Re-take - Useful Information for 2394 :

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2.5mm[SUP]2[/SUP] / 1.5mm[SUP]2[/SUP] twin T&E cable 22m long . if you look at O.S.G. Table 11 you will see that the résistance of a copper 2.5mm[SUP]2[/SUP] conductor has a résistance of 7.41mΩ per metre

Résistance of the Line-conductor will be : 7.41 x 22 / 1000 = 0.163Ω
divide the largest conductor by the smallest to find the ratio of the conductors .. ( how much bigger is the larger conductor ) 2.5 ÷ 1.5 = 1.67

2.5mm[SUP]2 [/SUP]conductor is 1.67 x larger than the 1.5mm[SUP]2 [/SUP] conductor ; therefore , it must have 1.67 x less résistance than 1.5mm[SUP]2 [/SUP] conductor .
if you now multiply the résistance of the line conductor by 1.67 : 0.163 x 1.67 = 0.27Ω this is the résistance of the 1.5mm[SUP]2 [/SUP] conductor

You can check this by looking at O.S.G. Table 11 you can see that the résistance of 1.5mm[SUP]2 [/SUP] copper is 12.10mΩ per metre . Therefore , 22 metres of 1.5mm[SUP]2 [/SUP] copper will be : 22 x 12.10 / 1000 = 0.266Ω

your final check ; if you look in O.S.G. Table 11 , for the résistance of a 2.5mm[SUP]2[/SUP] / 1.5mm[SUP]2[/SUP] twin T&E cable will see that it has a résistance of 19.51mΩ per metre , and that 22 metres of it will have a résistance of : 22 x 19.51 / 1000 = 0.429Ω .

The résistance value of the 2.5mm[SUP]2[/SUP] is 0.163Ω ....... 2.5mm[SUP]2 [/SUP] copper will be 7.41 x 22 / 1000 = 0.163Ω
The résistance value of the 1.5mm[SUP]2[/SUP] is 0.266Ω ....... 1.5mm[SUP]2 [/SUP] copper will be : 22 x 12.10 / 1000 = 0.266Ω

if you add them together ( 0.163Ω + 0.266Ω = 0.429Ω ) Finally ; 0.429 is the résistance of your 2.5mm[SUP]2[/SUP] / 1.5mm[SUP]2[/SUP] measured as one cable .

 

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Common problems : ( IR ) :icon_bs:

• Low-résistance résistance could be found if a building has been unused for a period of time , due to the installation being affected by dampness in the accessories .

• Low-résistance résistance readings will also often be found where a building has been recently-plastered . :35:

 

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Earthing :
All electrical circuits in a installation must have a protective-earth-conductor ( PE ) , commonly referred to as the circuit-protective-conductor

 

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Test 1 , trouble downloading in forum .

Section A .... Please read the Question carefully ←

The questions in sample test 2394-302 are repeated below with sample answers , and comments and advice where appropriate .

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

A) BS-7671:2008(2011) and IET Guidance Note 3 .
Com ) 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 .

 

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Test 2 ,

Section A

The questions in sample test 2394-302 are repeated below with sample answers , and comments and advice where appropriate .

1 b) State the scope of the Minor Electrical Installation Works Certificate ... ( MEIWC )

A) Alteration or addition to an existing circuit .

Com ) A key part of this answer is the reference to ((( an existing circuit ))) An alteration or addition to an existing installation is NOT within the scope of a Minor Electrical Installation Works Certificate

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

 

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Test 3 ,

Section A .. Q/As PS this one has my full attention.

The questions in sample test 2394-302 are repeated below with sample answers , and comments and advice where appropriate .

1 c ) State what must be verified when inspecting electrical equipment , during an initial verification .

A)
Equipment is to British Standards
Equipment is correctly selected and erected
Equipment is not damaged

Com ) The question refers to the inspection of electrical equipment and NOT to the inspection . BS-7671: refer specifically to what must be verified when inspecting electrical equipment .

((( Equipment is installed to the requirements of BS-7671: ))) is an acceptable alternative to ((( correctly selected and erected ))) as this is a requirement of The Wiring Regulations . it is NOT an acceptable alternative to ((( Equipment is to British Standards ))) but reference to European or International standards’ would also be acceptable .

 

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Test 4

Section A

The questions in sample test 2394-302 are repeated below with sample answers , and comments and advice where appropriate .

2 c ) List two labels that would normally be present on a newly completed domestic installation

A) :30:
Next inspection notice .
Earthing and bonding notice .

Com) The key word in this question is ((( normally ))) The examiner is looking for labels that are ((( normally ))) present on a new domestic installation . Answers that include labels that , under certain conditions are present , but are not ((( normally ))) present would not be acceptable .

Again , because the question has asked for two answers , only the first two answers given by the candidate would be considered .

An RCD notice would also be an acceptable answer .

 

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Section A
The questions in sample test 2394 & 2395 are repeated below with sample answers , and comments and advice where appropriate .

3 c ) (i) List the measurements to be taken , at the main switch of a three-phase TN-S system , in order to determine the installation prospective fault current ( Ipƒ )

A) :30:
L1 to L2
L1 to L3
L2 to L3

Com ) There is no need to carry out any other tests to determine ( PFC ) because on a three-phase system the largest fault current will be due to a symmetrical short-circuit , that is a short-circuit between all line conductors at the same time . A test between line conductors is an acceptable approximation . if additional tests were included in the answer then this would not make the answer invalid .

