculator
a pen with black or blue ink
drawing instruments
one enclosed source document

General instructions
• This examination consists of six structured questions , Candidates must answer all six questions :
• Section A - three structured questions , each carrying 15 marks
• Section B - three structured scenario-based , questions each carrying 15 marks
• The terminology used in answering this paper should be in accordance with current IET Publications
• Show all calculations . if you use a calculator , show sufficient steps to justify your answers
• Write all your working out and answers in this booklet

Example .
Section A - All questions carry equal marks . A) all three questions . Show all calculations'
1) The electrical installation in a craft workshop is scheduled for a periodic inspection and test for insurance purposes

a) State two statutory documents which apply to the inspection may need to refer to relating specifically to inspection and testing

i) The questions in Sample test 2395 are repeated below with sample answers , and comments and advice where appropriate .
i) The electrical installation in a craft workshop is schedule for a periodic inspection and test for insurance purposes .

a) State two statutory documents which apply to the inspection and testing process .
A)
Electricity at Work Regulations
Health and Safety at Work Regulations ( etc ) .......... What not to write Act

Com ) Abbreviations such as EWR and HSWA are acceptable . Candidates must correctly identify whether these are an Act or Regulations in order to achieve the marks

1 b) State three non-statutory documents which the inspector may need to refer to relating specifically to inspection and testing
A)
BS-7671:
On-Site-Guide
Guidance Note 3

Com) GS-38 is an acceptable alternative so any three from these four are acceptable . Abbreviations such as . O.S.G. and GN-3 are also acceptable answers . As the question asks for three items , the examiner will only mark the first three responses

1 c) State who the inspector will consult to establish the extent and limitations of the periodic inspection and test .
A)
The client
The insurance company

Com ) The person ordering the work or the person requiring the work are acceptable alternatives to the client . Note : Read the question carefully , the main question stem specifies that the work is for insurance purposes

The response must relate to the insurance company and so other interested third parties or any other specific third party such as licensing authority etc . will not receive a mark .

 

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Written Exams 2394-302:

Please read the question , PS this has been downloaded for a Reason . Making you aware :30:

This has got my attention Q/As

Section B
State the document to be completed by the inspector and given to the client on completion of the inspection and test

A) Electrical Installation Condition Report or EICR , Schedule of Inspections , Schedule of Test Results

Com )
These are the requirements identified in BS-7671: ............ Electrical Installation Condition Report or EICR , Schedule of Inspections , Schedule of Test Results

These are the requirements identified in BS-7671: Tiles used on the Standard Forms such as generic schedule of test results and Condition Report Inspection Schedule would also be acceptable

Your Q ) What not to do , Schedule of Tests , Schedule of items tested etc Will Not Attract Marks

 

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Exam Success - Inspection & Testing 2394 & 2395 .

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
A) r[SUP]1[/SUP] + r[SUP]2[/SUP] = 60 x ( 7.41 + 12.10 ) 1000 = 1.17Ω

R[SUP]1[/SUP] + R[SUP]2[/SUP] = 1.17 / 4 = 0.293Ω

Com ) 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 20°C , which is the same temperature as that which applies to the mΩ/m values in Figure 2 .

The calculation could have also been laid out as shown below

r[SUP]1[/SUP] = 60 x 7.41 / 1000 = 0.446Ω
r[SUP]2[/SUP] = 60 x 12.10 / 1000 = 0.726Ω
R[SUP]1[/SUP] + R[SUP]2 [/SUP] = 0.446 + 0.726 / 4 = 0.293Ω ... ( 0.446 + 0.726 = 1.172 ÷ 4 = 0.293Ω )