The measurement of L1 to N , L2 to N and L3 to N would be an acceptable Alternative method ( see answer 3 c (ii) below

3 c (ii) Explain how the recorded value of prospective fault current ( Ipƒ ) is determined following the test in c (i) above

A ) The highest value of the three measurements :30:

Com ) 3 c (i) and (ii) are linked and the answer to (ii) is dependent on the test method used in (i) if the answer to (i) was to measure between L and N then this answer would be ((( the largest value x 2 ))) if the answer to (i) included tests to earth then this answer must state ((( the largest line to neutral value x 2 )))

 

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-&-s Guidance on Sitting the e-vole multiple choice examination

Effective methods of answering questions

In order to have the best chance of success it is essential to read the question carefully and make sure you understand what is being asked . The answers provided will include one correct answer and understanding the question is key to selecting the right response .

Based on their experience candidates sometimes believe that the answer they want to give is not included in the choices .
In such instances the best approach is the consider the options given and select the one which is most appropriate for the question .:30:

One of the key features of the system is the ability to flag a question where you are unsure of the answer .
This is registered by the system and a flag indicator is placed next to the question .
This allows you to identify and return to flagged questions at any time during the exam .

 

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Wording of Questions :6:

Direct measurement
This indicates that a test is required and the results are not to be established by using a CALCULATION . :13:

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 starting how to determine the value by calculation using Zs = Ze + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) will result in no marks being awarded for the answer .

 

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State : Don’t go overboard with the word (( State )) ▼ ▼ ▼ Please read the Q ) :30:

This means the answer is expected to be a short statement, not a long or rambling paragraph.
The response to this type of question may even be just a single word or group of words which may not need to be a complete sentence .

Example .. (( just a single word )) (( group of words ))

1 a (iii) State the title given in law to the inspector whilst carrying out the inspection of an electrical installation
A) Dutyholder ... (( just a single word ))

Com) This question refers to the requirements of The Electricity at Work Regulations and the term (( Dutyholder )) refers to anyone having a duty of care to others .

5 a (ii) State the document that specifies the requirements for the test leads .
A) Leads to GS-38 . .... (( group of words )) PS This is not rambling paragraph.

2 a (ii) State the test voltage to be applied for the insulation résistance test .
A) 500 volts ... PS This is not rambling paragraph.

2 a (iii) State the effect on the value of insulation résistance produced by cable length .
A) As length increases résistance decreases ... PS This is not rambling paragraph.

Com ) An alternative answer includes as length decreases résistance increases .
Alternative terms such as higher or lower are acceptable .

 

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List : Don’t go overboard with the word (( List )) ▼ ▼ ▼ Please read the Q ) :30:

This means you should produce (( a simple list of items (( or )) actions ))

The answer should be similar to that produced for the “ state “ question , However , on this occasion the items would be expected to follow a sequence and form a (( List )) is used to indicate this requirements .

Example ..

2 c ) (( list )) two labels that would normally be presented on a newly completed domestic installation .

A )
• Next inspection notice
• Earthing and bonding notice Etc

1 d ) (( List )) five characteristics of the supply which must be recorded on an Electrical Installation Certificate .

A)
• Earthing arrangements
• Number and type of live conductors
• Nominal voltage
• Nominal ƒrequency
• PFC

Com) Because the question has asked for five answers , only the first five answers given by the candidate would be considered .

:svengo: Acceptable answers must be those characteristics that are recorded on an Electrical Installation Certificate under the heading “ Supply characteristics and Earthing Arrangements “

“ Type of earthing “ , “ external earth fault loop impedance “ , Ze “ , “ ac/dc “ , “ Nature of supply “ would gain a mark but only is none of the other answers given by the candidate included items from that section .

“ Protective device “ , “ main fuse “ and “ earth loop impedance “ would not score marks because they are VAGUE .

 

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Explain : Don’t go overboard with the word (( Explain )) ▼ ▼ ▼ Please read the Q ) :30:

We are not Story telling here . :svengo:

Explain briefly : This requires a brief explanation ; (( usually no more than one or two sentences )) it does not require paragraphs of explanation and the word (( briefly )) is used to indicate this requirement .

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

A) 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 from 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 .

Com ) The question asks 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
A) To remove parallel earth paths so that the intended fault path can be confirmed to be reliable

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

3 b (ii) Explain : why the earthing conductor is connected to the MET when measuring prospective earth fault current .
A ) This is the condition that exists at the time of a fault and therefore is the only way to determine the maximum fault current to earth when carrying out the test .

Com) In this case the purpose of the test is to determine the maximum prospective earth fault current . This will occur when the installation is energised and all earthing arrangements are in place , so the test must be carried out under these conditions .

 

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Please read the Q ) carefully Q/As :30:

Describe :
These questions often relate to test procedures and you are required to demonstrate your knowledge of the test process . Look at the number of MARKs available to give you an indication of how much detail you need to go into .

Describe , in detail :
This indicates that a more detailed answer is required and again the number of MARKs available for the question gives an indication of the depth of the answer required

A series of short bullet pointed statements is a very effective method of providing an answer , but remember that all necessary information must be included

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

5 ( a ) i , ii , iii .

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 .
A ) Use an earth fault loop impedance tester

5 a (ii) State the document that specifies the requirements for the test leads
A) Leads to GS-38

5 a (iii) Describe : in detail , how the test would be carried out
• Supply on
• Local isolator off
• 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

Com ) The structure of this 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

This 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 + R test and the results is then added to Ze , 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 :13:

 

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This is You’re Q ) :30:

Consider the number of marks available for the question or part-question . This provides a valuable indication of the depth of the answer required
a question which carries one mark will require a much simpler answer than one for which fifteen marks are available .

Take a little longer to read the question carefully to ensure you are quite clear about what is required

Structure of the Exam

Each paper is divided into two sections, Section A and Section B.

Section A of each paper has three questions which are often divided into a number of parts ( a , b , c , and i) ii) iii) and so on ) with each part of the question relating to a different leaning outcome . The number of marks available for each part of the question is shown on the paper and this can be used to indicate how long to spend on your Answer .

Section B also has three questions, but these relate to the scenario contained within a “ Source Document “
These questions may also be divided into parts but often relate to a single learning outcome .

Candidates are expected to display an in-depth knowledge of the particular subject . Typical examples include describing a test-procedure or evaluating test-results.

Show all Calculations :

Again the examiner is trying to help you score as many marks as possible . Where a calculation is required and the only thing offered by the candidate is the numerical answer , then if it is wrong , the candidate would score no marks . if the candidate includes each step of the calculation then marks will be awarded for each correct step . it is always in your best interest to show all stages of the process .

Exam conditions you are under pressure . ... little longer to read the question
Where relevant , remember to show the applicable units which apply to your answer . e.g. V , Ω , kA . etc

Take your Q from this . Written Exams . What can go Wrong in my Q/As :wink_smile:

You are expected to be able to describe the procedures for carrying out activities . ( INCLUDING ) the inspection and testing of installations and circuit’s ( Take your Q ) ►►► These descriptions should follow the format given in IET Guidance Note 3

▼▼▼▼▼ learn by mistakes’
Common errors when answering questions that relate to the scenario are :

• not obtaining permission for isolation or for testing to proceed
• no isolation procedure mentioned when it is appropriate
• no instrument and lead check carried out
• incorrect procedures described , such as not being able to describe the ((( three steps in IET Guidance Note 3 ))) for ring-final-circuit continuity
• not describing the test process in the correct sequence
• failure to consider the safety aspects necessary for the testing process
• failure to reinstate the installation safety once testing is complete
▼▼▼▼▼ learn by mistakes’
Common errors .
A common area for error is the application of the ((( rule of thumb ))) to the maximum tabulated values of earth-fault-loop-impedance ( these maximum values will be given in the scenario or question information ) in order to compare these with the measured values . When candidates do not correctly apply the ((( rule of thumb ))) , it shows they are unable to correctly identify compliance with BS-7671: and therefore no marks are awarded .

 

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▼▼▼▼▼ learn by mistakes’
Common errors when answering questions : :30:


((( No instrument and lead check carried out ))) The full monty Q/As ..Please read the Questions , -&-s will obviously , designed to trap the unwary :icon_bs:

((( lead check carried out )))
((( No instrument check carried out )))

Q) Which publication specifically indentifies the requirements for (( test leads and probes )) to be used when carrying out tests at 230V a.c.
• a) BS-7671:
• b) HSE Guidance GS-38 ***
• c) Electricity at Work Regulations
• b) Provision and Use of Work Equipment Regulations

Q) Test instruments should be calibrated in accordance with the manufactures’ instructions to ensure accurate test results . In addition to calibration which of the following should be carried out and recorded .
• a) Regular confirmation of the instrument’s compliance with BS-7671:
• b) Extension of the instrument warranty period
• c) Regular instrument accuracy checks ***
• d) Closed circuit voltage checks

Com) Regular instrument accuracy checks are required to ensure the instrument continues to ((( provide accurate results ))
Your Q ) ► 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 .

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

Com) Where the test voltages are (( ≤ 50V a.c. )) the requirements for GS-38 compliant leads is not necessary where the short-circuit fault current is unlikely to cause a high energy flashover . Test current for this test is (( ≥ 200mA ))

Q) Which of the following requirements from GS-38 applies to test equipment which requires more than one test lead .
• a) The leads must be at least in in length
• b) The leads must have a csa of at least 1.5mm[SUP]2 [/SUP]
• c) The leads must be colour coded for identification ***
• d) The leads must be permanently attached to the instrument

Com) Item ( c ) is the only one the listed items described in ((( GS-38 )))

 

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Show all Calculations : :45:

Again the examiner is trying to help you score as many marks as possible . Where a calculation is required and the only thing offered by the candidate is the numerical answer , then if it is wrong , the candidate would score no marks . if the candidate includes each step of the calculation then marks will be awarded for each correct step . it is always in your best interest to show all stages of the process .

Extracts :

Section B : Source Document
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 .. ( using you symbols’ Ω )
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

The calculation could have also been laid out as shown below

Extracts .

r[SUP]1 [/SUP] = 60 x 7.41 / 1000 = 0.445Ω .. ( using you symbols’ Ω )
r[SUP]2[/SUP] = 60 x 12.10 / 1000 = 0.726? .... PS. What have I left out !
R[SUP]1[/SUP] + R[SUP]2 [/SUP] = 0.445 + 0.726 / 4 = 0.293? .... PS. ^^^

Confirm of Compliance :

Some questions are intended to establish your ability to confirm that measured test results meet the requirements of BS-7671: In order to do this you will be expected to show what steps are taken for this process and any calculations that may be involved . You will also be expected to indentify appropriate action for any situations where the results do not meet the requirements . This will be different for initial verification ( 2394 ) compared with periodic inspection ( 2395 )

 

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Written Examination 2395-

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

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

You are required to be able to :
Select the test instrument and their accessories for test 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: and IET Guidance Note 3
To include :

Continuity including
o main protective bonding conductor(s)
o circuit protective conductor(s)
o ring final circuit(s)

Insulation résistance
Polarity
External earth fault loop impedance ( Ze )
System earth fault loop impedance ( 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: and IET Guidance Note 3 including :

• Electrical Installation Certificate
• Schedule of Inspections
• Schedule of Test results ... Generic Schedule of Test results

 

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2395-

Outcome 6 - Understanding the requirements for testing before circuits are ((( Energised )))

You are required to be able to :
State why it is necessary to verify the continuity , to include:
Protective bonding conductor(s)
Circuit protective conductor(s)
Ring final circuit(s)

State the methods for verifying the continuity , to include :
Protective conductor(s)
Ring final circuit(s) conductors
Explain the factors that effect conductor 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 - Understanding the requirements for testing ((( Energised installations )))

You are required to be able 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

 

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2395-

Outcome 4 – Understanding the difference between peridic inspection and initinal verification .

You are reqiured to be able to :

State the reasons for requiring a periodic inspection as identified in IET Guidance Note 3
State the need to determine the Extent and Limitations of a periodic inspection with the client and intersted third parties before work begins
Explain the application of sampling when carrying out periodic inspection and testing to include :

Factors which determine the extent of sampling
Situations where sampling may not be appropriate

Indentify the need to record agrement with the client and thiord parties on the condition report
Explain the reasons why testing may be undertaken in a diffrent order to that identified in BS-7671: for initinal verification
Indentify the considerations which need to be made during a periodic inspection to ensure the safety of the persons and livestock on the premises
State the purpose of the observations and classification codes in regards to :

• The observations to be recorded
• Appropraite 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: and IET Guidance Note 3
Explain the action required by the inspector when the Extent and Limitions agreed may not be achived 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

 

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Q/As 2394

A 100mA BS-EN-61008 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 test current when testing the RCD

100mA & 200mS
100mA & 300mS *** :icon_bs:
500mA & 200mS
500mA & 300mS

The RCD is provided for fault-protection and not additional protection and the ( 1 x IΔn ) is the maximum test current that needs to be applied

As this is a BS-EN-61008 device the maximum disconnection time is ( 300mS )

Re-cap NOTE : ... ((( BS- )))
A maximum disconnection time of ( 200mS ) applies to some older RCDs manufactured to a ((( British Standard ))) but not to BS-EN-61008 devices

 

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Revision : 2394:

List the Instruments used for : :yes:
a) Continuity of circuit-protective-conductor(s)
b) Continuity of ring-final-circuit(s)
c) Insulation résistance ( IR )

List the Units used to measure with the following instrument

a) Low résistance ohmmeter
Instruments to - GN-3 P/82 ... BS-EN-61557-4 ( part 4 )

b) Insulation résistance tester’s
Instruments conforming to - GN-3 P/83 ... BS-EN-61557-2 ( part 2 )

Earth fault loop impedance tester’s
Instruments conforming to - GN-3 P/83 ... BS-EN-61557-3 ( part 3 )

Earth electrode résistance tester’s
► GN-3 - 2008 P/84 .
The instrument potential and current spikes are within the operating limits of the instrument .. it may be helpful to note that instruments complying with BS-EN-61557-5 ( part 5 ) incorporate this facility . Care should be exercised to ensure that temporary spikes are positioned with reasonable accuracy .

c) RCD tester’s
Instruments conforming to - GN-3 P/84 ... BS-EN-61557-6 ( part 6 )

Phase rotation instruments
BS-EN-61557-7 ( part 7 )

 

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Ask the Question , What can Guidance Note 3 do for YOU. :svengo: It’s a must in any Exams’

a) List two methods utilised for Basic protection ... usually provided by insulation and / or enclosures

► GN-3 - 2008: Basic protection 416
Insulation of live parts
Although protection by insulation is the usual method , there are other basic protection methods . 416.1.

Barriers or enclosures
Where live parts are protected by barriers or enclosures , these should be checked for adequacy and security . 416.2.

► GN-3 - 2011: P/19 . Basic protection 416
Basic protection is most usually provided by insulation and / or enclosures . The inspection of this measure is to check that insulation has not been damaged during installation and that enclosures have been selected for at least IPXXB or IP2X and , for top surfaces , at least IPXXD or IP4X , and are not damaged . ( Insulation résistance is of course a fundamental test to be carried out )

b) List one method utilised for Fault protection
► GN-3 - 2011: P/19 . Fault protection Sec 411 ( 1 )
Fault protection
The various methods of fault protection are classified in a number of subsections in BS-7671: and are :
( 1 ) Automatic disconnection of supply .

P/20 . Method 1 .
Automatic disconnection of supply ( ADS )
For each circuit , automatic disconnection is required and , although the main part of verification is measurement of earth fault loop impedance in order to confirm disconnection times , there are inspection aspects to consider for verifying ADS as follows :

Presence of appropriate protective conductor(s)
Earthing-conductor
Circuit-protective-conductors
Protective bonding conductors
- Main bonding conductors
- Supplementary bonding conductors ( where required )

312.2. The earthing system must be determined e.g.
TN-C-S ( Protective multiple earthing ( PME ))
TN-S system
TT system ( earth electrode(s))

411.4.5. The earth fault loop impedance must be appropriate for the protective device , i.e. RCD or Overcurrent device .

BS-7671:2011: P/23 :icon_bs:
Basic protection .
Protection against electric shock under fault-free conditions .

Note : For low voltage installations , systems and equipment, basic protection generally corresponds to protection against direct contact , that is “ contact of person or livestock with live parts “

BS-7671:2011: P/28 :icon_bs:
Fault protection .
Protection against electric shock under single fault conditions .

Note : For low voltage installations , systems and equipment , fault protection generally corresponds to protection against indirect contact , mainly with regards to failure of basic insulation .

Indirect contact is “ contact of persons or livestock with exposed-conductive-parts which have become live under fault conditions “

411 Protective Measure : Automatic Disconnection of Supply .
(ii) fault protection is provided by protective earthing , protective equipotential bonding and automatic disconnection in case of a fault . refer

410.3.3. The following protective measures generally are permitted :
(i) Automatic disconnection of supply - section 411.1.

P/51 Note : In electrical installations the most commonly used protective measure is automatic disconnection of supply .

 

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R/P29 . Inspection ; Examination of an electrical installation using all the senses as appropriate .
R/P36 . Testing ; Implementation of measures to assess an electrical installation by means of which its effectiveness is proved . This includes ascertaining values by means of appropriate measuring instruments , where measured values are not detectable by inspection .

R/P 22 . 135 Periodic inspection and testing
135.1. It is recommended that every electrical installation is subjected to periodic inspection and testing , in accordance with Chapter 62 .

135 Periodic inspection and testing
Installations must be inspected and tested periodically to ensure that they are safe for continued use .

Chapter 13 will ensure that all of these principles have been addressed and that the best possible protection is in place .

Chapter 13 : Fundamental principles
135 Periodic inspection and testing .

R/P 36 . Verification . :icon_bs:
All measures by means of which compliance of the electrical installation with the relevant requirements of BS-7671: are checked , comprising inspection , testing and certification .

Chapter 13 : Fundamental principles
134 : Erection and initial verification of electrical installations
134.1. Erection
134.2. Initial verification

 

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Requirements of BS-7671: :icon_bs:

Replacing a consumer unit in an existing installation is an addition or alteration to that installation. The work must therefore be designed, erected and verified in accordance with the requirements of the current edition of BS-7671: and must not impair the safety of the existing installation. ( Regulations 110.1 (vi) & 610.4 .

610.4 .. Verification
For an addition or alteration to an existing installation
it shall be verified that the addition or alteration complies with the Regulations and does not impair the safety of the existing installation

P/390 re-cap : EIC - Safety certificate
Addition to an existing installation
Alteration to an existing installation

 

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State three non-statutory documents which the inspector may need to refer to relating specifically to inspection and testing
BS-7671:
On Site Guide
Guidance Note 3 :35:

Inspection and testing of Electrical Installations

The British Standard for electrical installations is BS-7671:208:2011: The requirement for Electrical installations Within this standard , Regulation 610.1

Requires that (( every installation )) shall be inspected and tested to verify , so far as is reasonably practicable, that the Regulations have been met before being put into service. The requirements are stated in the following Regulations:

Regulation 134 .. Initial verification
134.2.1. During erection and on completion of an installation or an addition or alteration to an installation and before it is put into service , appropriate inspection and testing shall be carried out by competent persons to verify that the requirements of this Standard have be met .

Regulation 621.1. States that :
Where required periodic inspection and testing of (( every installation )) shall be carried out in accordance with regulations 621.2 to 621.5 in order to determine as far as is reasonably practicable, whether the installation is in a satisfactory condition for continued service .

17[SUP]th[/SUP] Edition requirements for testing RCDs
Requirements in terms of verification of installed RCDs :

612.8.1. requires the effectiveness of automatic disconnection of supply by RCD to be verified using test equipment meeting the requirements of BS-EN-61557-6 ( Electrical safety in low voltage distribution system up to 1000V a.c. & 1500V d.c. – Equipment for testing , measuring or monitoring of protective measures . Residual current devices ( RCD ) in TT , TN systems )

This is to confirm that the relevant requirements of chapter 41 ( Protection against electric shock ) are met .

BS-EN-61557-6 has requirements for the following tests to be applied to RCDs :

Non-tripping ( 50% or ½ ) test .. RCD should not trip .
The purpose of this test is to confirm that the RCD of any type or trip is not overly sensitive and is a measure intended to enable unsuitable RCDs to be indentified and removed from service .

Tripping current test :
The purpose of this test is to confirm that the residual operating current of the (( protective-device )) is less than or equal to the rated residual operating current . This is a measure of the continued effectiveness of the device to work as required by BS-7671: and in accordance with its product specification when installed for the purpose of providing automatic disconnection in the event of a fault . it does not demonstrate its suitability in terms of providing additional protection .

Note : GN-3 tell us – The test should be performed in both the positive & negative half-cycles . ( 0° & 180° )

Tripping ( 100% / 1 x ) test
5 x IΔn ( 500% ) fast trip

RCDs ( G ) should be tested at ( 50% , 100% , 500% ) 5 x if providing additional protection
Q ) 30mA BS-EN-61009-1 is installed on a socket-outlet circuit to provide (( additional protection )) Which of the following identifies the maximum test current too be applied and the maximum disconnection time that test current .

A ) 150mA and 40mS .. 5 x 30mA = 150
The RCBO is provided for (( additional protection and the 5 x IΔn 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.

612.13.1. requires :
Where fault protection and / or additional protection is to be provided by an RCD , the (( effectiveness )) of any test facility incorporated in the device shall be (( verified ))

415.1.1. States :
That where an RCD having an IΔn of 30mA is installed to provide additional protection . it’s operating time should not exceed 40mS at a residual current of 5 IΔn .

Q - Explain why the sequence of testing for ((( Periodic ))) inspection may be different to ((( That ))) given in BS-7671: for initial verification
You’re Q . (( 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 .

 

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Sect 514 . Presence of danger notices and other warning notices

GN-3 P/25 . refer to . :aureola:

Extracts .
514.10. Voltage :
► Where a nminal voltage exceeding 230V to earth exists within an iten of equipment or enclosure and where the presence of such a voltage would not normally be expected .

The wording of this regulation was revised for Amendment No 1 to BS-7671:2008: and is carified that only “ unsual “ system voltage exceeding 230V to earth require waring labels .

Anexample would be the use of a 690V three-phase a.c. power tranformer used on an American air base located in the UK .

 

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GN-3 . P/32
612.2.1. Continuity of protective-conductor(s) Etc main & supplementary bonding

Regulation 411.3.1.1. ((( requires ))) that installations which provide protection against electric shock using automatic disconnection of supply ( ADS ) must have a ((( circuit-protective-conductor ))) run to and terminated at each point in the wiring and at each accessory .

Regulation 612.2.1. (((requires ))) that a continuity check be carried out on all circuits including ring-circuits

There are two widely used ((test methods)) that have evolved for checking conductor continuity. “ Test method 1 “ uses the circuit cable shorted out.

“ Test method 2 “ uses a supplementary length of test cable (this method being popularly known as the “ wandering lead “ method.

Test method 1 . as well as checking the continuity of the protective-conductor . also measures ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) which , when added to the external impedance ( Ze ) enables the earth-fault-loop-impedance ( Zs ) to be checked against the design . ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) is the sum of the résistance of the line conductor ( R[SUP]1[/SUP] ) and the circuit-protective-conductor ( R[SUP]2[/SUP] )

 

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Periodic inspection of electrical installations ( -&-s ) :30:

Candidates should be aware that generally the installations being inspected and tested (( are energised ))
-&-s . unless they are given information to the contrary. ◄◄◄ Exams :13:

Don’t fall on our Laurels
To be so satisfied with your own achievements that you make no effort to improve

 

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Facts : -&-s

The three-step test is not needed for radial circuits. Therefore the time needed to comply with BS-7671 testing requirements is greatly reduced.

Ring-final-circuit
GN-3 reminds us .

Continuity of ring-final-circuit conductor(s)
612.2.2. A three-step test ◄► is required to ((( Verify the continuity of the ))) Line , Neutral , Protective-conductors

1 ) Step .
2) Step .
3) Step .

Correct wiring of every ring-final-circuit
The test results show if the ring has been interconnected to create an apparently continuous ring-circuit which is in fact broken or connected as a (( figure of eight )) configuration

I have a funny side as well . Amberleaf . :smilewinkgrin:

When mosses find the 10 commandment a Conner broken off. The IET got their little hands on it . split it into the BS-7671:2008:2011: & GN-3 making Outstanding information . Guidance Notes , BS-7671:2008:2011: has Stated the facts British Standards ... Facts

 

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demonstrate that candidates are not aware of the ((( periodic inspection process ))) That minimal dismantling should be involved and the extent and limitations section of the standard form in BS-7671 & GN3

 

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Q) What is the equation used to determine Earth fault Loop Impedance ( i.e.: Zs = ? ) Zs = Ze + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )

Q) List three-items of information relating to the incoming supply that should be listed on the ((( Generic Schedule of test results )))
Page 391 .. Nature of Supply Parameters ( EIC )

U/Uo ( [SUP]1 [/SUP]) single-phase 230V
Nominal frequency ( ƒ ) ( [SUP]1 [/SUP]) 50Hz
Prospective fault current ( Ipƒ ) ( [SUP]2 [/SUP]) .. kA
External loop impedance ( Ze ) ( [SUP]2 [/SUP]) .. 0.18Ω

Why is it necessary to ((( Verify ))) the continuity of circuit-protective-conductor(s) prior to undertaken any further testing
How important is circuit-protective-conductor(s) CPCs

• Insulation résistance checks ( IR ) .. No circuit-protective-conductor , incomplete
• RCD tests .. relies on circuit-protective-conductor for ( ADS )
• Loop impedance tests ( Zs loop ) circuit-protective-conductor(s) & ( Ze loop ) you must confirm you have an Earthing-conductor or other means earth electrodes

State the danger that may arise if earth fault loop impedance tests are undertaken prior to verifying the Continuity of the circuit-protective-conductor :icon_bs:

Method 1 method :- relies on verifying continuity when undertaken tests . circuit-protective-conductor(s)

R/P196 . Initial verification
Defects or omissions revealed during inspection and testing of the installation work covered by the Certificate shall be made good before the Certificate is issued .

R/P190 . If any test indicates a failure to comply , that test and any preceding test , the results of which may have been influenced by the fault indicated , shall be repeated after the fault has been rectified .

 

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R/P 46 . 314 Division of installation

i) In the event of a Fault
By dividing the installation into circuits
Separate circuits also provide you with a means of ((( Isolation ))) for a section of an installation . :icon_bs:

 

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2011: 131.2. Protection against electric shock :icon_bs:

“ Protection against direct contact “ 131.2.1. - Basic protection
“ Protection against indirect contact “ 131.2.2. - Fault protection

131.2.1. Basic protection ( protection against direct contact )
Note : for low voltage installations , systems and equipment , “ Basic protection “ generally corresponds to protection against “ direct contact “

Persons and livestock shall be protected against dangers that may arise from contact with live parts of the installation

This protection can be achieved by one of the following methods :

i) Preventing a current from passing through the body of any person or any livestock
ii) Limiting the current which can pass through a body to a non-hazardous value

131.2.2. Fault protection ( protection against indirect contact )
Note: for low voltage installations , systems and equipment , “ fault protection “ generally corresponds to protection against “ indirect contact “ mainly with regards to failure of basic insulation

Persons and livestock shall be protected against dangers that may arise from contact with exposed-conductive-parts during fault

This protection can be achieved by one of the following methods :

i) Preventing a current resulting from a fault from passing through the body of any person or any livestock
ii) Limiting the magnitude of a current resulting from a fault , which can pass through a body , to a non-hazardous value
iii) Limiting the duration of a current resulting from a fault , which can pass through a body , to a non-hazardous time period

In connection with fault protection , the application of the method of protective equipotential bonding is one of the important principles for safety

 

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Q) Which measurement would you use when recording the continuity of the ring final conductors . ( mΩ , mS , Ω , MΩ ) -&-s

Q) Whilst conducting a circuit-protective-conductor continuity test , GN-3 recommends a temporary link to be made ?
A) Between Line and CPC in the consumer unit

Continuity of ring-final-circuit conductor(s) (( :leaving: THREE-STEPS TEST )) -&-s .. to verify the continuity :13:

As GN-3 reminds us ; Initial check for continuity
2.7.6. A three-step test is required to verify the continuity of the Line , Neutral , Protective-conductors . etc

Step 1 . Connections for testing , initial check for continuity at ends of ring
The line , neutral and protective-conductors are visually identified at the distribution board or consumer unit and the (( end-to-end résistance )) of each is measured separately. ................ making me / Step 1

Check between each end in turn (( L / L , N / N & Cpc / Circuit-protective-conductor ))
Testing results - Little r[SUP]S[/SUP] ( r[SUP]1[/SUP] , r[SUP] N[/SUP] , r[SUP]2[/SUP] ) r[SUP]1 [/SUP]Line , r[SUP] N[/SUP] Neutral , r[SUP]2[/SUP] Circuit-protective-conductor .

R/P 402 . Generic Schedule of Test Results . (( Am using the wording - Generic Schedule etc ) -&-s GN-3 & BS-7671: States this
Ring final circuit continuity ( Ω ) 10 , 11 , 12 .

As GN-3 reminds us ; Step 1 .
A finite reading confirms that there is No open-circuit on the ring conductors under test .

Q) A continuity test is conducted on a ring final circuit , 6 sockets give a ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) reading of 0.41Ω but one socket gives a reading of 0.69Ω .
What could this indicate ? “ Houston you have a problem “ remember that you .Pass or Fail . -&-s

Trapped circuit-protective-conductor in the back of a box
Spur on the circuit
High résistance fault
Short circuit ... 0.00 ... As your Résistance approaches Zero, your current approaches Infinity.

R/P 34 . Short-circuit current .
An Overcurrent resulting from a fault of negligible impedance between ( live-conductors / L/N ) having a difference in potential under normal operating conditions

 

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My main point is to make you aware of the (( :skep: THREE-STEPS TEST )) -&-s .. to verify the continuity , (( Ring-final-circuits ))

Step 2 . ((Cross connect )) Line and Neutral

GN-3 reminds us : The open ends of the Line & Neutral conductor(s) are then connected together so that the outgoing Line-conductor is connected to the returning Neutral-conductor and vice versa (( refer to Figure 2.2b )) P/37 connecting for testing Step 2 .

• Measure between Line-conductor and Neutral-conductor at each socket-outlet .
Values should be the same at each socket-outlet .. should be ( r[SUP]1[/SUP] + r[SUP] N[/SUP] ) / 4

Step 3 . ((Cross connect )) Line and Circuit-protective-conductors
• Measure between Line-conductor and Circuit-protective-conductors at each socket-outlet .
Values should be the same at each socket-outlet .. should be ( r[SUP]1[/SUP] + r[SUP] 2[/SUP] ) / 4
(( refer to Figure 2.2c )) P/37 connecting for testing Step 3 .

Value is recorded as ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) on the . (( Am using the wording - Generic Schedule of Test Results ) -&-s GN-3 & BS-7671: States this
R/P402 . Continuity ( Ω ) ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) 13 .

You have proven continuity long before now . Step 1 : Little r[SUP]S[/SUP] ( r[SUP]1[/SUP] , r[SUP] N[/SUP] , r[SUP]2[/SUP] )

This is still a Dead test :- Why is it ( r[SUP]1[/SUP] + r[SUP] 2[/SUP] ) / 4
By Cross connecting the opposing Lines and circuit-protective-conductors creates a perfect resistive circle
( By Cross connecting the ) Lines and circuit-protective-conductors , resistances are in parallel

As GN-3 reminds us .
A higher résistance value will be recorded at any Socket-outlet wired as Spurs . (( watch this in Exams Q/As ))

Schedule of Test Results :leaving:
The value can be used to determine the earth-fault-loop-impedance ( Zs system ) of the circuit to verify compliance with the loop impedance requirements of the Regulations

 

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Testing 2012
Questions related to testing appeared to create difficulty for candidates :rant:

The question relating to the testing of ring final circuit conductors was generally poorly answered with marks lost due to incomplete procedures, incorrect terminology when referring to conductors, incorrect instrument names, failure to state the need to test at each socket and failure to state the conductors between which the tests are carried out. ((( Step 1 , Step 2 , Step 3 )))

 

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Definitions

R/P 28 . Final circuit .
A circuit connected directly to current-using equipment , or to a socket-outlets or socket-outlets or other outlet points for the connection of such equipment .

A radial final circuit is not defined in Part 2 of BS-7671: but is generally considered to be a final-circuit connected to the supply at one end only

R/P 28 . Ring final circuit .
A circuit connected directly to current-using equipment , or to a socket-outlet or socket-outllets, or other outlet points for the connection of such equipment .

P/34 ( Spur ) A branch from a ring or radial-final-circuit .

O.S.G. p/68 . 7.2.2. Socket-outlet circuit .
As a rule of thumb for rings , unfused spur lengths should not exceed 1/8 the cable length from the spur to the furthest point of the ring .

 

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O.S.G. P/129 . Table D1 Spacings of supports for cables in accessible positions

Cable overall diameter (d) mm

Non-armoured cable thermosetting or thermoplastic ( PVC ) Sheathed cables ( † )

Up to d ≤ 9 .. Horizontal 2 . 250 , Vertical 3 . 400
Exceeding 9 but not exceeding 15 .. 9 < d ≤ 15 .. Horizontal 300 , Vertical 400
Exceeding 15 but not exceeding 20 .. 15 < d ≤ 20 .. Horizontal 350 , Vertical 450
Exceeding 20 but not exceeding 40 .. 20 < d ≤ 40 .. Horizontal 400 , Vertical 550

Cable overall diameter (d) mm

Armoured cable maximum support spacing ( † )

Up to d ≤ 9 .. Horizontal 6 . 250 , Vertical 7 . 400
Exceeding 9 but not exceeding 15 .. 9 < d ≤ 15 .. Horizontal 350 , Vertical 450
Exceeding 15 but not exceeding 20 .. 15 < d ≤ 20 .. Horizontal 400 , Vertical 550
Exceeding 20 but not exceeding 40 .. 20 < d ≤ 40 .. Horizontal 450 , Vertical 600

Note : Wiring used in the electrical installation of a caravan must be of a type listed in Regulation 721.521.2.

721.521.2. Types of wiring system

The wiring systems shall be installed using one or more of the following :
i) Insulated single-core cables , with flexible class 5 conductors , in non-metallic conduit
ii) Insulated single-core cables , with stranded class 2 condutors ( mininum of 7 strands ) in non-metallic conduit
iii) Sheathed flexible cables .

All cables shall , as a minimum , meet the requirements of BS-EN-60332-1-2.
Non-metallic conduits shall comply with BS-EN-61386-21.
Cable management systems shall comply with BS-EN-61386.

In Caravans maximum support spacing ( † )

Up to d ≤ 9 .. Horizontal 4 . 250 for all sizes , Vertical 5 . 400 for all sizes
Exceeding 9 but not exceeding 15 ..
Exceeding 15 but not exceeding 20 ..
Exceeding 20 but not exceeding 40 ..

* For flat cables taken as the dimension of the major axis .
† ) The spacings stated for horizontal runs may be applied also to runs at an angle of more than 30° from the vertical . for runs at an angle of 30° or less from the vertical , the vertical spacings are applicable .

- Spacings smaller than given in the O.S.G. will often be necessary for good workmanship / visual appearance .
- Horizontal spacings include for runs at an Angle of more than 30° from the vertical
- Vertical spacings include for runs at an Angle of 30° or less from the vertical

Cross-section through a flat-type cable indicating the major axis .. ¦ ← Major axis → ¦

 

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Initial Verification , Order of tests

Order of tests for the initial verification of an installation as required by Regulation 612.1. of BS-7671:
Which also requires that :

Testing

i) The test results are compared with the relevant criteria .. (( where required ))
ii) Any test that indicates a failure to comply with the criteria is repeated after the fault is rectified , Together with any preceding test influenced by the fault .

Test must not be carried out until inspection has been completed , as required by Regulation 611.1.

610.1.
Precautions shall be taken to avoid danger to (( persons )) and livestock , and to avoid damage to (( property )) and installed equipment during testing

BS-7671:2008:2011: 612.2. to 612.6.
Lists the order of tests (( where relevant )) to be carried out before the supply is connected or with the supply disconnected as appropriate .

612.7.
Where the earthing system incorporates an earth-electrode as part of the installation , the earth-résistance to Earth shall be measured .